Prof. Dr. Mathias Ulbricht

Technical Chemistry
University of Duisburg-Essen

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  • A mixed-charge polyelectrolyte complex nanofiltration membrane: Preparation, performance and stability
    Zelner, M. and Jahn, P. and Ulbricht, M. and Freger, V.
    Journal of Membrane Science 636 (2021)
    Ion selectivity of nanofiltration (NF) membranes is a critical factor in NF treatment of scaling-prone multi-ion effluents, such as wastewater. When removal of multivalent ions in such effluents is unnecessary or undesired, adjusting their rejection may mitigate scaling, in which case membranes combining oppositely charged electrolytes enable a tunable selectivity towards such ions. Here we report the fabrication of a new tunable and highly stable polyelectrolyte complex NF membrane prepared by successively coating an ultrafiltration membrane support with negatively charged Nafion and positively charged polyvinylamine (PVAm) layers. While Nafion thickness controls the membrane permeability, the second PVAm coating is critical for eliminating defects in the Nafion layer and readily tunes the membrane net charge and, hence, ion selectivity via PVAm concentration in the coating solution. In this manner, a membrane with good permeability, balanced charge, and, therefore, equal (“symmetric”) rejection of divalent anions and cations is obtained. The membrane performance is unaffected by exposure to 10% salt in water; such remarkable stability for a polyelectrolyte-based membrane makes it potentially attractive for the treatment of wastewater effluents and brackish water sources. © 2021 Elsevier B.V.
    view abstract10.1016/j.memsci.2021.119579
  • Amphiphilic poly(arylene ether sulfone) multiblock copolymers with quaternary ammonium groups for novel thin-film composite nanofiltration membranes
    Wieczorek, J. and Ulbricht, M.
    Polymer 217 (2021)
    Amphiphilic poly(arylene ether sulfone) (PAES) multiblock copolymers with quaternary ammonium groups were evaluated as tunable, size-selective barrier material in thin-film composite (TFC) nanofiltration membranes. Using a two-step synthesis, well-defined PAES multiblock copolymers with molecular weight (Mn) of at least 50 kg/mol were obtained. Conversion to anion-exchange polymers was accomplished by block-selective bromination of methyl side groups at adjusted degree of functionalization and subsequent quantitative amination using triethanolamine. A library of copolymers with varied block length ratios and ion-exchange capacities (IEC; up to 2 mmol/g) was obtained. PAES multiblock copolymers with suited hydrophilic/hydrophobic balance to yield films that are stable in water were further evaluated. Film casting of solutions of anion-exchange copolymers on a porous polyacrylonitrile support and solvent evaporation yielded TFC membranes with barrier layer thickness in the range of 1.5–1.9 μm. Nanofiltration performance was measured with glycerine, glucose, sucrose, NaCl, MgCl2 and FeCl3 in water. While for a random copolymer with similar composition and same thickness, no water flux could be measured, the novel TFC membranes had permeances in the range of 1 L m−2 bar−1·h−1, at >99.9% rejection for glucose. Permeance increased and rejection (for glycerine and salt) decreased systematically with increasing IEC; an additional influence of block length ratio was identified. A membrane made from a block copolymer with longer hydrophobic block and moderate IEC of 0.9 mmol/g showed the best “trade-off” between permeability and selectivity. Furthermore, the stability of the novel membranes under oxidative disinfection conditions was demonstrated. © 2021 Elsevier Ltd
    view abstract10.1016/j.polymer.2021.123446
  • Artificial weathering mechanisms of uncoated structural polyethylene terephthalate fabrics with focus on tensile strength degradation
    Asadi, H. and Uhlemann, J. and Stranghoener, N. and Ulbricht, M.
    Materials 14 (2021)
    In the past five decades, reinforced coated textile membranes have been used increasingly as building materials, which are environmentally exposed. Thus, their weathering degradation over the service life must be taken into account in design, fabrication, and construction. Regarding such structural membranes, PVC (polyvinylchloride)-coated PET (polyethylene terephthalate) fabric is one of the most common commercially available types. This paper focuses on the backbone of it, i.e., the woven PET fabric. Herein, weathering of uncoated PET, as the load-bearing component of the composite PET-PVC, was studied. This study assessed the uniaxial tensile strength degradation mechanisms of uncoated PET fabric during artificial accelerated weathering tests. For this purpose, exploratory data analysis was carried out to analyze the chemical and physical changes which were traced by Fourier transform infrared spectroscopy and molecular weight measurements. Finally, with the help of degradation mechanisms determined from the aforementioned evaluations, a degradation pathway network model was constructed. With that, the relationship between applied stress, mecha-nistic variables, structural changes, and performance level responses (tensile strength degradation) was assessed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/ma14030618
  • Concentration polarization enabled reactive coating of nanofiltration membranes with zwitterionic hydrogel
    May, P. and Laghmari, S. and Ulbricht, M.
    Membranes 11 (2021)
    In this study, the bottleneck challenge of membrane fouling is addressed via establishing a scalable concentration polarization (CP) enabled and surface‐selective hydrogel coating using zwitterionic cross‐linkable macromolecules as building blocks. First, a novel methacrylate‐based copolymer with sulfobetain and methacrylate side groups was prepared in a simple three‐step syn-thesis. Polymer gelation initiated by a redox initiator system (ammonium persulfate and tetrameth-ylethylenediamine) for radical cross‐linking was studied in bulk in order to identify minimum (“critical”) concentrations to obtain a hydrogel. In situ reactive coating of a polyamide nanofiltration membrane was achieved via filtration of a mixture of the reactive compounds, utilizing CP to meet critical gelation conditions solely within the boundary layer. Because the feasibility was studied and demonstrated in dead‐end filtration mode, the variable extent of CP was estimated in the frame of the film model, with an iterative calculation using experimental data as input. This allowed to dis-cuss the influence of parameters such as solution composition or filtration rate on the actual polymer concentration and resulting hydrogel formation at the membrane surface. The zwitterionic hydro-gel‐coated membranes exhibited lower surface charge and higher flux during protein filtration, both compared to pristine membranes. Salt rejection was found to remain unchanged. Results further reveal that the hydrogel coating thickness and consequently the reduction in membrane permeance due to the coating can be tuned by variation of filtration time and polymer feed concentration, il-lustrating the novel modification method’s promising potential for scale‐up to real applications. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/membranes11030187
  • Cotton as Precursor for the Preparation of Porous Cellulose Adsorbers
    Wittmar, A.S.M. and Baumert, D. and Ulbricht, M.
    Macromolecular Materials and Engineering 306 (2021)
    Natural biopolymer-based porous spherical adsorbers from cellulose have good efficiency for removal of metal ion pollutants from aqueous media. However, high purity celluloses, most commonly used as precursors for preparation of the adsorber spheres, require complex synthesis processes, which consume energy and chemicals, and may thus lead to other types of pollution. In this work, the possibility to prepare cellulose-based porous spherical adsorbers directly from cotton, using an ionic liquid-based platform is analyzed in detail. The dissolution of microcrystalline cellulose (MCC), as reference, and of cotton in ionic liquid-based solvents and the properties of the obtained polymer solutions are investigated in order to evaluate their processability toward porous macrospheres using the drop shaping cum non-solvent induced phase separation process. The properties of the prepared spheres are assessed. The dissolution of cotton is more difficult than the dissolution of MCC and the formed cotton-based solutions are considerably more viscous, which makes their processability possible only after careful adjustment of the cotton solution concentration. The maximum adsorption capacities toward Cu2+ are ≈110 and ≈72 mg/g for the porous cotton-based spheres prepared from 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]):dimethylsulfoxide (DMSO) = 2:1 and 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]):DMSO = 2:1 solutions, respectively. © 2021 The Authors. Macromolecular Materials and Engineering published by Wiley-VCH GmbH
    view abstract10.1002/mame.202000778
  • Feasibility of graphene-polymer composite membranes for forward osmosis applications
    Akca, S. and Arpaçay, Pi. and McEvoy, N. and Prymak, O. and Blau, W.J. and Ulbricht, M.
    Materials Advances 2 (2021)
    This paper assesses the feasibility of fabricating thin-film composite membranes from stacked graphene nanosheets in combination with a polymer as a selective layer on a macroporous support membrane for utilization in osmosis applications. Reproducible dispersion procedures based on the liquid-phase exfoliation technique have been established to fabricate multi-layer graphene from graphite with the assistance of the high boiling point solvent N-methylpyrrolidone (NMP) or the low boiling point solvent ethanol. A high graphene yield of up to 7.2% with a concentration of 0.36 mg mL-1 was achieved in the NMP-based dispersions. Membrane fabrication toward a graphene-polymer sandwich architecture has been developed, in which graphene laminates modified with or without a chemical cross-linker are placed in between two polyethyleneimine (PEI layers) laminated onto the support membrane (either nylon or polyethersulfone microfiltration membranes). Graphene-polymer composite membranes were successfully fabricated via the pressure-assisted filtration technique and the performance of the membranes was studied in terms of pure water permeability and dextran rejection. The best performing membranes had water permeability varying from 33-77 L m-2 h-1 bar-1 and rejection of dextran 2000 kDa up to 96%; the selective layer has a thickness of ∼1 μm. Forward osmosis experiments with polyacrylic acid sodium salt as draw agent demonstrate the feasibility of using the established graphene-polymer composite membranes for such applications. This journal is © The Royal Society of Chemistry.
    view abstract10.1039/d1ma00424g
  • Novel finely structured polymer aerogels using organogelators as a structure-directing component
    Leven, F. and Ulbricht, M. and Limberg, J. and Ostermann, R.
    Journal of Materials Chemistry A 9 (2021)
    Sorbitol-based organogelators were used to obtain nanostructured, robust polyolefin gels that could be freeze-dried into aerogels. Finding the ideal ratio of polymer to gelator led to homogeneous, fine structures with good mechanical stability and low thermal conductivity. The influence of polymer type, molecular weight and concentration was studied with regard to structure, compressive strength and thermal conductivity and a mechanism for the structure formation was postulated. Moreover, Soxhlet extraction was shown as a route to optimize the drying process and partially recover the gelator that is required as a structure-directing component, but partially also necessary in the final composite. The materials presented here are novel and useful composite aerogels with potential applications as insulating materials, porous supports, adsorbents, catalyst carriers and membranes. © 2021 The Royal Society of Chemistry.
    view abstract10.1039/d1ta06161e
  • Poly(ether sulfone) hollow fiber membranes prepared via nonsolvent-induced phase separation using the green solvent Agnique® AMD 3 L
    Uebele, S. and Johann, K.S. and Goetz, T. and Gronwald, O. and Ulbricht, M. and Schiestel, T.
    Journal of Applied Polymer Science 138 (2021)
    In recent years, the development of sustainable membrane manufacturing processes by the use of environmentally friendly solvents has become a considerable challenge. In this work, poly(ether sulfone) (PES) hollow fiber membranes were manufactured by the nonsolvent-induced phase separation (NIPS) using the green solvent Agnique® AMD 3 L (N,N-dimethyl lactamide; AMD) and N-ethyl-2-pyrrolidone (NEP) as a conventional solvent. The effect of the solvent on the dope solution and membrane properties was investigated. The morphology, mechanical characteristics, barrier pore sizes as well as gas and water permeances of the hollow fibers prepared with AMD were evaluated and compared to membranes that were similarly prepared using NEP as solvent. Membranes prepared with AMD as polymer solvent and NEP as bore liquid exhibit the largest barrier pore size among all variations. Thus, highest water permeance of 406.9 ± 37.4 kg m−2 h−1 bar−1 was obtained with this combination. Whereas AMD as sole solvent in membrane preparation decreases membrane permeances caused by a denser membrane structure. Nevertheless, AMD is a promising solvent for a sustainable membrane fabrication providing membrane properties that are competitive with membranes manufactured using the conventional solvent NEP. © 2021 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals LLC.
    view abstract10.1002/app.50935
  • Polyelectrolyte functionalisation of track etched membranes: Towards charge-tuneable adsorber materials
    Wiedenhöft, L. and Elleithy, M.M.A. and Ulbricht, M. and Schacher, F.H.
    Membranes 11 (2021)
    Porous adsorber membranes are promising materials for the removal of charged pol-lutants, such as heavy metal ions or organic dyes as model substances for pharmaceuticals from water. Here, we present the surface grafting of polyethylene terephthalate (PET) track-etched membranes having well defined cylindrical pores of 0.2 or 1 µm diameter with two polyelectrolytes, poly(2-acrylamido glycolic acid) (PAGA) and poly(N-acetyl dehydroalanine) (PNADha). The poly-electrolyte functionalised membranes were characterised by changes in wettability and hydraulic permeability in response to the external stimuli pH and the presence of Cu2+ ions. The response of the membranes proved to be consistent with functionalisation inside the pores, and the change of grafted polyelectrolyte macro-conformation was due to the reversible protonation or binding of Cu2+ ions. Moreover, the adsorption of the model dye methylene blue was studied and quanti-fied. PAGA-grafted membranes showed an adsorption behavior following the Langmuir model for methylene blue. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/membranes11070509
  • Polyzwitterionic hydrogel coating for reverse osmosis membranes by concentration polarization-enhanced in situ “click” reaction that is applicable in modules
    Laghmari, S. and May, P. and Ulbricht, M.
    Journal of Membrane Science 629 (2021)
    The methodology for a polyzwitterionic anti-fouling hydrogel coating for reverse osmosis polyamide (PA) thin-film composite (TFC) membranes by concentration polarization-enhanced in situ thiol-ene “click” reaction has been developed. A copolymer with zwitterionic sulfobetain and reactive methacrylate side groups as well as a bis-thiol crosslinker in water were used as reactive system. By means of rheology, best suited solution composition parameters for efficient cross-linking at ambient temperature toward stable hydrogels were established first. Thereafter, factors that influence hydrogel coating of PA TFC membranes were investigated in dead-end filtrations, such as copolymer concentration, flux and stirring speed. It was found that hydrogel formation will occur within the first few minutes if the critical reactant concentration required for cross-linking is reached at the membrane surface and further filtration/reaction time will increase hydrogel layer thickness. Specific parameters, selected based on results of dead-end filtration experiments yielding thick hydrogel coatings (1–2 μm, in dry state), lead to only very thin hydrogel layers under cross-flow conditions in a spacer-filled channel. However, such thin hydrogel-coated membranes had also very good antifouling properties compared to the unmodified membrane. The extent of coating can be adjusted toward thicker hydrogels by increasing flux also under cross-flow conditions in a spacer-filled channel. Finally, the feasibility of the hydrogel coating of PA TFC membranes in industrial spiral-wound modules and the use of such modules for treatment of cooling water in a steel manufacturing plant were demonstrated. Overall, suited materials and methods as well as partial fundamental understanding of the influence of parameters that can be used for a scalable antifouling hydrogel coating of membranes in spiral-would modules have been established in this work. © 2021 Elsevier B.V.
    view abstract10.1016/j.memsci.2021.119274
  • Preparation and characterization of asymmetric hollow fiber polyvinyl chloride (PVC) membrane for forward osmosis application
    Behboudi, A. and Ghiasi, S. and Mohammadi, T. and Ulbricht, M.
    Separation and Purification Technology 270 (2021)
    PVC hollow fiber (HF) membrane for forward osmosis (FO) application as a potential candidate for water desalination was fabricated by altering the spinning conditions. High molecular weight polyvinylpyrrolidone (PVP) was used as a blending additive to control the phase inversion process by increasing viscosity leading to delayed demixing as observed on the ternary phase diagram and confirmed by the simulation results, and forming dense barrier layer structure by providing chain entanglements with the PVC matrix. PVP/PVC ratio of 5/100 was proved to offer suited membrane morphology and selective layer. Different air gap distances and bore fluid flow rates were investigated to achieve proper fabrication parameters. The prepared membranes presented high flux and salt rejection in nanofiltration (NF) and FO tests. The best-suited membrane demonstrated the structural parameter of 389 µm with a narrow pore size distribution and a molecular weight cut-off of 490 Da. In different draw solution (DS) concentrations, it was observed that the membranes perform well in all conditions. Considering the PVC-PVP chain entanglements and mobility and the possibility of PVP being washed away, the membranes’ performance at different temperatures indicated that 25–45 °C would be the safe operating range for the fabricated membranes with stable values of 31.0–33.4 LMH and 0.17–0.18 (FO mode) and 33.0–33.4 LMH and 0.23–0.24 (PRO mode) for water flux and specific reverse salt flux. © 2021 Elsevier B.V.
    view abstract10.1016/j.seppur.2021.118801
  • Preparation and characterization of hydrophilic and antibacterial silver decorated silica-grafted-poly(vinylpyrrolidone) (Ag-SiO2-PVP) nanoparticles for polymeric nanocomposites
    Ahsani, M. and Sabouri, R. and Ulbricht, M. and Hazrati, H. and Jafarizad, A. and Yegani, R.
    Journal of Applied Polymer Science (2021)
    Hydrophilic antibacterial silver decorated silica-grafted-poly(vinylpyrrolidone) (Ag-SiO2-PVP) nanoparticles were successfully synthesized in multiple steps. In this regard, silanization of the silica nanoparticles was performed with different concentrations of vinyltrimethoxysilane (VTS) to generate vinyl groups onto the nanoparticles surface. Obtained results showed that by increasing the VTS concentration the amount of vinyl groups on the surface of the silica nanoparticles increased while nanoparticles agglomeration did not occur. Then, poly(vinylpyrrolidone) PVP brushes were grafted onto the silanized silica nanoparticles (SiO2-VTS) via grafting-through polymerization method to obtain PVP-grafted silica nanoparticles (SiO2-PVP). Fourier transform infrared spectroscopy, thermal gravimetric analysis, and dynamic light scattering confirmed the successful generation of the vinyl groups and PVP brushes onto the silica nanoparticles. Finally, Ag-SiO2-PVP nanoparticles were prepared by synthesizing silver nanoparticles onto the SiO2-PVP nanoparticles to render them antibacterial. Energy dispersive X-ray spectroscopy showed that highest grafting of silver nanoparticles onto the SiO2-PVP nanoparticles was obtained for the nanoparticles with highest content of vinyl groups. X-ray photoelectron spectroscopy was used to identify the elements and their chemical structure for the synthesized nanoparticles. Plate colony counting method was applied to assess the antibacterial effects of the Ag-SiO2-PVP nanoparticles which revealed outstanding bactericidal properties of them. © 2021 Wiley Periodicals LLC.
    view abstract10.1002/app.50977
  • Soft synthetic microgels as mimics of mycoplasma
    Büning, D. and Schumacher, J. and Helling, A. and Chakroun, R. and Ennen-Roth, F. and Gröschel, A.H. and Thom, V. and Ulbricht, M.
    Soft Matter 17 (2021)
    Artificial model colloids are of special interest in the development of advanced sterile filters, as they are able to efficiently separate pleomorphic, highly deformable and infectious bacteria such as mycoplasma, which, until now, has been considered rather challenging and laborious. This study presents a full range of different soft to super soft synthetic polymeric microgels, including two types with similar hydrodynamic mean diameter,i.e., 180 nm, and zeta potential,i.e., −25 ± 10 mV, but different deformability, synthesized by inverse miniemulsion terpolymerization of acrylamide, sodium acrylate andN,N′-methylenebisacrylamide. These microgels were characterized by means of dynamic, electrophoretic and static light scattering techniques. In addition, the deformability of the colloids was investigated by filter cake compressibility studies during ultrafiltration in dead-end mode, analogously to a study of real mycoplasma,i.e.,Acholeplasma laidlawii, to allow for a direct comparison. The results indicate that the variation of the synthesis parameters,i.e., crosslinker content, polymeric solid content and content of sodium acrylate, has a significant impact on the swelling behavior of the microgels in aqueous solution as well as on their deformability under filtration conditions. A higher density of chemical crosslinking points results in less swollen and more rigid microgels. Furthermore, these parameters determine electrokinetic properties of the more or less permeable colloids. Overall, it is shown that these soft synthetic microgels can be obtained with tailor-made properties, covering the size of smallest species of and otherwise similar to real mycoplasma. This is a relevant first step towards the future use of synthetic microgels as mimics for mycoplasma. © The Royal Society of Chemistry 2021.
    view abstract10.1039/d1sm00379h
  • Studying Fluid Characteristics Atop Surface Patterned Membranes via Particle Image Velocimetry
    Denizer, D. and ElSherbiny, I.A.M. and Ulbricht, M. and Panglisch, S.
    Chemie-Ingenieur-Technik (2021)
    Surface patterning is a recent promising approach to promote performance of pressure-driven membranes in water treatment and desalination. Nevertheless, knowledge about foulant deposition mechanisms, especially at early stage of filtration, is still lacking. The applicability of particle imaging velocimetry to study fluid characteristics atop surface patterned thin-film composite membranes was investigated at different operating conditions. This work is an important first step toward reliable understanding of the impacts of topographical membrane surface modification on hydrodynamic conditions and foulant deposition mechanisms. © 2021 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH
    view abstract10.1002/cite.202100043
  • Surface Modification of Ready-to-Use Hollow Fiber Ultrafiltration Modules for Oil/Water Separation
    Idrees, H. and ElSherbiny, I.M.A. and Hecket, M. and Ke, Q. and Staaks, C. and Khalil, A.S.G. and Ulbricht, M. and Panglisch, S.
    Chemie-Ingenieur-Technik (2021)
    Reusing wastewater from oil-related industries is becoming increasingly important, especially in water-stressed oil-producing countries. Before oily wastewater can be discharged or reused, it must be properly treated, e.g., by membrane-based processes like ultrafiltration. A major issue of the applied membranes is their high fouling propensity. This paper reports on mitigating fouling inside ready-to-use ultrafiltration hollow-fiber modules used in a polishing step in oil/water separation. For this purpose, in-situ polyzwitterionic hydrogel coating was applied. The membrane performance was tested with oil nano-emulsions using a mini-plant system. The main factors influencing fouling were systematically investigated using statistical design of experiments. © 2021 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH
    view abstract10.1002/cite.202100044
  • Three-Dimensional Analysis of the Natural-Organic-Matter Distribution in the Cake Layer to Precisely Reveal Ultrafiltration Fouling Mechanisms
    Wu, S. and Hua, X. and Ma, B. and Fan, H. and Miao, R. and Ulbricht, M. and Hu, C. and Qu, J.
    Environmental Science and Technology 55 (2021)
    Cake layer formation is the dominant ultrafiltration membrane fouling mechanism after long-term operation. However, precisely analyzing the cake-layer structure still remains a challenge due to its thinness (micro/nano scale). Herein, based on the excellent depth-resolution and foulant-discrimination of time-of-flight secondary ion mass spectrometry, a three-dimensional analysis of the cake-layer structure caused by natural organic matter was achieved at lower nanoscale for the first time. When humic substances or polysaccharides coexisted with proteins separately, a homogeneous cake layer was formed due to their interactions. Consequently, membrane fouling resistances induced by proteins were reduced by humic substances or polysaccharides, leading to a high flux. However, when humic substances and polysaccharides coexisted, a sandwich-like cake layer was formed owing to the asynchronous deposition based on molecular dynamics simulations. As a result, membrane fouling resistances were superimposed, and the flux was low. Furthermore, it is interesting that cake-layer structures were relatively stable under common UF operating conditions (i.e., concentration and stirring). These findings better elucidate membrane fouling mechanisms of different natural-organic-matter mixtures. Moreover, it is demonstrated that membrane fouling seems lower with a more homogeneous cake layer, and humic substances or polysaccharides play a critical role. Therefore, regulating the cake-layer structure by feed pretreatment scientifically based on proven mechanisms should be an efficient membrane-fouling-control strategy. © 2021 American Chemical Society.
    view abstract10.1021/acs.est.1c00435
  • Water influence on the uniaxial tensile behavior of polytetrafluoroethylene-coated glass fiber fabric
    Asadi, H. and Uhlemann, J. and Stranghoener, N. and Ulbricht, M.
    Materials 14 (2021)
    Polytetrafluoroethylene (PTFE)-coated glass fiber fabrics are used for long-lasting membrane structures due to their outstanding mechanical properties, chemical stabilities, and satisfying service life. During their operation time, different environmental impacts might influence their per-formance, especially regarding the mechanical properties. In this contribution, the impact of water on the tensile strength deterioration was assessed experimentally, providing evidence of consider-able but partially reversible loss of strength by up to 20% among the various types of investigated industrially established fabrics. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/ma14040846
  • A swift technique to hydrophobize graphene and increase its mechanical stability and charge carrier density
    Madauß, L. and Pollmann, E. and Foller, T. and Schumacher, J. and Hagemann, U. and Heckhoff, T. and Herder, M. and Skopinski, L. and Breuer, L. and Hierzenberger, A. and Wittmar, A. and Lebius, H. and Benyagoub, A. and Ulbricht, M. and Joshi, R. and Schleberger, M.
    npj 2D Materials and Applications 4 (2020)
    Despite the improvement of the quality of CVD grown single-layer graphene on copper substrates, transferring the two-dimensional layer without introducing any unintentional defects still poses a challenge. While many approaches focus on optimizing the transfer itself or on necessary post-transfer cleaning steps, we have focused on developing a pre-treatment of the monolayer graphene on copper to improve the quality and reproducibility of the transfer process. By pressing an ethylene-vinyl acetate copolymer foil onto the monolayer graphene on copper using a commercially available vacuum bag sealer graphene is stabilized by the attachment of functional carbon groups. As a result, we are able to transfer graphene without the need of any supporting layer in an all-H2O wet-chemical transfer step. Despite the general belief that the crumbling of graphene without a support layer in a H2O environment is caused due to differences in surface energy, we will show that this assumption is false and that this behavior is caused rather by the polar interactions between graphene and water. Suppressing these interactions protects graphene from ripping and results in extremely clean, highly crystalline graphene with a coverage close to 100%. © 2020, The Author(s).
    view abstract10.1038/s41699-020-0148-9
  • Cellulose/chitosan porous spheres prepared from 1-butyl-3-methylimidazolium acetate/dimethylformamide solutions for Cu2+ adsorption
    Wittmar, A.S.M. and Klug, J. and Ulbricht, M.
    Carbohydrate Polymers 237 (2020)
    A series of cellulose/chitosan blend porous spheres were prepared by dropping cum phase separation from 1-butyl-3-methylimidazolium acetate/dimethylformamide based solutions via coagulation in water. Special attention was given to the investigation of the phase separation process initiated with water in relation with the different chitosan content in polymer solutions. The increase of the chitosan fraction in the biopolymer solution led to a destabilization of the solutions by lower amounts of water. Both viscosity of the polymer and stability of the solution played a very important role to the spheres structure formation. It was observed that the SBET seems to decrease at the increase of the chitosan content in the porous material. Despite the decrease of porosity, the increase of the chitosan fraction in the blend had a beneficial influence on the adsorber properties of the spheres, due to the amino groups in the chitosan units. © 2020 Elsevier Ltd
    view abstract10.1016/j.carbpol.2020.116135
  • Design and synthesis of organic polymers for molecular separation membranes
    Ulbricht, M.
    Current Opinion in Chemical Engineering 28 (2020)
    Nowadays most membrane separation processes utilize membranes made from organic polymers because shape and structure can be tailored to the needs of a specific application with scalable fabrication processes such as solution casting and phase separation, coating and interfacial polymerization. This short review discusses recent progress for membranes suited for molecular separation in aqueous and organic liquids by nanofiltration, dialysis, electrodiaysis or pervaporation. Important achievements for bulk polymers suited as membrane material have been made by special processing of cellulose, development of highly stable polymers, microporous polymers and microphase-segregating copolymers. Ultrathin barrier layers are critical to combine target selectivity with high flux. Hence the scope of layer-by-layer and self-assembly of polymers as well as interfacial polymerization of standard monomers and advanced building blocks has been expanded, with the aim to obtain in situ on supports microporous materials with suited functional groups or molecular cavities. Overall, there is an increasing number of approaches which enable a precise tailoring of selectivity and boosting the flux at the same time. Hence, much higher overall separation performance compared to state-of-the-art membranes is in principle feasible. © 2020 The Author(s)
    view abstract10.1016/j.coche.2020.02.002
  • Development of a bone substitute material based on additive manufactured Ti6Al4V alloys modified with bioceramic calcium carbonate coating: Characterization and antimicrobial properties
    Surmeneva, M.A. and Chudinova, E.A. and Chernozem, R.V. and Lapanje, A. and Koptyug, A.V. and Rijavec, T. and Loza, K. and Prymak, O. and Epple, M. and Wittmar, A. and Ulbricht, M. and Surmenev, R.A.
    Ceramics International 46 (2020)
    This investigation shows that composite structures based on additive manufactured electron beam melted Ti6Al4V scaffolds coated with calcium carbonate particles can be used as a potential biocomposites for bone substitutes. A continuous bioceramic coating of CaCO3 was deposited on additive manufactured titanium alloy under the influence of ultrasound. XRD analysis revealed the formation of a mixture of calcite and vaterite phases. CaCO3 coating led to decreasing roughness of additively manufactured (AM) scaffolds and improved surface hydrophilicity. In vitro assay demonstrated enhanced inorganic bone phase formation on the surface of CaCO3-coated AM scaffolds compared to as-manufactured ones. The short-term adhesion of S. aureus onto sample surface was evaluated by fluorescent microscopy 0, 3, and 72 h after cell seeding. It revealed that the surface modification resulted in the decreased number of bacteria attached to the surface after CaCO3 deposition. The morphology, roughness, solubility and superhydrophilic character of the CaCO3 coated EBM-manufactured Ti6Al4V alloy surface are suggested as factors contributing to preventing S. aureus adhesion. Thus, the developed biocomposites based on additively manufactured Ti6Al4V alloy scaffolds and CaCO3 coating can be successfully used in bone tissue regeneration providing the effective growth of inorganic bone phase and preventing the bacteria adhesion. © 2020 Elsevier Ltd and Techna Group S.r.l.
    view abstract10.1016/j.ceramint.2020.07.041
  • Fabrication of a novel and highly selective ion-imprinted PES-based porous adsorber membrane for the removal of mercury(II) from water
    Esmali, F. and Mansourpanah, Y. and Farhadi, K. and Amani, S. and Rasoulifard, A. and Ulbricht, M.
    Separation and Purification Technology 250 (2020)
    Herein, poly(ether sulfone) based ion imprinted membranes (IIM) were prepared through phase inversion, using ion imprinted polymer (IIP) particles obtained by radical copolymerization of acrylamide, acrylonitrile and ethyleneglycoldimethacrylate along with a template of Hg(II) complexed with bathophenanthroline (BPh). Optimization of the ability for Hg(II) removal from water and pure water flux of the IIM were investigated through Central Composite Design (CCD) combined with Response Surface Methodology (RSM). Accordingly, the optimized factors were obtained as IIP percentage of 2.5 wt% used in membrane preparation, as well as trans-membrane pressure of 0.19 bar, pH 7.95 and Hg(II) concentration of 4 ppm during filtration through the membrane. Using the optimum parameters, the removal percentage and flux of IIM were about 98.1% and 37.5 kg/m2 h, respectively. The maximum adsorption capacity of IIM was 432 mg/m2 (or 21.6 mg/g), almost four times higher than that of non-imprinted membrane (NIM; 105 mg/m2) (or 5.25 mg/g) which was prepared using copolymer particles prepared without the Hg(II) template. The IIM showed a high selectivity toward Hg(II) ions compared to other metal ions and could be effectively recycled for at least 6 times without any major loss of adsorption capacity. The synthesized imprinted membranes have demonstrated considerable potentials to selectively separate mercury(II) from simulated industrial wastewater. © 2020 Elsevier B.V.
    view abstract10.1016/j.seppur.2020.117183
  • Factors affecting the nonsolvent-induced phase separation of cellulose from ionic liquid-based solutions
    Wittmar, A.S.M. and Koch, D. and Prymak, O. and Ulbricht, M.
    ACS Omega 5 (2020)
    In the present work, we report for the first time an in-depth study of the factors influencing porous cellulose film structure formation during the nonsolvent-induced phase separation (NIPS) process from biopolymer solutions in ionic liquid-based solvents. The length of the alkyl chain of the ionic liquid's cation, the solvent/co-solvent ratio, and the type of the cellulose precursor used were found to have great influence both on cellulose solution formation and properties and to the NIPS process with water acting as nonsolvent. In the undiluted form, both studied ionic liquids proved to dissolve almost equally well the cellulose; however, due to differences in viscosities of the formed biopolymer solutions and due to differences in miscibility with water of the two ionic liquids, the used ionic liquid had a strong influence on the film's porous structure formation. The use of increasing amounts of an aprotic co-solvent, here dimethylsulfoxide, improved biopolymer solubilization and also led to the formation of a more pronounced macroporous structure during the NIPS process. The cellulose type also affected the porous structure generation during the NIPS process: with the increase of the molecular weight of the precursor, the viscosity of the formed biopolymer solution increased and the tendency to generate macroporous structures decreased. © 2020 American Chemical Society
    view abstract10.1021/acsomega.0c03632
  • High performance isotropic polyethersulfone membranes for heavy oil-in-water emulsion separation
    Abdel-Aty, A.A.R. and Aziz, Y.S.A. and Ahmed, R.M.G. and ElSherbiny, I.M.A. and Panglisch, S. and Ulbricht, M. and Khalil, A.S.G.
    Separation and Purification Technology 253 (2020)
    Isotropic polyethersulfone (PES) membrane for separation of oil-in-water nanoemulsion was successfully developed using non-solvent vapor-induced phase separation (VIPS). The surface and structural properties of the fabricated PES membranes were thoroughly characterized using various techniques. The membrane separation performance was evaluated in terms of permeate flux, oil rejection, antifouling capability, and water flux recovery. Remarkably improved surface hydrophilicity for isotropic PES membrane (contact angle, CA = 39°) compared to anisotropic PES membrane (CA = 70°), resulting in superior pure water permeance, attaining 4721 L/h⋅m2⋅bar at operating pressure of 0.5 bar. The isotropic PES membrane achieved superior crude oil-in-water nanoemulsion separation (permeance of 713 L/h⋅m2⋅bar and 100% rejection) at oil concentration of 1 g/L. At extremely high oil concentration of 50 g/L, the PES membrane was not completely fouled and showed permeance of 65 L/h⋅m2⋅bar and 98.2% rejection. Moreover, the flux recovery of the fouled isotropic PES membrane exceeded 59.5% over three subsequent cycles of filtration and back-washing with water. Overall, this study might provide substantial guidance for large-scale manufacturing and application of isotropic PES membrane in treating practically challenging emulsified oil-in-water nanoemulsion under harsh conditions. © 2020 Elsevier B.V.
    view abstract10.1016/j.seppur.2020.117467
  • High-performance positively charged hollow fiber nanofiltration membranes fabricated via green approach towards polyethyleneimine layer assembly
    Ghiasi, S. and Behboudi, A. and Mohammadi, T. and Ulbricht, M.
    Separation and Purification Technology 251 (2020)
    In this study, high performance positively charged hyper-branched polyethyleneimine (PEI) nanofiltration (NF) layer was assembled successfully on negatively charged polyethersulfone/polyimide (PES/PI) hollow fiber ultrafiltration (UF) membranes under different conditions. In accordance with principles of green chemistry, glutaraldehyde (GA) as cross-linker and purely aqueous solutions were used as a less hazardous alternative compared to, e.g. trimesoyl chloride in an organic solvent. The effects of the surface roughness and charge of the substrate UF membranes, due to the presence of PI, and various fabrication conditions, such as pH of PEI aqueous solution, GA/PEI ratio and crosslinking reaction time, were investigated and discussed. Electron microscopy images revealed the successful assembly of the PEI NF layer at uniform coverage of the PES/PI UF membranes. It was found that the varied preparation conditions drastically affect the membrane surface hydrophilicity, surface zeta potential, permeation flux, and salt rejection. The membrane fabricated at optimum conditions had a molecular weight cut-off of ≤ 400 Da; steric hindrance and Donnan exclusion resulted to achieve salt rejections of 94.2% and 87.4% for MgCl2 and MgSO4, respectively. Moreover, fabricated membranes were tested through three cycles of six-hour filtrations and over 95% flux recovery after the filtration of salts via the backwashing process was recorded. © 2020 Elsevier B.V.
    view abstract10.1016/j.seppur.2020.117313
  • Hydrophilic poly(phenylene sulfone) membranes for ultrafiltration
    Gronwald, O. and Frost, I. and Ulbricht, M. and Kouchaki Shalmani, A. and Panglisch, S. and Grünig, L. and Handge, U.A. and Abetz, V. and Heijnen, M. and Weber, M.
    Separation and Purification Technology 250 (2020)
    Poly(alkylene oxide) based tri- and multiblock oligomers with hydrophobic poly(phenylene sulfone) blocks were evaluated as dope solution additives used for preparation of improved poly(phenylene sulfone) (PPSU) flat sheet (FS) and single bore (SB) ultrafiltration membranes by non-solvent induced phase separation (NIPS). Identical polymer dope recipes were used in both of FS membrane preparation and SB fiber spinning processes. PPSU membranes modified with 9.2 wt % Pluronic® F127 based additive, M2 (7.5 kDa PPSU/ Pluronic® F127), or Lutensol® AT80 based additive, T2 (7.5 kDa PPSU/ Lutensol® AT80), displayed compared to pristine PPSU membranes elevated hydraulic permeance ranging from 485 to 674 kg m−2 bar-1h−1 (pristine PPSU: 310 – 464 kg m−2 bar-1h−1), higher molecular weight cut-off values from 37.0 to 53.5 kDa (pristine PPSU: 21.4 – 23.7 kDa), lower contact angles of 46.4° and 49.8° (pristine PPSU: 86.7°) and reduced fouling propensity with irreversible fouling values of 10 % (pristine PPSU: 15 %) for diluted potting soil extract as model substance. The combined analysis methods of X-ray photoelectron spectroscopy (XPS) and proton nuclear magnetic resonance spectroscopy (1H NMR) indicated modest surface enrichment of the additives in the filtration layer. Consequently, PPSU ultrafiltration membranes modified with additives T2 and M2 provide interesting alternatives to poly(ether sulfone) (PESU) and poly(vinylidene fluoride) (PVDF) based membranes for surface water filtration combining both excellent filtration characteristics with a long lifetime due to its higher chemical resistance. © 2020 Elsevier B.V.
    view abstract10.1016/j.seppur.2020.117107
  • Improving the efficiency of Nafion-based proton exchange membranes embedded with magnetically aligned silica-coated Co3O4 nanoparticles
    Pourzare, K. and Mansourpanah, Y. and Farhadi, S. and Hasani Sadrabadi, M.M. and Frost, I. and Ulbricht, M.
    Solid State Ionics 351 (2020)
    In this study, Nafion proton exchange membranes with incorporated silica-coated Co3O4 nanoparticles (Nafion/CT) were prepared. The nanoparticles were synthesized and characterized using FT-IR spectroscopy, XRD, magnetic measurements, TEM, SEM, and EDX spectroscopy. Thereafter, the nanoparticles were employed as an effective additive so as to improve the Nafion/CT properties. To do so, the spherical core-shell nanoparticles (Co3O4 diameter 12 nm; SiO2 layer thickness 20 nm) were aligned by a magnetic field in the Nafion matrix during solution casting and solvent evaporation. The thus obtained nanocomposite membranes, including control samples without particles or with particles but without alignment, were investigated with respect to their structure by SEM, EDX, and XPS analyses, and also with regard to their water uptake, proton conductivity, and methanol permeability. Overall, the aligned nanocomposite membranes showed much better performance than that of randomly dispersed nanocomposite membranes. The data indicate that regarding aligned structure, the proton transfer channels in the membrane matrix become less tortuous so that proton transfer through the membrane occurs faster while at the same time methanol transfer is partially blocked. The Nafion/CT nanocomposite membrane containing 1 wt% of CT exhibited a proton/methanol selectivity at 25 °C of 6.04 × 104 S s−1 cm−3, whereas the pristine Nafion membrane showed a selectivity of 4.2 × 104 S s−1 cm−3. The nanofiller alignment by magnetic field improved the proton conductivity at 90 °C from 0.14 S cm−1 (no field) to 0.18 S cm−1. © 2020
    view abstract10.1016/j.ssi.2020.115343
  • Mixed Poiseuille-Knudsen flow model for Gas Liquid Displacement porometry data treatment
    Islam, M.A. and Hossain, M.S. and Garcia-Payo, C. and Khayet, M. and Ulbricht, M.
    Journal of Membrane Science 612 (2020)
    A comprehensive methodology has been developed for treating Gas Liquid Displacement (GLD) porometry data with a flow model called Weber model (WM) describing mixed Poiseuille-Knudsen flow regime. The model has been applied in two options: i) considering that the gas viscosity in porometry experiments is the same as that available in reference books for Poiseuille flow regime and ii) equating the expression for Darcy coefficient in gas flow to that obtained in additional liquid permeability experiments and thus leaving the gas viscosity to be an adaptable parameter. In the analysis of GLD porometry data for a range of different microfiltration membranes, it is found that with the WM in both options identical relative pore-number distribution is estimated; and this distribution satisfactorily reproduces both dry and wet flow data from the GLD experiments. The absolute pore-number distributions obtained by the two options are quite similar, but differ in the absolute value of the pore numbers. The pore-number distribution obtained by the second option describes the liquid permeability well, while the first option fails. The WM as a method of GLD porometry data treatment is quite similar to the earlier introduced variable viscosity Poiseuille model (VVPM), and the variable viscosity from the latter model appears to be a combined effect of an uncertainty about actual gas viscosity and the contribution of Knudsen flow. It is concluded that a standard test method for determining pore-size distribution by GLD porometry must include prediction or description of liquid permeability of the membrane. Then, any acceptable gas flow model with adjusted Darcy coefficient obtained from liquid permeability experiment will be suitable for advanced GLD porometry data treatment, beyond the methods typically implemented in gas flow-based porometers, currently used in academia and industry. © 2020 Elsevier B.V.
    view abstract10.1016/j.memsci.2020.118422
  • Modification of polysulfone ultrafiltration membranes via addition of anionic polyelectrolyte based on acrylamide and sodium acrylate to the coagulation bath to improve antifouling performance in water treatment
    Plisko, T.V. and Bildyukevich, A.V. and Burts, K.S. and Hliavitskaya, T.A. and Penkova, A.V. and Ermakov, S.S. and Ulbricht, M.
    Membranes 10 (2020)
    Surface modification of polysulfone ultrafiltration membranes was performed via addition of an anionic polymer flocculant based on acrylamide and sodium acrylate (PASA) to the coagulation bath upon membrane preparation by non-solvent induced phase separation (NIPS). The effect of PASA concentration in the coagulant at different coagulation bath temperatures on membrane formation time, membrane structure, surface roughness, hydrophilic-hydrophobic balance of the skin layer, surface charge, as well as separation and antifouling performance was studied. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, contact angle and zeta potential measurements were utilized for membrane characterization. Membrane barrier and antifouling properties were evaluated in ultrafiltration of model solutions containing human serum albumin and humic acids as well as with real surface water. PASA addition was found to affect the kinetics of phase separation leading to delayed demixing mechanism of phase separation due to the substantial increase of coagulant viscosity, which is proved by a large increase of membrane formation time. Denser and thicker skin layer is formed and formation of macrovoids in membrane matrix is suppressed. FTIR analysis confirms the immobilization of PASA macromolecules into the membrane skin layer, which yields improvement of hydrophilicity and change of zeta potential. Modified membrane demonstrated better separation and antifouling performance in the ultrafiltration of humic acid solution and surface water compared to the reference membrane. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/membranes10100264
  • One-step preparation of antifouling polysulfone ultrafiltration membranes via modification by a cationic polyelectrolyte based on polyacrylamide
    Plisko, T.V. and Bildyukevich, A.V. and Burts, K.S. and Ermakov, S.S. and Penkova, A.V. and Kuzminova, A.I. and Dmitrenko, M.E. and Hliavitskaya, T.A. and Ulbricht, M.
    Polymers 12 (2020)
    A novel method for one-step preparation of antifouling ultrafiltration membranes via a non-solvent induced phase separation (NIPS) technique is proposed. It involves using aqueous 0.05-0.3 wt. % solutions of cationic polyelectrolyte based on a copolymer of acrylamide and 2-acryloxyethyltrimethylammonium chloride (Praestol 859) as a coagulant in NIPS. Asystematic study of the effect of the cationic polyelectrolyte addition to the coagulant on the structure, performance and antifouling stability of polysulfone membranes was carried out. The methods for membrane characterization involved scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), contact angle and zeta-potential measurements and evaluation of the permeability, rejection and antifouling performance in human serum albumin solution and surface water ultrafiltration. It was revealed that in the presence of cationic polyelectrolyte in the coagulation bath, its concentration has a major influence on the rate of "solvent-non-solvent" exchange and thus also on the rate of phase separation which significantly affects membrane structure. The immobilization of cationic polyelectrolyte macromolecules into the selective layer was confirmed by FTIR spectroscopy. It was revealed that polyelectrolyte macromolecules predominately immobilize on the surface of the selective layer and not on the bottom layer. Membrane modification was found to improve the hydrophilicity of the selective layer, to increase surface roughness and to change zeta-potential which yields the substantial improvement of membrane antifouling stability toward natural organic matter and human serum albumin. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/POLYM12051017
  • One-step preparation of porous cellulose/chitosan macro-spheres from ionic liquid-based solutions
    Wittmar, A.S.M. and Böhler, H. and Kayali, A.L. and Ulbricht, M.
    Cellulose 27 (2020)
    Abstract: Environmentally friendly and easily biodegradable porous adsorbents for water purification based on cellulose and chitosan blends have been prepared by a green technology utilizing room temperature ionic liquids as main solvent component. The dissolution and re-precipitation mechanisms for the two biopolymers and of their mixtures have been studied in detail, targeting to optimize the composition of the casting solutions and make them adequate for preparation of porous polymer spheres by the “dropping cum phase separation” technique. With the increase of the chitosan content in the sample the time required for the polymer dissolution was increasing and the amount of water necessary to destabilize the formed casting solution was decreasing. Further on, the viscosities of the casting solutions had a strong impact on the formation of the porous structure during the non-solvent induced phase separation process. For the blend spheres prepared from 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]) based solutions materials with higher specific surface areas and improved Cu2+ adsorption capacity were obtained at the increase of the chitosan fraction in the polymer blend. For the samples prepared from 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) based solutions no such a trend has been observed. Graphic abstract: [Figure not available: see fulltext.]. © 2020, Springer Nature B.V.
    view abstract10.1007/s10570-020-03165-y
  • Polyethyleneoxide-b-poly(Isopropyl methacrylate) diblock copolymers as novel material for ultrafiltration membranes
    Gaalken, J. and Ulbricht, M.
    Journal of Polymer Science 58 (2020)
    Amphiphilic polyethyleneoxide-b-poly(isopropyl methacrylate) (PEO-b-PiPMA) diblock copolymers (BCP) with different molar masses are synthesized via atom transfer radical polymerization (ATRP). For that functionalized PEO monomethyl ether with two different molar masses, 10 and 20 kDa, are used as macroinitiator to obtain BCP in a molar mass range relevant for membrane fabrication. The BCP are used in the nonsolvent induced phase separation (NIPS) with the aim to obtain iso-porous ultrafiltration membranes due to combination with its self-assembling properties (SNIPS). In various experiments, a strong effect of PEO homopolymer (hPEO) on the membrane formation process can be proven in which fractions of BCP with low molar mass might also play a role. These impurities are left in the BCP after ATRP due to incomplete purification. Under specific conditions, they induce formation of void-like superstructures on the membrane surface and in the cross section by a templating mechanism. Probably, large compound micelles play a key role in this scenario hindering the favored SNIPS process. The superstructure formation can be avoided by extensive purification of the BCP via dialysis or extraction. From the purified polymers, self-supported ultrafiltration membranes with an integrated hydrophilic component are success-fully fabricated. Although they do not lead to isoporous surfaces after semiempirical determination of suitable solvent systems for the SNIPS process, there are convincing indications that the trade-off relation between selectivity and permeability can be overcome. © 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc.
    view abstract10.1002/pol.20190155
  • Polymer nanocomposite ultrafiltration membranes: The influence of polymeric additive, dispersion quality and particle modification on the integration of zinc oxide nanoparticles into polyvinylidene difluoride membranes
    Berg, T.D. and Ulbricht, M.
    Membranes 10 (2020)
    This study aims to improve the understanding of the influence of metal oxide nanofillers on polyvinylidene difluoride (PVDF) ultrafiltration membranes. Zinc oxide nanoparticles were chosen as the model filler material. The membranes were prepared by non-solvent induced phase separation from PVDF solutions in N-methylpyrrolidone. The influences of the addition of polyvinylpyrrolidone (PVP), the nanoparticle dispersion quality, and a surface modification of the ZnO particles with PVP on the nanofiller integration into the polymer matrix and the resulting membrane separation performance, were evaluated. Unmodified and PVP-modified nanoparticles were characterized by evaluation of their Hansen solubility parameters. The membranes were characterized by ultrafiltration experiments, scanning electron microscopy (SEM) and with respect to mechanical properties, while the dope solutions were analyzed by rheology in order to judge about dispersion quality. Pure water permeability and solute rejection data revealed that the dominant effect of the addition of pristine ZnO nanoparticles was a major decrease in permeability caused by pore blocking. In SEM analyses, it was seen that the plain nanofiller did not integrate well into the polymer matrix. Importantly, it was found that the surface modification of the nanofiller, as well as a high dispersion quality, can be strategically used to enhance the integration of the nanofiller and thus suppress pore blocking, leading to membranes with high ultrafiltration rejection and permeability simultaneously. Overall, the study provides relevant insights into a new approach to integrating nanofillers into polymer nanocomposite membranes for improving their properties and performance. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/membranes10090197
  • Preparation and characterization of polyzwitterionic hydrogel coated polyamide-based mixed matrix membrane for heavy metal ions removal
    Pakizeh, M. and May, P. and Matthias, M. and Ulbricht, M.
    Journal of Applied Polymer Science 137 (2020)
    A novel polyzwitterionic hydrogel coated mixed matrix membrane (MMM) was successfully prepared, characterized and used for Cu2+, Mn2+, and Pb2+ heavy metal ions removal from water. Hydrophilic and porous covalent organic framework (COF) nanoparticles (NP) as filler were synthesized from melamine and terephthalaldehyde, and then incorporated into polyamide (PA) thin film composite (TFC) membrane. The hydrogel coating was applied by using a tailored cross-linkable polymer system in combination with concentration polarization enabled cross-linking. The effects of COF NP loading into PA layer and polyzwitterionic hydrogel coating on the membrane morphology and separation performance were studied using different analyses. The MMM prepared with a COF NP loading of 0.02 wt/wt% in the hexane dispersion used for NP deposition during PA layer formation (leading to 0.42 g/m2) exhibited an increased pure water permeability of around 200% compared with the neat PA TFC membrane while the Mn2+ ion rejection maintained above 98%. Scanning electron microscopy surface images and zeta potential profiles showed that the hydrogel was successfully deposited on the membrane surface. Furthermore, the hydrogel coating could decrease net surface charge of membranes but did not significantly influence the heavy metal ions rejections under nanofiltration conditions. The results of filtration experiment with protein solution indicated that the hydrogel coated membranes exhibited superior antifouling property, as shown by higher flux recovery ratio after washing with water, compared with neat PA TFC membrane and not coated MMM, respectively. © 2020 Wiley Periodicals LLC
    view abstract10.1002/app.49595
  • Preparation of antibiofouling nanocomposite PVDF/Ag-SiO2 membrane and long-term performance evaluation in the MBR system fed by real pharmaceutical wastewater
    Ahsani, M. and Hazrati, H. and Javadi, M. and Ulbricht, M. and Yegani, R.
    Separation and Purification Technology 249 (2020)
    In this work, the Ag-SiO2 nanoparticles were successfully synthesized and their antibacterial property was confirmed using the plate colony counting method. The SiO2 and Ag-SiO2 nanoparticles were used to prepare the PVDF/SiO2 and PVDF/Ag-SiO2 nanocomposite membranes, respectively. Pure water flux, contact angle and mechanical strength measurement analyses were conducted to characterize and compare the performance of the neat and nanocomposite membranes. Moreover, in order to investigate the structure of the prepared membranes scanning electron microscope (SEM) was used to obtain surface and cross-section images. A long-term filtration test was carried out in a bench scale submerged membrane bioreactor (MBR) system, fed by real pharmaceutical wastewater, to evaluate the antibiofouling performance of the prepared neat and nanocomposite membranes. In comparison to the neat PVDF, the pure water flux of the nanocomposite PVDF membrane (PVDF/Ag-SiO2; 0.6 wt%) increased about 60% and the water contact angle decreased from about 99° to 89°. The obtained results showed that the nanocomposite PVDF/Ag-SiO2 membrane exhibits considerable antibiofouling properties such that the accumulated dried biofilm as well as the extra cellular polymeric substances (EPSs) collected from the cake layer decreased considerably for the nanocomposite membrane. Moreover, the flux recovery ratio increased from 58% for the neat PVDF membrane to 76% for the nanocomposite PVDF/Ag-SiO2 membrane. The excitation and emission matrix (EEM) fluorescence spectroscopy analysis revealed that the accumulated protein on the surface of nanocomposite membranes decreased considerably in a way that the peak corresponding to tryptophan protein-like substances diminished completely, indicating the high antibiofouling potential of nanocomposite membranes. The chemical oxygen demand (COD) and ammonium removal efficiencies of the neat and nanocomposite membranes were higher than 90% and 95%, respectively, indicating negligible impact of the membrane modification on the effluents’ quality. © 2020
    view abstract10.1016/j.seppur.2020.116938
  • Tailored CNTs buckypaper membranes for the removal of humic acid and separation of oil-in- water emulsions
    Elnabawy, E. and Elsherbiny, I.M.A. and Abdelsamad, A.M.A. and Anis, B. and Hassan, A. and Ulbricht, M. and Khalil, A.S.G.
    Membranes 10 (2020)
    Carbon nanotubes (CNTs) are a robust material and proven as a promising candidate for a wide range of electronic, optoelectronic and environmental applications. In this work, two different methods were utilized for the preparation of CNTs exhibiting different aspect ratios via chemical vapor deposition (CVD). The as-prepared CNTs were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption isotherms, thermogravimetric analysis and Raman spectroscopy in order to investigate their morphological and structural properties. Free-standing CNTs “buckypaper” membranes were fabricated, characterized and tailored to meet the requirements of two applications, i.e., (1) the removal of humic acid (HA) from water and (2) separation of oil-in-water emulsions. It was revealed that the hydrophobic buckypapers showed high separation performance for Shell oil-in-water emulsions filtration, with up to 98% through the accumulation of oil droplets onto the membrane surface. The absorption capacity of buckypaper membranes for various organic liquids (oil, chloroform and toluene) was evaluated over 10 absorption cycles to investigate their recyclability and robustness. Moreover, surface modification was introduced to the pristine CNTs to increase their surface hydrophilicity and improve the pure water permeability of buckypapers. These modified buckypapers showed high flux for HA solutions and excellent HA rejection efficiency up to 95%via size exclusion and electrostatic repulsion mechanisms. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/membranes10050097
  • Tailoring and remotely switching performance of ultrafiltration membranes by magnetically responsive polymer chains
    Vu, A. and Sengupta, A. and Freeman, E. and Qian, X. and Ulbricht, M. and Wickramasinghe, S.R.
    Membranes 10 (2020)
    Magnetically responsive ultrafiltration membranes were prepared by grafting poly(2-hydroxyethyl methacrylate) chains from the outer surface of 100-kDa regenerated cellulose ultrafiltration membranes. Surface-initiated atom transfer radical polymerization was used to graft the polymer chains. Grafting from the internal pore surface was suppressed by using glycerol as a pore-filling solvent during initiator immobilization at varied densities. Glycerol suppresses the initiator attachment to the pore surface. Polymerization times of up to four hours were investigated. Superparamagnetic nanoparticles were covalently attached to the chain end. Membrane performance was determined using bovine serum albumin and dextran as model solutes. Increasing the grafted polymer chain density and length led to a decrease in the permeate flux and an increase in the apparent rejection coefficient. In an oscillating magnetic field, movement of the grafted polymer chains led to a decrease in the permeate flux, as well as an increase in the apparent rejection coefficient of the model solutes. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/membranes10090219
  • TETA-anchored graphene oxide enhanced polyamide thin film nanofiltration membrane for water purification; performance and antifouling properties
    Izadmehr, N. and Mansourpanah, Y. and Ulbricht, M. and Rahimpour, A. and Omidkhah, M.R.
    Journal of Environmental Management 276 (2020)
    This work investigates the performance and structure of polyamide thin film nanocomposite (PA-TFN) membrane incorporated with triethylenetetramine-modified graphene oxide (GO-TETA). The embedment of GO-TETA nanosheets within the structure of PA-TFN membrane was evaluated at different concentrations (0.005, 0.01, 0.03 wt%; in aqueous piperazine (PIP)) through interfacial polymerization (IP). The physicochemical properties of the prepared membrane were investigated by SEM, AFM, water contact angle, and zeta potential as well as ATR-IR spectroscopy. The presence of longer chains of amino groups (in comparison with the directly linked amino ones) among the stacked GO nanosheets was assumed to increase interlayer spacing, resulting in remarkable changes in water permeance and separation behavior of modified polyamide (PA) membrane. It is seen that GO-TETA nanosheets were uniformly distributed in the matrix of PA layer. With increasing the concentration of GO-TETA, the flux of TFN membranes under 6 bar was increased from 49.8 l/m2 h (no additive) to 73.2 l/m2 h (TFN comprising 0.03 wt% GO-TETA. In addition, more loading GO-TETA resulted in a significant decrease in the average thickness of the polyamide layer from ~380 to ~150 nm. Furthermore, addition of GO-TETA improved the hydrophilicity of nanocomposite membranes, resulting in superb water flux recovery (antifouling indicator) as high as 95% after filtration of bovine serum albumin solution. Also, the retention capability of the TFN membranes towards some textile dyes increased as high as 99.6%. © 2020 Elsevier Ltd
    view abstract10.1016/j.jenvman.2020.111299
  • The Investigation of the Influence of Low-Temperature Plasma and Steam Sterilization on the Properties of Track Membranes Made of Polyethylene Terephthalate
    Filippova, E.O. and Karpov, D.A. and Pichugin, V.F. and Ulbricht, M.
    Inorganic Materials: Applied Research 11 (2020)
    Abstract: The influence of modification by low-temperature atmospheric-pressure plasma and steam sterilization on the properties of track membranes based on polyethylene terephthalate is studied. It is found that the action of hot steam under pressure changes the topography of the surface of the membranes with the formation of artifacts in the form of large oval-shaped protrusions with a height of 300–400 nm and a density of up to 0.007 protrusions/μm2 on the surface, increases the surface roughness by 40% and the wetting angle by 9°–18° for the initial membranes and by 36.8°–39.6° for the membranes modified in plasma, and decreases their surface energy to the initial value of 33 mJ/m2. Despite the morphological and structural changes in the surface, sterilization by hot steam under pressure does not lead to any noticeable change in the surface charge and ζ potential of the track membranes. Hot steam under pressure does not promote further crystallization of the membrane, keeping the polymer with a crystalline phase of 40–42%. Thus, to preserve the properties acquired by the membrane after the plasma treatment, it is necessary to search for a different sterilization method (gamma radiation, ethylene oxide sterilization). © 2020, Pleiades Publishing, Ltd.
    view abstract10.1134/S2075113320050111
  • Thinking the future of membranes: Perspectives for advanced and new membrane materials and manufacturing processes
    Nunes, S.P. and Culfaz-Emecen, P.Z. and Ramon, G.Z. and Visser, T. and Koops, G.H. and Jin, W. and Ulbricht, M.
    Journal of Membrane Science 598 (2020)
    The state-of-the-art of membrane technology is characterized by a number of mature applications such as sterile filtration, hemodialysis, water purification and gas separation, as well as many more niche applications of successful membrane-based separation and processing of fluid mixtures. The membrane industry is currently employing a portfolio of established materials, mostly standard polymers or inorganic materials (not originally developed for membranes), and easily scalable manufacturing processes such as phase inversion, interfacial polymerization and coating. Innovations in membranes and their manufacturing processes must meet the desired intrinsic properties that determine selectivity and flux, for specific applications. However, tunable and stable performance, as well as sustainability over the entire life cycle of membrane products are becoming increasingly important. Membrane manufacturers are progressively required to share the carbon footprint of their membrane modules with their customers. Environmental awareness among the world's population is a growing phenomenon and finds its reflection in product development and manufacturing processes. In membrane technology one can see initial steps in this direction with the replacement of hazardous solvents, the utilization of renewable materials for membrane production and the reuse of membrane modules. Other examples include increasing the stability of organic membrane polymers and lowering the cost of inorganic membranes. In a long-term perspective, many more developments in materials science will be required for making new, advanced membranes. These include “tools” such as self-assembly or micro- and nano-fabrication, and “building blocks”, e.g. tailored block copolymers or 1D, 2D and 3D materials. Such membranes must be fabricated in a simpler manner and be more versatile than existing ones. In this perspective paper, a vision of such LEGO®-like membranes with precisely adjustable properties will be illustrated with, where possible, examples that already demonstrate feasibility. These include the possibility to switch properties using an external stimulus, adapting a membrane's selectivity to a given separation, or providing the ability to assemble, disassemble and reassemble the membrane on a suitable support as scaffold, in situ, in place and on-demand. Overall, it is foreseen that the scope of future membrane applications will become much wider, based on improved existing membrane materials and manufacturing processes, as well as the combination of novel, tailor-made “building blocks” and “tools” for the fabrication of next-generation membranes tuned to specific applications. © 2020 Elsevier B.V.
    view abstract10.1016/j.memsci.2019.117761
  • Tunable and switchable nanoparticle separation with thermo-responsive track-etched membranes prepared by controlled surface-initiated polymerization of poly(N-isopropylacrylamide)
    Daumann, K. and Frost, S. and Ulbricht, M.
    RSC Advances 10 (2020)
    This work describes how the control of grafting density and grafted chain length of a thermo-responsive polymer in membrane pores can be utilized to tune the pore size and the switchability of size-based selectivity in the ultrafiltration range. Using a previously established methodology for controlled synthesis, surface-initiated atom transfer polymerization (ATRP) of poly(N-isopropylacrylamide) (PNIPAAm) to the pore walls of poly(ethylene terephthalate) track-etched membranes with experimentally determined pore diameters of 35 nm (PET30) and 110 nm (PET80) is performed. Characterization in this study is mainly done with filtration experiments, making use of the well-defined pore structure of the base membranes. It is demonstrated that both the gravimetrically determined degree of functionalization and the effective pore size determined from water permeability are a linear function of ATRP time. For the grafted PET30 membranes, it is shown that the rejection of lysozyme (diameter ∼ 4 nm) can be switched between 99% at 23 °C and 65% at 45 °C for the membrane with the highest degree of functionalization. For the grafted PET80 membranes, it is found that two different types of membranes can be obtained. Membranes with long grafted chains at low grafting density show very large changes of water permeability as a function of temperature (effective pore size switching ratio of up to 10) and, for example, rejection for 20 nm silica particles of 95% and 23% at 23 °C and 45 °C, respectively. Membranes with PNIPAAm at high grafting density show much lower switching ratios (as low as 1.4, for long enough grafted chains). Effective pore size and thermo-responsive change of pore size can therefore be tuned by the combination of both synthesis parameters, initiator density and ATRP time. The switchable thermo-responsive separation of two colloids with a tailored membrane is demonstrated for mixtures of bovine serum albumin (BSA; ∼7 nm) and silica nanoparticles (20 nm); at 23 °C silica is completely rejected and only BSA is in the permeate; at 40 °C both colloids permeate through the membrane. © The Royal Society of Chemistry 2020.
    view abstract10.1039/d0ra03418e
  • β-Cyclodextrin-based star polymers for membrane surface functionalization: Covalent grafting via “click” chemistry and enhancement of ultrafiltration properties
    Büning, J. and Frost, I. and Okuyama, H. and Lempke, L. and Ulbricht, M.
    Journal of Membrane Science 596 (2020)
    This work provides the proof-of-concept that surface functionalization of porous membranes with well-defined star-like polymers of varied number of arms and arm length leads to a tunable effective thickness of grafted layers and a specific influence on size-selective sieving through ultrafilter pores. Alkyl-brominated β-cyclodextrine with either 7 or 21 initiator sites per molecule was synthesized and further used for controlled atom transfer radical polymerization of copolymers of 2-dimethylamino(ethyl) methacrylate (DMAEMA) and propargyl methacrylate (PgMA), leading to star polymers with either 7 or 21 arms. Alkyne-containing PgMA segments enable the “click” coupling while DMAEMA segments provide the bulk of the polymer. Star polymers were characterized with respect to chemical structure and molecular weight (M). During ultrafiltration (UF) through cellulose membranes with different molecular weight cut-off, rejection was not simply correlated with star polymer M but was governed by macromolecular architecture, i.e. the smaller colloidal diameter for macromolecules of same M but 21 instead of 7 arms. Azide-functionalized poly(ethylene terephthalate) (PET) track-etched (TE) membranes and cellulose UF membranes were prepared by polymer-analogous surface functionalization so that the alkyne-substituted star polymers could be “click”-grafted. Isoporous PET TE membranes with a nominal pore diameter of 200 nm were used as model system to study the grafting and its effects onto pore size via the reduction of hydraulic permeability. Effective grafted layer thickness in the range of 10–50 nm correlated with macromolecular structure and architecture. For “click”-functionalized cellulose UF membranes, the effective pore size in the barrier layer was influenced by grafted star polymers, and a pronounced additional influence of the architecture and arm length of the grafted star polymer on macromolecular sieving was observed. Of particular interest are results with the more flexible 7-armed star polymers (compared to 21-armed counterparts); their grafting at the UF membrane pores of similar dimension leads to a large increase of test solute rejection at very low reduction of convective water flux, both compared to the unmodified membrane. © 2019 Elsevier B.V.
    view abstract10.1016/j.memsci.2019.117610
  • Adhesion, proliferation, and osteogenic differentiation of human mesenchymal stem cells on additively manufactured Ti6Al4V alloy scaffolds modified with calcium phosphate nanoparticles
    Chudinova, E.A. and Surmeneva, M.A. and Timin, A.S. and Karpov, T.E. and Wittmar, A. and Ulbricht, M. and Ivanova, A. and Loza, K. and Prymak, O. and Koptyug, A. and Epple, M. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 176 (2019)
    In the present study, biocomposites based on 3D porous additively manufactured Ti6Al4V (Ti64) scaffolds modified with biocompatible calcium phosphate nanoparticles (CaPNPs) were investigated. Ti64 scaffolds were manufactured via electron beam melting technology using an Arcam machine. Electrophoretic deposition was used to modify the scaffolds with CaPNPs, which were synthesized by precipitation in the presence of polyethyleneimine (PEI). Dynamic light scattering revealed that the CaP/PEI nanoparticles had an average size of 46 ± 18 nm and a zeta potential of +22 ± 9 mV. Scanning electron microscopy (SEM) revealed that the obtained spherical CaPNPs had an average diameter of approximately 90 nm. The titanium-based scaffolds coated with CaPNPs exhibited improved hydrophilic surface properties, with a water contact angle below 5°. Cultivation of human mesenchymal stem cells (hMSCs) on the CaPNPs-coated Ti64 scaffolds indicated that the improved hydrophilicity was beneficial for the attachment and growth of cells in vitro. The Ti6Al4V/CaPNPs scaffold supported an increase in the alkaline phosphatase (ALP) activity of cells. In addition to the favourable cell proliferation and differentiation, Ti6Al4V/CaPNPs scaffolds displayed increased mineralization compared to non-coated Ti6Al4V scaffolds. Thus, the developed composite 3D scaffolds of Ti6Al4V functionalized with CaPNPs are promising materials for different applications related to bone repair. © 2018 Elsevier B.V.
    view abstract10.1016/j.colsurfb.2018.12.047
  • Analysis of wake structures in bubbly flows using Particle Image Velocimetry (PIV)
    Lewandowski, B. and Fertig, M. and Krekel, G. and Ulbricht, M.
    Chemical and Process Engineering - Inzynieria Chemiczna i Procesowa 40 (2019)
    The flow structure around rising single air bubbles in water and their characteristics, such as equivalent diameter, rising velocity and shape, was investigated using Particle Image Velocimetry (PIV) and Shadowgraphy in a transparent apparatus with a volume of 120 mL. The effect of different volumetric gas flow rates, ranging from 4 μL/min to 2 mL/min on the liquid velocity was studied. Ellipsoidal bubbleswere observedwith a rising velocity of 0.25-0.29m/s. It was found that a Kármán vortex street existed behind the rising bubbles. Furthermore, the wake region expanded with increasing volumetric gas flow rate as well as the number and size of the vortices. © 2019 Polish Academy of Sciences. All rights reserved.
    view abstract10.24425/cpe.2018.124996
  • Application of Raman spectroscopy to the flotation process of fluorite
    Lewandowski, B. and Said, B.B. and Ulbricht, M. and Krekel, G.
    Minerals Engineering 135 (2019)
    Exact knowledge of the content of the various components in a flotation system is critical in both product analysis and process control. In the present work, FT Raman spectroscopy was successfully applied to an industrial fluorite flotation system for quantification of calcium fluoride (CaF 2 ). In a first step, an artificial model system consisting of CaF 2 , barium sulphate and silica was set up to test feasibility of FT Raman spectroscopy and to generate a calibration curve. An empirical model was developed, which incorporates effects of particle size on Raman shift and peak area, so that a CaF 2 quantification is feasible independent of particle size. Conversely, the empirical model provides information about the approximate particle size in the analysed sample. A cross-validation using X-ray fluorescence spectroscopy showed excellent quantification of CaF 2 in seven industrial fluorite samples with CaF 2 weight fraction in a range from 7% to 98% with absolute differences of less than 5%. In a first laboratory batch-flotation experiment, the CaF 2 content of the froth product could be quantified successfully providing additional information about the approximate median particle size of the concentrate, making FT Raman spectroscopy superior to commonly applied X-ray fluorescence spectroscopy. © 2019 Elsevier Ltd
    view abstract10.1016/j.mineng.2019.02.038
  • Decreased bacterial colonization of additively manufactured Ti6Al4V metallic scaffolds with immobilized silver and calcium phosphate nanoparticles
    Surmeneva, M. and Lapanje, A. and Chudinova, E. and Ivanova, A. and Koptyug, A. and Loza, K. and Prymak, O. and Epple, M. and Ennen-Roth, F. and Ulbricht, M. and Rijavec, T. and Surmenev, R.
    Applied Surface Science 480 (2019)
    The design of an ideal bone graft substitute has been a long-standing effort, and a number of strategies have been developed to improve bone regeneration. Electron beam melting (EBM) is an additive manufacturing method allowing for the production of porous implants with highly defined external dimensions and internal architectures. The increasing surface area of the implant may also increase the abilities of pathogenic microorganisms to adhere to the surfaces and form a biofilm, which may result in serious complications. The aim of this study was to explore the modifications of Ti6Al4V alloy scaffolds to reduce the abilities of bacteria to attach to the EBM-manufactured implant surface. The layers composed of silver (Ag), calcium phosphate (CaP) nanoparticles (NPs) and combinations of both were formed on the EBM-fabricated metallic scaffolds by electrophoretic deposition in order to provide them with antimicrobial properties. The assay of bacterial colonization on the surface was performed with the exposure of scaffold surfaces to Staphylococcus aureus cells for up to 17 h. Principal component analysis (PCA) was used to assess the relationships between different surface features of the studied samples and bacterial adhesion. The results indicate that by modifying the implant surface with appropriate nanostructures that change the hydrophobicity and the surface roughness at the nano scale, physical cues are provided that disrupt bacterial adhesion. Our results clearly show that AgNPs at a concentration of approximately 0.02 mg/сm 2 that were deposited together with CaPNPs covered by positively charge polyethylenimine (PEI) on the surface of EBM-sintered Ti6Al4V scaffolds hindered bacterial growth, as the total number of attached cells (NAC) of S. aureus remained at the same level during the 17 h of exposure, which indicates bacteriostatic activity. © 2019 Elsevier B.V.
    view abstract10.1016/j.apsusc.2019.03.003
  • Functionalization of titania nanotubes with electrophoretically deposited silver and calcium phosphate nanoparticles: Structure, composition and antibacterial assay
    Chernozem, R.V. and Surmeneva, M.A. and Krause, B. and Baumbach, T. and Ignatov, V.P. and Prymak, O. and Loza, K. and Epple, M. and Ennen-Roth, F. and Wittmar, A. and Ulbricht, M. and Chudinova, E.A. and Rijavec, T. and Lapanje, A. and Surmenev, R.A.
    Materials Science and Engineering C 97 (2019)
    Herein TiO2 nanotubes (NTs) were fabricated via electrochemical anodization and coated with silver and calcium phosphate (CaP) nanoparticles (NPs) by electrophoretic deposition. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed that Ag and CaP NPs were successfully deposited onto the TiO2 NTs. Using X-ray diffraction, only anatase and Ti were observed after deposition of Ag and CaP NPs. However, X-ray photoelectron spectroscopy (XPS) analysis revealed that the binding energy (BE) of the Ag and CaP NP core levels corresponded to metallic Ag, hydroxyapatite and amorphous calcium phosphate, based on the knowledge that CaP NPs synthesized by precipitation have the nanocrystalline structure of hydroxyapatite. The application of Ag NPs allows for decreasing the water contact angle and thus increasing the surface free energy. It was concluded that the CaP NP surfaces are superhydrophilic. A significant antimicrobial effect was observed on the TiO2 NT surface after the application of Ag NPs and/or CaP NPs compared with that of the pure TiO2 NTs. Thus, fabrication of TiO2 NTs, Ag NPs and CaP NPs with PEI is promising for diverse biomedical applications, such as in constructing a biocompatible coating on the surface of Ti that includes an antimicrobial effect. © 2018 Elsevier B.V.
    view abstract10.1016/j.msec.2018.12.045
  • Functionalization of Ultrafiltration Membranes for Integration of Specific Adsorber Properties [Funktionalisierung von Ultrafiltrationsmembranen zur Integration von spezifischen Adsorbereigenschaften]
    Koch, D. and Ulbricht, M.
    Chemie-Ingenieur-Technik 91 (2019)
    By integrating a water-soluble polymer, which has the ability to complex heavy metal ions into ultrafiltration membranes, the separation process could be enhanced to enable also filtration of these species. In this work, a membrane and an adsorber polymer were functionalized with complementary reactive groups so that the adsorber polymer could be immobilized in the porous support layer of the ultrafiltration membrane via click reaction. The separation performances and membrane characteristics of the synthesized membranes are comparable to those of conventional UF membranes. © 2019, Wiley-VCH Verlag. All rights reserved.
    view abstract10.1002/cite.201900046
  • Glucose-Responsive Polymeric Hydrogel Materials: From a Novel Technique for the Measurement of Glucose Binding toward Swelling Pressure Sensor Applications
    Walter, S.V. and Ennen-Roth, F. and Büning, D. and Denizer, D. and Ulbricht, M.
    ACS Applied Bio Materials 2 (2019)
    This work presents new insights into material design and physicochemical interactions that are relevant for the use of glucose-responsive polymeric hydrogels in continuously operating biosensor systems. Investigated hydrogels were based on either acrylamide or N-isopropylacrylamide, covalently cross-linked by N,N′-methylenebis(acrylamide), and 3-acrylamidophenylboronic acid and (N-(3-dimethylaminopropyl)) acrylamide were the comonomers to enable selective glucose binding at a physiological pH. A novel assay for the determination of the amount of bound glucose inside the hydrogel was developed, enabling the direct recording of these receptor effects parallel to the determination of the change of water content, i.e., free swelling. Binding isotherms, affinity constants, and maximum degree of complexation of boronic acid groups with glucose were determined. The affinity toward glucose could be increased 3-fold compared to literature values for phenylboronic acid free in solution by the use of a suitable hydrogel composition. The library of differently composed materials was then evaluated in a pressure sensor setup. Thereby, the long-term use of the hydrogels was established, and the hydrogels could be analyzed for a period of three months without the reduction of the pressure signal sensitivity. Based on all results, a composition that is suitable for efficient glucose recognition was identified, at which up to 25% water was released at 37 °C and pH 7.4 and a change of the glucose concentration from 0 to 10 mM. In the physiologically relevant range (3-10 mM), a linear dependence of the swelling pressure on the glucose concentration was found, allowing an accurate determination of glucose concentration. Overall, the obtained results provide significant progress in efforts to enable glucose detection by a robust sensor setup. © 2019 American Chemical Society.
    view abstract10.1021/acsabm.9b00168
  • Influence of Calcium-Phosphate Coating on Wettability of Hybrid Piezoelectric Scaffolds
    Zviagin, A. and Chernozem, R. and Surmeneva, M. and Loza, K. and Prymak, O. and Ulbricht, M. and Epple, M. and Surmenev, R.
    IOP Conference Series: Materials Science and Engineering 597 (2019)
    Herein, electrospun biodegradable scaffolds based on polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB) and polyaniline (PANi) polymers were fabricated. A calcium-phosphate (CaP) coating was deposited on the surface of the scaffolds via an improved soaking process. Influence of the deposition cycles and ethanol concentration in the solution on the relative increase of the scaffolds weight and water contact angle (WCA) are determined. The characterization of the molecular and crystal structure confirmed the formation of CaP phase. Importantly, WCA results showed that the pristine scaffolds have the hydrophobic surface, while the deposition of CaP coating onto scaffolds allows to significantly improve the surface wetting behavior, and infiltration of the water droplets into the CaP-coated scaffolds was observed. Thus, the fabricated hybrid biodegradable piezoelectric scaffolds can be utilized for regenerative medicine. © Published under licence by IOP Publishing Ltd.
    view abstract10.1088/1757-899X/597/1/012061
  • Influence of flow alterations on bacteria retention during microfiltration
    Helling, A. and Grote, C. and Büning, D. and Ulbricht, M. and Wessling, M. and Polakovic, M. and Thom, V.
    Journal of Membrane Science 575 (2019)
    Microfiltration membranes retain bacteria predominantly by size-exclusion. However, some empirical data points towards the fact, that alterations in flow rate as well as changes in the quality of adhesive interactions between the membrane surface and the bacteria can affect their retention. For parvo virus retaining normal flow virus-filters, systematic investigations have been undertaken to characterize the impact of flow alterations as well as modulations of particle-membrane interactions on virus particle retention. For depth filters used, e.g., for the clarification of fermentation broths, it is well known that alterations in flow rate typically lead to elevated levels of turbidity. This work adopts the acquired knowledge from virus- and depth-filters and investigates their applicability for bacteria retention by microfiltration membranes. It presents particle retention data for mycoplasma and Gram-negative and Gram-positive bacteria. Single layer flat sheet PES model microfiltration membranes with maximum pore sizes varying from 0.3 to 1.5 µm and an overall low retention were used in order to easily detect and differentiate their retention properties for the different particle species. The event of particle breakthrough is elucidated depending on the adsorptive character of the membrane surface, the pore size, and changes in flow rate including the interruption of flow. Moreover, this work investigates how the chemical and physical solution properties influence bacterial retention. These properties include the temperature of the fluid, the presence of a surfactant, the salt concentration and the pH. Flow interruptions using B. diminuta were also applied to commercially available PES sterilizing-grade microfiltration membranes showing no bacterial breakthrough. © 2019 Elsevier B.V.
    view abstract10.1016/j.memsci.2019.01.021
  • Influence of Lipase Immobilization Mode on Ethyl Acetate Hydrolysis in a Continuous Solid-Gas Biocatalytic Membrane Reactor
    Vitola, G. and Mazzei, R. and Poerio, T. and Barbieri, G. and Fontananova, E. and Büning, D. and Ulbricht, M. and Giorno, L.
    Bioconjugate Chemistry 30 (2019)
    Solid-gas biocatalysis was performed in a specially designed continuous biocatalytic membrane reactor (BMR). In this work, lipase from Candida rugosa (LCR) and ethyl acetate in vapor phase were selected as model enzyme and substrate, respectively, to produce acetic acid and ethanol. LCR was immobilized on functionalized PVDF membranes by using two different kinds of chemical bond: electrostatic and covalent. Electrostatic immobilization of LCR was carried out using a membrane functionalized with amino groups, while covalent immobilization was carried out using membrane, with or without surface-immobilized polyacrylamide (PAAm) microgels, functionalized with aldehyde groups. These biocatalytic membranes were tested in a solid-gas BMR and compared in terms of enzyme specific activity, catalytic activity, and volumetric reaction rate. Results indicated that lipase covalently immobilized is more effective only when the immobilization is mediated by microgels, showing catalytic activity doubled with respect to the other system with covalently bound enzyme (4.4 vs 2.2 μmol h-1). Enzyme immobilized by ionic bond, despite a lower catalytic activity (3.5 vs 4.4 μmol h-1), showed the same specific activity (1.5 mmol·h-1·g-1 ENZ) of the system using microgels, due to a higher enzyme degree of freedom coupled with an analogously improved enzyme hydration. Using the optimized operating conditions regarding immobilized enzyme amount, ethyl acetate, and molar water flow rate, all three BMRs showed continuous catalytic activity for about 5 months. On the contrary, the free enzyme (in water/ethyl acetate emulsion) at 50 °C was completely inactive and at 30 °C (temperature optimum) has a specific activity 2 orders of magnitude lower (8.4 × 10-2 mmol h-1 g-1) than the solid-gas biocatalytic membrane reactor. To the best of our knowledge, this is the first example of solid-gas biocatalysis, working in the gaseous phase in which a biocatalytic membrane reactor, with the enzyme/substrate system lipase/ethyl acetate, was used. Copyright © 2019 American Chemical Society.
    view abstract10.1021/acs.bioconjchem.9b00463
  • Influence of surface micro-patterning and hydrogel coating on colloidal silica fouling of polyamide thin-film composite membranes
    Elsherbiny, I.M.A. and Khalil, A.S.G. and Ulbricht, M.
    Membranes 9 (2019)
    In this work, colloidal fouling by silica particles of different sizes on micro-patterned pristine and poly-(N-isopropylacylamide)-coated polyamide (PA) thin-film composite (TFC) membranes was studied. The competing impacts of surface micro-patterning vs. surface chemical modification on enhancing antifouling propensity in unstirred dead-end filtration conditions were systematically explored. Spatially selective deposition of silica microparticles (500 nm), driven by unequal flow distribution, was observed on micro-patterned membranes such that silica particles accumulated preferentially within the surface pattern’s valleys, while keeping apexes regions not fouled. This interesting phenomenon may explain the substantially enhanced antifouling propensity of micro-patterned PA TFC membranes. A detailed mechanism for spatially selective deposition of silica microparticles is proposed. Furthermore, micro-imprinted surface patterns were revealed to influence deposition behavior/packing of silica nanoparticles (50 nm) resulting in very limited flux decline that was, almost, recovered under influence of triggering stirring stimulus during a continued silica filtration experiment. The current findings provide more insights into the potency of surface micro-patterning consolidated with hydrogel coating toward new fouling-resistant PA TFC membranes. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/membranes9060067
  • Investigation of virus retention by size exclusion membranes under different flow regimes
    Kosiol, P. and Kahrs, C. and Thom, V. and Ulbricht, M. and Hansmann, B.
    Biotechnology Progress 35 (2019)
    Virus removal by filter membranes is regarded as a robust and efficient unit operation, which is frequently applied in the downstream processing of biopharmaceuticals. The retention of viruses by virus filtration membranes is predominantly based on size exclusion. However, recent results using model membranes and bacteriophage PP7 point to the fact that virus retention can also significantly be influenced by adsorptive interactions between virus, product molecules, and membranes. Furthermore, the impact of flow rate and flow interruptions on virus retention have been studied and responsible mechanisms discussed. The aim of this investigation was to gain a holistic understanding of the underlying mechanisms for virus retention in size exclusion membranes as a function of membrane structure and membrane surface properties, as well as flow and solution conditions. The results of this study contribute to the differentiation between size exclusion and adsorptive effects during virus filtration and broaden the current understanding of mechanisms related to virus breakthroughs after temporary flow interruptions. Within the frame of a Design of Experiments approach it was found that the level of retention of virus filtration membranes was mostly influenced by the membrane structure during typical process-related flow conditions. The retention performance after a flow interruption was also significantly influenced by membrane surface properties and solution conditions. While size exclusion was confirmed as main retention mechanism, the analysis of all results suggests that especially after a flow interruption virus retention can be influenced by adsorptive effects between the virus and the membrane surface. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2747, 2019. © 2018 American Institute of Chemical Engineers
    view abstract10.1002/btpr.2747
  • Material Selection Box for the Production of Advanced Polymer Membranes for Water Treatment [Material-Auswahlbox zur Herstellung fortgeschrittener Polymermembranen für die Wasseraufbereitung]
    Panglisch, S. and Kouchaki Shalmani, A. and Weber, M. and Gronwald, O. and Berg, P. and Heijnen, M. and Krug, M. and Koti, M. and Nahrstedt, A. and Abetz, V. and Handge, U.A. and Grünig, L. and Ulbricht, M. and Stratmann, I.
    Chemie-Ingenieur-Technik 91 (2019)
    Within the framework of the MABMEM research project, new high-performance membranes are being developed for sustainable water management. The performance of the membranes will be evaluated in comparative and standardized fouling tests as well as in terms of the removal of trace impurities on a laboratory scale. Seven candidates are currently being tested in demonstrator trials with real-water matrix in a waterworks for the direct treatment of dam water without prior coagulation over a period of 6 months. Subsequently, the new membrane materials will be operated with the effluent of a wastewater treatment plant. © 2019, Wiley-VCH Verlag. All rights reserved.
    view abstract10.1002/cite.201900038
  • Microfiltration membrane characterization by gas-liquid displacement porometry: Matching experimental pore number distribution with liquid permeability and bulk porosity
    Islam, M.A. and Ulbricht, M.
    Journal of Membrane Science 569 (2019)
    The variable viscosity Poiseuille model (VVPM), developed recently to treat gas-liquid displacement (GLD) porometry data for track-etched polyethylene terephthalate (PET) membranes, is applied to polyethersulfone (PES) and polypropylene (PP) microfiltration membranes prepared by phase inversion. It is found that in general aspects the pore size distribution as estimated by the model, with the intrinsic assumption of isolated capillary pores, perfectly reproduces wet and dry fluxes during porometry measurements, but the estimated porosity appeared to be much higher than unity. To eliminate the discrepancy, two additional parameters, namely non-uniformity and tortuosity coefficient, have been introduced in the flux and porosity estimating equations. The apparent viscosity of the gas in porometry analysis is found to be several fold higher than that available in literature, and also the viscosity range appeared to be membrane type dependent. The pore size distribution curve shifts along the diameter axis depending on the gas flow direction applied in porometry data acquisition. However, because the membranes had narrow pore size disribution, the estimated parameters had been averaged within acceptable confidence range. With the inclusion of non-uniformity and tortuosity of the capillaries, the revised version of the VVPM made an advancement in porometry data analysis of membranes with both isolated and interconnected pore structure; it characterizes the assumed model capillaries in terms of Young-Laplace pore diameter, but also non-uniformity and tortuosity of pores. The procedure for data treatment has been illustrated in detail and the method could easily be adapted to gas-liquid displacement porometer software system for regular data treatment. Based on a set of readily available experimental data, including the typical output from standard GLD porometry, the here established extended version of the VVPM allows the step-by-step determination of all the parameters which characterize the pore structure of the membranes. Also the absolute pore number density distributions can be obtained, including estimates of additional pore characteristics such as non-uniformity and tortuosity. © 2018 Elsevier B.V.
    view abstract10.1016/j.memsci.2018.09.030
  • Nanofillers dissolution as a crucial challenge for the performance stability of thin-film nanocomposite desalination membranes
    Abdelsamad, A.M.A. and Matthias, M. and Khalil, A.S.G. and Ulbricht, M.
    Separation and Purification Technology 228 (2019)
    With the aim to improve the intrinsic separation performance, integration of nanofillers toward polyamide thin-film nanocomposite (TFN) membranes is a very active research area. Mesoporous silica nanoparticles (MSN), among other types of nanomaterials, are often used for that purpose. However, one of the distinguishing features of MSN is their dissolution in basic aqueous solutions. To date, no investigation in the literature has considered to study the influence of MSN nanofillers dissolution on the separation performance of the respective TFN polyamide membranes. This paper investigates how hydrophobic functionalization of MSN can improve the stability of MSN in aqueous solutions and enhance the stability of the respective TFN membranes over a prolonged filtration time at different pH values. The results showed that TFN membranes containing the octadecyltrichlorosilane-functionalized MSN had only ≈ 6% decline in salt rejection compared to ≈ 35% decline for the membrane containing unfunctionalized nanofillers accompanied by increasing water permeability after 240 h filtration time (120 h at pH 5, then 120 h at pH 9). Furthermore, the durability of the barrier layer after a prolonged use for desalination was also investigated via filtration of solutions of dextran with different molecular weight and assessing the dextran rejection for the native and used membranes. From the results of all parallel analyses of nanofiller and TFN membrane structure it is concluded that OTS functionalization of MSN cannot only enhance the TFN membrane separation performance, but also reduce the dissolution tendency of MSN. This was attributed to the formation of a protective organic layer leading to significantly enhanced long-time stability of the respective TFN membranes. © 2019 Elsevier B.V.
    view abstract10.1016/j.seppur.2019.115767
  • Optical Measurement Method of Particle Suspension in Stirred Vessels
    Wolinski, S. and Ulbricht, M. and Schultz, H.J.
    Chemie-Ingenieur-Technik 91 (2019)
    Suspending particles in liquids is an important and versatile case for industrial stirring processes. By using advanced optical, non-invasive measurement techniques like particle image velocimetry (PIV), it is possible to gain deep insights into the involved fluid dynamics without affecting the flow. However, for suspensions, the application of PIV is not trivial since both, suspended and tracer particles are present and need to be discerned during experiments. The here presented method development solves this problem and thus leads to a better insight into turbulent kinetic energy distribution, which can be utilized for process optimization through improved stirred vessel design. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cite.201800099
  • Photocatalytic and magnetic porous cellulose macrospheres for water purification
    Wittmar, A.S.M. and Fu, Q. and Ulbricht, M.
    Cellulose (2019)
    Abstract: In this work, we report the preparation of photocatalytically active and easy to recycle porous cellulose-based spheres from polymer solutions in ionic liquid/dimethylsulfoxide mixtures by using the dropping cum phase separation technique. The factors affecting the sphere structure formation in relation to their efficiency as photocatalysts have been studied in detail. It was found that the increase of the nanoparticulate dopant fraction (TiO 2 and/or Fe 3 O 4 ) in the casting solution led to the formation of nanocomposites with a higher specific surface area as well as with enhanced photocatalytic activity. The embedment of the TiO 2 nanoparticles in the polymeric matrix did not change the bandgap of the photocatalyst. Furthermore, the co-doping with Fe 3 O 4 had no negative impact on the photocatalytic activity of the TiO 2 doped porous cellulose spheres. The addition of a moderate amount of dimethylsulfoxide led to an improvement of the photocatalytic activity of the formed nanocomposites, due to an increase of the matrix porosity without an agglomeration of the active nanoparticles. However, higher fractions of dimethylsulfoxide led to the agglomeration of the photocatalytic nanoparticles and therefore a decrease of the photocatalytic activity of the hybrid materials. The obtained porous spheres could be successfully recycled and reused in at least five consecutive cycles for the photocatalytic degradation of the model organic pollutant Rhodamine B in aqueous solution. Additionally, the prepared porous spheres also exhibited good adsorber properties toward Cu 2+ ions which were used in this study as model metal ion pollutant in water. Graphical abstract: [Figure not available: see fulltext.]. © 2019, Springer Nature B.V.
    view abstract10.1007/s10570-019-02401-4
  • Piezoelectric 3-D Fibrous Poly(3-hydroxybutyrate)-Based Scaffolds Ultrasound-Mineralized with Calcium Carbonate for Bone Tissue Engineering: Inorganic Phase Formation, Osteoblast Cell Adhesion, and Proliferation
    Chernozem, R.V. and Surmeneva, M.A. and Shkarina, S.N. and Loza, K. and Epple, M. and Ulbricht, M. and Cecilia, A. and Krause, B. and Baumbach, T. and Abalymov, A.A. and Parakhonskiy, B.V. and Skirtach, A.G. and Surmenev, R.A.
    ACS Applied Materials and Interfaces (2019)
    Elaboration of novel biocomposites providing simultaneously both biodegradability and stimulated bone tissue repair is essential for regenerative medicine. In particular, piezoelectric biocomposites are attractive because of a possibility to electrically stimulate cell response. In the present study, novel CaCO3-mineralized piezoelectric biodegradable scaffolds based on two polymers, poly[(R)3-hydroxybutyrate] (PHB) and poly[3-hydroxybutyrate-co-3-hydroxyvalerate] (PHBV), are presented. Mineralization of the scaffold surface is carried out by the in situ synthesis of CaCO3 in the vaterite and calcite polymorphs using ultrasound (U/S). Comparative characterization of PHB and PHBV scaffolds demonstrated an impact of the porosity and surface charge on the mineralization in a dynamic mechanical system, as no essential distinction was observed in wettability, structure, and surface chemical compositions. A significantly higher (4.3 times) piezoelectric charge and a higher porosity (∼15%) lead to a more homogenous CaCO3 growth in 3-D fibrous structures and result in a two times higher relative mass increase for PHB scaffolds compared to that for PHBV. This also increases the local ion concentration incurred upon mineralization under U/S-generated dynamic mechanical conditions. The modification of the wettability for PHB and PHBV scaffolds from hydrophobic (nonmineralized fibers) to superhydrophilic (mineralized fibers) led to a pronounced apatite-forming behavior of scaffolds in a simulated body fluid. In turn, this results in the formation of a dense monolayer of well-distributed and proliferated osteoblast cells along the fibers. CaCO3-mineralized PHBV surfaces had a higher osteoblast cell adhesion and proliferation assigned to a higher amount of CaCO3 on the surface compared to that on PHB scaffolds, as incurred from micro-computed tomography (μCT). Importantly, a cell viability study confirmed biocompatibility of all the scaffolds. Thus, hybrid biocomposites based on the piezoelectric PHB polymers represent an effective scaffold platform functionalized by an inorganic phase and stimulating the growth of the bone tissue. © 2019 American Chemical Society.
    view abstract10.1021/acsami.9b04936
  • Porous poly(vinylidene fluoride) membranes with tailored properties by fast and scalable non-solvent vapor induced phase separation
    Alexowsky, C. and Bojarska, M. and Ulbricht, M.
    Journal of Membrane Science 577 (2019)
    Hydrophobic and highly porous poly(vinylidene fluoride) (PVDF) membranes with isotropic cross section as well as tunable and narrow barrier pore size distribution in the range from ~0.1 to ~1 µm have been prepared using the non-solvent vapor induced phase separation (VIPS) technique. The process conditions have been tuned to suit an industrial scale up, using a short production time and dimethyl sulfoxide (DMSO) as solvent for PVDF, instead of commonly used hazardous chemicals. Factors like kind of solvent, the relative humidity of air, the exposure time to humid air and the mass fraction of PVDF in the casting solutions have been used to tune membrane characteristics. Interestingly, it was revealed that DMSO as a less common solvent for PVDF shows better qualities regarding upscaling than other more frequently used polar aprotic solvents (e.g. dimethylacetamide) when using VIPS under suited conditions. The phenomenon was explained through investigations of the membrane formation step, in particular by water uptake and cloud point measurements, as well as structure and performance analyses, e.g. by scanning electron microscopy, gas flow/liquid dewetting permpometry, gas and water vapor permeability analyses and liquid water entry pressure measurements. Lab-scale manufactured membranes showed pore characteristics and performance desired for membrane contactor applications. Furthermore, fabrication on a roll-to-roll machine using a nonwoven support and the established VIPS conditions was realized in a short manufacturing time; resulting membranes structure and characteristics were found to be similar to the ones for the lab-scale membranes. Overall, the combination of PVDF with DMSO gives promising opportunities for a more eco-friendly industrial fabrication of porous membranes with advanced properties via VIPS. © 2019 Elsevier B.V.
    view abstract10.1016/j.memsci.2019.01.033
  • Preparation of Ultrafiltration Membranes from Solutions of Cellulose in Ionic Liquids [Herstellung von Ultrafiltrations-Membranen aus Lösungen von Cellulose in ionischen Flüssigkeiten]
    Tran, D.H. and Ulbricht, M.
    Chemie-Ingenieur-Technik 91 (2019)
    Novel ultrafiltration membranes are prepared from solution of cellulose in ionic liquids by phase inversion on filter paper as support. Membrane performance can be adjusted by varying the casting solution composition. The addition of dimethyl sulfoxide leads to a change in solvent quality of the used ionic liquid, which has a direct influence on the membrane structure formation. However, it does not have a big influence on the membrane performance but can benefit the processing of cellulose to membranes via reducing the viscosity of the solution and costs by decreasing the amount of ionic liquid. © 2019, Wiley-VCH Verlag. All rights reserved.
    view abstract10.1002/cite.201900044
  • Recovery of Water from Concentration of Copper Mining Effluents Using Direct Contact Membrane Distillation
    Jimenez, Y.P. and Ulbricht, M.
    Industrial and Engineering Chemistry Research 58 (2019)
    In the present work, the water recovery and concentration of H2SO4 and metals from a copper mining effluent by membrane distillation was studied. The performance of the direct contact membrane distillation was analyzed by estimating the water flux, the water recovery, and the concentration factor for acid and metals, taking into account the structural properties of the membrane, transport phenomena, and the most sensitive process parameters, with the objective to determine the feasibility of the process. The results show that, with increasing temperature gradient, the transmembrane flux improves, that the solution concentration has a negligible effect, and that there is a proportional relation between vapor pressure and flux. Considering a feed temperature of 60 °C and coolant inlet temperature of 20 °C, for the aqueous acid solutions formed by copper sulfate after 5 h, a concentration factor of 1.4 was obtained and, for the synthetic effluents, the concentration factor after 10 h was 1.65 (water recovery of 40%). Of all the membranes tested, a laminated polyvinylidene difluoride (PVDF) membrane with a nominal pore size of 0.2 μm had the best performance. A model that includes the Pitzer equation to determine the vapor pressure of the solutions was developed to analyze the experimental tests and predict the flux; the model reproduces the experimental data with a maximum deviation of 7%. The feasibility for separation of acid and copper from concentrated mining effluents (rich in copper) by membrane distillation was analyzed through a conceptual process design; this analysis determined that it is possible to recover acid and copper by solvent extraction after three stages of membrane distillation. The total cost estimated (0.739 $m-3) proves that the process is competitive with other desalination methods. Copyright © 2019 American Chemical Society.
    view abstract10.1021/acs.iecr.9b02499
  • Relationship between bubble characteristics and hydrodynamic parameters for single bubbles in presence of surface active agents
    Lewandowski, B. and Fertig, M. and Ulbricht, M. and Krekel, G.
    Chemical Engineering Science 199 (2019)
    Rising single air bubbles were investigated in aqueous solutions of hexadecylamine (HDA) and methyl isobutyl carbinol (MIBC) as surface active agents at varying concentrations at a constant gas flow rate. Shadowgraphy was applied to determine main bubble characteristics, such as equivalent diameter, morphology, and rising velocity. From these characteristics, critical parameters like the concentration at the minimum bubble velocity were derived. Simultaneous application of Particle Image Velocimetry (PIV) provided information about hydrodynamic parameters, e.g. the induced liquid velocities and vortex shedding. From surface tension measurements, the concentration of adsorbed species on the interface and packing densities of HDA and MIBC on the bubble surface could be calculated. HDA exhibited a better adsorption and a higher packing density on the bubble surface compared to MIBC due to the ionic character and the straight hydrocarbon chain. The bubble characteristics were therefore more strongly affected by HDA than by MIBC. Combining the Shadowgraphy and PIV results it was found that the mean liquid velocity as well as the amount of induced turbulent kinetic energy increased with increasing concentration of surfactants in the solutions, while the investigated bubble characteristics such as equivalent diameter and rising velocity decreased. The increase in mean liquid velocity and induced turbulent kinetic energy could be correlated with the oscillating frequency of the bubble trajectory, which also increased with increasing surfactant concentration. The vortex shedding process could be visualised using Proper Orthogonal Decomposition (POD) revealing the micro-process of energy cascading. © 2019 Elsevier Ltd
    view abstract10.1016/j.ces.2019.01.026
  • Smart Polymeric Membranes with Magnetic Nanoparticles for Switchable Separation
    Ulbricht, M.
    RSC Smart Materials 2019-January (2019)
    This chapter provides an overview on the topic of magneto-responsive membranes for switchable mass separation. The combination of concepts, materials and methods in the field of filtration membranes with the application of magnetic materials and magnetic fields is described. Combining organic polymer-based membranes with inorganic magnetic nanoparticles is the most efficient approach to obtain "smart" membranes that can show large and reversible changes in barrier and surface properties upon activation with static or alternating magnetic fields of different frequencies. Two general approaches can be distinguished: (i) addressing secondary interactions during membrane separation such as concentration polarization or fouling, or (ii) focussing on intrinsic membrane barrier properties. Until now, the most progress toward switchable separations has been achieved by membranes that change effective pore size in the micro- or ultrafiltration range, either via reversible deformations induced by static or low frequency magnetic fields or via the synergistic combination of magneto-heating by stimulation with high frequency alternating magnetic fields and thermo-responsive hydrogels as building blocks for mixed matrix composite membranes. This pioneering work will trigger much more research and development toward real applications, e.g., in bioseparations and/or for bioanalytical or biomedical applications, wherever the option of remote-controlled switching of separation selectivity is of interest. © The Royal Society of Chemistry 2019.
    view abstract10.1039/9781788016377-00297
  • Star Polymers as Functional Building Blocks for Novel Nanofiltration Membranes [Sternpolymere als funktionale Bausteine für neuartige Nanofiltrationsmembranen]
    Schnecke, V. and Ulbricht, M.
    Chemie-Ingenieur-Technik 91 (2019)
    Interest in thin-film membranes with properties specially tailored to the respective separation process is growing. In order to obtain such membranes with high permselectivity and fouling resistance, established membrane systems are combined with new building blocks. Star polymers are a class of promising building blocks. In this study, star polymers with anion exchange groups of variable molecular weight and low polydispersity were synthesized by atom transfer radical polymerization. The anion exchange groups were tertiary amino and quaternary ammonium groups. The resulting star polymers were integrated into polyamide thin-film composite membranes using interfacial polymerization. © 2019, Wiley-VCH Verlag. All rights reserved.
    view abstract10.1002/cite.201900043
  • Surface modification of water purification membranes
    Szymczyk, A. and van der Bruggen, B. and Ulbricht, M.
    Surface Modification of Polymers: Methods and Applications (2019)
    The only methods to increase water supply beyond what is available from the hydrological cycle are desalination and water reuse. Of particular relevance for water purification are micro- and ultrafiltration membranes with a porous barrier enabling separation of particles mainly based on size, and nanofiltration and reverse osmosis membranes with a dense barrier layer where transport and selectivity are mainly based on solubility and diffusivity in/through the barrier. Membrane coating refers to a variety of post-modification techniques leading to the formation of one of several layer(s) on top of an existing membrane surface without the creation of covalent bonds. Grafting is a surface modification technique involving the chemical attachment of compounds to the membrane surface. Combining plasma treatment with graft polymerization allows avoiding the progressive loss of surface characteristics after plasma modification. Membrane surface modification by plasma-induced graft polymerization has been successfully used to functionalize membranes made of various polymers such as polysulfone and polycarbonate. © 2020 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstract10.1002/9783527819249.ch13
  • Tailoring Surface Characteristics of Polyamide Thin-Film Composite Membranes toward Pronounced Switchable Wettability
    ElSherbiny, I.M.A. and Khalil, A.S.G. and Ulbricht, M.
    Advanced Materials Interfaces 6 (2019)
    This work is the first attempt to imitate the well known, bio-inspired, super-hydrophilicity/-hydrophobicity phenomena by polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membranes, without impairing their high separation ability. Two interdisciplinary approaches, “surface micropatterning” and “double stimuli responsivity,” are successfully consolidated to obtain novel PA TFC membranes that are capable of reversibly switching between strong surface hydrophilicity and surface hydrophobicity, upon changing temperature and pH. Efficient micropatterned PA TFC membranes are developed using two techniques, namely phase separation micromolding and microimprinting lithography. Poly(N-isopropylacrylamide) (PNIPAAm) homopolymer and random copolymers of PNIPAAm with poly(acrylic acid) are specifically coated on the micropatterned PA TFC membranes employing carbodiimide coupling. Contact angle measurements reveal that the dual surface responsivity, derived by the grafted polyacrylamide-based polymer coatings, is successfully amplified by virtue of promoting the membranes' surface roughness via “surface micropatterning.” Interestingly, most of the new surface modified PA TFC membranes also exhibit an improvement in the separation performance compared to their precursors. This work emphasizes the successful combination of “surface micropatterning” and “double stimuli responsivity” to prepare new tailored micropatterned surface-coated membranes, and their potential toward enhanced separation performance and innovative membrane-based desalination applications. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/admi.201801408
  • Visualization of flow conditions inside spiral jet mills with different nozzle numbers– Analysis of unloaded and loaded mills and correlation with grinding performance
    Luczak, B. and Müller, R. and Kessel, C. and Ulbricht, M. and Schultz, H.J.
    Powder Technology 342 (2019)
    Plenty of operational and geometric parameters have effects on spiral jet milling. Changes in the parameters cause distinctions in the flow conditions inside the mill and thereby also lead to consequences regarding the milled product. A new type of experimental spiral jet mill apparatus with almost entire optical accessibility enables a very convenient variation of the operational and geometric parameters as well as the determination of the flow conditions inside the spiral jet mill via non-invasive optical methods. Particle Image Velocimetry (PIV) measurements with diethylhexyl sebacat (DEHS) tracer droplets as well as solid barium sulphate micro particles were carried out to investigate the flow conditions inside the spiral jet mill. The differences between the net milling gas velocity fields and the velocity fields of loaded spiral jet mills were exposed. With the mill being loaded, the comminution zone decreases in the horizontal direction as well as decreases and deflects in the vertical direction. Besides, the analysis of the velocity fields inside the mill apparatus showed that decreasing milling nozzle numbers lead to increasing velocities inside the spiral jet mill, even if the mass flow rate of the gas supply is kept constant and the nozzle jet velocity is limited to sonic velocity at choked flow. With decreasing milling nozzle numbers, broader comminution zones and increasing lengths of the milling jets were investigated. As a consequence, a better grinding efficiency was expected and also confirmed with decreasing milling nozzle number by grinding experiments, as the new type of experimental apparatus was constructed in a fully operative way concerning the grinding ability. © 2018 Elsevier B.V.
    view abstract10.1016/j.powtec.2018.09.078
  • A comparative study on the photocatalytic degradation of organic dyes using hybridized 1T/2H, 1T/3R and 2H MoS2 nano-sheets
    Saber, M.R. and Khabiri, G. and Maarouf, A.A. and Ulbricht, M. and Khalil, A.S.G.
    RSC Advances 8 (2018)
    MoS2 is a very attractive material and has been well studied for potential applications in various areas. However, due to the wide variety of factors affecting the molecular and electronic structure of MoS2, several contradictory reports about the adsorptive and photocatalytic properties of such materials have been published. In most of these reports, the effect of the actual phase of the materials on the properties was neglected. Here, different phases of MoS2 nanosheets (1T/2H, 1T/3R and 2H) have been obtained using the hydrothermal method with different Mo : S molar ratios and different autoclave filling ratios. The obtained materials have been thoroughly characterized using Raman, UV-vis, powder XRD, SEM, TEM and XPS measurements in order to accurately identify the existing phases in each material. A comparative study of the photocatalytic organic dye degradation efficiency under white light irradiation has been conducted using methyl orange to correlate the different activity of each material to the respective phase composition. The results indicate a much higher performance of the 1T/2H phase compared to the 2H and 3R phases. Detailed computational studies of the different phases revealed the emergence of mid-gap states upon introducing 1T sites into the 2H lattice. This leads to the improvement of the photocatalytic activity of 1T/2H compared to the other prepared materials. © 2018 The Royal Society of Chemistry.
    view abstract10.1039/c8ra05387a
  • Advances in Multi-Scale Pores and Channels Systems
    Hou, X. and Siwy, Z.S. and Ulbricht, M.
    Small 14 (2018)
    view abstract10.1002/smll.201800908
  • An automated image analysing routine for estimation of equivalent diameter in high-speed image sequences with high accuracy and its validation
    Lewandowski, B. and Ulbricht, M. and Krekel, G.
    Experimental Thermal and Fluid Science 98 (2018)
    Bubbly flow plays an important role in industrial processes. Obtaining detailed information on the flow is, however, a challenging task. One of the key process parameters is the diameter of the bubbles, which is often determined as equivalent diameter. In this study, an automatic image analysis routine for time-resolved analysis and estimation of equivalent diameter of rising single bubbles in high-speed image sequences with high accuracy is developed using the open source software KNIME. Common estimation techniques for the equivalent diameter, e.g. based on the major/minor axes, are compared to a novel rotation algorithm, where the detected bubble segments are rotated by 180° in 1° steps, for the determination of the Feret diameter. Additionally, the elongation is measured as a morphological parameter and the centroid positions are determined. In combination with the frame rate of the image sequences the ascent rates can be calculated in form of a Bubble Tracking Velocimetry (BTV). The routine was validated using static computer generated geometrical shapes as well as precision grade solid glass spheres with diameters of 0.7–2.5 mm under dynamic (settling) conditions. High-speed image sequences were recorded and analysed with a critical statistical evaluation. It could be shown that the deviation between measured diameter and real diameter of the glass spheres is less than 1.5% when using the rotating Feret diameter algorithm. Settling velocities were determined with a maximum error of 3%. A first test of the analysing routine in a bubbly flow showed that it is unaffected by dirt, small tracer particles or internals in the viewing area, which makes a combined Particle Image Velocimetry (PIV) and Shadowgraphy analysis feasible. © 2018 Elsevier Inc.
    view abstract10.1016/j.expthermflusci.2018.05.016
  • Calorimetric studies of PEO-b-PMMA and PEO-b-PiPMA diblock copolymers synthesized via atom transfer radical polymerization
    Chaudhury, S. and Gaalken, J. and Meyer, J. and Ulbricht, M.
    Polymer (United Kingdom) 139 (2018)
    Poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) and poly(ethylene oxide)-b-poly(isopropyl methacrylate) (PEO-b-PiPMA) diblock copolymers of different block ratios have been synthesized using atom transfer radical polymerization with functionalized PEO monomethylether as macroinitiator. The phase separation between the constituent blocks of the copolymers has been investigated by differential scanning calorimetry (DSC). In PEO-b-PMMA, the constituent blocks are completely miscible irrespective of their molar mass and block ratios. This behaviour remains the same for PEO-b-PiPMA with ≤15% PEO fraction; phase separation could only be observed for PEO-b-PiPMA with higher PEO content. These observations are supported by results of atomic force microscopy studies of films of two copolymers with comparable molecular weight and PEO fraction (≥24% PEO); a very well developed lamellar morphology was only observed for PEO-b-PiPMA, while the block domains were randomly dispersed in PEO-b-PMMA. Interestingly, the phase separation behaviour in PEO-b-PMMA with >30% PEO fraction has been found to be strongly dependent on its processing and thermal history. On the contrary, phase separation in PEO-b-PiPMA BCPs with ≥24% PEO fraction has not been affected by its processing or thermal history. Results indicate that the use of a block-selective solvent for the precipitation of the diblock copolymer promotes the formation of microphase separated structures even for copolymers with miscible blocks. The findings are relevant for ongoing attempts to utilize the microphase separation of such polymers to obtain well-defined nanoporous membranes and other materials. © 2018 Elsevier Ltd
    view abstract10.1016/j.polymer.2018.01.082
  • Controlling external versus internal pore modification of ultrafiltration membranes using surface-initiated AGET-ATRP
    Carter, B.M. and Sengupta, A. and Qian, X. and Ulbricht, M. and Wickramasinghe, S.R.
    Journal of Membrane Science 554 (2018)
    The activators generated electron transfer (AGET) method coupled with atom transfer radical polymerization (ATRP) is shown to be a simple and well controlled approach for surface-initiated polymerization of 2-hydroxyethyl methacrylate (HEMA) on regenerated cellulose (RC) membranes. The AGET-ATRP method has been optimized with respect to the initiator concentration, the polymerization reaction time and the reducing agent (activator) concentration. Control of polymer grafting on the external membrane surface versus the internal pore surface of RC ultrafiltration membranes was investigated using different pore filling solvents having a wide range of viscosity and reactivity during ATRP initiator immobilization via acylation of RC hydroxyl groups. The effectiveness of the pore filling solvent in limiting grafting inside the membrane pores was found to depend on both its viscosity and reactivity. Rejection of BSA and dextran was used to probe changes in pore size. Glycerol was found to be the most effective pore filling solvent, indicated by a significant degree of modification of the membrane surface with grafted polyHEMA but only a very minor increase in solute rejection. © 2018 Elsevier B.V.
    view abstract10.1016/j.memsci.2018.02.066
  • Determination of pore size gradients of virus filtration membranes using gold nanoparticles and their relation to fouling with protein containing feed streams
    Kosiol, P. and Müller, M.T. and Schneider, B. and Hansmann, B. and Thom, V. and Ulbricht, M.
    Journal of Membrane Science 548 (2018)
    Virus filtration membranes contribute to the virus safety of biopharmaceutical drugs due to their capability to retain virus particles mainly based on size-exclusion mechanisms. Typical product molecules like monoclonal antibodies with 9–12 nm in hydrodynamic diameter have to be transmitted by >95% while small viruses, e.g. parvoviridae (B19, MVM, PPV) with a diameter of 18–26 nm, have to be retained by at least 99.99%. Therefore, membrane fouling caused by product aggregates, which are similar in size compared to the viruses that have to be retained, is a common observation. Minimal membrane fouling is a requirement for economical processes and is influenced by both the membrane surface chemistry and the membrane structure, particularly with regard to the pore size gradient (PSG). In this work, virus filtration membranes were challenged with gold nanoparticles (GNPs) in order to determine PSGs for a wide range of different commercial and non-commercial parvovirus retentive membranes differing in structure, material and surface chemistry. GNP adsorption to the membrane material was suppressed by the use of an anionic surfactant, allowing to gain insights into size-exclusion properties of the membranes. Membrane performance with regard to fouling was further investigated by determination of protein mass throughputs up-to a defined membrane flux decay using solutions containing intravenous immunoglobulin (IVIG) as model protein. Additionally, the fouling mechanism of IVIG was investigated and confirmed to be caused by trace amounts of species larger than IVIG monomers and dimers, which were already present in the feed. The fouling results are discussed in relationship to the determined PSGs, since the porous support structure of virus filtration membranes can act as a depth pre-filter protecting the separation-active layer from particulate foulants. © 2017 Elsevier B.V.
    view abstract10.1016/j.memsci.2017.11.048
  • Experimental analysis of the flow conditions in spiral jet mills via non-invasive optical methods
    Luczak, B. and Müller, R. and Ulbricht, M. and Schultz, H.J.
    Powder Technology 325 (2018)
    Although most of the parameters affecting spiral jet milling have already been studied, there are no investigations of several parameters and their effects on the flow conditions over the entire cross-section inside the spiral jet mill via non-invasive methods. In order to vary several geometrical and operative parameters and to determine the flow conditions inside the jet mill, a new type of experimental spiral jet mill apparatus was designed and constructed. It has an almost entire optical accessibility and its highly modular construction enables a very convenient variation of the geometric parameters. This paper describes the new type of mill apparatus and preliminary experimental results concerning the flow conditions inside the spiral jet mill as well as grinding effects under different conditions on particle size distributions of barium sulphate micro particles. © 2017 Elsevier B.V.
    view abstract10.1016/j.powtec.2017.10.048
  • Influence of controlled functionalization of mesoporous silica nanoparticles as tailored fillers for thin-film nanocomposite membranes on desalination performance
    Abdelsamad, A.M.A. and Khalil, A.S.G. and Ulbricht, M.
    Journal of Membrane Science 563 (2018)
    Thin film nanocomposite (TFN) membranes comprising of controlled functionalized mesoporous silica nanoparticles (MSN) blended in the polyamide (PA) barrier layer were prepared via interfacial polymerization of m-phenylenediamine and trimesoyl chloride on a porous polyethersulfone support membrane. MSN were synthesized by sol-gel process and then functionalized with octadecyltrichlorosilane (OTS) using post-grafting method. The nitrogen adsorption measurements demonstrated that the hydrophobic alkyl chains of OTS can be grafted onto the internal pores of MSN or just be located on the external particle surface, depending on the functionalization procedure and the OTS concentration. The functionalized nanoparticles with a diameter of about 80 nm were thereafter easily dispersed in the organic phase during the interfacial polymerization. Evaluation of membranes’ performance was based on water and ethanol permeability measurements, in addition to salt rejection from aqueous solutions. The results indicated that the functionalization of the external surface of MSN only, without extension to the interior pores surface, significantly increased both water and ethanol permeabilities. Contrarily, the surface modification of the MSN internal pores only increased the permeability of ethanol and reduced the water permeability, mainly due to the hydrophobicity of OTS. The influence of nanoparticles loading, as well as the concentration of OTS and thus the extent of MSN functionalization on the separation performance of TFN membranes were also investigated. TFN membranes prepared using the optimized MSN functionalization and loading yielded up to 63% higher water permeability compared to the reference thin film composite membrane without sacrificing the membrane selectivity. This work clearly emphasizes the direct relationship between the internal pores of MSN as functional nanofiller in the PA barrier layer and increasing or decreasing the water permeability of resulting TFN membranes. © 2018 Elsevier B.V.
    view abstract10.1016/j.memsci.2018.05.043
  • Interfacial Polymerization of Zwitterionic Building Blocks for High-Flux Nanofiltration Membranes
    Duong, P. and Daumann, K. and Hong, P. and Ulbricht, M. and Nunes, S.P.
    Langmuir (2018)
    A simple scalable strategy is proposed to fabricate highly permeable antifouling nanofiltration membranes. Membranes with a selective thin polyamide layer were prepared via interfacial polymerization incorporating building blocks of zwitterionic copolymers. The zwitterionic copolymer, poly(aminopropyldimethylaminoethyl methacrylate)-co-poly(sulfobetaine methacrylate) with an average molecular weight of 6.1 kg mol-1 was synthesized in three steps: (i) polymerization of dimethylaminoethyl methacrylate to yield the base polymer by atom transfer radical polymerization (ATRP), (ii) fractional sulfobetainization via quaternization, and (iii) amination via quaternization. The effect of the zwitterionic polymer content on the polyamide surface characteristics, fouling resistance, and permeance is demonstrated. The zwitterion-modified membrane becomes more hydrophilic with lower surface roughness, as the zwitterionic polymer fraction increases. The excellent fouling resistance of the zwitterion-modified membrane was confirmed by the negligible protein adsorption and low bacteria fouling compared to a pristine membrane without zwitterionic segments. In addition, the zwitterion-modified membranes achieve a water permeation around 135 Lm-2h-1bar-1, which is 27-fold higher than that of the pristine membrane, along with good selectivity in the nanofiltration range, confirmed by the rejection of organic dyes. This permeance is about 10 times higher than that of other reported loose nanofiltration membranes with comparable dye rejection. The newly designed membrane is promising as a highly permeable fouling resistant crosslinked polyamide network for various water treatment applications. Copyright © 2018 American Chemical Society.
    view abstract10.1021/acs.langmuir.8b00960
  • On the potential of using dual-function hydrogels for brackish water desalination
    Ali, W. and Gebert, B. and Altinpinar, S. and Mayer-Gall, T. and Ulbricht, M. and Gutmann, J.S. and Graf, K.
    Polymers 10 (2018)
    Although current desalination technologies are mature enough and advanced, the shortage of freshwater is still considered as one of the most pressing global issues. Therefore, there is a strong incentive to explore and investigate new potential methods with low energy consumption. We have previously reported that reversible thermally induced sorption/desorption process using polymeric hydrogels hold promise for water desalination with further development. In order to develop a more effective hydrogels architecture, polyelectrolyte moieties were introduced in this work as pendent chains and a thermally responsive polymer as network backbone using reversible addition-fragmentation chain transfer (RAFT) polymerisation. The ability of the comb-type polymeric hydrogels to desalinate water was evaluated. These hydrogels were proved to absorb water with low salinity from brine solution of 2 g L-1 NaCl and release the absorbed water at relatively low temperature conditions of 50 °C. The fraction of the grafted polyacrylic acid and the comb-chain length were varied to understand their influence on the swelling/deswelling behaviour for these hydrogels. The ionic fraction in the hydrogels and the resulting hydrophilic/hydrophobic balance are crucial for the proposed desalination process. In contrast, the comb-chain length impacted the swelling behaviour of hydrogels but showed relatively little influence on the dewatering process. © 2018 by the authors.
    view abstract10.3390/polym10060567
  • Poly(ethylene oxide)-block-poly(methyl methacrylate) diblock copolymers as functional additive for poly(vinylidene fluoride) ultrafiltration membranes with tailored separation performance
    Meyer, J. and Ulbricht, M.
    Journal of Membrane Science 545 (2018)
    In this work, poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers were established as functional additive for polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes, originally with the intention to increase their hydrophilicity and thereby decrease fouling. Additionally, however, it was found that copolymer micelles can be induced by complexing the PEO block of PEO-b-PMMA with specific metal salts. The formation of micelles as function of specific solution compositions was observed in dynamic light scattering and rheology experiments; the formation of PEO-metal ion complexes was shown via proton nuclear magnetic resonance (1H NMR) spectroscopy. Integration of micelle-forming compositions into typical PVDF-based casting solutions for UF membranes could lead to a higher surface porosity and a more regular barrier pore structure through microphase separation during the nonsolvent induced phase separation process used for membrane preparation. It was found that membranes containing small amounts of PEO-b-PMMA show a significantly higher permeance than membranes made from an otherwise equal casting solution without the copolymer, while maintaining the solute rejection properties. By using different types and amounts of metal salts to complex the PEO block it was possible to tailor the molecular weight cut-off of the membranes between 30 kDa and 110 kDa. Fouling studies in lab-scale cross-flow filtration cells showed an increased relative flux recovery compared to membranes without the functional copolymer additive. The results of this study are relevant because small fractions of a tailored diblock copolymer and metal salt as additives allow tailoring the barrier and separation properties at significantly higher overall performance within an otherwise unchanged membrane manufacturing process. © 2017 Elsevier B.V.
    view abstract10.1016/j.memsci.2017.09.034
  • Polyarylsulfone-based blend ultrafiltration membranes with combined size and charge selectivity for protein separation
    Emin, C. and Kurnia, E. and Katalia, I. and Ulbricht, M.
    Separation and Purification Technology 193 (2018)
    Current research is actively devoted to the development of high-performance ultrafiltration membranes with high permeability at maximum selectivity for dedicated separations. This work reports the preparation of polymer blend charged ultrafiltration membranes for the improvement of fractionation selectivity. Flat sheet membranes made from polysulfone and various types of sulfonated poly(arylsulfone)s were prepared via non-solvent induced phase separation. Membrane morphology, hydrophilicity and surface charge were assessed by scanning electron microscopy, contact angle and zeta potential measurements, respectively. The separation performances, i.e. selectivity factor, permeability, and permeability recovery, were evaluated by ultrafiltration of model proteins – bovine serum albumin (BSA) and hemoglobin (Hb). Results showed that the membrane charge can be tuned by adjusting the fraction of sulfonated groups via the type of sulfonated polymer in the blend used for membrane preparation. Hence, a broad range of ultrafiltration membranes with different barrier pore sizes, permeability properties and surface charge was established. Pronounced differences between the effects of different types of sulfonated poly(arylsulfone)s at the same degree of sulfonation and mass fraction in the membranes had been found and related to different barrier structures formed during phase separation. Successful separation of protein mixtures was achieved by additionally adjusting filtration parameters. Overall, this work provides guidelines for a versatile and easy method to tailor membrane properties for the selective separation of binary mixtures of biomacromolecules with nearly identical molecular weight and potentially also to solve other separation problems. © 2017 Elsevier B.V.
    view abstract10.1016/j.seppur.2017.11.008
  • Potassium-sensitive poly(: N -isopropylacrylamide)-based hydrogels for sensor applications
    Büning, D. and Ennen-Roth, F. and Walter, S.V. and Hennecke, T. and Ulbricht, M.
    Polymer Chemistry 9 (2018)
    Host-guest interactions for sensor applications have been widely applied to various platforms ranging from hard to soft nanoparticles or bulk materials. Their combination with stimuli-responsive polymers such as thermosensitive polymeric hydrogels allows for their potential applications in biomedical devices or even implants. Here, we present a systematic guideline to design high performance hydrogels for in vivo sensor applications. We report on the synthesis via in situ cross-linking copolymerization and characterization of poly(N-isopropylacrylamide)-based hydrogels with a tailored volume phase transition temperature (VPTT) by copolymerization with hydrophilic comonomers, namely uncharged acrylamide, and zwitterionic N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-(dimethyl)ammonium betaine and N,N-dimethyl-N-(2-methacrylamidopropyl)-N-(3-sulfopropyl)ammonium betaine. Moreover, these hydrogels are able to recognize potassium through the incorporation of 4-acryloylamidobenzo-15-crown-5 as a host comonomer in the network. Along with the thorough investigation of the VPTT of the hydrogels by differential scanning calorimetry and swelling experiments, a novel methodology was developed for a fast and easy assessment of the VPTT of hydrogels' in the case that this kind of transition changes from the 1st to 2nd order. Thus, comonomers were evaluated regarding their ability to shift the VPTT of the hydrogels combined with a maximum volume change upon temperature change. The impact of total monomer concentration, crown ether content and imprinting with potassium ions during synthesis on the material performance was addressed as well. Potassium recognition and cross-sensitivity against sodium were investigated exemplarily for acrylamide-containing hydrogels under physiologically relevant conditions. Materials which have fine potassium sensing performances for physiologically relevant ion concentrations (around 5 mM potassium) were identified and exhibit low cross-sensitivities for sodium ions (around 125 mM). By the incorporation of hydrophilic monomers, the VPTT could successfully be shifted and therefore allows accurate determination of the potassium ion concentration also at physiologically relevant temperatures (37 to 39 °C). To the best of our knowledge, this is the first system that allows the determination of low potassium ion concentrations under physiologically relevant conditions. Thus, these materials enable future biosensor or implant applications for patients with, e.g., hyperkalemia. © 2018 The Royal Society of Chemistry.
    view abstract10.1039/c8py00490k
  • A highly selective protein adsorber via two-step surface-initiated molecular imprinting utilizing a multi-functional polymeric scaffold on a macroporous cellulose membrane
    Liu, D. and Ulbricht, M.
    RSC Advances 7 (2017)
    Although molecularly imprinted materials using small organic molecules as templates have been well established, development of such materials for protein separation is still rather challenging. We therefore describe herein a two-step surface imprinting method established with a hydrophilic macroporous cellulose membrane with relatively large specific surface area. In the first step, tailor-made multi-functional polymer chains were grafted on the cellulose membrane using photo-initiated graft copolymerization, enabled by a surface-immobilized photo-initiator. This scaffold allowed the preorganization of the template protein lysozyme (Lys) on the surface of the membrane pores. Notably, the scaffold-grafted membrane showed already a significant adsorption selectivity versus the very similar protein cytochrome C (CyC). In the second step, surface-initiated cross-linking copolymerization, enabled by a photo-initiator immobilized in the scaffold layer, resulted in a protein-imprinted cellulose membrane. Imprinting efficiency was further improved by optimization of monomer concentrations in the second step. Protein selectivity of the best imprinted cellulose membrane for Lys over CyC reached a very remarkable value of about 45, measured with 1 : 1 mixtures of the two proteins. We envision that this property of a protein-imprinted cellulose membrane, which is based on the tailored binding selectivity achieved using the two-step functionalization method, could be largely beneficial for separation and purification of target proteins from complex mixtures. © The Royal Society of Chemistry.
    view abstract10.1039/c6ra28403e
  • Determination of pore size distributions of virus filtration membranes using gold nanoparticles and their correlation with virus retention
    Kosiol, P. and Hansmann, B. and Ulbricht, M. and Thom, V.
    Journal of Membrane Science 533 (2017)
    Virus filtration membranes contribute substantially to the virus safety of biopharmaceutical drugs due to their capability to retain viral particles mainly based on the size-exclusion mechanisms. In this work, virus filtration membranes were challenged with gold nanoparticles (GNPs) in order to determine pore size distributions (PSDs) for a wide range of different commercial and non-commercial parvovirus retentive membranes differing in structure, material and surface chemistry. The retention mechanism of GNPs was investigated and effectively shifted towards size-exclusion by using an anionic surfactant to suppress particle adsorption to the membrane surface. This allowed insights into the relevance of particle retention based on size-exclusion mechanisms of the respective membranes. Membrane PSDs investigated through GNP challenges were for some membranes compared with PSDs investigated by liquid-liquid displacement porometry (LLDP). In addition, virus retention performance using Pseudomonas aeruginosa bacteriophage PP7 as accepted model virus was determined for the entire set of membranes and correlated with the cut-off pore size obtained from experiments using GNPs. Exemplarily, retention was examined for one membrane type using a set of different sized viruses or phages (PCV-2, PP7, MVM, HAV) ranging from 18 to 28 nm and compared to GNP retention. © 2017 Elsevier B.V.
    view abstract10.1016/j.memsci.2017.03.043
  • Development of a Novel Immobilization Method by Using Microgels to Keep Enzyme in Hydrated Microenvironment in Porous Hydrophobic Membranes
    Vitola, G. and Büning, D. and Schumacher, J. and Mazzei, R. and Giorno, L. and Ulbricht, M.
    Macromolecular Bioscience 17 (2017)
    Using colloidal polyacrylamide (PAAm) microgels as carriers, a novel strategy for covalent immobilization of enzymes maintained in hydrated microenvironment on/in a macroporous surface-functionalized hydrophobic polyvinylidene fluoride (PVDF) membrane is developed. The PAAm microgels are synthesized by inverse miniemulsion polymerization, and first the parameters are investigated which are suited to obtain particles in the desired size range, 100-200 nm, with narrow size distribution. Amino functions are then imparted to the microgels applying the Hofmann reaction. The modification is confirmed by Fourier-transform infrared spectroscopy analysis, ninhydrin test, and elemental analysis. In addition, functionalized microgels are characterized by dynamic light scattering. The amino-functionalized PAAm microgels are then immobilized on pre-modified PVDF membrane having aldehyde functionalities on the surface. Afterward, unreacted aldehyde groups still present on the membrane where quenched by ethanolamine and the enzyme lipase from Candida rugosa (LCR) is subsequently immobilized on the microgels loaded PVDF membrane via glutaraldehyde cross-linking, exploiting the free amino groups on immobilized microgels. Catalytic efficiency of LCR immobilized by this strategy is evaluated using para-nitrophenyl palmitate as substrate and compared with LCR directly immobilized on PVDF membrane without microgels. Results show that LCR immobilized by means of microgels exhibits better performance with a 2.3-fold higher specific biocatalytic activity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/mabi.201600381
  • Enzymatic hydrolysis of poly(ethyleneterephthalate) used for and analysed by pore modification of track-etched membranes
    Gamerith, C. and Gajda, M. and Ortner, A. and Acero, E.H. and Guebitz, G.M. and Ulbricht, M.
    New Biotechnology (2017)
    The potential of limited enzymatic poly(ethylene terephthalate) (PET) surface hydrolysis for the modification of track-etched (TE) membranes was investigated. Cutinases 1 and 2 from Thermobifida cellulosilytica as well as a fusion protein of cutinase 1 with the polymer binding module from the polyhydroxyalkanoate depolymerase of Alcaligenes faecalis (Thc_Cut1_PBM) were shown to hydrolyse highly crystalline PET TE membranes with a pore diameter of ∼120. nm at very narrow size distribution. Furthermore the effects of surface chemistry were investigated by comparison of enzymatic hydrolysis by Thc_Cut1_PBM of "as received" PET TE membranes with two surface functionalized versions towards a "hydrophilic" and a more "hydrophobic" surface. The effects of adsorbed protein and the efficacy of cleaning steps after enzymatic treatment were elucidated by complementary methods for surface analysis and membrane characterization. With the optimized cleaning protocol, all adsorbed protein could be removed from the enzyme-treated membranes and effects of chemical surface functionalization of the PET TE membranes were demonstrated. The highest efficiency of enzymatic surface hydrolysis was observed for the original PET TE membranes, leading to an 0.36% weight loss corresponding to a removal of ∼3. nm PET from the entire surface of the porous membrane. This correlates very well with the measured increase of barrier pore diameter by 4. nm (a radius reduction? of 2. nm), leading to about a two-fold increased water permeability. © 2017 Elsevier B.V.
    view abstract10.1016/j.nbt.2017.06.007
  • Fabrication of modified polyethersulfone membranes for wastewater treatment by submerged membrane bioreactor
    Abdel-Karim, A. and Gad-Allah, T.A. and El-Kalliny, A.S. and Ahmed, S.I.A. and Souaya, E.R. and Badawy, M.I. and Ulbricht, M.
    Separation and Purification Technology 175 (2017)
    Polyethersulfone (PES) flat sheet membranes were fabricated using different additives, i.e. polyvinylpyrrolidone (PVP), linear Pluronic 31R1, and star-like Tetronic 904, with different contents, by nonsolvent-induced phase separation method at similar preparation conditions. Their effects on characteristics and performance of the flat sheet PES membranes were investigated in order to select the best membrane to be applied in submerged membrane bioreactor (SMBR). The characteristics of the fabricated membranes were investigated by using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), mechanical stability measurements, contact angle (CA) measurement, shrinkage measurement, and membrane porosity analysis. The membranes performance was examined by investigation of pure water permeability (PWP) and bovine serum albumin (BSA) rejection analyses. The characteristics and the performance of the neat PES membrane have been improved by the action of these additives. For instance, there is an increase in the PWP from 2.2 L m−2 h−1 bar−1 for neat PES membrane to more than 40, 116, and 64 L m−2 h−1 bar−1 for PES-PVP (3 wt.%), PES-P31R1 (5 wt.%), and PES-T904 (5 wt.%) modified membranes, respectively. Also, these membranes showed 60–70% BSA rejection compared to ∼90% for neat PES membrane. To sum up, these mentioned three membranes are considered as promising membranes for SMBRs. © 2016 Elsevier B.V.
    view abstract10.1016/j.seppur.2016.10.060
  • Fabrication of nanoporous graphene/polymer composite membranes
    Madauß, L. and Schumacher, J. and Ghosh, M. and Ochedowski, O. and Meyer, J. and Lebius, H. and Ban-D'Etat, B. and Toimil-Molares, M.E. and Trautmann, C. and Lammertink, R.G.H. and Ulbricht, M. and Schleberger, M.
    Nanoscale 9 (2017)
    Graphene is currently investigated as a promising membrane material in which selective pores can be created depending on the requirements of the application. However, to handle large-area nanoporous graphene a stable support material is needed. Here, we report on composite membranes consisting of large-area single layer nanoporous graphene supported by a porous polymer. The fabrication is based on ion-track nanotechnology with swift heavy ions directly creating atomic pores in the graphene lattice and damaged tracks in the polymer support. Subsequent chemical etching converts the latent ion tracks in the supporting polymer foil, here polyethylene terephthalate (PET), into open microchannels while the perfectly aligned pores in the graphene top layer remain unaffected. To avoid unintentional damage creation and delamination of the graphene layer from the substrate, the graphene is encapsulated by a protecting poly(methyl methacrylate) (PMMA) layer. By this procedure a stable composite membrane is obtained consisting of nanoporous graphene (coverage close to 100%) suspended across selfaligned track-etched microchannels in a polymer support film. Our method presents a facile way to create high quality suspended graphene of tunable pore size supported on a flexible porous polymeric support, thus enabling the development of membranes for fast and selective ultrafiltration separation processes. This journal is © The Royal Society of Chemistry.
    view abstract10.1039/c7nr02755a
  • Hollow fiber membrane lumen modified by polyzwitterionic grafting
    Lieu Le, N. and Quilitzsch, M. and Cheng, H. and Hong, P.-Y. and Ulbricht, M. and Nunes, S.P. and Chung, T.-S.
    Journal of Membrane Science 522 (2017)
    In this study, we demonstrate an effective way to modify the lumen of polyetherimide hollow fibers by grafting zwitterionic poly(sulfobetaine) to increase the membrane resistance to fouling. Surface-selective grafting of the protective hydrogel layers has been achieved in a facile two-step process. The first step is the adsorption of a macromolecular redox co-initiator on the lumen-side surface of the membrane, which in the second step, after flushing the lumen of the membrane with a solution comprising monomers and a complementary redox initiator, triggers the in situ cross-linking copolymerization at room temperature. The success of grafting reaction has been verified by the surface elemental analyses using X-ray photoelectron spectroscopy (XPS) and the surface charge evaluation using zeta potential measurements. The hydrophilicity of the grafted porous substrate is improved as indicated by the change of contact angle value from 44° to 30°, due to the hydration layer on the surface produced by the zwitterionic poly(sulfobetaine). Compared to the pristine polyetherimide (PEI) substrate, the poly(sulfobetaine) grafted substrates exhibit high fouling resistance against bovine serum albumin (BSA) adsorption, E. coli attachment and cell growth on the surface. Fouling minimization in the lumen is important for the use of hollow fibers in different processes. For instance, it is needed to preserve power density of pressure-retarded osmosis (PRO). In high-pressure PRO tests, a control membrane based on PEI with an external polyamide selective layer was seriously fouled by BSA, leading to a high water flux drop of 37%. In comparison, the analogous membrane, whose lumen was modified with poly(sulfobetaine), not only had a less water flux decline but also had better flux recovery, up to 87% after cleaning and hydraulic pressure impulsion. Clearly, grafting PRO hollow fiber membranes with zwitterionic polymeric hydrogels as a protective layer potentially sustains PRO performance for power generation. © 2016 Elsevier B.V.
    view abstract10.1016/j.memsci.2016.08.038
  • How Do Polyethylene Glycol and Poly(sulfobetaine) Hydrogel Layers on Ultrafiltration Membranes Minimize Fouling and Stay Stable in Cleaning Chemicals?
    Le, N.L. and Ulbricht, M. and Nunes, S.P.
    Industrial and Engineering Chemistry Research 56 (2017)
    We compare the efficiency of grafting polyethylene glycol (PEG) and poly(sulfobetaine) hydrogel layer on poly(ether imide) (PEI) hollow-fiber ultrafiltration membrane surfaces in terms of filtration performance, fouling minimization and stability in cleaning solutions. Two previously established different methods toward the two different chemistries (and both had already proven to be suited to reduce fouling significantly) are applied to the same PEI membranes. The hydrophilicity of PEI membranes is improved by the modification, as indicated by the change of contact angle value from 89° to 68° for both methods, due to the hydration layer formed in the hydrogel layers. Their pure water flux declines because of the additional permeation barrier from the hydrogel layers. However, these barriers increase protein rejection. In the exposure at a static condition, grafting PEG or poly(sulfobetaine) reduces protein adsorption to 23% or 11%, respectively. In the dynamic filtration, the hydrogel layers minimizes the flux reduction and increases the reversibility of fouling. Compared to the pristine PEI membrane that can recover its flux to 42% after hydraulic cleaning, the PEG and poly(sulfobetaine) grafted membranes can recover their flux up to 63% and 94%, respectively. Stability tests show that the poly(sulfobetaine) hydrogel layer is stable in acid, base and chlorine solutions, whereas the PEG hydrogel layer suffers alkaline hydrolysis in base and oxidation in chlorine conditions. With its chemical stability and pronounced capability of minimizing fouling, especially irreversible fouling, protective poly(sulfobetaine) hydrogel layers have great potential for various membrane-based applications. © 2017 American Chemical Society.
    view abstract10.1021/acs.iecr.7b01241
  • How to design a proper membrane for a membrane contactor-based air conditioning system
    Bojarska, M. and Alexowsky, C. and Gaeta, S. and Lazzari, S. and Bottino, A. and Cattaneo, C. and Capanelli, G. and Ulbricht, M.
    2017 12th International Conference on Ecological Vehicles and Renewable Energies, EVER 2017 (2017)
    This paper is dedicated to the development of a proper membrane for a membrane contactor-based air conditioning system. Based on mass transfer analysis and knowledge of membrane formation, guidelines for the most appropriate membrane were made. © 2017 IEEE.
    view abstract10.1109/EVER.2017.7935952
  • Hydrophilic polyethersulfone-based microfiltration membranes by electrospinning of polymer blends
    Abdelsamad, A.M.A. and Kwankhao, B. and Gad-Allah, T.A. and Khalil, A.S.G. and Badawy, M.I. and Bahners, T. and Ulbricht, M.
    Desalination and Water Treatment 86 (2017)
    Polyethersulfone (PES) is considered one of the most popular polymers used for the fabrication of microfiltration membranes. In this study, we demonstrate the preparation of PES nanofibrous membranes via electrospinning technique for water purification. The amphiphilic polyethyleneoxide/ polypropylenoxide multiblock copolymer (Tetronic 901) was used to improve the hydrophilicity of the relatively hydrophobic PES membrane. The water contact angle measurements confirmed the improvement of the hydrophilicity of the blended membrane surfaces. The effect of Tetronic additive on the morphology of the electrospun nanofibers as well as on the stability and performance of the prepared membranes was studied. The results indicated that the water permeability of the blended membranes was higher than that of original PES membrane. After membranes cleaning, the permeability loss decreased from 68% for PES membrane to only 34% for the 3 wt% Tetronic-containing PES membrane, indicating less fouling tendency of the polymer blend membranes. © 2017 Desalination Publications. All rights reserved.
    view abstract10.5004/dwt.2017.21323
  • Improvement of virus removal using ultrafiltration membranes modified with grafted zwitterionic polymer hydrogels
    Lu, R. and Zhang, C. and Piatkovsky, M. and Ulbricht, M. and Herzberg, M. and Nguyen, T.H.
    Water Research 116 (2017)
    Potable water reuse has been adopted by cities suffering water scarcity in recent years. The microbial safety in water reuse, especially with respect to pathogenic viruses, is still a concern for water consumers. Membrane filtration can achieve sufficient removal of pathogenic viruses without disinfection byproducts, but the required energy is intensive. In this study, we graft-polymerized zwitterionic SPP ([3-(methacryloylamino) propyl] dimethyl (3-sulfopropyl) ammonium hydroxide) on a 150 kDa ultrafiltration polyethersulfone membrane to achieve a significantly higher virus removal. The redox-initiated graft-polymerization was performed in an aqueous solution during filtration of the monomer and initiators, allowing for functionalizing the membrane pores with hydrophilic polySPP. Bacteriophage MS2 and human adenovirus type 2 (HAdV-2) were used as surrogates for pathogenic human norovirus and human adenovirus. The grafting resulted in ∼18% loss of the membrane permeability but an increase of 4 log10 in HAdV-2 removal and 3 log10 in MS2 removal. The pristine and the grafted membranes were both conditioned with soluble microbial products (SMP) extracted from a full-scale membrane bioreactor (MBR) in order to test the virus removal after fouling the membranes. After fouling, the HAdV-2 removal by the grafted membrane was 1 log10 higher than that of the pristine membrane. For MS2, the grafted membrane after fouling with SMP achieved an additional 5 log10 removal compared to the unmodified membrane. The simple graft-polymerization functionalization of commercialized membrane achieving enhanced virus removal efficiency highlights the promise of membrane filtration for pathogen control in potable water reuse. © 2017
    view abstract10.1016/j.watres.2017.03.023
  • Ionic Liquid-Based Route for the Preparation of Catalytically Active Cellulose-TiO2 Porous Films and Spheres
    Wittmar, A. and Ulbricht, M.
    Industrial & Engineering Chemistry Research 56 (2017)
    The present work evaluates the possibilities of processing cellulose with ionic liquids and functional nanoparticles like TiO2 toward a new generation of porous nanocomposites, shaped as films or spheres, which may find direct application in water purification, catalysis, and selfcleaning materials. The focus was set on the factors controlling the formation of the porous film structure during the nonsolvent induced phase separation process from polymer solutions in ionic liquids via immersion in water and during the porous film drying step. Temperature and cosolvent addition facilitate cellulose solubilization and help control the phase separation by improving the mass transfer. The complex relation between the catalytic activity of the porous TiO2-cellulose nanocomposite materials obtained under different processing conditions and their structure has been studied during the photodegradation of model organic dyes like rhodamine B and methylene blue. After drying, the catalytic activity of the nanocomposites decreases as a consequence of the reformation of the intra- and intermolecular hydrogen bonds in cellulose which diminish the flexibility and the mobility of the fine cellulose fibrils network.
    view abstract10.1021/acs.iecr.6b04720
  • Model-dependent analysis of gas flow/pore dewetting data for microfiltration membranes
    Islam, M.A. and Hossain, M.S. and Ulbricht, M.
    Journal of Membrane Science 533 (2017)
    A reliable methodology for the treatment of gas/liquid displacement (GLD) permporometry data and the determination of pore-number distribution of microfiltration membranes was developed in this work. Models according to Poiseuille, Klinkenberg and Forchheimer were initially chosen to describe the gas flux through the dry and the wet membrane. The gas viscosity was considered to be constant, but unknown. Thereafter, it was shown that by the introduction of the concept of “variable viscous resistance”, the GLD porometry data could be treated more easily to determine the pore-number distribution. For that, two new models were established, the variable viscosity Poiseuille model for gas flow and the unified Poiseuille model for gas and liquid flow. Three levels of validity test, namely, ‘prediction of dry flux’, ‘simultaneous reproduction of dry and wet flow curve’ and ‘prediction of integral relative flow’ had been applied to rank the model-adequacy. Consistent results in terms of differently defined averaged pore diameters (Weber-type, flow-averaged and mean flow) had been obtained with all the developed models. The predictability of liquid flow through microfiltration membranes based on GLD porometry data had been discussed and it was found that for satisfactory prediction, the gas viscosity should be considered a model-dependent parameter. Finally, experimentally obtained permeability data of a reference liquid were correlated with GLD porometry data in order to find the absolute pore-number distribution and to estimate the membrane porosity. For a membrane with straight non-intersecting pore channels, the porosity was found to be in the same range as that determined experimentally. Hence, this work provides a significant progress for the detailed analysis of barrier properties of microfiltration membranes. © 2017 Elsevier B.V.
    view abstract10.1016/j.memsci.2017.03.012
  • Nano-sized metal organic framework to improve the structural properties and desalination performance of thin film composite forward osmosis membrane
    Zirehpour, A. and Rahimpour, A. and Ulbricht, M.
    Journal of Membrane Science 531 (2017)
    In the present study, nano-sized metal-organic framework (MOF) particles consisting of silver (I) and 1,3,5-benzene tricarboxylic acid were synthesized and applied to improve the structural properties as well as desalination performance of thin-film composite (TFC) forward osmosis (FO) membranes. The MOF nanocrystals were incorporated into the polyamide layer of membranes through interfacial polymerization. Characterizations by Field emission scanning electron microscopy and X-ray photoelectron spectroscopy enabled the detection of MOF nanocrystals within the selective layer of the resultant membranes. The MOF incorporation led to changes of the membrane active layer in terms of hydrophilicity and transport properties, without detrimental effects on the layer selectivity. These features enhanced pure water permeability of the membranes to 129%, which was provided through 0.04% MOF loading of the organic phase during interfacial polymerization. As a result, the modified membrane exhibited an enhanced FO seawater desalination performance in comparison with the control membrane. The performance stability of TFC membrane was also improved by presence of MOF in active layer (as seen by a water flux decline of about 7% for modified membrane against about 18% for unmodified membrane when tested with real seawater). This study demonstrates the potential of MOF particles to enhance desalination performance of TFC membranes in FO systems. © 2017 Elsevier B.V.
    view abstract10.1016/j.memsci.2017.02.049
  • Particle Image Velocimetry Compared to CFD Simulation of Stirred Vessels with Helical Coils
    Jahrling, K. and Wolinski, S. and Stefan, A. and Helle, H. and Bliem, V. and Ulbricht, M. and Schultz, H. J.
    Chemie Ingenieur Technik 89 (2017)
    The results of measurements using two different particle image velocimetry (PIV) systems (2D-PIV versus stereo-PIV) are compared and the obtained data with a coupled CFD simulation are also correlated. A stirred vessel with internal helical coil as additional heat exchanger is analyzed with these settings. Results for the velocity fields and turbulent kinetic energy distribution are shown and the feasibility of stereo-PIV measurements by using refractive index matching fluid is proven. This investigation provides a good accordance and consistency between the different PIV systems and the related CFD.
    view abstract10.1002/cite.201600145
  • Photocatalytic and Magnetic Porous Cellulose-Based Nanocomposite Films Prepared by a Green Method
    Wittmar, A. and Fu, Q. and Ulbricht, M.
    ACS Sustainable Chemistry and Engineering 5 (2017)
    The present work expands our previous studies related to cellulose processing with room-temperature ionic liquids and simultaneous integration of functional nanoparticles toward photocatalytically active and easily recyclable nanocomposite porous films based on a renewable matrix material. Porosity can be tuned by the selection of phase separation conditions for the films obtained from the casting solutions of cellulose in ionic liquids or their mixture with an organic co-solvent. TiO2 nanoparticles confer to the nanocomposite photocatalytic activity, while Fe3O4 nanoparticles make it magnetically active. The photocatalytic activity of the cellulose film containing 10 mg of TiO2 was 1 order of magnitude lower than that of the same amount of pure TiO2 nanopowder, due to the reduction of the active catalytic surface which can be reached by UV irradiation after embedment in the polymer matrix. However, this fixation in a solid polymer support allows facile recovery of the catalyst after use. The rate constant when using the cellulose nanocomposite doped with TiO2 and Fe3O4 (k ≈ 0.0019 min-1) is very close to that for the corresponding composite containing only TiO2 (k ≈ 0.0017 min-1), suggesting that co-doping with Fe3O4 nanoparticles did not diminish the photocatalytic activity of the final composite, which can be easily separated from solution with a magnet. Additionally, by Fe3O4 doping, the composite material's temperature can be homogeneously increased by ∼12 K via exposure to a high-frequency alternating magnetic field (AMF) for 5 min. For an optimal thermal response to AMF, the magnetite nanoparticles have to be homogeneously dispersed within the polymer matrix. The preparation method for the casting solution has been found to play an essential role for the one-step fabrication of multifunctional cellulose-based nanocomposite materials. © 2017 American Chemical Society.
    view abstract10.1021/acssuschemeng.7b01830
  • Removal of humic acid and chloroform from drinking water by using commercial nanofiltration and reverse osmosis membranes
    Abdel-Karim, A. and Gad-Allah, T.A. and Badawy, M.I. and Khalil, A.S.G. and Ulbricht, M.
    Desalination and Water Treatment 59 (2017)
    The removal of disinfection byproducts (DBPs) or their precursors has become an essential step during water treatment processes due to their negative health effects. In this work, the efficiency of commercial nanofiltration (NF) and reverse osmosis (RO) membranes for the removal of chloroform (CF, as the major component of DBPs formed during the chlorination of River Nile water) and humic acid (HA, as the main precursor of DBPs) from drinking water was investigated. Six different commercial membranes were used including NF-90 and NF-270 for NF process and TM-820, SW-30, BW-30 and XLE for RO process. The surface and structural properties of the commercial membranes were characterized using different techniques. From the rejection tests, the whole six membranes removed ca. 100% of HA. In case of CF, NF-90 rejected about 92%, while NF-270 rejected only 76%. The rejection of CF using RO membranes ranged from 94% to 98.5%. CF rejection using the best membranes (SW-30 and BW-30) was tested in a long term filtration experiment (up to 21 h). During this experiment, BW-30 and SW-30 had high rejection efficiency for CF with only a slight decrease in the flux. The current results demonstrate that both SW-30 and BW-30 membranes can be used efficiently to control the DBPs level in drinking water. © 2017 Desalination Publications. All rights reserved.
    view abstract10.5004/dwt.2016.0398
  • Surface micro-patterning as a promising platform towards novel polyamide thin-film composite membranes of superior performance
    ElSherbiny, I.M.A. and Khalil, A.S.G. and Ulbricht, M.
    Journal of Membrane Science 529 (2017)
    Novel and efficient micro-patterned polyamide (PA) thin-film composite (TFC) membranes are successfully fabricated. Polyethersulfone support membranes are micro-patterned using two microfabrication methods, combined processes of vapor- and non-solvent-induced phase separation micro-molding, as well as micro-imprinting lithography. PA layer is successfully adapted on the developed micro-patterned supports and the impact on the membrane performance as a result of the difference in micro-patterning resolution is explored. The patterned PA TFC membranes exhibit superior water permeability, ~2–2.4 times compared to the flat PA TFC membranes, without sacrificing the membrane selectivity. This is mainly due to the distinguishable enhancement in membrane active surface area (~40–70%) and the increasing of the surface roughness upon micro-patterning. Furthermore, the concentration polarization analysis using different membrane orientations, with patterned grooves “parallel” and “perpendicular” to the direction of feed flow, and various feed concentrations is carried out. The results explicit the merits of implementing the micro-patterned TFC membranes in producing specific surface-induced mixing effects, which are found to reduce the concentration polarization, even at a high feed concentration. Moreover, the fidelity of the micro-patterning methods used in this work is comprehensively studied and different mechanisms for membrane surface patterning are proposed. © 2017 Elsevier B.V.
    view abstract10.1016/j.memsci.2017.01.046
  • Tunable magneto-responsive mesoporous block copolymer membranes
    Tang, Y. and Lin, X. and Ito, K. and Hong, L. and Ishizone, T. and Yokoyama, H. and Ulbricht, M.
    Journal of Membrane Science 544 (2017)
    Mesoporous magneto-responsive membranes with remote-controllable step-wise tunable changes of sieving barrier pore size were successfully prepared. The membranes were composed of a thin mesoporous size-selective layer containing iron oxide nanoparticles (IONPs) embedded in poly(oligo(ethylene glycol) methyl ether methacrylate)-block-polystyrene-block-poly(oligo(ethylene glycol) methyl ether methacrylate) (PMEOnMA-b-PS-b-PMEOnMA), on top of a polyvinylidene fluoride (PVDF) macroporous support membrane. IONPs and PMEOnMA-b-PS-b-PMEOnMA mixture solutions were spun-cast on PVDF membranes, and then mesopores were introduced into the hydrophilic PMEOnMA domains by controlled selective swelling with a mixture of methanol and supercritical CO2. The loaded IONPs aggregated into small clusters (0.1–1 µm) and were finely dispersed in the PMEOnMA-b-PS-b-PMEOnMA mesoporous top layer. No defect was found in the membranes with IONPs based on water and dextran ultrafiltration performances, and scanning electron microscopy (SEM) images showed that their barrier pore sizes were almost identical to those of no IONPs containing membranes. Upon stimulation with alternating magnetic field with different input energy, the water permeability as well as the dextran rejection were tuned into different levels, indicating that the sieving barrier pore size distribution of these thin-film mixed matrix nanocomposite membranes was step-wise adjustable. © 2017 Elsevier B.V.
    view abstract10.1016/j.memsci.2017.08.069
  • A fast and reliable approach to benchmark low pressure hollow fibre filtration membranes for water purification
    Yangali-Quintanilla, V.A. and Holm, A.H. and Birkner, M. and D'Antonio, S. and Stoltze, H.W.C. and Ulbricht, M. and Zheng, X.
    Journal of Membrane Science 499 (2016)
    In this study a benchmark protocol for low pressure hollow fibre membranes was developed and evaluated. The benchmark approach involved three main steps: first a systematic membrane characterisation, then a short-term bench-scale testing evaluated by a scoring system, and finally a long-term full scale performance comparison. Four different hollow fibre membranes were characterized with respect to electrical charge, hydrophobicity, surface morphology et al. All hollow fibre membranes and two types of water (river water and secondary effluent) were used in a controlled filtration protocol. The performance of these membranes were evaluated according to the scoring system which included the effect of fouling (TMP development), hydraulic permeability recovery, and membrane chemical cleaning under both moderate and high fluxes. A key result of this study is that the overall performance of the membranes in long-term can be qualitatively predicted using a short-term bench scale test and a scoring system. The benchmark of membranes in the full scale tests showed results comparable to the results obtained in bench-scale. Detailed comparison of the scores from bench and full scale tests highlights some challenges in applying such approach in practice. The study found very limited relationship between membrane characteristics and filtration performance. It was observed that some membrane characteristics influence fouling at the beginning of fouling formation, but the effects were reduced over time as the membrane underwent more intense fouling and several cleaning cycles. © 2015 Elsevier B.V.
    view abstract10.1016/j.memsci.2015.10.048
  • Antifouling and Antibacterial Multifunctional Polyzwitterion/Enzyme Coating on Silicone Catheter Material Prepared by Electrostatic Layer-by-Layer Assembly
    Vaterrodt, A. and Thallinger, B. and Daumann, K. and Koch, D. and Guebitz, G.M. and Ulbricht, M.
    Langmuir 32 (2016)
    The formation of bacterial biofilms on indwelling medical devices generally causes high risks for adverse complications such as catheter-associated urinary tract infections. In this work, a strategy for synthesizing innovative coatings of poly(dimethylsiloxane) (PDMS) catheter material, using layer-by-layer assembly with three novel functional polymeric building blocks, is reported, i.e., an antifouling copolymer with zwitterionic and quaternary ammonium side groups, a contact biocidal derivative of that polymer with octyl groups, and the antibacterial hydrogen peroxide (H2O2) producing enzyme cellobiose dehydrogenase (CDH). CDH oxidizes oligosaccharides by transferring electrons to oxygen, resulting in the production of H2O2. The design and synthesis of random copolymers which combine segments that have antifouling properties by zwitterionic groups and can be used for electrostatically driven layer-by-layer (LbL) assembly at the same time were based on the atom-transfer radical polymerization of dimethylaminoethyl methacrylate and subsequent partial sulfobetainization with 1,3-propane sultone followed by quaternization with methyl iodide only or octyl bromide and thereafter methyl iodide. The alternating multilayer systems were formed by consecutive adsorption of the novel polycations with up to 50% zwitterionic groups and of poly(styrenesulfonate) as the polyanion. Due to its negative charge, enzyme CDH was also firmly embedded as a polyanionic layer in the multilayer system. This LbL coating procedure was first performed on prefunctionalized silicon wafers and studied in detail with ellipsometry as well as contact angle (CA) and zetapotential (ZP) measurements before it was transferred to prefunctionalized PDMS and analyzed by CA and ZP measurements as well as atomic force microscopy. The coatings comprising six layers were stable and yielded a more neutral and hydrophilic surface than did PDMS, the polycation with 50% zwitterionic groups having the largest effect. Enzyme activity was found to be dependent on the depth of embedment in the multilayer coating. Depending on the used polymeric building block, up to a 60% reduction in the amount of adhering bacteria and clear evidence for killed bacteria due to the antimicrobial functionality of the coating could be confirmed. Overall, this work demonstrates the feasibility of an easy to perform and shape-independent method for preparing an antifouling and antimicrobial coating for the significant reduction of biofilm formation and thus reducing the risk of acquiring infections by using urinary catheters. © 2016 American Chemical Society.
    view abstract10.1021/acs.langmuir.5b04303
  • Assessing biofouling resistance of a polyamide reverse osmosis membrane surface-modified with a zwitterionic polymer
    Marré Tirado, M.L. and Bass, M. and Piatkovsky, M. and Ulbricht, M. and Herzberg, M. and Freger, V.
    Journal of Membrane Science 520 (2016)
    Desalination and water treatment by reverse osmosis (RO) can highly increase clean water supply in today's world. However, biofouling of polyamide (PA) RO membranes is a serious obstacle for a wider use of this technology. One of the promising ways of biofouling control is membranes surface modification with zwitterionic polymers. A number of published works showed that zwitterionic coatings can improve the resistance of PA membranes to the initial bacteria adhesion, however no long-term experiments with real treated water effluents were conducted. In this work a commercial PA RO membrane was surface-modified with a zwitterionic polymer and its resistance to biofouling was tested in both short-term bacteria adhesion experiments and longer filtration tests conducted using real treated wastewater effluents, spiked with a small level of nutrients. The obtained results showed that, initially, there was a clear improvement in the biofouling resistance of the modified membranes and their permeation flux remained stable, in contrast to the non-modified counterpart. However, eventually, the permeabilities of the two membranes declined to a similar degree. The results indicate that antifouling coatings might not promise a better membrane performance in long term. The analysis of the biofilms grown on the pristine and the modified membranes suggested that adaptation capabilities of biofilms overcame the favorable changes in surface properties of the membrane achieved by the modification. The presented results emphasized the importance of long-term filtration experiments as an ultimate test for assessing biofouling resistance of the modified desalination membranes. © 2016 Elsevier B.V.
    view abstract10.1016/j.memsci.2016.07.027
  • Capillary pore membranes with grafted diblock copolymers showing reversibly changing ultrafiltration properties with independent response to ions and temperature
    Gajda, M. and Ulbricht, M.
    Journal of Membrane Science 514 (2016)
    Track-etched polyethylene terephthalate membranes with a pore size of 110 nm have been modified by a grafted diblock copolymer structure in order to obtain dual-responsive ultrafiltration membranes. The temperature-responsive poly-N-isopropylacrylamide (PNIPAAm) and the ion-responsive poly-N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium betaine (PSPE) were grafted from the pore walls by sequential surface-initiated atom transfer radical polymerization. To achieve a well controlled pore functionalization, the polymerization rate had been adjusted to a very slow chain growth. A successful grafting of PSPE as first block and of PNIPAAm as second block could be demonstrated. To study the temperature and ion responsivity, hydraulic permeability and dextran diffusion experiments at 25 °C and 40 °C with different salt solutions had been carried out. It could be shown that such membranes can change their barrier pore size from a more open to a more closed state in dependency of temperature as well as kind of ions and their concentration in the feed. The grafted layer thickness showed a particularly strong increase in the presence of KClO4. Like expected for a well defined polymer brush, an expanded or collapsed state for each of the individual blocks could be obtained. In presence of KClO4 at 25 °C both blocks are expanded and the pores are in a more closed state. If one of these stimuli is changed, for example when temperature is increased to 40 °C or ions are removed, the block copolymer brushes collapse partially what leads to more open pores. However, if both stimuli are applied together, i.e. if temperature is 40 °C and no ions are in solution, diblock copolymers collapse fully what leads to fully opened pores. It had also been demonstrated that this dual responsivity and the magnitude of the effects depend very strongly on the absolute degree of grafting and the ratio between the two different responsive polymer blocks. Furthermore, the ability of changing effective membrane barrier pore size by ions and temperature has been investigated in more detail by dextran diffusion experiments, and very pronounced and reversible changes of molecular sieving curve and molecular weight cut-off could be obtained. © 2016 Elsevier B.V.
    view abstract10.1016/j.memsci.2016.05.001
  • Degradation of Polymeric Brominated Flame Retardants: Development of an Analytical Approach Using PolyFR and UV Irradiation
    Koch, C. and Dundua, A. and Aragon-Gomez, J. and Nachev, M. and Stephan, S. and Willach, S. and Ulbricht, M. and Schmitz, O. J. and Schmidt, T. C. and Sures, B.
    Environmental Science & Technology 50 (2016)
    Many well-established methods for studying the degradation of brominated flame retardants are not useful when working with polymeric and water insoluble species. An example for this specific class of flame retardants is PoIyFR (polymeric flame retardant; CAS No 1195978-93-8), which is used as a substituent for hexabromocyclododecane. Although it has been on the market for two years now, almost no information is available about its long time behavior in the environment. Within this study, we focus on how to determine a possible degradation of both pure PolyFR as well as PolyFR in the final insulation product, expanded polystyrene foam. Therefore, we chose UV radiation followed by analyses of the total bromine content at different time points via ICP-MS and identified possible degradation products such as 2,4,6-tribromophenol through LC-MS. These results were then linked with measurements of the adsorbable organically bound bromine and total organic carbon in order to estimate their concentrations. With respect to the obtained H-1 NMR, GPC, and contact angle results, the possibility for further degradation was discussed, as UV irradiation can influence the decomposition of molecules in combination with other environmental factors like biodegradation.
    view abstract10.1021/acs.est.6b04083
  • Effect of annealing temperature on pore formation in preparation of advanced polyethylene battery separator membranes
    Knoche, T. and Lund, R. and Prymak, O. and Epple, M. and Ulbricht, M.
    Materials Today Communications 8 (2016)
    Polymeric separator membranes are a key component in modern lithium ion batteries, as they are placed between anode and cathode to prevent short-circuiting while at the same time allowing an efficient diffusion of Li ions. Manufacturing conditions must be finely tuned to reach the many diverse and conflicting requirements for battery separators used in modern consumer applications as well as in electric vehicles. Little has been published about these proprietary combined extrusion/biaxial stretching processes. This work presents a closer look on one of the key aspects of separator membrane formation. Extruded sheets of high density polyethylene containing a hydrocarbon solvent as plasticizer were stretched in machine direction and annealed at temperatures between 100 °C and 120 °C, i.e., in a range between the onset of melting and actual melting temperature, as deduced from differential scanning calorimetry. The formation of stacked-lamellar morphologies as seen in scanning electron microscopy required a minimum strain and was also influenced by processing temperatures. The increase of the annealing temperature led to a significant increase in crystallinity and chain orientation as revealed by texture analysis, performed using X-ray powder diffraction studies on samples after dedicated preparation. After a second stretching step in transversal direction, a clear correlation to separator membrane permeability and porosity was found, with a higher crystallinity leading to lower Gurley values, i.e. higher permeabilities. The effects of blending high density with ultra-high molecular weight polyethylene of different molecular weight onto structure and morphology were also elucidated in detail. In light of the growing market of electric vehicles, high performance and safety are the main focus during separator production. The influence of important production parameters on final membrane properties is discussed. © 2016 Elsevier Ltd.
    view abstract10.1016/j.mtcomm.2016.04.003
  • Erratum to “Capillary pore membranes with grafted diblock copolymers showing reversibly changing ultrafiltration properties with independent response to ions and temperature” (Journal of Membrane Science (2016) 514 (510–517))
    Gajda, M. and Ulbricht, M.
    Journal of Membrane Science 517 (2016)
    view abstract10.1016/j.memsci.2016.06.018
  • Improved Antifouling Properties of Polydimethylsiloxane Films via Formation of Polysiloxane/Polyzwitterion Interpenetrating Networks
    Dundua, A. and Franzka, S. and Ulbricht, M.
    Macromolecular Rapid Communications 37 (2016)
    Nonspecific adsorption of proteins is a challenging problem for the development of biocompatible materials, as well as for antifouling and fouling-release coatings, for instance for the marine industry. The concept of preparing amphiphilic systems based on low surface energy hydrophobic materials via their hydrophilic modification is being widely pursued. This work describes a novel two-step route for the preparation of interpenetrating polymer networks of otherwise incompatible poly(dimethylsiloxane) and zwitterionic polymers. Changes in surface hydrophilicity as well as surface charge at different pH values are investigated. Characterization using atomic force microscopy provides thorough insight into surface changes upon hydrophilic modification. Protein fouling of the materials is assessed using fibrinogen as a model protein. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/marc.201600473
  • Macro-initiator mediated surface selective functionalization of ultrafiltration membranes with anti-fouling hydrogel layers applicable to ready-to-use capillary membrane modules
    Quilitzsch, M. and Osmond, R. and Krug, M. and Heijnen, M. and Ulbricht, M.
    Journal of Membrane Science 518 (2016)
    A new process for surface selective graft modification of ultrafiltration (UF) membranes with protective hydrogel layers was developed. The process uses a random copolymer of n-butylmethacrylate and N,N-dimethylaminoethylmethacrylate as a redox co-initiator (“macro-initiator”). Due to its molecular weight, the macro-initiator is completely rejected by the used Multibore® polyethersulfone UF membranes. Zwitterionic [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl) ammonium hydroxide and bifunctional N,N′-methylenebis(acrylamide) were used as monomers for “macro-initiator”-mediated, surface selective cross-linking polymerization toward anti-fouling hydrogel layers. The functionalization comprises two main steps; i) adsorption of the macro-initiator to the barrier layer surface of the membrane, e.g. during a short ultrafiltration; ii) grafting of the hydrogel layer after bringing the membrane in contact with a solution containing monomer(s) and a dissolved initiator (here ammonium persulfate) which is complementary to the co-initiator for a predetermined reaction time at room temperature. Hydrogel-grafted flat sheet and capillary UF membranes showed dextran sieving curves shifted to lower molecular weight values, increased total organic carbon rejection and improved anti-fouling behaviour in filtration tests with flower soil extract as model foulant. Furthermore, stability tests with sodium hydroxide and hydrogen peroxide solutions showed good chemical stability of graft-functionalized membranes. The obtained results are very promising for future applications, since the presented technique can be applied in ready-to-use membrane modules and capillary membranes easily. © 2016 Elsevier B.V.
    view abstract10.1016/j.memsci.2016.07.007
  • Magnetoresponsive Poly(ether sulfone)-Based Iron Oxide cum Hydrogel Mixed Matrix Composite Membranes for Switchable Molecular Sieving
    Lin, X. and Nguyen Quoc, B. and Ulbricht, M.
    ACS Applied Materials and Interfaces 8 (2016)
    Stimuli-responsive membranes that can adjust mass transfer and interfacial properties "on demand" have drawn large interest over the last few decades. Here, we designed and prepared a novel magnetoresponsive separation membrane with remote switchable molecular sieving effect by simple one-step and scalable nonsolvent induced phase separation (NIPS) process. Specifically, poly(ether sulfone) (PES) as matrix for an anisotropic membrane, prefabricated poly(N-isopropylacrylamide) (PNIPAAm) nanogel (NG) particles as functional gates, and iron oxide magnetic nanoparticles (MNP) as localized heaters were combined in a synergistic way. Before membrane casting, the properties of the building blocks, including swelling property and size distribution for NG, and magnetic property and heating efficiency for MNP, were investigated. Further, to identify optimal film casting conditions for membrane preparation by NIPS, in-depth rheological study of the effects of composition and temperature on blend dope solutions was performed. At last, a composite membrane with 10% MNP and 10% NG blended in a porous PES matrix was obtained, which showed a large, reversible, and stable magneto-responsivity. It had 9 times higher water permeability at the "on" state of alternating magnetic field (AMF) than at the "off"-state. Moreover, the molecular weight cutoff of such membrane could be reversibly shifted from ∼70 to 1750 kDa by switching off or on the external AMF, as demonstrated in dextran ultrafiltration tests. Overall, it has been proved that the molecular sieving performance of the novel mixed matrix composite membrane can be controlled by the swollen/shrunken state of PNIPAAm NG embedded in the nanoporous barrier layer of a PES-based anisotropic porous matrix, via the heat generation of nearby MNP. And the structure of such membrane can be tailored by the NIPS process conditions. Such membrane has potential as enabling material for remote-controlled drug release systems or devices for tunable fractionations of biomacromolecule/-particle mixtures. © 2016 American Chemical Society.
    view abstract10.1021/acsami.6b09369
  • Membrane-based purification of proteins from nanoparticle dispersions: Influences of membrane type and ultrafiltration conditions
    Alele, N. and Ulbricht, M.
    Separation and Purification Technology 158 (2016)
    The combination of nanoparticles with proteins to form functional hybrid systems is receiving undiminished attention because of its many biotechnological and medical applications. The separation of these hybrid materials from unbound free biomolecules has posed difficult challenges to fractionation and purification. Here, a model study has been carried out by removing proteins (bovine serum albumin (BSA) or lysozyme (LYS)) from the dispersion mixtures with silica nanoparticles (nominal size 20 nm) using ultrafiltration (UF) membranes. Regenerated cellulose (RC) and polyethersulfone (PES) membranes with nominal molecular weight cut-off (NMWCO) of 100 kDa, and a PES UF membrane (NMWCO 300 kDa) functionalized with UV-grafted amphoteric polymer hydrogel layer consisting of N-[3-(dimethylamino)propyl]-acrylamide (DMAPAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and having an experimentally determined cut-off of 180 kDa (identical with the experimental data for PES 100 kDa) were studied. Membrane properties and filtration conditions, in particular pH value and flux, were selected or adapted based on data for single component feeds to achieve maximum protein transmission, complete silica retention and, hence, maximum silica/protein selectivity. Batch dead-end and continuous diafiltration processes were used for fractionation and purification. Overall, the performance of PES UF membranes was inferior compared to the other membranes because of too strong fouling. With membrane RC 100, the transmission data of LYS and BSA from the mixture with silica were 80% and 30%, respectively. With the hydrogel-functionalized PES membrane, the respective transmissions from the mixture were ∼35% and ∼15% for LYS and BSA, respectively. In both cases, quantitative rejection of silica could be achieved. Using continuous diafiltration, membrane RC 100 had better purification efficiency, removing a total of 91% of LYS using 6 diavolumes (DV) in 2.4 h and 84% of BSA using 10 DV in 5.5 h. With the hydrogel-functionalized PES membrane, 82% of LYS and 74% of BSA were removed using 6 and 10 DV within larger time, i.e. 4.0 and 6.8 h, respectively. Importantly, the retained silica nanoparticles remained stable in the dispersion, without any indication of aggregation. Overall, this study will add valuable knowledge to the most efficient use of ultrafiltration sieving properties for the removal or purification of proteins from systems comprising other colloidal particles having a size which is larger by a factor of only 3-10. © 2015 Published by Elsevier B.V.
    view abstract10.1016/j.seppur.2015.11.031
  • Monoclonal antibody capture from cell culture supernatants using epitope imprinted macroporous membranes
    Schwark, S. and Sun, W. and Stute, J. and Lütkemeyer, D. and Ulbricht, M. and Sellergren, B.
    RSC Advances 6 (2016)
    Epitope-imprinted membranes targeting the C-terminal fragment of the immunoglobuline G (IgG) heavy chain was developed and used for the purification of a commercial monoclonal antibody. The membranes exhibited strongly enhanced IgG affinity when compared with non-imprinted or IgG imprinted membranes reflected in binding selectivities in a protein mixture (IgG/HSA 1:10 w/w) of up to 40, and the elution of 95 to 100% pure IgG after washing. The dynamic binding capacity amounted to 3.9 mg mL-1 membrane volume with minor loss in performance upon repeated cleaning with alkali. The depletion of host cell proteins from a cell culture broth after production of anti-IL8 antibody using the best performing imprinted membrane under low-salt conditions reached 88% (0.7-1.2 log units) implying an effective removal of impurities from the cell culture supernatant. © 2016 The Royal Society of Chemistry.
    view abstract10.1039/c6ra06632a
  • Novel magneto-responsive membrane for remote control switchable molecular sieving
    Lin, X. and Huang, R. and Ulbricht, M.
    Journal of Materials Chemistry B 4 (2016)
    Stimuli-responsive separation membranes with tunable molecular scale pore size, which are desirable for on-demand sieving of targeted macromolecules, have attracted increasing attention in recent years. In this study, novel magneto-hydrogel pore-filled composite membranes with excellent magneto-responsivity and tunability for molecular sieving have been developed. Such membranes comprising magnetic nanoparticles (MNPs) as localized heater which can be excited by high frequency alternating magnetic field (AMF), poly(N-isopropylacrylamide) (PNIPAAm) hydrogel network as the sieving medium and actuator, and polyethylene terephthalate (PET) track-etched membrane as robust support, have been prepared via in situ reactive pore-filling functionalization. Rheological study has been carried out first to investigate the influence of MNPs and initiation methods on gelation kinetics and microstructure of the MNP-PNIPAAm composite hydrogels, and to identify proper conditions for further pore-filling functionalization. Then AMF distribution of chosen field condition and its heating effectiveness for MNPs and MNP-PNIPAMm composite hydrogel were studied. Pre-functionalization of the PET membranes with linear polymer chains with different composition were compared with respect to their effects for achieving desired MNP loading and fixation of the hydrogel network in the pores. At last, in situ reactive pore-filling functionalization was carried out to immobilize robust magneto-hydrogel in the pores of the membranes. Conditions were investigated and optimized to obtain functionalized membranes with high MNP loading and suited PNIPAM network properties, i.e. good stimuli-responsivity and sieving in the ultrafiltration range. The excellent thermo- and magneto-responsivity of obtained pore-filled membranes was proved by its large and reversible change of water permeability in response to switching on and off the AMF. Finally, it was demonstrated by filtration of dextrans with different molecular weights that the membranes had ultrafiltration properties and that large changes of their molecular sieving performance could be obtained by "remote control" with the external AMF. © 2016 The Royal Society of Chemistry.
    view abstract10.1039/c5tb02368h
  • Oxygen and ammonia plasma treatment of poly(3-hydroxybutyrate) films for controlled surface zeta potential and improved cell compatibility
    Syromotina, D.S. and Surmenev, R.A. and Surmeneva, M.A. and Boyandin, A.N. and Epple, M. and Ulbricht, M. and Oehr, C. and Volova, T.G.
    Materials Letters 163 (2016)
    The oxygen and ammonia radio-frequency (RF) plasma treatment of poly(3-hydroxybutyrate) P3HB films was performed. We revealed significant changes in the topography, a decrease in the surface zeta potential from -63 to -75 mV after the oxygen-plasma treatment and an increase after ammonia plasma treatment from -63 to -45 mV at a pH of 7.4. Investigations into the NIH 3T3 fibroblast adhesion and growth demonstrated the best cell vitality and a higher cell number for the ammonia plasma treatment at 150 W. © 2015 Elsevier B.V.
    view abstract10.1016/j.matlet.2015.10.080
  • Preparation and characterization of low fouling novel hybrid ultrafiltration membranes based on the blends of GO-TiO2 nanocomposite and polysulfone for humic acid removal
    Kumar, M. and Gholamvand, Z. and Morrissey, A. and Nolan, K. and Ulbricht, M. and Lawler, J.
    Journal of Membrane Science 506 (2016)
    In this work, graphene oxide (GO)-TiO2 nanocomposite was synthesized by in situ sol-gel reaction at pH=2 using GO nanosheets suspension and titanium isopropoxide precursor. The synthesized GO-TiO2 nanocomposite was explored as a filler to fabricate improved antifouling novel hybrid ultrafiltration membranes for removal of humic acid from aqueous solution. Membranes were fabricated from polymer blend solutions containing polysulfone and GO-TiO2 with varied loading amount (0-5 wt%) by the non-solvent induced phase separation (NIPS) method. Contact angle, atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and outer surface zeta potential studies were conducted in order to characterise the membranes in terms of roughness, structure, surface properties and charge. The porous hydrophilic hybrid membranes were shown to have an asymmetric structure with improved surface roughness. The water permeability and antifouling capacity of hybrid membranes with 10 ppm HA solution were dependent on the loading amount of GO-TiO2. Incorporation of GO-TiO2 nanocomposite was found to improve the antifouling characteristics of the membranes when challenged with HA solutions. Irreversible HA fouling was substantially reduced with increased loading of GO-TiO2 nanocomposite (wt%). The lowest irreversible fouling ratio (3.2%) was obtained for the membrane containing 5 wt% nanocomposite (to total wt% of PSf, MG-5). Ultrafiltration of HA solutions of varied concentrations using hybrid membranes was studied at pH=7 and 1 bar feed pressure. The removal efficiency of hybrid membranes for HA was controlled by the membrane surface charge concentration, porosity and HA exclusion. The membrane MG-5 had the highest HA removal efficiency for 10 ppm HA solution at pH=7. © 2016 Published by Elsevier B.V.
    view abstract10.1016/j.memsci.2016.02.005
  • Surface wettability and energy effects on the biological performance of poly-3-hydroxybutyrate films treated with RF plasma
    Syromotina, D.S. and Surmenev, R.A. and Surmeneva, M.A. and Boyandin, A.N. and Nikolaeva, E.D. and Prymak, O. and Epple, M. and Ulbricht, M. and Oehr, C. and Volova, T.G.
    Materials Science and Engineering C 62 (2016)
    The surface properties of poly-3-hydroxybutyrate (P3HB) membranes were modified using oxygen and an ammonia radio-frequency (RF, 13.56 MHz) plasma. The plasma treatment procedures used in the study only affected the surface properties, including surface topography, without inducing any significant changes in the crystalline structure of the polymer, with the exception being a power level of 250 W. The wettability of the modified P3HB surfaces was significantly increased after the plasma treatment, irrespective of the treatment procedure used. It was revealed that both surface chemistry and surface roughness changes caused by the plasma treatment affected surface wettability. A treatment-induced surface aging effect was observed and resulted in an increase in the water contact angle and a decrease in the surface free energy. However, the difference in the water contact angle between the polymers that had been treated for 4 weeks and the untreated polymer surfaces was still significant. A dependence between cell adhesion and proliferation and the polar component of the surface energy was revealed. The increase in the polar component after the ammonia plasma modification significantly increased cell adhesion and proliferation on biodegradable polymer surfaces compared to the untreated P3HB and the P3HB modified using an oxygen plasma. © 2016 Elsevier B.V.
    view abstract10.1016/j.msec.2016.01.075
  • Ultrafiltration membrane-based purification of bioconjugated gold nanoparticle dispersions
    Alele, N. and Streubel, R. and Gamrad, L. and Barcikowski, S. and Ulbricht, M.
    Separation and Purification Technology 157 (2016)
    Functionalization of nanoparticles (NP) with biomolecules to form bioconjugated systems has received large attention in biomedical applications. However, purification of these nanoparticle bioconjugates from unbound free biofunctional ligands (e.g., peptides) remains a significant challenge in the production of well-defined materials. The conventional separation methods often compromise the product's properties and recovery. In this work, removal of excess of unbound peptides after the bioconjugation step to yield functionalized gold nanoparticles (AuNP) was achieved by exploiting the sieving properties of commercial regenerated cellulose (RC) ultrafiltration (UF) membranes. The RC membrane with nominal molecular weight cut-off (NMWCO) of 30 kDa precisely fractionated the mixtures and purified gold nanoparticle-peptide bioconjugates in a pressure driven semi-continuous diafiltration process. The RC 30 kDa membrane showed absolute rejection of the bioconjugated AuNP and the recovery of AuNP-peptide bioconjugate in the retentate was >87% relative to the initial amount in the mixture. In addition, the separation efficiency and throughput results were much better compared to the centrifugal membrane filtration method using an analogous membrane. All results indicate that by choice of an appropriate membrane type and barrier pore size, and with optimized solution chemistry and filtration parameters, ultrafiltration membranes, and in particular RC membranes, can be very well suited for the purification of bioconjugated nanoparticle dispersions, and the diafiltration mode is very well suited for upscaling. © 2015 Elsevier B.V.
    view abstract10.1016/j.seppur.2015.11.033
  • Untersuchung der Gasdichteverteilung in begasten Rührkesseln mit eintauchenden Rohrschlangen
    Stefan, A. and Wünscher, P. and Schultz, H.J. and Ulbricht, M.
    Chemie-Ingenieur-Technik 88 (2016)
    view abstract10.1002/cite.201650341
  • Vergleich von Tubebaffles und Rohrschlangen in Bezug auf thermische und mechanische Energieeintragung in Rührreaktoren
    Jährling, K. and Wolinski, S. and Ulbricht, M. and Schultz, H.J.
    Chemie-Ingenieur-Technik 88 (2016)
    view abstract10.1002/cite.201650211
  • Correlation between surface properties and wettability of multi-scale structured biocompatible surfaces
    Gorodzha, S.N. and Surmeneva, M.A. and Prymak, O. and Wittmar, A. and Ulbricht, M. and Epple, M. and Teresov, A. and Koval, N. and Surmenev, R.A.
    IOP Conference Series: Materials Science and Engineering 98 (2015)
    The influence of surface properties of radio-frequency (RF) magnetron deposited hydroxyapatite (HA) and Si-containing HA coatings on wettability was studied. The composition and morphology of the coatings fabricated on titanium (Ti) were characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). The surface wettability was studied using contact angle analysis. Different geometric parameters of acid-etched (AE) and pulse electron beam (PEB)-treated Ti substrates and silicate content in the HA films resulted in the different morphology of the coatings at micro- and nano- length scales. Water contact angles for the HA coated Ti samples were evaluated as a combined effect of micro roughness of the substrate and nano-roughness of the HA films resulting in higher water contact angles compared with acid-etched (AE) or pulse electron beam (PEB) treated Ti substrates. © Published under licence by IOP Publishing Ltd.
    view abstract10.1088/1757-899X/98/1/012026
  • Design of Thermally Responsive Polymeric Hydrogels for Brackish Water Desalination: Effect of Architecture on Swelling, Deswelling, and Salt Rejection
    Ali, W. and Gebert, B. and Hennecke, T. and Graf, K. and Ulbricht, M. and Gutmann, J.S.
    ACS Applied Materials and Interfaces 7 (2015)
    In this work, we explore the ability of utilizing hydrogels synthesized from a temperature-sensitive polymer and a polyelectrolyte to desalinate salt water by means of reversible thermally induced absorption and desorption. Thus, the influence of the macromolecular architecture on the swelling/deswelling behavior for such hydrogels was investigated by tailor-made network structures. To this end, a series of chemically cross-linked polymeric hydrogels were synthesized via free radical-initiated copolymerization of sodium acrylate (SA) with the thermoresponsive comonomer N-isopropylacrylamide (NIPAAm) by realizing different structural types. In particular, two different polyNIPAAm macromonomers, either with one acrylate function at the chain end or with additional acrylate functions as side groups were synthesized by controlled polymerization and subsequent polymer-analogous reaction and then used as building blocks. The rheological behaviors of hydrogels and their estimated mesh sizes are discussed. The performance of the hydrogels in terms of swelling and deswelling in both deionized water (DI) and brackish water (2 g/L NaCl) was measured as a function of cross-linking degree and particle size. The salt content could be reduced by 23% in one cycle by using the best performing material. (Figure Presented). © 2015 American Chemical Society.
    view abstract10.1021/acsami.5b03878
  • Detoxification of hexavalent chromium in wastewater containing organic substances using simonkolleite-TiO2 photocatalyst
    Abdel Moniem, S.M. and Ali, M.E.M. and Gad-Allah, T.A. and Khalil, A.S.G. and Ulbricht, M. and El-Shahat, M.F. and Ashmawy, A.M. and Ibrahim, H.S.
    Process Safety and Environmental Protection 95 (2015)
    Innovative simple method for the preparation of simonkolleite-TiO<inf>2</inf> photocatalyst with different Zn contents was achieved. The prepared photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR, Raman and diffuse reflectance spectroscopy techniques. The photocatalytic activities of the materials were evaluated for the simultaneous detoxification of hexavalent chromium (Cr(VI)) and oxidation of organic compounds commonly present in wastewater under simulated solar light. The best photoreduction efficiency of Cr(VI) has been achieved at 1000 ppm simonkolleite-TiO<inf>2</inf> photocatalyst of 5% Zn/TiO<inf>2</inf> weight ratio, and pH value of 2.5 to enhance the adsorption onto catalyst surface. Photoreduction was significantly improved by using formic acid as holes scavenger owing to its chemical adsorption on the catalyst surface. Finally, 100% photoreduction of Cr(VI) could be achieved using formic/simonkolleite-TiO<inf>2</inf> systems under sunlight.
    view abstract10.1016/j.psep.2015.03.010
  • Electropolymerized molecularly imprinted polypyrrole film for sensing of clofibric acid
    Schweiger, B. and Kim, J. and Kim, Y.J. and Ulbricht, M.
    Sensors (Switzerland) 15 (2015)
    Piezoelectric quartz crystals and analogous gold substrates were electrochemically coated with molecularly imprinted polypyrrole films for pulsed amperometric detection (PAD) of clofibric acid, a metabolite of clofibrate. Cyclic voltammetry data obtained during polymerization and deposited weight estimations revealed a decrease of the polymerization rate with increasing clofibric acid concentration. XPS measurements indicated that clofibric acid could be removed after imprinting with an aqueous ethanol solution, which was further optimized by using PAD. Zeta potential and contact angle measurements revealed differences between molecularly imprinted (MIP) and non-imprinted polymer (NIP) layers. Binding experiments with clofibric acid and other substances showed a pronounced selectivity of the MIP for clofibric acid vs. carbamazepine, but the response of MIP and NIP to 2,4-dichlorophenoxyacetic acid was higher than that for clofibric acid. A smooth surface, revealed by AFM measurements, with roughness of 6–8 nm for imprinted and non-imprinted layers, might be a reason for an excessively low density of specific binding sites for clofibric acid. Furthermore, the decreased polymerization rate in the presence of clofibric acid might not result in well-defined polymer structures, which could be the reason for the lower sensitivity. © 2015 by the authors; licensee MDPI, Basel, Switzerland.
    view abstract10.3390/s150304870
  • Isotropic macroporous polyethersulfone membranes as competitive supports for high performance polyamide desalination membranes
    ElSherbiny, I.M.A. and Ghannam, R. and Khalil, A.S.G. and Ulbricht, M.
    Journal of Membrane Science 493 (2015)
    Novel macroporous isotropic polyethersulfone (PES) base membranes were developed using combined processes of vapor- and non-solvent-induced phase separation. Optimization of different preparation parameters was carried out. The newly prepared PES membranes exhibited well-defined isotropic porous structures with optimized average barrier pore diameter of 100. nm as well as hydrophilic surface and high water permeability. These isotropic membranes together with two more supports (i.e. commercial PES microfiltration and anisotropic hydrophobic polysulfone membranes), were utilized for the fabrication of polyamide (PA) thin-film composite (TFC) desalination membranes. The resulted PA TFC membranes showed significantly different film morphologies, surface characteristics as well as separation performance. The PA TFC membranes based on the hydrophilic PES supports with isotropic and optimized pore size, developed in this study, showed superior water permeability compared to the composite membranes based on the other supports, without compromising the salt rejection and providing high stability for the PA selective layer. © 2015 Published by Elsevier B.V.
    view abstract10.1016/j.memsci.2015.05.064
  • Materials science: gating mechanism under pressure
    Ulbricht, M.
    Nature 519 (2015)
    Liquid-filled pores in membranes have been designed to reversibly open and close, allowing only particular fluids through at given pressures. This enables tunable and gated separations of mixtures of immiscible fluids. SEE LETTER P.70
    view abstract10.1038/519041a
  • Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: Improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro
    Surmeneva, M.A. and Kleinhans, C. and Vacun, G. and Kluger, P.J. and Schönhaar, V. and Müller, M. and Hein, S.B. and Wittmar, A. and Ulbricht, M. and Prymak, O. and Oehr, C. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 135 (2015)
    Thin radio-frequency magnetron sputter deposited nano-hydroxyapatite (HA) films were prepared on the surface of a Fe-tricalcium phosphate (Fe-TCP) bioceramic composite, which was obtained using a conventional powder injection moulding technique. The obtained nano-hydroxyapatite coated Fe-TCP biocomposites (nano-HA-Fe-TCP) were studied with respect to their chemical and phase composition, surface morphology, water contact angle, surface free energy and hysteresis. The deposition process resulted in a homogeneous, single-phase HA coating. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells (hMSCs) was studied using biological short-term tests in vitro. The surface of the uncoated Fe-TCP bioceramic composite showed an initial cell attachment after 24 h of seeding, but adhesion, proliferation and growth did not persist during 14 days of culture. However, the HA-Fe-TCP surfaces allowed cell adhesion, and proliferation during 14 days. The deposition of the nano-HA films on the Fe-TCP surface resulted in higher surface energy, improved hydrophilicity and biocompatibility compared with the surface of the uncoated Fe-TCP. Furthermore, it is suggested that an increase in the polar component of the surface energy was responsible for the enhanced cell adhesion and proliferation in the case of the nano-HA-Fe-TCP biocomposites. © 2015 Elsevier B.V.
    view abstract10.1016/j.colsurfb.2015.07.057
  • Novel functionalization of porous polypropylene microfiltration membranes: Via grafted poly(aminoethyl methacrylate) anchored Schiff bases toward membrane adsorbers for metal ions
    Farjadian, F. and Schwark, S. and Ulbricht, M.
    Polymer Chemistry 6 (2015)
    In this work we introduce novel synthetic methods for the modification of a macroporous polypropylene (PP) membrane with poly(2-aminoethyl methacrylate) (polyAEMA) and subsequently anchoring a Schiff base with the aim of adsorbing specific metal ions from aqueous solution. The Schiff base synthesis on the surface of the PP membrane was done by a sequence of reactions. First the hydrophobic character of a commercial PP membrane (pore diameter 0.4 μm) was modified via UV irradiation-induced "grafting-from" of poly(2-hydroxyethyl methacrylate) (polyHEMA). The hydroxyl groups of polyHEMA were then reacted with the pre-synthesized photoinitiator 4-ethoxy-5-oxo-4,5-diphenylpentanoyl bromide. UV-irradiation was thereafter used for the "grafting-from" of polyAEMA. The free amino groups of this grafted comb-like brush layer on the surface were reacted with salicylaldehyde to form a Schiff base. ATR-FTIR spectroscopy was carried out to determine the functional groups' introduction and conversion. Scanning electron microscopy images showed the changes between unmodified and modified membranes. The specific surface area was determined by nitrogen adsorption and BET analysis, and the water permeability was also measured. The efficiency of membrane adsorbers with a Schiff base in the grafted layer in binding to Cu(ii) ions was determined by atomic absorption spectroscopy. Overall, the established functionalization sequences and the obtained functionality have potential for the development of efficient adsorber materials. This journal is © The Royal Society of Chemistry 2015.
    view abstract10.1039/c4py01521e
  • Poly(N,N-dimethylaminoethyl methacrylate) Brushes: PH-Dependent Switching Kinetics of a Surface-Grafted Thermoresponsive Polyelectrolyte
    Thomas, M. and Gajda, M. and Amiri Naini, C. and Franzka, S. and Ulbricht, M. and Hartmann, N.
    Langmuir 31 (2015)
    The temperature-dependent switching behavior of poly(N,N-dimethylaminoethyl methacrylate) brushes in alkaline, neutral, and acidic solutions is examined. A novel microscopic laser temperature-jump technique is employed in order to study characteristic thermodynamic and kinetic parameters. Static laser micromanipulation experiments allow one to determine the temperature-dependent variation of the swelling ratio. The data reveal a strong shift of the volume phase transition of the polymer brushes to higher temperatures when going from pH = 10 to pH = 4. Dynamic laser micromanipulation experiments offer a temporal resolution on a submillisecond time scale and provide a means to determine the intrinsic rate constants. Both the swelling and the deswelling rates strongly decrease in acidic solutions. Complementary experiments using in situ atomic force microscopy show an increased polymer layer thickness at these conditions. The data are discussed on the basis of pH-dependent structural changes of the polymer brushes including protonation of the amine groups and conformational rearrangements. Generally, repulsive electrostatic interactions and steric effects are assumed to hamper and slow down temperature-induced switching in acidic solutions. This imposes significant restrictions for smart polymer surfaces, sensors, and devices requiring fast response times. © 2015 American Chemical Society.
    view abstract10.1021/acs.langmuir.5b03448
  • Quaternized polysulfone and graphene oxide nanosheet derived low fouling novel positively charged hybrid ultrafiltration membranes for protein separation
    Kumar, M. and McGlade, D. and Ulbricht, M. and Lawler, J.
    RSC Advances 5 (2015)
    Low fouling novel positively charged hybrid ultrafiltration membranes with adjustable charge density were fabricated from blends of polysulfone (PSf) and quaternized polysulfone (QPSf) in combination with varied fractions of graphene oxide (GO) nanosheets by a non-solvent induced phase separation method. Fourier transform infrared spectroscopy in the attenuated total reflection mode, scanning electron microscopy, outer surface zeta potential and contact angle studies were conducted to characterize the morphologies of hybrid membranes, structures, charge and surface properties. Results confirmed the fabrication of porous, hydrophilic and positively charged membranes. The water permeabilities (flux) and antifouling ability of membranes with protein solution were dependent on the fraction of quaternary ammonium groups and GO nanosheets in the membranes matrix. Antifouling ability of membranes was improved after the incorporation of GO nanosheets. In addition, irreversible protein fouling of membranes was substantially decreased with increasing fraction of GO nanosheets (%). The transmission of protein as a function of solution pH and the fraction of GO nanosheets (%) in the membranes was studied for two model proteins (bovine serum albumin; BSA or lysozyme; LYZ). The transmission of BSA or LYZ was controlled by size exclusion and the fraction of GO nanosheets in the membrane matrix. The highest transmission of proteins at their isoelectric points was obtained for membrane containing 2 wt% of GO nanosheets to total weight of polymers. © The Royal Society of Chemistry 2015.
    view abstract10.1039/c5ra06893b
  • Routes towards catalytically active TiO2 doped porous cellulose
    Wittmar, A. and Thierfeld, H. and Köcher, S. and Ulbricht, M.
    RSC Advances 5 (2015)
    Cellulose-TiO<inf>2</inf> nanocomposites have been successfully prepared by non-solvent induced phase separation, either from cellulose solutions in ionic liquids or from cellulose acetate solutions in classical organic solvents followed by deacetylation ("regeneration"). Commercially available titania nanoparticles from gas phase synthesis processes have been used and processed as dispersions in the respective polymer solution. The used TiO<inf>2</inf> nanoparticles have been characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD), and their dispersions in ionic liquids and organic solvents have been evaluated by dynamic light scattering (DLS) and advanced rheology. The intermediate polymer solutions used in the phase separation process have been studied by advanced rheology. The resulting nanocomposites have been characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Special attention has been given to the complex relationship between the characteristics of the phase separation process and the porous structure of the formed nanocomposites. Two catalytic tests, based on the photocatalytic degradation of model organic dyes under UV irradiation, have been used for the characterization of the TiO<inf>2</inf> doped nanocomposites. The proof-of-concept experiments demonstrated the feasibility of photocatalyst immobilization in porous cellulose via phase separation of nanoparticle dispersions in polymer solutions, as indicated by UV-activated dye degradation in aqueous solution. © The Royal Society of Chemistry.2015.
    view abstract10.1039/c5ra03707g
  • Selective transport of Fe(III) using ionic imprinted polymer (IIP) membrane particle
    Djunaidi, M.C. and Jumina and Siswanta, D. and Ulbricht, M.
    AIP Conference Proceedings 1699 (2015)
    The membrane particles was prepared from polyvinyl alcohol (PVA) and polymer IIP with weight ratios of 1: 2 and 1: 1 using different adsorbent templates and casting thickness. The permeability of membrane towards Fe(III) and also mecanism of transport were studied. The selectivity of the membrane for Fe(III) was studied by performing adsorption experiments also with Cr(III) separately. In this study, the preparation of Ionic Imprinted Polymer (IIP) membrane particles for selective transport of Fe (III) had been done using polyeugenol as functional polymer. Polyeugenol was then imprinted with Fe (III) and then crosslinked with PEGDE under alkaline condition to produce polyeugenol-Fe-PEGDE polymer aggregates. The agrregates was then crushed and sieved using mesh size of 80 and the powder was then used to prepare the membrane particles by mixing it with PVA (Mr 125,000) solution in 1-Methyl-2-pyrrolidone (NMP) solvent. The membrane was obtained after casting at a speed of 25?m/s and soaking in NaOH solution overnight. The membrane sheet was then cut and Fe(III) was removed by acid to produce IIP membrane particles. Analysis of the membrane and its constituent was done by XRD, SEM and size selectivity test. Experimental results showed the transport of Fe(III) was faster with the decrease of membrane thickness, while the higher concentration of template ion correlates with higher Fe(III) being transported. However, the transport of Fe(III) was slower for higher concentration of PVA in the membrane. IImparticles works through retarded permeation mechanism, where Fe(III) was bind to the active side of IIP. The active side of IIP membrane was dominated by the -OH groups. The selectivity of all IIP membranes was confirmed as they were all unable to transport Cr (III), while NIP (Non-imprinted Polymer) membrane was able transport Cr (III). © 2015 AIP Publishing LLC.
    view abstract10.1063/1.4938355
  • Selective transport of Fe(III) using polyeugenol as functional polymer with ionic imprinted polymer membrane method
    Djunaidi, M.C. and Jumina and Siswanta, D. and Ulbricht, M.
    Asian Journal of Chemistry 27 (2015)
    The synthesis of ionic imprinted polymer-Fe membrane using eugenol derivative (polyeugenol) had been done followed by its utilization study as functional polymer for selective transport of Fe(III). Eugenol was polymerized using BF3-diethyl ether as catalyst. The polyeugenol was then bounded with an ion template [Fe(III)] followed by in situ crosslinking with polyethylene glycol diglycidyl ether and membrane base poly(vinyl alcohol) (PVA, Mr = 125,000) in 1-methyl-2-pyrrolidone. A membrane was obtained after casting at 25 m/s and soaking in NaCl solution for 2 days. The membrane soaked further in 0.1 M HCl solution to release Fe(III). The membrane was then analyzed using IR spectrometry, TGA-DTA, SEM and size selective test. Different optimizations steps were carried out for both the synthesis conditions and transport experiments. The selectivity of ionic imprinted polymer membrane for Fe(III) was studied using Cr(III), in separated systems with Cr(III) and Fe(III) in different solutions as well as using binary mixture solutions of the two metals. Experimental results indicate that the crosslinked ionic imprinted polymer membranes are more selective than non-imprinting polymers and as well as its constituents.
    view abstract10.14233/ajchem.2015.19228
  • Thin-film composite membranes for organophilic nanofiltration based on photo-cross-linkable polyimide
    Behnke, S. and Ulbricht, M.
    Reactive and Functional Polymers 86 (2015)
    This work demonstrates that it is possible to prepare new, competitive thin-film composite (TFC) membranes with a polyolefin ultrafiltration membrane as support and with a non-porous photo-cross-linked polyimide as separation layer for organic solvent nanofiltration. The commercial polyimide Lenzing P84® was modified by a polymer-analogous reaction to introduce side groups with carbon-carbon double bonds to increase its photo-reactivity with respect to cross-linking. Polymer characterization revealed that this was successfully achieved at acceptable level of main chain scission. The higher reactivity of the photo-cross-linkable polyimide had been confirmed by comparison with the original polymer; i.e., shorter gelation times upon UV irradiation, higher suppression of swelling by solvents and complete stability in strong solvents for not cross-linked polyimide such as dimethylformamide (DMF) had been obtained. For films from unmodified and modified polyimide, the degree of swelling in various solvents could be adjusted by UV irradiation time. Photo-cross-linking of the original polyimide did not lead to stability in DMF. TFC membranes had been prepared by polymer solution casting on a polyethylene ultrafiltration membrane, UV irradiation of the liquid film and subsequent solvent evaporation. Polyimide barrier film thicknesses between 10 and 1 μm were obtained by variation of cast film thickness. Performance in organic solvent nanofiltration was analyzed by using hexane, toluene, isopropanol and DMF as well as two dyes with molar masses of ∼300 and ∼1000 g/mol. Permeances of TFC membranes from unmodified polyimide were low (< 0.1 L/hm2 bar) while rejections of up to 100% for the dye with ∼1000 g/mol could be achieved. TFC membranes from modified and photo-cross-linked polyimide had adjustable separation performance in DMF with a trade-off between permeance and selectivity, in the same range (e.g.: 0.3 L/hm2 bar and 97% rejection for the dye with ∼1000 g/mol) as a commercial conventional polyimide membrane tested in parallel. The established membrane preparation method is promising because by tuning the degree of cross-linking of the polymeric barrier layer, the membrane separation performance could be tailored within the same manufacturing process. © 2014 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.reactfunctpolym.2014.09.027
  • Two step and one step preparation of porous nanocomposite cellulose membranes doped with TiO2
    Wittmar, A. and Vorat, D. and Ulbricht, M.
    RSC Advances 5 (2015)
    Cellulose-TiO2 nanocomposites have been successfully prepared by non-solvent induced phase separation from cellulose acetate solutions in classical organic solvents followed by deacetylation ("regeneration"). The cellulose deacetylation has been performed either sequentially, i.e. after the completion of the phase separation process, or simultaneously, i.e. during the phase separation process. Commercially available titania nanoparticles from gas phase synthesis processes have been used and processed as a dispersion in the respective polymer solutions. The resulting nanocomposites have been characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Special attention has been given to the complex relation between the conditions of the deacetylation process, the structure of the resulting TiO2 doped cellulose membranes and their corresponding catalytic activities. Two catalytic activity tests, based on the photocatalytic degradation of model organic dyes under UV irradiation, have been used for the functional characterization of the TiO2 doped nanocomposites. The performed experiments demonstrated the successful photocatalyst immobilization in porous cellulose acetate together with good catalytic activity of this nanocomposite intermediate. By simply varying the conditions of the cellulose deacetylation, nanocomposite cellulose membranes with different structures and properties have been obtained. However after the regeneration of cellulose a partial decrease of the catalytic activity was observed. © 2015 The Royal Society of Chemistry.
    view abstract10.1039/c5ra16337d
  • Ultrafiltration membranes with markedly different pH- and ion-responsivity by photografted zwitterionic polysulfobetain or polycarbobetain
    Birkner, M. and Ulbricht, M.
    Journal of Membrane Science 494 (2015)
    Stimuli-responsive ultrafiltration (UF) membranes were synthesized via photo-initiated "grafting from" of the zwitterionic monomers N-(3-sulfopropyl)-N-methacroyl-oxyethyl-N,N-dimethyl-ammonium betaine (sulfobetaine methacrylate, SPE) and 2-carboxy-N,N-dimethyl-N-(2'-(methacryl-oyloxy)ethyl)ethan-aminium inner salt (carbobetaine methacrylate, CBMA) onto commercial polyethersulfone UF membranes. The effects of kosmotropic and chaotropic potassium salts and pH on flux were determined in order to investigate the stimuli-responsive behavior of the polyzwitterion-grafted membranes. PolySPE showed the expected stimuli-responsiveness based on the "anti-polyelectrolyte" effect. The degree of swelling of grafted sulfobetaine polymer increased and water permeability decreased with increasing salt concentration; and the results can be related to the "Hofmeister series", i.e. the magnitude of the effect increased with increasing chaotropic character of the anion, in the order: SO<inf>4</inf>2-<H<inf>2</inf>PO<inf>4</inf>-<Cl-<ClO<inf>4</inf>-. However, the carbobetaine polymer (polyCBMA) did not show such anti-polyelectrolyte behavior at pH values in neutral and basic range. In contrast to the "strong-strong" type zwitterionic material polySPE, the swelling behavior of the "strong-weak" polyCBMA was significantly influenced by pH value because protonation of carboxylic acid side groups changes the grafted chains from net neutral zwitterionic into polycationic with ordinary polyelectrolyte properties. Hence, permeability of polyCBMA-grafted membranes increased with increasing salt concentration at pH=3. Furthermore, the rejection of dextrans as a function of electrolyte concentration and pH was determined and all results were in agreement with changes of water fluxes. For specific salt conditions, large and reversible changes of dextran rejection were found, confirming the possibilities of adjusting the sieving properties of the responsive zwitterionic membranes. Detailed studies by zetapotential measurements were also performed to investigate the specific effects of ion type, electrolyte concentration and pH onto the stimuli-responsive changes of surface charge of grafted membranes. All results support that the effects of the grafted zwitterionic polymers on the barrier properties of the UF membranes can be described with a pore-opening/-closing mechanism based on reversible deswelling/swelling of grafted chains on the pore walls in response to composition changes with respect to salt (for polySPE) or salt and pH value (polyCBMA). © 2015 Published by Elsevier B.V.
    view abstract10.1016/j.memsci.2015.07.046
  • Block copolymer photo-grafted poly(ethylene terephthalate) capillary pore membranes distinctly switchable by two different stimuli
    Geismann, C. and Tomicki, F. and Ulbricht, M.
    Separation Science and Technology (Philadelphia) 44 (2014)
    Track-etched poly(ethylene terephthalate) capillary pore membranes with a pore diameter of 690 nm were functionalized via photo-initiated “living” radical graft polymerization with block copolymers of acrylic acid and N-isopropylacrylamide. Preadsorbed xanthone was more efficient than benzophenone in order to achieve higher grafting efficiency and “living” character, including the option to reinitiate a grafted homopolymer to obtain grafted diblock copolymers. Characterizations were mainly done with water flux and dextran diffusion experiments at temperatures below and above the lower critical solution temperature (32°C) of poly(N-isopropylacrylamide) and pH values below and above the pKa value (4.5) of poly(acrylic acid). Block sequences and relative block lengths were identified to obtain stimuli-responsive membranes which have no measurable water flux and allow only low dextran diffusion rates at 25°C and pH 7 (“closed state”), and which reversibly open their pores by either increase of temperature or decrease of pH, or by the combination of both stimuli. © Taylor & Francis Group, LLC.
    view abstract10.1080/01496390903212755
  • Erratum to: Wettability of Thin Silicate-Containing Hydroxyapatite Films formed by RF-Magnetron Sputtering
    Gorodzha, S.N. and Surmeneva, M.A. and Surmenev, R.A. and Gribennikov, M.V. and Pichugin, V.F. and Sharonova, A.A. and Pustovalova, A.A. and Prymak, O. and Epple, M. and Wittmar, A. and Ulbricht, M. and Gogolinskii, K.V. and Kravchuk, K.S.
    Russian Physics Journal 56 (2014)
    view abstract10.1007/s11182-014-0180-3
  • Fabrication of Ag/TiO2 photocatalyst for the treatment of simulated hospital wastewater under sunlight
    Badawy, M.I. and Souaya, E.M.R. and Gad-Allah, T.A. and Abdel-Wahed, M.S. and Ulbricht, M.
    Environmental Progress and Sustainable Energy 33 (2014)
    In this study, photocatalytic activity of titanium dioxide was modified by doping with silver metal. This was done by simple preparation procedure at room temperature. Different preparation conditions were studied and their effects on photocatalytic activity were investigated. The obtained nanopowders were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), specific surface area measurement, UV-Visible absorption, and transmission electron microscope (TEM). Photocatalytic activities of the prepared samples under simulated sunlight were evaluated with respect to their efficiencies for the degradation of five pharmaceutical compounds commonly present in hospital wastewater. Prepared samples showed very high efficiency for photodegradation of the studied pharmaceutical compounds. Maximum photodegradation rate of the simulated hospital wastewater was obtained using 1000 ppm of the material with 0.1% Ag/TiO2 (weight ratio) calcined at 300°C and pH 5. However, the best pH of the degradation of each pharmaceutical compound varies according to the pKa. © 2013 American Institute of Chemical Engineers.
    view abstract10.1002/ep.11869
  • Low fouling negatively charged hybrid ultrafiltration membranes for protein separation from sulfonated poly(arylene ether sulfone) block copolymer and functionalized multiwalled carbon nanotubes
    Kumar, M. and Ulbricht, M.
    Separation and Purification Technology 127 (2014)
    Low fouling negatively charged hybrid ultrafiltration membranes with adjustable charge density were fabricated from blends of poly(arylene ether sulfone) (PAES) block copolymer and the sulfonated copolymer (S-PAES) in combination with different fractions of sulfonic acid functionalized multiwalled carbon nanotubes (MWCNT-SO3H) by non-solvent induced phase separation method. Porous hybrid membrane morphologies, structure and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, as well as contact angle and zeta potential measurements. Results confirmed that the fabricated membranes were hydrophilic and negatively charged in the studied pH range 3-10. The water permeabilities and increased protein fouling resistances of the membranes were dependent on the fraction of MWCNT-SO3H in the membranes. The protein transmission as function of pH value and fraction of MWCNT-SO3H was studied for two model proteins (bovine serum albumin and myoglobin) and found to be controlled by size exclusion and the content of MWCNT-SO3H. The highest transmission of proteins at their isoelectric points was obtained for the membrane containing 2 wt% of MWCNT-SO3H relative to total membrane polymer. The selectivity of the hybrid membranes for the separation of the binary protein mixture could be systematically increased by increasing surface charge density by increasing fraction of MWCNT-SO3H. Consequently, the trade-off relationship between permeability and selectivity for conventional ultrafiltration membranes where separation is based on size exclusion solely could be overcome and performance be tuned by a small fraction of a functional additive. © 2014 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.seppur.2014.03.003
  • Macroinitiator-mediated photoreactive coating of membrane surfaces with antifouling hydrogel layers
    Lei, J. and Ulbricht, M.
    Journal of Membrane Science 455 (2014)
    Applying a hydrophilic layer to the membrane surface is one common strategy to control membrane fouling. This work focuses on hydrophilic membrane coating materials synthesized from poly(ethylene glycol) (PEG)-based hydrogels and application of thin hydrogel layers from such polymers on the surface of composite polyamide nanofiltration membranes. The approach of using macroinitiator-mediated synthesis cum anchoring of a hydrogel layer on the membrane was explored to reduce or avoid homopolymerization in bulk solution and prevent delamination of the antifouling layer from membrane surface. Cationic macroinitiators were based on poly(2-dimethylamino-ethyl methacrylate-co-2-hydroxyethyl methacrylate) obtained by radical copolymerization and comprised photoinitiator side groups linked to the poly(2-hydroxyethyl methacrylate) segments. Adsorption of the macroinitiator to the membrane surface and preparation of hydrogel coatings on polyamide composite membranes via photo-initiated in situ graft and cross-linking copolymerization were studied in detail. The modification degree and its effect on the membrane properties was characterized with respect to membrane chemistry by ATR-IR spectroscopy, surface charge by zeta potential, surface wettability by contact angle, and with respect to pure water permeability and salt rejection. The propensity to protein fouling was also investigated. The results indicate that hydrogel modified membranes have an improved fouling resistance compared to pristine membranes, and that this approach has the potential to become a generic approach for a controlled surface functionalization using a simple two-step protocol. © 2014.
    view abstract10.1016/j.memsci.2013.12.059
  • Magnetic Fe3O4 nanoparticle heaters in smart porous membrane valves
    Gajda, A.M. and Ulbricht, M.
    Journal of Materials Chemistry B 2 (2014)
    The application of magnetic nanoparticles (NPs) in membrane technology is still very new and combinations of such NPs and separation membranes are essentially unexplored. By the integration of NPs into polymeric membranes it is possible to create new functionalities based on the synergies of the materials. Here nanoparticle polymer hybrid membranes were created by immobilizing (super)paramagnetic Fe3O4 NPs on the walls of track-etched polyethylene terephthalate pores and further functionalization with poly(N-isopropylacryl amide) (PNIPAAm). The hybrid system can be controlled via local heat generation by the NPs induced by an external high frequency electromagnetic field, i.e., effective membrane pore size can be switched by the magnetic field due to the synergy between the nanoparticle functionality and the temperature-responsive properties of PNIPAAm. Analytical characterizations showed a successful and stable NP integration and the feasibility of functionalization with grafted PNIPAAm in the presence of immobilized NPs on the membrane pore surface. The valve function of the nanoparticle polymer hybrid materials with an external control via a high frequency electromagnetic field was demonstrated in water permeability experiments, but such systems will have significant potential for other applications such as drug release or mass separation. © 2014 The Royal Society of Chemistry.
    view abstract10.1039/c3tb21400a
  • Novel ultrafiltration membranes with adjustable charge density based on sulfonated poly(arylene ether sulfone) block copolymers and their tunable protein separation performance
    Kumar, M. and Ulbricht, M.
    Polymer (United Kingdom) 55 (2014)
    A novel poly(arylene ether sulfone) (PAES) block copolymer was prepared from previously synthesized fluoride terminated oligomer (A16) and hydroxyl terminated oligomer (B12) by aromatic nucleophilic substitution polycondensation reaction. PAES was subsequently sulfonated under controlled conditions to yield a copolymer (S-PAES) with sulfonic acid groups selectively in the B12 segments and without chain degradation. Non-solvent induced phase separation method was used to prepare a series of ultrafiltration membranes from blends of S-PAES and PAES with varied ratios and, hence, sulfonic acid group densities. Porous membrane morphologies, structure and surface properties were characterized comprehensively using scanning electron microscopy, Fourier transform infrared spectroscopy in the attenuated total reflection mode, as well as contact angle and zeta potential measurements. Studies of membrane performance revealed systematically increasing water permeabilities and reduced protein fouling tendencies with increasing fraction of S-PAES in the membrane. The protein transmission as function of pH value (and hence protein charge) was studied for two model proteins (bovine serum albumin and lysozyme) and found to be controlled by combined size exclusion and charge effects. The selectivity for the separation of the binary protein mixture could be systematically increased with increasing membrane charge density (by increasing S-PAES fraction). Consequently, the trade-off relationship between permeability and selectivity for conventional ultrafiltration membranes where separation is based on size exclusion solely could be overcome. Due to their high stability and tunable functionality, the PAES block copolymers have also large potential as membrane material for other applications. © 2013 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.polymer.2013.09.003
  • Poly (N-Isopropylacrylamide) hydrogel networks and sieving characteristics
    Adrus, N. and Ayub, N.F. and Ulbricht, M.
    Jurnal Teknologi (Sciences and Engineering) 69 (2014)
    The three-dimensional of hydrogel networks within nm range can microscopically be considered as "porous"mesh. This feature may imply that hydrogel networks possess sieving characteristics; i.e. exclusion of solutes or molecules based on size. In this study the network and sieving characteristics of poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were investigated. PNIPAAm hydrogels were prepared via free radical using N-isopropylacrylamide (NIPAAm) as main monomers and N,N-methylenebisacrylamide (MBAAm) as crosslinkers. As the composition of the hydrogels was varied, the mesh sizes of the resulting hydrogels were in the range of 4.0 to 11.0 nm. These data were obtained from swelling experiments. Dextrans as test solutes with molecular weight in the range of 4 to 2000 kg/mol were used in partitioning experiments to investigate the sieving of the hydrogel networks. The partitioning data indicated that of hydrogel networks excluded the solutes which were bigger than its mesh sizes. The experimental results not only show a good correlation of sieving coefficient on the size basis but also nicely fitted to the partition data estimated from the Ogston model. Undoubtedly, PNIPAAm hydrogel networks possessed sieving characteristics to separate molecules exclusively and selectively as a function of size. © 2014 Penerbit UTM Press. All rights reserved.
    view abstract10.11113/jt.v69.3164
  • Stable zinc oxide nanoparticle dispersions in ionic liquids
    Wittmar, A. and Gautam, D. and Schilling, C. and Dörfler, U. and Mayer-Zaika, W. and Winterer, M. and Ulbricht, M.
    Journal of Nanoparticle Research 16 (2014)
    The influence of the hydrophilicity and length of the cation alkyl chain in imidazolium-based ionic liquids on the dispersability of ZnO nanoparticles by ultrasound treatment was studied by dynamic light scattering and advanced rheology. ZnO nano-powder synthesized by chemical vapor synthesis was used in parallel with one commercially available material. Before preparation of the dispersion, the nanoparticles characteristics were determined by transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Hydrophilic ionic liquids dispersed all studied nanopowders better and in the series of hydrophilic ionic liquids, an improvement of the dispersion quality with increasing length of the alkyl chain of the cation was observed. Especially, for ionic liquids with short alkyl chain, additional factors like nanoparticle concentration in the dispersion and the period of the ultrasonic treatment had significant influence on the dispersion quality. Additionally, nanopowder characteristics (crystallite shape and size as well as the agglomeration level) influenced the dispersion quality. The results indicate that the studied ionic liquids are promising candidates for absorber media at the end of the gas phase synthesis reactor allowing the direct preparation of non-agglomerated nanoparticle dispersions without supplementary addition of dispersants and stabilizers. © Springer Science+Business Media 2014.
    view abstract10.1007/s11051-014-2341-2
  • Wettability of Thin Silicate-Containing Hydroxyapatite Films Formed by RF-Magnetron Sputtering
    Gorodzha, S.N. and Surmeneva, M.A. and Surmenev, R.A. and Gribennikov, M.V. and Pichugin, V.F. and Sharonova, A.A. and Pustovalova, A.A. and Prymack, O. and Epple, M. and Wittmar, A. and Ulbricht, M. and Gogolinskii, K.V. and Kravchuk, K.S.
    Russian Physics Journal 56 (2014)
    Using the methods of electron and atomic force microscopy, X-ray structural analysis and measurements of the wetting angle, the features of morphology, structure, contact angle and free surface energy of silicon-containing calcium-phosphate coatings formed on the substrates made from titanium VT1-0 and stainless steel 12Cr18Ni10Ti are investigated. It is shown that the coating - substrate system possesses bimodal roughness formed by the substrate microrelief and coating nanostructure, whose principal crystalline phase is represented by silicon-substituted hydroxiapatite with the size of the coherent scattering region (CSR) 18-26 nm. It is found out that the formation of a nanostructured coating on the surface of rough substrates makes them hydrophilic. The limiting angle of water wetting for the coatings formed on titanium and steel acquires the values in the following ranges: 90-92 and 101-104°, respectively, and decreases with time. © 2014 Springer Science+Business Media New York.
    view abstract10.1007/s11182-014-0157-2
  • ZnO-modified hybrid polymers as an antibacterial finish for textiles
    Farouk, A. and Moussa, S. and Ulbricht, M. and Schollmeyer, E. and Textor, T.
    Textile Research Journal 84 (2014)
    The antibacterial activity of ZnO is reported by several authors. We present the preparation and application of inorganic–organic hybrid polymers modified/filled with ZnO nanoparticles of varying particle sizes. Inorganic–organic hybrid polymers employed here are based on 3-glycidyloxypropyltrimethoxysilane (GPTMS). ZnO is prepared by hydrolysis of zinc acetate in different solvents (methanol, ethanol or 2-propanol) using lithium hydroxide (LiOH ċ H2O). The hybrid materials prepared are applied to cotton (100%) and cotton/polyester (65/35%) fabrics. The antibacterial performance of these sol-gel derived hybrid materials is exemplarily investigated against Gram-negative bacterium Escherichia coli and Gram–positive Micrococcus luteus. Effects of particle size and concentration for the antibacterial performance are examined. Literature discusses various (active) species and processes responsible for the antibacterial action of ZnO. Therefore, particular attention is paid to investigate active species available in the described systems as well as to observe possible interaction between the nanoparticles and bacteria; the first results are presented. © 2014, SAGE Publications. All rights reserved.
    view abstract10.1177/0040517513485623
  • Advanced ultrafiltration membranes based on functionalized poly(arylene ether sulfone) block copolymers
    Kumar, M. and Ulbricht, M.
    RSC Advances 3 (2013)
    In this study, poly(arylene ether sulfone) (PAES) block copolymer was synthesized from fluoride-terminated oligomer (A<inf>16</inf>) and hydroxyl terminated oligomer (B<inf>12</inf>) by aromatic nucleophilic substitution (S<inf>N</inf>Ar) polycondensation reaction. Then allylic free radical substitution reaction at methyl side group using N-bromosuccinimide and benzoyl peroxide was performed to synthesize PAES-CH<inf>2</inf>Br block copolymer. The chemical structure of PAES and PAES-CH<inf>2</inf>Br block copolymers was confirmed by 1H-NMR spectroscopy. Gel permeation chromatography was applied to determine the molecular weight and the degree of polymerization of A<inf>16</inf> and B<inf>12</inf> oligomers, PAES and PAES-CH<inf>2</inf>Br block copolymers. The synthesized block copolymer had high molecular weight and multiblock structure. Non-solvent induced phase separation of blends of PAES-CH<inf>2</inf>Br and PAES block copolymers followed by heterogeneous quaternization using trimethyl amine led to hydrophilic positively charged ultrafiltration membranes. Fourier transform infrared spectroscopy in the attenuated total reflection mode, scanning electron microscopy, contact angle, and outer surface zeta potential studies were performed to characterize the resulting membranes. The results confirmed that the prepared membranes were porous, hydrophilic and positively charged. Membranes were also characterized with respect to permeability and then used in ultrafiltration of bovine serum albumin and lysozyme model solutions at varied pH values. Membrane performance depended on the positive charge density which could be adjusted by varying the fraction of PAES-CH<inf>2</inf>Br in the membrane. Due to the combined effects of size exclusion and charge repulsion, permeability, antifouling properties and protein separation selectivity of membranes could be increased simultaneously with increasing charge density. © The Royal Society of Chemistry 2013.
    view abstract10.1039/c3ra41483c
  • Antibody-imprinted membrane adsorber via two-step surface grafting
    Yin, D. and Ulbricht, M.
    Biomacromolecules 14 (2013)
    In this work, a recently established, novel two-step imprinting strategy combining surface imprinting and scaffold imprinting was applied successfully to prepare a molecularly imprinted polymer (MIP) adsorber for immunoglobulin G (IgG). Track-etched polyethylene terephthalate (PET) membranes with previously introduced aliphatic C-Br groups as initiator on the pore surface were used to prepare first a functional polymer scaffold, grafted poly(methacrylic acid), via surface-initiated atom transfer radical polymerization (SI-ATRP). After template protein (IgG) binding to the scaffold, UV-initiated cross-linking copolymerization of acrylamide and methylenebisacrylamide (MBAA) as second step lead to a grafted MIP hydrogel layer. The influences of the three independent parameters, scaffold chain length by SI-ATRP time, degree of cross-linking of the MIP layer by MBAA content, and grafted MIP layer thickness by UV irradiation time, were studied to optimize protein binding capacity and selectivity. The results were also compared to previously obtained data for lysozyme imprinting using the same method, and significant effects of protein size on imprinting efficiency could be identified. The best IgG MIP membrane adsorber was then used to separate IgG from mixtures with human serum albumin (HSA), demonstrating IgG binding capacities and eluted IgG purities, which were almost independent of the excess of HSA. The results of this study are a significant extension of the scope of molecular imprinting toward large target bionanoparticles. The transfer of the approach from the model PET to other base membranes with higher specific surface area is straightforward, and the resulting affinity materials would, in principle, be suited for "capturing" of an antibody from a complex mixture. © 2013 American Chemical Society.
    view abstract10.1021/bm401444y
  • Designing magnetic field responsive nanofiltration membranes
    Yang, Q. and Himstedt, H.H. and Ulbricht, M. and Qian, X. and Ranil Wickramasinghe, S.
    Journal of Membrane Science 430 (2013)
    Base, thin film composite polyamide, nanofiltration membranes have been modified using surface initiated atom transfer radical polymerization to graft poly(2-hydroxyethyl methacrylate) (polyHEMA) chains from the surface of the membrane. A modified Gabriel synthesis procedure was used to attach superparamagnetic (Fe3O4) nanoparticles to the chain ends. Chain density and chain length were independently varied by adjusting the initiator density and polymerization time. Membranes were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements. The performance of modified membranes was investigated by determining deionized water fluxes as well as permeate fluxes and salt rejection for aqueous feed streams containing 500ppm CaCl2 and 2000ppm MgSO4. All experiments were conducted in dead end mode. Modified membranes display a reduced permeate flux and increased salt rejection compared to unmodified membranes in the absence of a magnetic field. Since both grafted chain density and chain length are expected to affect membrane performance differently, the decrease in permeate flux and increase in salt rejection is not directly proportional to the increase in grafted polymer weight. Modified membranes display both increased permeate fluxes and increased salt rejection in the presence of an oscillating magnetic field compared to their performance in the absence of an oscillating magnetic field. Magnetically responsive membranes could represent a new class of fouling resistant membranes. © 2012 Elsevier B.V.
    view abstract10.1016/j.memsci.2012.11.068
  • Grafting of titanium dioxide microspheres with a temperature-responsive polymer via surface-initiated atom transfer radical polymerization without the use of silane coupling agents
    Smirnov, E.A. and Meledina, M.A. and Garshev, A.V. and Chelpanov, V.I. and Frost, S. and Wieneke, J.U. and Ulbricht, M.
    Polymer International 62 (2013)
    Titania microspheres with narrow size distribution and diameters of about 1 μm were prepared and subsequently functionalized using surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide. The ATRP initiator was immobilized on the particle surface via acylation of surface hydroxyl groups with α-bromoisobutyryl bromide. Subsequently, an established ATRP reaction system was used for the preparation of titania surface-grafted poly(N-isopropylacrylamide) (PNiPAAm). Characterization was performed with electron microscopies, X-ray diffraction, infrared spectroscopy and dynamic light scattering. It was found that the particle size in aqueous dispersions changed reversibly with temperature as expected for a shell of PNiPAAm, a polymer with a lower critical solution temperature at 32 °C. This confirmed the successful preparation of functional, stimuli-responsive TiO2 microparticles via a straightforward controlled surface-initiated polymerization method. © 2012 Society of Chemical Industry.
    view abstract10.1002/pi.4377
  • Hofmeister effect of sodium halides on the switching energetics of thermoresponsive polymer brushes
    Naini, C.A. and Thomas, M. and Franzka, S. and Frost, S. and Ulbricht, M. and Hartmann, N.
    Macromolecular Rapid Communications 34 (2013)
    A laser temperature-jump technique is used to probe the impact of sodium halides on the temperature-dependent switching kinetics and thermodynamics of poly(N-isopropylacrylamide) brushes. An analysis on the basis of a two-state model reveals van't Hoff enthalpy and entropy changes. Sodium halides increase the endothermicity and the entropic gain of the switching process below and above Tc following the Hofmeister series: NaCl &gt; NaBr &gt; NaI. In contrast, enthalpic and entropic changes at Tc remain virtually unaffected. This provides an unprecedented insight into the underlying switching energetics of this classic stimuli-responsive polymer. Because of its model character, these results represent an essential reference on the way to unpuzzle the molecular driving forces of the Hofmeister effect. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/marc.201200681
  • Influence of the cation alkyl chain length of imidazolium-based room temperature ionic liquids on the dispersibility of TiO2 nanopowders
    Wittmar, A. and Gajda, M. and Gautam, D. and Dörfler, U. and Winterer, M. and Ulbricht, M.
    Journal of Nanoparticle Research 15 (2013)
    The influence of the length of the cation alkyl chain on the dispersibility by ultrasonic treatment of TiO2 nanopowders in hydrophilic imidazolium-based room temperature ionic liquids was studied for the first time by dynamic light scattering and advanced rheology. TiO2 nanopowders had been synthesized by chemical vapor synthesis (CVS) under varied conditions leading to two different materials. A commercial nanopowder had been used for comparison. Characterizations had been done using transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Primary particle sizes were about 6 and 8 nm for the CVS-based and 26 nm for the commercial materials. The particle size distribution in the dispersion was strongly influenced by the length of the cation alkyl chain for all the investigated powders with different structural characteristics and concentrations in the dispersion. It was found that an increase of the alkyl chain length was beneficial, leading to a narrowing of the particle size distribution and a decrease of the agglomerate size in dispersion. The smallest average nanoparticle sizes in dispersion were around 30 nm. Additionally, the surface functionality of the nanoparticles, the concentration of the solid material in the liquid, and the period of ultrasonic treatment control the dispersion quality, especially in the case of the ionic liquids with the shorter alkyl chain. The influence of the nanopowders characteristics on their dispersibility decreases considerably with increasing cation alkyl chain length. The results indicate that ionic liquids with adapted structure are candidates as absorber media for nanoparticles synthesized in gas phase processes to obtain liquid dispersions directly without redispergation. © 2013 Springer Science+Business Media Dordrecht.
    view abstract10.1007/s11051-013-1463-2
  • Nanofiltration Separation of Aqueous Polyethyleneglycol - Salt Mixtures
    Jimenez, Y.P. and Alele, N. and Galleguillos, H.R. and Ulbricht, M.
    Separation Science and Technology (Philadelphia) 48 (2013)
    To investigate nanofiltration (NF) separation for recycling polyethylenglycol (PEG) from an ion partition process using an aqueous two-phase system, fractionation performance of five different NF membranes (NF270, SR3, SR100, SR2, and BW30) with solutions of NaNO3, KClO4, and PEG 4000 in water comprising various mixtures were studied. PEG rejections and salt passage were analyzed and explained based on size exclusion as well as electrostatic interactions. The highest permeate flux at high rejection of PEG as well as the lowest salt rejections were obtained with SR2 and NF270 membranes. Similar salt rejections were observed for mixed solute solutions and complex mixtures, all following this trend: SR3 &gt; NF270 &gt; SR2. The PEG rejections were well above 95%. This study also revealed that high salt passage of above 90% could be achieved with the same NF membrane only by unstirred conditions through concentration polarization mechanism; however, at the expense of low flux, especially with high PEG concentrations. © 2013 Copyright Taylor and Francis Group, LLC.
    view abstract10.1080/01496395.2012.746367
  • Novel antifouling positively charged hybrid ultrafiltration membranes for protein separation based on blends of carboxylated carbon nanotubes and aminated poly(arylene ether sulfone)
    Kumar, M. and Ulbricht, M.
    Journal of Membrane Science 448 (2013)
    In this study, an aminated hydrophilic poly(arylene ether sulfone) (APAES) multiblock copolymer was prepared from previously synthesized bromomethylated poly(arylene ether sulfone) (PAES-CH2Br) block copolymer via in situ amination with triethanolamine. Novel positively charged hybrid ultrafiltration membranes were fabricated by film casting with non-solvent induced phase separation of blends of PAES and APAES block copolymers with carboxylated multiwalled carbon nanotubes (MWCNT-COOH). Fourier transform infrared spectroscopy in the attenuated total reflection mode, scanning electron microscopy as well as contact angle and outer surface zeta potential studies were performed to characterize the membranes in detail. The results confirmed that the fabricated membranes were porous, hydrophilic, positively charged, and had improved antifouling capacity. The hybrid membranes were used in ultrafiltration of ovalbumin and lysozyme model solutions (individually) at varied pH values. Membrane performance depended on the contents of MWCNT-COOH, which could be adjusted by varying its fraction in the membrane casting solutions. Due to the combined effects of size exclusion and charge repulsion, the permeability, antifouling properties and separation selectivity of the hybrid ultrafiltration membranes could be improved simultaneously by increasing of charge density and fraction of MWCNT-COOH. © 2013.
    view abstract10.1016/j.memsci.2013.07.055
  • Preparation of a silicate-containing hydroxyapatite-based coating by magnetron sputtering: Structure and osteoblast-like MG63 cells in vitro study
    Surmeneva, M.A. and Kovtun, A. and Peetsch, A. and Goroja, S.N. and Sharonova, A.A. and Pichugin, V.F. and Grubova, I.Y. and Ivanova, A.A. and Teresov, A.D. and Koval, N.N. and Buck, V. and Wittmar, A. and Ulbricht, M. and Prymak, O. and Epple, M. and Surmenev, R.A.
    RSC Advances 3 (2013)
    Silicate-containing hydroxyapatite-based coatings with different structure and calcium/phosphate ratios were prepared by radio-frequency magnetron sputtering on silicon and titanium substrates, respectively. Scanning electron microscopy, X-ray diffraction and IR spectroscopy were used to investigate the effect of the substrate bias on the properties of the silicate-containing hydroxyapatite-based coatings. The deposition rate, composition, and microstructure of the deposited coatings were all controlled by changing the bias voltage from grounded (0 V) to -50 and -100 V. The biocompatibility was assessed by cell culture with human osteoblast-like cells (MG-63 cell line), showing a good biocompatibility and cell growth on the substrates. © 2013 The Royal Society of Chemistry.
    view abstract10.1039/c3ra40446c
  • Protein-selective adsorbers by molecular imprinting via a novel two-step surface grafting method
    Yin, D. and Ulbricht, M.
    Journal of Materials Chemistry B 1 (2013)
    Molecularly imprinted polymers (MIP) offer in principle a robust, cost-efficient alternative to antibodies, but it is still a challenge to develop such materials for protein recognition. Here, we report the molecular imprinting of a functional polymeric hydrogel layer with lysozyme as the template in a two-step grafting procedure by a novel initiation approach on track-etched polyethylene terephthalate membrane surface. This is based on surface functionalization with aliphatic C-Br groups which can be used as an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP) and photo-initiated copolymerization. At first, the scaffold poly(methacrylic acid) (PMAA) was obtained through SI-ATRP of poly(tert-butyl methacrylate) and subsequent hydrolysis. Thereafter, it was assembled with the template to form a stable PMAA/lysozyme complex. In the second step, a polyacrylamide (PAAm) hydrogel was synthesized via UV-initiated surface grafting/crosslinking copolymerization around the scaffold/protein complex. Finally, the template was eluted to yield the grafted hydrogel layer with binding sites having complementary size, shape and appropriate arrangement of the functional groups to rebind lysozyme. The selectivity of lysozyme recognition, relative to cytochrome C with a similar size and isoelectric point, was increased by optimization of the scaffold chain length, UV grafting/crosslinking time and the chemical crosslinking degree of the PAAm-based hydrogel. The feasibility for the development of protein MIP in a straightforward way by independent optimization of crucial parameters-structures of scaffold with functional groups and of the crosslinked hydrogel matrix-have been demonstrated. © The Royal Society of Chemistry.
    view abstract10.1039/c3tb20333f
  • Rheological studies on PNIPAAm hydrogel synthesis via in situ polymerization and on resulting viscoelastic properties
    Adrus, N. and Ulbricht, M.
    Reactive and Functional Polymers 73 (2013)
    Bulk poly(N-isopropylacrylamide) hydrogels were prepared via free radical polymerization. Two different initiation methods were studied: redox- and photoinitiation. It was demonstrated that the desired final properties of resulting hydrogels, i.e., high monomer conversion (>95%) and adjustable swelling were only obtained by selecting best suited initiation conditions. For redox polymerization, this was achieved by tuning the ratio of accelerator N,N,N′,N′-tetramethylethylenediamine to initiator ammonium persulfate. The key parameters for achieving optimum photopolymerization conditions were photoinitiator concentration and UV irradiation time. With help of in situ rheological measurements, optimum conditions could be further verified and quantified by monitoring the liquid-to-gel transition. Overall, photoiniated crosslinking copolymerization was postulated to offer better options for in situ preparation of tailored functional hydrogels, in particular for the integration of smart soft matrices within membrane pores or other microsystems via a rapid reaction. Rheology was also used to investigate the hydrogel after ex situ preparation, revealing "perfect" soft-rubbery behavior. A good correlation between the mesh sizes determined from swelling and rheology was also found. In conclusion, rheology has been found to be a powerful tool because it provides valuable data on polymerization and gelation kinetics as well as information about the hydrogels microstructure based on their viscoelastic character. © 2012 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.reactfunctpolym.2012.08.015
  • Synthesis and characterization of poly(ethylene glycol) methacrylate based hydrogel networks for anti-biofouling applications
    Lei, J. and Mayer, C. and Freger, V. and Ulbricht, M.
    Macromolecular Materials and Engineering 298 (2013)
    A series of hydrogels based on poly(ethylenglycol) methyl ether methacrylate (PEGMEMA) is synthesized using macromonomers of three different molecular weights, in combination with varied degrees of chemical crosslinking. The effects of PEGMEMA, initiator, and crosslinker concentrations on gel yield and swelling properties are studied. In addition, the chemical structure of the gels is characterized by FTIR and solid-state NMR spectra. The swelling and rheological behaviors of hydrogels as well as protein partitioning into the gels are discussed in terms of the network mesh size. Low protein sorption and bacteria deposition tendencies indicate that PEGMEMA-based hydrogels could be highly beneficial for uses as fouling-resistant materials, for instance, as protective coatings for desalination membranes. The storage modulus correlates well with the swelling ratio for different hydrogels prepared from a variety of PEG monomers with different degrees of crosslinking, and these properties show a profound influence on protein uptake and bacterial adhesion. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/mame.201200297
  • The rubber elasticity of poly(N-isopropylacrylamide) hydrogel networks
    Adrus, N. and Ulbricht, M.
    Advanced Materials Research 812 (2013)
    We report here on the characterization of classical bulk poly(N-isopropylacrylamide) (PNIPAAm) hydrogel networks. The classical PNIPAAm hydrogels were prepared from Nisopropylacrylamide (NIPAAm) as a main monomer and N,N'-methylenebisacrylamide (MBAAm) as a crosslinker. The viscoelastic character of bulk hydrogels was examined using rheological measurements under frequency sweep mode (20 °C). A range of frequency, ω from 0.1 to 100 rad/s, was employed as this is a typical range for 'rubber plateau'. Within this range, almost frequency independent of storage moduli (G'; ~ 104 Pa as a function of hydrogel compositions were obtained. Indeed, the 'perfect' soft-rubbery behaviour of PNIPAAm hydrogels could be confirmed and thus enabled the estimation of mesh size. Interestingly, the mesh size rubbery hydrogels determined from rheological data was in a good agreement to that from swelling experiments (~ 4 to 9 nm). © (2013) Trans Tech Publications, Switzerland.
    view abstract10.4028/www.scientific.net/AMR.812.210
  • Thermoresponsive ultrafiltration membranes for the switchable permeation and fractionation of nanoparticles
    Frost, S. and Ulbricht, M.
    Journal of Membrane Science 448 (2013)
    Poly(ethylene terephthalate) track-etched ultrafiltration membranes (110. nm pore diameter) have been functionalized with the thermo-responsive polymer poly(N-isopropylacrylamide) (PNIPAAm) via surface-initiated Atom Transfer Radical Polymerization (SI-ATRP). The PNIPAAm chain lengths, i.e. degree of graft functionalization, inside the membrane pores could be controlled very well with polymerization time. Importantly, gas flow/pore dewetting permporometry measurements demonstrated that the pore diameter in the dry state could be reduced and that the narrow pore size distribution of the membranes was not changed during the grafting process. Both hydrodynamic pore diameters of the membranes and grafted hydrodynamic layer thickness on the pore walls as well as their response to temperature could be estimated by measuring water permeability and applying Hagen-Poiseuille law. Defined temperature-induced swelling/deswelling ratios of ~2 had been observed. These data indicate that PNIPAAm chains in the brush state had been achieved. The ultrafiltration membrane pores could be switched between more open and more closed states. For example, the hydrodynamic pore diameter could be switched from 21. nm at 23. °C to 69. nm at 45. °C. For the same type of membrane the rejection of monomodal 21. nm silica nanoparticles could be switched from 99% at 23. °C to only 35% at 45. °C. The rejection for larger monomodal 35. nm silica nanoparticles was above 90% for every functionalized membrane irrespective of the temperature. For an exemplary functionalized membrane evidence for a switchable size-selective NP fractionation has been found. A mixture of the 21 and the 35. nm silica nanoparticles was ultrafiltered through the membrane and at 23. °C only the smaller ones could be found in the permeate whereas at 45. °C also the larger nanoparticles were able to pass the membrane. © 2013.
    view abstract10.1016/j.memsci.2013.07.036
  • Tuning the nanofiltration performance of thin film strong polyelectrolyte hydrogel composite membranes by photo-grafting conditions
    Bernstein, R. and Antón, E. and Ulbricht, M.
    Journal of Membrane Science 427 (2013)
    Polyethersulfone ultrafiltration membranes were converted into charged nanofiltration membranes having a strong polyelectrolyte hydrogel as selective barrier layer through the UV-photo initiated graft polymerization technique. This was accomplished by using vinyl sulfonic acid as the functional monomer and N,N'-methylenbisacrylamide as a cross linker monomer (Bernstein et al., ACS Applied Materials & Interfaces, 4 (2012) 3438-3446). In this research the resulting composite membranes were further characterized using different methods (ATR-FTIR spectroscopy, zeta potential, contact angle, scanning electron microscopy). ATR-FTIR data were used to quantify the degree of grafting. The composite membranes' zeta potential was negative throughout the pH range and as high as -70. mV. The hydrogel composite membranes were also very hydrophilic with a contact angle of 11°. The membrane performance-salt rejection and water permeability-obtained at varied functionalization conditions-molecular weight cut-off of the base membrane, monomer concentration, cross linker fraction, UV irradiation intensity and time-was systematically investigated and the results were correlated to the membrane characterization data. Separation performance was also tested using mixed salt solutions. Larger composite membrane samples were prepared and long-term stability of nanofiltration (NF) performance was evaluated in cross-flow experiments. The performance of the best of the newly fabricated composite membranes was comparable to other polyelectrolyte-based NF membranes as well as to some commercial NF membranes presented in the literature. © 2012 Elsevier B.V.
    view abstract10.1016/j.memsci.2012.09.034
  • Cross-flow ultrafiltration of protein solutions through unmodified and surface functionalized polyethersulfone membranes - Effect of process conditions on separation performance
    Peeva, P.D. and Knoche, T. and Pieper, T. and Ulbricht, M.
    Separation and Purification Technology 92 (2012)
    In the present work, polyethersulfone ultrafiltration membranes were UV-initiated grafted with poly(ethylene glycol) methacrylate by varying the UV irradiation dose. The flux and selectivity performance of the prepared low-fouling thin-layer hydrogel composite membranes were tested in cross-flow filtration experiments and compared to unmodified commercial membranes with similar properties (water permeability and molecular weight cut-off). Here, the effects of feed composition (single proteins and protein mixtures), pH and cross-flow velocity were evaluated. Furthermore, the stability of these membranes was tested during three cycles of ultrafiltration and cleaning. The results showed that the performed surface hydrophilization increased the permeate flux and stabilized the membrane selectivity (relevant for separation of protein mixtures). The proteins charge was still important for flux and rejection during ultrafiltration with functionalized membranes. Increasing cross-flow velocity was more efficient for these membranes, since fouling effects were minimized by the grafted hydrogel layer. Furthermore, the membrane stability after three cycles of ultrafiltration and chemical cleaning at pH = 13 was proven and the cleanability of the hydrogel composite ultrafiltration membranes was much better compared to that of comparable unmodified polyethersulfone ultrafiltration membranes. © 2012 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.seppur.2012.03.013
  • Dispersions of silica nanoparticles in ionic liquids investigated with advanced rheology
    Wittmar, A. and Ruiz-Abad, D. and Ulbricht, M.
    Journal of Nanoparticle Research 14 (2012)
    The colloidal stabilities of dispersions of unmodified and surface-functionalized SiO 2 nanoparticles in hydrophobic and hydrophilic imidazolium-based ionic liquids were studied with advanced rheology at three temperatures (25, 100, and 200 °C). The rheological behavior of the dispersions was strongly affected by the ionic liquids hydrophilicity, by the nanoparticles surface, by the concentration of the nanoparticles in the dispersion as well as by the temperature. The unmodified hydrophilic nanoparticles showed a better compatibility with the hydrophilic ionic liquid. The SiO 2 surface functionalization with hydrophobic groups clearly improved the colloidal stability of the dispersions in the hydrophobic ionic liquid. The temperature increase was found to lead to a destabilization in all studied systems, especially at higher concentrations. The results of this study imply that ionic liquids with tailored properties could be used in absorbers directly after reactors for gas-phase synthesis of nanoparticles or/and as solvents for their further surface functionalization without agglomeration or aggregation. © Springer Science+Business Media B.V. 2012.
    view abstract10.1007/s11051-011-0651-1
  • Dispersions of various titania nanoparticles in two different ionic liquids
    Wittmar, A. and Ulbricht, M.
    Industrial and Engineering Chemistry Research 51 (2012)
    The dispersibility of different lab-made and commercial TiO 2 nanoparticles prepared by gas-phase processes in room temperature ionic liquids was for the first time studied by dynamic light scattering and advanced rheology. The characterization of the nanopowders has been done with transmission electron microscopy, X-ray diffraction analysis, nitrogen adsorption, and Brunauer-Emmett-Teller (BET) analysis and FT-IR spectroscopy. The colloidal stabilities of the resulting dispersions were strongly influenced by particle characteristics such as aggregation level, mean particle size, and surface functionality. The period of the ultrasound treatment, the powder concentration in the dispersion, and the hydrophilicity of the ionic liquid were also important influences. It was found that most types of powders disperse better in the hydrophilic ionic liquid because of the hydroxyl groups and adsorbed water present on the powders' surfaces. The best dispersions over a broader concentration range were obtained for a lab-made powder produced by chemical vapor synthesis (aerosol method) which had the smallest nonaggregated particles. © 2012 American Chemical Society.
    view abstract10.1021/ie203010x
  • Effect of membrane hydrophilization on ultrafiltration performance for biomolecules separation
    Susanto, H. and Roihatin, A. and Aryanti, N. and Anggoro, D.D. and Ulbricht, M.
    Materials Science and Engineering C 32 (2012)
    This paper compares the performance of different hydrophilization methods to prepare low fouling ultrafiltration (UF) membranes. The methods include post-modification with hydrophilic polymer and blending of hydrophilic agent during either conventional or reactive phase separation (PS). The post-modification was done by photograft copolymerization of water-soluble monomer, poly(ethylene glycol) methacrylate (PEGMA), onto a commercial polyethersulfone (PES) UF membrane. Hydrophilization via blend polymer membrane with hydrophilic additive was performed using non-solvent induced phase separation (NIPS). In reactive PS method, the cast membrane was UV-irradiated before coagulation. The resulting membrane characteristic, the performance and hydrophilization stability were systematically compared. The investigated membrane characteristics include surface hydrophilicity (by contact angle /CA/), surface chemistry (by FTIR spectroscopy), and surface morphology (by scanning electron microscopy). The membrane performance was examined by investigation of adsorptive fouling and ultrafiltration using solution of protein or polysaccharide or humic acid. The results suggest that all methods could increase the hydrophilicity of the membrane yielding less fouling. Post-modification decreased CA from 44.8 ± 4.2 o to 37.8 ± 4.2 o to 42.5 ± 4.3 o depending on the degree of grafting (DG). The hydrophilization via polymer blend decreased CA from from 65 o to 54 o for PEG concentration of 5%. Nevertheless, decreasing hydraulic permeability was observed after post-modification as well as during polymer blend modification. Stability examination showed that there was leaching out of modifier agent from the membrane matrix prepared via conventional PS after 10 days soaking in both water and NaOH. Reactive PS could increase the stability of the modifier agent in membrane matrix. © 2012 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.msec.2012.04.036
  • Factors affecting the sieving behavior of anti-fouling thin-layer cross-linked hydrogel polyethersulfone composite ultrafiltration membranes
    Peeva, P.D. and Million, N. and Ulbricht, M.
    Journal of Membrane Science 390-391 (2012)
    Anti-fouling thin-layer hydrogel composite membranes based on polyethersulfone (PES) ultrafiltration (UF) membranes were synthesized by addition of the crosslinking agents N,N'-methylene bisacrylamide (MBAA) and pentaerythritol triallyl ether (PETAE) to the modifier solution of poly(ethylene glycol)400 methacrylate (PEGMA) in water under variation of the UV irradiation intensity and dose. The resulting membrane properties were characterized by means of water permeability, degree of grafting (DG), modification depth and skin-layer cross-section structure (scanning electron microscopy; SEM) as well as sieving/rejection behavior via filtration of polyethylene glycol (PEG) and dextran mixtures with wide molecular weight distribution (MWD) in water, the latter as additional study to already performed experiments on protein rejection [1]. For better understanding of the obtained results, bulk hydrogels were also prepared and the degree of swelling (DS) was determined. The performed experiments showed that the used crosslinkers changed the hydrogel layer structure and properties, which significantly affected the sieving/rejection behavior of the composite membranes. Using test solutions with low fouling tendency facilitated the validation of the obtained data in comparison to the previously reported protein rejection results. It was shown that polyPEGMA/MBAA composite membranes exhibited higher solute rejection, while polyPEGMA/PETAE showed lower solute rejection compared to uncrosslinked polyPEGMA composite membranes prepared with the same UV irradiation dose. Increasing the amount of crosslinkers amplified these effects. Furthermore, a trade-off analysis between water permeability and molecular weight cut-off (MWCO) for virgin and composite membranes was done in order to evaluate the membrane performance improvement by the composite membranes. The obtained results showed that the prepared composite membranes exhibited better fluxes and selectivity compared to commercial membranes with analogous characteristics. © 2011 Elsevier B.V.
    view abstract10.1016/j.memsci.2011.11.025
  • Low-fouling uf membranes for water treatment by surface modification with hydrogel layers via a new macro-initiator
    Quilitzsch, M. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.852
  • Macroinitiator mediated photoreactive coating of membrane surfaces with antifouling hydrogel layers
    Lei, J. and Freger, V. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.443
  • Magnetically responsive membranes
    Yang, Q. and Himstedt, H.H. and Qian, X. and Ulbricht, M. and Wickramasinghe, S.R.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.366
  • Molecularly imprinted stimuli-responsive hydrogels for protein recognition
    Adrus, N. and Ulbricht, M.
    Polymer (United Kingdom) 53 (2012)
    Temperature-responsive poly(N-isopropylacrylamide)-based (PNIPAAm) hydrogels were imprinted with lysozyme via in situ photo-initiated crosslinking polymerization. The three-dimensional network of the hydrogels was tailored by tuning the ionic content through methacrylic acid as template-binding comonomer while keeping the ratio between crosslinker (N,N′-methylenebisacrylamide) and N-isopropylacrylamide fixed. Moderate salt concentrations (0.3 m NaCl) were found to be suited for template removal without phase separation of the hydrogel. Swelling and protein (lysozyme and cytochrome C) binding were investigated for imprinted and nonimprinted gels at temperatures below and above the lower critical solution temperature of PNIPAAm (32 °C). Imprinted gels showed a much higher affinity, selectivity and binding capacity for lysozyme compared to the nonimprinted reference materials. Protein binding capacity was strongly reduced above 32 °C, to zero for nonimprinted and to small values for imprinted gels. Most important, specific lysozyme binding to the imprinted gels caused a large concentration dependent deswelling. This effect was much smaller for nonimprinted gels, and the response could be modulated by the content of the comonomer methacrylic acid. Overall, this approach is interesting for the development of novel sensors or materials for controlled release applications. © 2012 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.polymer.2012.07.062
  • Novel anion-exchange ulrafiltration membranes for protein separation based on functionalized poly (arylene ether sulfone) block copolymer
    Kumar, M. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.1003
  • Novel hydrogel pore-filled composite membranes with tunable and temperature-responsive size-selectivity
    Adrus, N. and Ulbricht, M.
    Journal of Materials Chemistry 22 (2012)
    Hydrogel pore-filled composite membranes (HPFCM) based on polyethylene terephthalate (PET) track-etched membranes with pore diameters between 200 and 5000 nm and temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were successfully prepared. A premodification of the pore walls by grafted linear PNIPAAm led to stable anchoring of crosslinked PNIPAAm prepared in a subsequent step. Proper tuning of photopolymerization conditions resulted in a desired microstructure of the hydrogels and thus tailored barrier properties of the composite membranes. The very interesting separation performance of HPFCM was due to diversification of the hydrogel network that caused adjustable sieving properties via synthesis conditions and also largely switchable barrier properties in response to the temperature. The interplay between the immobilized hydrogel and various pore sizes of the membrane support was also investigated. The base membrane provides mechanical support and confines the hydrogel within its pores, and it thus allows using the hydrogel mesh size for size-selective solute transport. Completely stable and selective HPFCM were only obtained with base pore sizes of about 2 μm or smaller. The size-selectivity (molecular weight cut-off) of the same HPFCM was higher under diffusive than under convective flow conditions; this is presumably mainly caused by elasticity deformation of the hydrogel network. The apparent cut-off from diffusion experiments was well correlated to the mesh-size of the hydrogel determined from the Darcy model applied to permeability data obtained under convective flow conditions. Upon temperature increase beyond 32 °C, flux increased and rejection decreased very strongly; this remarkable change between macromolecule-size selective ultrafiltration and microfiltration/filtration behavior was fully reversible. © 2012 The Royal Society of Chemistry.
    view abstract10.1039/c2jm15022k
  • Novel membrane adsorbers with grafted zwitterionic polymers synthesized by surface-initiated ATRP and their salt-modulated permeability and protein binding properties
    Yang, Q. and Ulbricht, M.
    Chemistry of Materials 24 (2012)
    A novel zwitterionic polymer functionalized porous membrane adsorber was obtained by grafting poly(N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium betaine) (polySPE) to poly(ethylene terephthalate) (PET) track-etched membrane surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The ATRP conditions were optimized, the thus established grafting was well-controlled, and the degree of grafting could be adjusted. Functionalized membranes with a degree of grafting of about 3.5 μg/cm 2 relative to the specific surface area showed almost zero values of zeta potential estimated from the trans-membrane streaming potential measurements. Typical "anti-polyelectrolyte" effect was observed for the polySPE grafted membranes. Flux through the membrane was reduced by adding chaotropic chloride and perchlorate salts to the solution which extended the polySPE chains grafted on the membrane pore wall. Perchlorate salt exhibited much stronger effect on polySPE chain conformation than chloride salt and for a membrane with a degree of grafting of 2.7 μg/cm 2, even 2 mM KClO 4 could extend the thickness of the polymer layer to more than two times (∼43 nm) of that in pure water (∼20 nm). On the contrary, small amounts of kosmotropic ions (10 mM SO 4 2-) further "salted out" the polySPE chains and led to a slightly increased flux. PolySPE grafted PET membranes with different degree of grafting were then used as membrane adsorber for protein binding. Human IgG was used as model protein and the binding capacity was evaluated under both static (no convective flow through the membrane) and dynamic conditions (flow-through conditions). Static adsorption experiments showed that IgG could be loaded to the membrane at medium salt concentration and 85-95% of bound protein could be eluted at either low (zero) or very high salt concentrations. Dynamic flow-through experiments then revealed the influences of salt concentration and salt type on IgG binding. Effects of two chaotropic salts, NaCl and NaClO 4, were evaluated. Slight but not negligible binding of IgG from pure water was suppressed by adding NaCl. IgG binding was then increased in the NaCl concentration range of 100-500 mM and reached a maximum binding capacity value at about 500 mM. Further increase of NaCl concentration led to a decreased binding again. KClO 4 showed similar effects onto IgG binding, but this salt functions in a much lower and much narrower concentration range. All results with respect to grafted layer swelling and protein binding followed the empirical Hofmeister series. © 2012 American Chemical Society.
    view abstract10.1021/cm301116p
  • Novel modification of porous polypropylene microfiltration membrane grafted aminoethyl methacrylate anchored schiff-base for removal of Cu(II) from aqueous solution
    Farjadian, F. and Schwark, S. and Ulbricht, M.
    Euromembrane Conference 2012 44 (2012)
    view abstract10.1016/j.proeng.2012.08.952
  • Performance of thin-layer hydrogel polyethersulfone composite membranes during dead-end ultrafiltration of various protein solutions
    Peeva, P.D. and Knoche, T. and Pieper, T. and Ulbricht, M.
    Industrial and Engineering Chemistry Research 51 (2012)
    Low-fouling thin-layer hydrogel composite membranes were prepared during UV initiated grafting from of the hydrophilic monomer poly(ethylene glycol) methacrylate onto polyethersulfone (PES) ultrafiltration (UF) membranes. The selectivity of the functionalized membranes was adjusted by varying the UV irradiation dose and applying the cross-linking agent N,N'-methylene bisacrylamide. Virgin and composite membranes were tested in short (20-fold volume reduction) and long (24 h) dead-end (DE) filtration experiments of various protein solutions and the performance improvement by the membrane hydrophilization was evaluated. Moreover, the effects of membrane molecular weight cutoff, solute size, and solute charge (as function of pH) as well as cleaning were evaluated. The dominating fouling mechanisms were identified using the classical model equation proposed by Hermia [Hermia, J. Constant Pressure Blocking Filtration Laws-Application to Power Law Non-Newtonian Fluids. Trans. Inst. Chem. Eng. 1982, 60, 183] for DE filtration mode. The results showed that the surface functionalization improved the membrane performance during filtration of protein solutions. Moreover, the cleanability of functionalized membranes with water was much more effective compared to unmodified PES membranes. The performed fouling mechanism study clarified the occurring processes during filtrations with virgin and composite membranes. © 2012 American Chemical Society.
    view abstract10.1021/ie202893e
  • Potassium permeable barrier membrane for in vivo application
    Pieper, T. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.663
  • Smart porous polymer membrane valves by Integration of nanoparticle heaters
    Gajda, A. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.763
  • Surface modification of poly(ethylene terephthalate) fabric via photo-chemical reaction of dimethylaminopropyl methacrylamide
    Mohamed, N.H. and Bahners, T. and Wego, A. and Gutmann, J.S. and Ulbricht, M.
    Applied Surface Science 259 (2012)
    Photo-chemical reactions and surface modifications of poly(ethylene terephthalate) (PET) fabrics with the monomer dimethylaminopropyl methacrylamide (DMAPMA) and benzophenone (BP) as photo-initiator using a broad-band UV lamp source were investigated. The tertiary amino groups of the grafted poly(DMAPMA) chains were subsequently quaternized with alkyl bromides of different chain lengths to establish antibacterial activity. The surface composition, structure and morphology of modified PET fabrics were characterized by Fourier transform infrared spectroscopy (FTIR/ATR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). To evaluate the amount of quaternary and tertiary ammonium groups on the modified surface, PET was dyed with an acid dye which binds to the ammonium groups. Therefore, the color depth is a direct indicator of the amount of ammonium groups. The resulting antibacterial activity of the modified PET fabrics was tested with Escherichia coli. The results of all experiments show that a photochemical modification of PET is possible using DMAPMA, benzophenone and UV light. Also, the quaternization of tertiary amino groups as well as the increase in antibacterial activity of the modified PET by the established quaternary ammonium groups were successful. © 2012 Elsevier B.V.
    view abstract10.1016/j.apsusc.2012.07.029
  • Systematic investigation of dispersions of unmodified inorganic nanoparticles in organic solvents with focus on the hansen solubility parameters
    Wieneke, J.U. and Kommob, B. and Gaer, O. and Prykhodko, I. and Ulbricht, M.
    Industrial and Engineering Chemistry Research 51 (2012)
    Dispersions of unmodified nanoparticles (titanium dioxide, hydroxyapatite) were prepared by redispersion of nanoparticle powders in organic solvents using an ultrasound treatment. The dispersion quality was judged by dynamic light scattering (DLS) measurements and visual evaluation. Whereas "bad"solvents led to no or unstable dispersions with large particle diameters, dispersions made from the "good" solvents consisted of particles with relatively small diameters and were stable for several days or longer. For titanium dioxide, mixtures from four of the "good" solvents identified after first screening of a large set of solvents were prepared and tested as dispersion agent. Thus obtained dispersions showed superior properties compared to the previous dispersions, with small particles sizes and good long-time stability. Based on a rating of solvent quality and by calculation using the software HSPiP v3, the Hansen solubility parameters of the particles were then determined. Subsequently, entirely new solvent mixtures that could best fit these parameters were selected and found to also exhibit suitable properties as dispersion agent for the nanoparticles. The same iterative and quantitative approach worked also for the preparation of good and stable dispersions of hydroxyapatite. All results show that this is a promising methodology to disperse inorganic nanoparticles into suited organic solvents, for instance for the preparation of new polymeric nanocomposites. Furthermore, the method can be used to indirectly characterize the surface chemistry of nanoparticles. © 2011 American Chemical Society.
    view abstract10.1021/ie201973u
  • Thermoresponsive ultrafiltration membranes for the switchable transport and fractionation of nanoparticles
    Frost, S. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.302
  • Thin-film polyurethane composite nanofiltration membranes
    Kuhn, C. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.394
  • Toward protein-selective membrane adsorbers: A novel surface-selective photo-grafting method
    Schwark, S. and Ulbricht, M.
    European Polymer Journal 48 (2012)
    A novel heterogeneous photo-graft copolymerization method based on a covalently immobilized benzoin ether derivative, a "type I" photo-initiator, had been developed. This initiator starts radical polymerizations directly at the surface of different base materials. Three immobilization protocols for porous polyethyleneterephthalate (PET) and cellulose membranes had been established and the surface-initiated photo-grafting with various tailor-made acrylamide based functional monomers had been studied. One way of photo-initiator immobilization comprising an ester bond to the base cellulose enabled the determination of photo-initiator density and the analysis of the grafted copolymers after hydrolytic cleavage. The effects of photo-initiator density onto degree of grafting, grafted copolymer's molecular weight and grafting density had been elucidated. Furthermore, the compositions of selected grafted binary copolymers had been analyzed via 1H NMR spectroscopy and discussed in terms of relative monomer reactivity. Overall, the study provides a sound basis for the preparation of macroporous membrane adsorbers with systematically varied grafted copolymer layers toward tailored selectivity for proteins and other bionanoparticles. © 2012 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.eurpolymj.2012.08.003
  • Toward remote-controlled valve functions via magnetically responsive capillary pore membranes
    Himstedt, H.H. and Yang, Q. and Qian, X. and Ranil Wickramasinghe, S. and Ulbricht, M.
    Journal of Membrane Science 423-424 (2012)
    Polyethyleneterephthalate track-etched membranes with a pore diameter of 650nm were functionalized via surface-initiated atom transfer radical polymerization with grafted poly(2-hydroxyethylmethacrylate). Grafted chain length and density were varied. Superparamagnetic nanoparticles (Fe 3O 4; core diameter 15nm) were selectively covalently coupled to the end groups of the grafted chains. The membranes were characterized by grafting degree, X-ray photoelectron spectroscopy, electron microscopy, zeta potential and pore size in dry state via gas flow/pore dewetting permporometry. The results confirmed that all functionalization steps were well controlled. Water permeability measurements allowed estimation of the hydrodynamic pore diameter of the membranes, and, hence, the hydrodynamic polymer layer thickness on the pore walls. The water permeability of the nanoparticle hybrid membranes was then measured in a static or an alternating external magnetic field. Significant and reversible decreases of permeability were observed, with the largest effects for membranes with high polymer grafting density and long polymer chains (hydrodynamic layer thickness up to 100nm). The maximum change in effective pore diameter was only 6%. However, the estimated change of swollen polymer layer thickness (originally between 60 and 100nm) was up to 13nm. The functionality of the membranes can be tuned by variations of straightforward parameters such as pore size or grafted chain lengths. The study is also relevant as a model system for altering the effective thickness of grafted polymer layers on a surface by an external magnetic field for other applications, for instance in microfluidic systems. © 2012 Elsevier B.V.
    view abstract10.1016/j.memsci.2012.08.015
  • Two new preparations for organophilic nanofiltration membranes based on photo-crosslinked polyimide
    Behnke, S. and Ulbricht, M.
    Procedia Engineering 44 (2012)
    view abstract10.1016/j.proeng.2012.08.374
  • UV-photo graft functionalization of polyethersulfone membrane with strong polyelectrolyte hydrogel and its application for nanofiltration
    Bernstein, R. and Antón, E. and Ulbricht, M.
    ACS Applied Materials and Interfaces 4 (2012)
    A strong polyelectrolyte hydrogel was graft copolymerized on a polyethersulfone (PES) ultrafiltration (UF) membrane using vinyl sulfonic acid (VSA) as the functional monomer, and N,N′-methylenbisacrylamide (MBAA) as the cross-linker monomer. This was carried out in one simple step using the UV photoirradiation method. The effect of the polymerization conditions on the degree of grafting (DG) was investigated using the gravimetric method which measures the total hydrogel grafted on the membrane, and with ATR-FTIR spectroscopy which indicates the functional monomer fraction in the hydrogel layer. The VSA could not graft polymerize without the cross-linker as comonomer. An increase in the cross-linker fraction from 0.25 to 2.5 mol % (relative to the functional monomer VSA) resulted in a higher DG. Although the surface morphology changed upon modification, the resulting surface roughness as measured by AFM was very low. From the monitoring of DG with UV time (4.5-30 min) at constant conditions, it was deduced that during the early stages of the polymerization mainly the cross-linker was grafted, thus inducing the graft copolymerization of the functional monomer. Polymerization using a higher monomer concentration (12.5-40% VSA) at constant monomer/cross-linker ratio resulted in a higher VSA fraction in the grafted hydrogel, although the gravimetric DG was similar. Ion exchange capacity and X-ray photoelectron spectroscopy measured after modification under the different conditions supported these findings. The new membranes were tested under nanofiltration (NF) conditions. A NF membrane could be obtained when the MBAA fraction was above 0.25%. The Na 2SO 4 rejection was 90-99% and the permeability 10-1 L m -2 h -1 bar -1 when the MBAA fraction increased from 0.75 to 2.5%. The order of rejection of single salts solution was Na 2SO 4 &gt; MgSO 4 ≈ NaCl &gt; CaCl 2, as expected on the basis of Donnan exclusion for negatively charged NF membranes. An increase in the salts rejection with increasing degree of cross-linking and VSA fraction was attributed to an increase in the membrane charge density and to steric exclusion that also resulted in an increase of rejection for uncharged solutes such as sucrose or glucose. The new membrane presented a high, essentially unchanged Na 2SO 4 rejection (&gt;97%) in the range of salt concentrations up to 4 g/L, and only slightly reduced rejection (&gt;92%) at a concentration of 8 g/L; this can be related to its high barrier layer charge density measured by ion exchange capacity. In addition, because poly(vinyl sulfonic acid) (PVSA) is a strong polyelectrolyte the membrane separation performance was stable in the range of pH 1.5 to pH 10. © 2012 American Chemical Society.
    view abstract10.1021/am300426c
  • Amphiphilic gold nanoparticles: Synthesis, characterization and adsorption to PEGylated polymer surfaces
    Tarnawski, R. and Ulbricht, M.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 374 (2011)
    The direct synthesis of water-soluble gold nanoparticles with a mixed shell of two different thiols, 1-mercaptoundec-11-yl-hexa(ethylene glycol) (EG6) and dodecanethiol (C12), and their characterization are reported. Data from IR spectroscopy and contact angle (CA) measurements as well as the solubility of the nanoparticles in water support that the composition of the shell is in the range of the thiol ratio used for synthesis (EG6:C12 = 72:28). Results of transmission electron microscopy and atomic force microscopy (AFM) for deposited particles as well as the UV-vis spectrum in solution are in line with a size of ≤10. nm. Self-assembled monolayers (SAMs) as model surfaces were prepared from mixtures of EG6 and C12 on planar gold films. Polystyrene (PSt) spin-coated films on silicon wafers and on gold-coated surface plasmon resonance (SPR) sensor disks were used as substrates for surface functionalization via adsorption/self-assembly of a polystyrene poly(ethylene glycol) diblock copolymer (PSt- b-PEG) from aqueous solutions. CA and AFM results revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surface as a function of PSt- b-PEG concentration used for the modification. The adsorption of myoglobin and the novel gold nanoparticles to the PSt- b-PEGylated surfaces was analyzed by SPR. A control of adsorbed amounts by the degree of surface PEGylation, i.e. a reduction by up to 55% for the highest degree of modification, could be confirmed for both kinds of colloids. Adsorption of the novel gold nanoparticles to the mixed SAM surfaces as analyzed by SPR showed an even stronger dependency of surface composition. All experiments demonstrate that amphiphilic, water-soluble gold-based nanoparticles can be used as model colloids for the investigation of interactions with polymer surfaces of varied structure and architecture, and that they could be further developed for analytical or biological applications. © 2010 Elsevier B.V.
    view abstract10.1016/j.colsurfa.2010.10.027
  • Chemical and physical factors in design of antibiofouling polymer coatings
    Eshet, I. and Freger, V. and Kasher, R. and Herzberg, M. and Lei, J. and Ulbricht, M.
    Biomacromolecules 12 (2011)
    Because most "low fouling" polymers resisting bacterial attachment are hydrophilic, they are usually also significantly swollen. Swelling leads to purely physical dilution of interaction and weakens attachment; however, these nonspecific contributions are usually not separated from the specific effect of polymer chemistry. Taking advantage of the fact that chemistry and swelling of hydrogels may be independently varied through the fraction of a cross-linker, the roles of chemistry and physical dilution (swelling) in bacterial attachment are analyzed for selected hydrogels. Using as a quantitative indicator the rate of bacterial deposition in a parallel plate setup under defined flow conditions, the observed correlation of deposition rate with swelling provides a straightforward comparison of gels with different chemistries that can factor out the effect of swelling. In particular, it is found that chemistry appears to contribute similarly to bacterial deposition on hydrogels prepared from acrylamide and a zwitterioninic monomer 2-(methacryloyloxy)ethyl) dimethyl-(3-sulfopropyl) ammonium hydroxide so that the observed differences may be related to swelling only. In contrast, these gels were inferior to PEG-based hydrogels, even when swelling of the latter was lower, indicating a greater contribution of PEG chemistry to reduced bacterial deposition. This demonstrates that swelling must be accounted for when comparing different biofouling-resistant materials. Chemical and physical principles may be combined in hydrogel coatings to develop efficient antibiofouling surfaces. © 2011 American Chemical Society.
    view abstract10.1021/bm200476g
  • Composites of functional polymeric hydrogels and porous membranes
    Yang, Q. and Adrus, N. and Tomicki, F. and Ulbricht, M.
    Journal of Materials Chemistry 21 (2011)
    Polymeric hydrogels are a most interesting class of "soft matter" with several established and many more possible applications as functional materials. In this review we will focus on the combination of polymeric hydrogels and porous membranes which leads to composites with promising functionality for, e.g., mass separations, sensing and analytics, (bio)catalysis, biomedical engineering and micro-system technologies. The combination of a rigid porous membrane with a soft functional hydrogel by a suited preparation technique enables that the functionality of the hydrogel can be applied in a unique way. The most important preparation strategies for hydrogel composite membranes, i.e., pore-filling, various surface-grafting methods and combinations thereof, will be discussed. The structural diversity of the hydrogels is based on the use of a wide range of synthetic monomers, but biopolymers or their derivatives can also be applied. The interplay of the membrane pore structure, the structure of the hydrogel and the distribution of the hydrogel in the pore space can lead to different types of composite membranes with completely different potential applications. The focus will be on promising examples for the various types of functional composite membranes, i.e., macroporous membrane adsorbers, anti-fouling filtration membranes, hydrogel-based ultrafiltration membranes, other separation membranes with pore-filling hydrogel as selective material, stimuli-responsive membranes and porous membrane valves and gates, as well as biocompatible or bioactive membranes. © The Royal Society of Chemistry 2011.
    view abstract10.1039/c0jm02234a
  • Cylindrical membrane pores with well-defined grafted linear and comblike glycopolymer layers for lectin binding
    Yang, Q. and Ulbricht, M.
    Macromolecules 44 (2011)
    Glycopolymers with well-defined linear or comblike structure were grafted to poly(ethylene terephthalate) (PET) track-etched membrane surface by surface-initiated atom transfer radical polymerization (ATRP). Bromoalkyl initiator was directly immobilized onto PET membrane surface, and the ATRP of 2-lactobionamidoethyl methacrylate (LAMA) was then carried out to yield the grafted linear glycopolymer. Comblike poly(LAMA) was constructed on PET membrane by a two-step sequence. First, ATRP of 2-hydroxyethyl methacrylate (HEMA) was initiated from the PET surface, and alkyl bromide was then immobilized to poly(HEMA) chains. The initiator-immobilized poly(HEMA) served as a surface tethered macroinitiator for the ATRP of poly(LAMA) and resulted in comblike polyLAMA branches. The ATRP conditions for both LAMA and HEMA were optimized, and the thus-established grafting was well controlled. The dry layer thickness (DLT) of grafted polymers was deduced from results of capillary flow porometer measurements. Effective hydrodynamic layer thickness was estimated from pure water permeability. Data revealed that the grafted linear poly(LAMA) and poly(HEMA) had relatively low chain density and exhibited a collapsed coil conformation in dry state. After grafting of poly(LAMA) chains to poly(HEMA) this collapse was significantly hindered by the steric influence of poly(LAMA) branches on the poly(HEMA) main chains, and more than 3 times increase in DLT could be observed. Nonspecific protein binding, studied with bovine serum albumin, was very low for membranes with grafted linear poly(LAMA) while no adsorbed protein could be detected for the comblike poly(LAMA) architecture. Both membranes were then used for binding of peanut agglutinin, a lectin specifically binding to galactose. Under conditions where protein could only diffuse into the membrane pores, comblike poly(LAMA) showed only slight enhancement of binding capacity in comparison with the linear poly(LAMA). However, with convective flow through the membranes, binding capacity of the comblike poly(LAMA) layer was significantly increased and a capacity up to 23.6 mg/cm3 was achieved. Specific lectin binding with high capacities, corresponding to 3-dimensional protein stacking in the grafted layers, could be confirmed. © 2011 American Chemical Society.
    view abstract10.1021/ma1025972
  • Influence of alkyl chain length and molecular weight on the surface functionalization via adsorption/entrapment with biocidal cationic block copolymers
    Berndt, E. and Behnke, S. and Ulbricht, M.
    European Polymer Journal 47 (2011)
    Polysulfone (PSf) films were functionalized with block copolymers containing poly(n-butyl acrylate) (PBA) as anchor block which is able to firmly tether the biocidal quaternized poly(2-dimethylaminoethyl methacrylate) (PDMAEMAq) to the surface. Block copolymers were synthesized using sequential atom transfer radical polymerization (ATRP) and quaternization with methyl and/or octyl groups rendered the polymers biocidal. Upon reversible swelling of the PSf surface layer in the adsorption/entrapment process, incorporation of the block copolymer is anticipated to be stable; homopolymers, i.e., methyl- or octyl-quaternized PDMAEMAq, were investigated for comparison. The addition of salt to the functionalization solution containing the block copolymer induced a decrease in the critical micelle concentration and lead to higher functionalization efficiency. The impact of intra- or interchain interactions in these aggregates on adsorption and firm entrapment in PSf was determined by measuring contact angle, charge density and zeta potential. © 2011 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.eurpolymj.2011.09.019
  • Magnetically activated micromixers for separation membranes
    Himstedt, H.H. and Yang, Q. and Dasi, L.P. and Qian, X. and Wickramasinghe, S.R. and Ulbricht, M.
    Langmuir 27 (2011)
    Presented here is a radically novel approach to reduce concentration polarization and, potentially, also fouling by colloids present in aqueous feeds: magnetically responsive micromixing membranes. Hydrophilic polymer chains, poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted via controlled surface-initiated atom transfer radical polymerization (SI-ATRP) on the surface of polyamide composite nanofiltration (NF) membranes and then end-capped with superparamagnetic iron oxide magnetite (Fe3O4) nanoparticles. The results of all functionalization steps, that is, bromide ATRP initiator immobilization, SI-ATRP, conversion of PHEMA end groups from bromide to amine, and carboxyl-functional Fe3O4 nanoparticle immobilization via peptide coupling, have been confirmed by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). These nanoparticles experience a magnetic force as well as a torque under an oscillating external magnetic field. It has been shown, using particle image velocimetry (PIV), that the resulting movement of the polymer brushes at certain magnetic field frequencies induces mixing directly above the membrane surface. Furthermore, it was demonstrated that with such membranes the NF performance could significantly be improved (increase of flux and salt rejection) by an oscillating magnetic field, which can be explained by a reduced concentration polarization in the boundary layer. However, the proof-of-concept presented here for the active alteration of macroscopic flow via surface-anchored micromixers based on polymer-nanoparticle conjugates has much broader implications. © 2011 American Chemical Society.
    view abstract10.1021/la200223g
  • Photo-chemical surface modification for the control of protein adsorption on textile substrates
    Bahners, T. and Klingelhöller, K. and Ulbricht, M. and Wego, A. and Schollmeyer, E.
    Journal of Adhesion Science and Technology 25 (2011)
    Cell growth on fiber surfaces is an important aspect of many applications of technical textiles. The need to prevent clogging in artificial blood vessels or in textiles used for blood or water filtration as well as the anti-fouling properties of outdoor technical textiles are examples in this context. Since the adsorption of proteins forms the initial step of cell growth, a promising way to avoid biofouling is to prohibit protein adsorption by means of a suitable, permanent and non-toxic surface functionalization. Today, the deposition of poly(ethylene glycol)s (PEGs) is a well-known approach to decrease non-specific protein adsorption. In this work, a photo-chemical method to graft or cross-link PEGs on fiber surfaces was studied. Monomethacrylated PEG300MA and PEG2080MA as well as dimethacrylated PEG400DMA and PEG600DMA were considered, the numbers indicate average molar mass in g/mol. Textile fabrics made of poly(ethylene terephthalate) (PET) were impregnated with solutions of the PEGs and irradiated using either a KrCl* or a XeCl* excimer lamp (emission wavelengths 222 or 308 nm, respectively). Surface properties of the treated textiles were characterized as a function of process conditions using various surface sensitive analyses. UV cross-linking of PEG400DMA resulted in the deposition of a thick layer which effectively masked the texture of the fabric and its pore system. Much less coverage was observed in case of monomethacrylated PEGMAs, with a significant reduction in drop penetration time already after deposition of a marginal layer (less than 0.01 mg/mg). Highest reductions in adsorption of bovine serum albumin (BSA) were observed for samples prepared using PEG300MA or PEG400DMA under conditions where also the drop penetration time was at its minimum. The longer chain PEG2080MA was less effective. All results show clearly that the protein adsorption tendency can be significantly reduced by choice of suitable combinations of PEGylated monomer and UV irradiation conditions. © 2011 Koninklijke Brill NV, Leiden.
    view abstract10.1163/016942411X574925
  • Porous Flat Sheet, Hollow Fibre and Capsule Membranes by Phase Separation of Polymer Solutions
    Ulbricht, M. and Susanto, H.
    Membranes for Membrane Reactors: Preparation, Optimization and Selection (2011)
    view abstract10.1002/9780470977569.ch22
  • Porous Polymer Membranes by Manufacturing Technologies other than Phase Separation of Polymer Solutions
    Ulbricht, M. and Susanto, H.
    Membranes for Membrane Reactors: Preparation, Optimization and Selection (2011)
    view abstract10.1002/9780470977569.ch23
  • Preparation of thermo-responsive polypropylene membranes via surface entrapment of poly(N-isopropylacrylamide)-containing macromolecules
    Guo, H. and Ulbricht, M.
    Journal of Membrane Science 372 (2011)
    Thermo-responsive polypropylene (PP) microfiltration membranes have been fabricated via surface entrapment of poly(N-isopropylacrylamide) (PNIPAAm)-containing homopolymer and block copolymers. A previously developed approach based on using solutions of the polymeric modifier in a solvent which swells the base membrane polymer had been used, and conditions have been varied. One block copolymer of PNIPAAm with polybutylacrylate (PBA) had been selected as best suited modifier. Models related to the underlying deswelling/entrapment process which leads to fixation of the modifier have been considered. For PP membrane, characterization of pore size distribution in dry state revealed a significant decrease of pore size as a consequence of the entrapment modification. Surface properties have been analysed by ATR-FTIR spectroscopy and water contact angle measurements, which confirmed the presence of modifier and a strong improvement of surface and pore wettability. The thermo-sensitive properties of either outer surface and inner pore wall of modified PP membranes have been verified by temperature-dependence of captive bubble contact angle and water permeability, respectively, both due to hydratation/dehydratation and volume phase transition of PNIPAAm around the lower critical solution temperature (LCST) of the block copolymer PBA- b-PNIPAAm which was around 31-32. °C. The effects of protein desorption from the modified membrane where bovine serum albumin (BSA) had been previously adsorbed were studied by measuring water flux upon manipulating water temperature during water filtration cum washing. In addition, non-porous PP plates had been modified using the same procedure and all the surface characterization results showed similar modification efficiency and surface properties as for porous PP membranes, confirming the dominating role of entrapment of the amphiphilic functional macromolecules into the PP surface layer instead of simple deposition onto the surface. © 2011 Elsevier B.V.
    view abstract10.1016/j.memsci.2011.02.018
  • Probing the intrinsic switching kinetics of ultrathin thermoresponsive polymer brushes
    Amiri Naini, C. and Franzka, S. and Frost, S. and Ulbricht, M. and Hartmann, N.
    Angewandte Chemie - International Edition 50 (2011)
    Laser-stimulated polymer brushes: The temperature-dependent switching kinetics of surface-grafted thermoresponsive polymer brushes were investigated by a stroboscopic micromanipulation/-characterization technique for real-time parallel measurements (see picture). Intrinsic response times range from the microsecond to the millisecond time scale; these results could lead to fabrication of nanosized polymeric actuators and sensors with unprecedented responsivities. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201100140
  • Separation Membranes
    Ulbricht, M.
    Porous Polymers (2011)
    view abstract10.1002/9780470929445.ch8
  • Stimuli-responsive track-etched membranes via surface-initiated controlled radical polymerization: Influence of grafting density and pore size
    Tomicki, F. and Krix, D. and Nienhaus, H. and Ulbricht, M.
    Journal of Membrane Science 377 (2011)
    The surface-functionalization of poly(ethylene terephthalate) track-etched membranes of different nominal pore sizes (400, 1000 and 3000. nm) with stimuli-responsive poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) via surface-initiated (SI) atom transfer radical polymerization (ATRP) was performed. Variations of grafting density and grafted chain length were achieved by variation of synthesis conditions. It could be clearly demonstrated that mixtures of reaction solutions containing different ratios of acyl bromides, only one bearing the initiator group necessary for the SI ATRP, led to different initiator group densities on the resulting track-etched membrane surface which had been verified by X-ray photoelectron spectroscopy. Moreover the mass increase as function of reaction time strongly correlated with the amount of initiator bound to the membrane surface indicating that the ATRP reaction was not limited by monomer diffusion into the pores. Scanning electron microscopy images and permporometry measurements indicated an even functionalization on the entire membrane surface which was the basis for further investigations. The stimuli-responsive properties of PDMAEMA grafted track-etched membranes were studied by permeability measurements with citrate and glycine buffers as function of pH (2 and 10) and temperature (25 and 60 °C). By that the barrier properties of the membranes could be effectively changed in two steps. The results agree with the expectation that a change in grafting density and chain length has an effect on the stimuli-responsive properties of the membrane. Results for membranes having similar degrees of grafting clearly showed that the reversible swelling of grafted polymeric layers was more pronounced for lower grafting density. © 2011 Elsevier B.V.
    view abstract10.1016/j.memsci.2011.04.028
  • Ultrafiltration of humic acid solutions through unmodified and surface functionalized low-fouling polyethersulfone membranes - Effects of feed properties, molecular weight cut-off and membrane chemistry on fouling behavior and cleanability
    Peeva, P.D. and Palupi, A.E. and Ulbricht, M.
    Separation and Purification Technology 81 (2011)
    In the present work, polyethersulfone (PES) ultrafiltration (UF) membranes with molecular weight cut-off (MWCO) from 5 to 300 kDa were analyzed with respect to fouling during filtration of humic acid (HA) model solution. The impact of MWCO and prefiltration of the feed solution on the fouling behavior of these membranes is presented. Moreover, an UV-initiated graft copolymerization of poly(ethylene glycol) methacrylate (PEGMA) onto PES membranes was performed and the effect of the applied modification was examined in terms of MWCO and water permeability changes as well as performance during filtration of HA. Moreover, the fouling behavior and principles during the filtration were compared. Membranes with higher MWCO exhibited stronger flux decline during UF but better cleanability. Prefiltration through 0.45 μm filter improved the membrane performance during filtration of HA but the efficiency of physical cleaning was deteriorated. The applied modification improved the membrane performance during ultrafiltration and facilitated the physical cleaning. This work contributes to a better understanding of the relationships between membrane MWCO, solute size and size distribution, membrane surface chemistry and membrane fouling. © 2011 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.seppur.2011.07.005
  • Anti-nonspecific protein adsorption properties of biomimetic glycocalyx-like glycopolymer layers: Effects of glycopolymer chain density and protein size
    Yang, Q. and Kaul, C. and Ulbricht, M.
    Langmuir 26 (2010)
    In many cases, biomaterials surfaces are desired to be resistant to protein adsorption. A system fulfilling this task in nature is the so-called glycocalyx. The glycocalyx is an outer layer on the cell membrane with bound glycoproteins and glycolipids, exposing a pattern of carbohydrate groups. There is a growing interest to mimic this glycocalyx layer to have a tool to overcome the problems with uncontrolled protein adsorption on biomaterials. In this work a glycocalyx-like layer is artificially imitated by surface-initiated atom transfer radical polymerization (ATRP) of a glycomonomer, d-gluconamidoethyl methacrylate (GAMA), from a mixed self-assembled monolayer (SAM) of an ATRP initiator-immobilized hydroxyl-terminated thiol and a methyl-terminated thiol as diluent. Fourier transform infrared spectroscopy (FT/IR-ATR), contact angle, and ellipsometry measurements were employed to confirm the grafting of the glycopolymer. The anti-nonspecific protein binding properties of this glycopolymer layer were then investigated with surface plasmon resonance (SPR). Three proteins with different size, lysozyme, bovine serum albumin (BSA), and fibrinogen were used as model solutes to investigate the influence of protein size on the protein resistance behavior. The glycopolymer chain density was controlled during surface-initiated ATRP by varying the ratio of the components in the mixed SAM, and the chain length was adjusted by ATRP time. The effect of chain density in combination with the protein size was also evaluated. The most important results are that poly(GAMA) layers of higher grafting density show resistance to adsorption of the model proteins used in this work and that the amount of adsorbed protein depends on the length and density of the glycopolymer chains and also on the size of the proteins. © 2010 American Chemical Society.
    view abstract10.1021/la903895q
  • Fouling effects of humic and alginic acids in nanofiltration and influence of solution composition
    Zazouli, M.A. and Nasseri, S. and Ulbricht, M.
    Desalination 250 (2010)
    The objectives of this research were to investigate the combined and individual influence of hydrophobic and hydrophilic fractions of NOM on the fouling of thin-film composite nanofiltration (NF) membranes, and also the roles of solution chemistry on the permeate flux and fouling. Combined fouling is compared to the individual fouling behaviors (i.e., alginate or humic acid alone). Experiments were conducted using a "cross-flow" pilot-scale membrane unit with a full circulation mode. Fouling experiments were performed with individual and combined humic acid and alginate. The results demonstrated that increasing organic concentration increased greatly the rate and extent of flux reduction. Individual alginate fouling was more detrimental than individual humic acid fouling, and alginate exhibited greater flux decline than humic acid fouling alone at the same conditions. A higher flux decline was observed with increasing proportions of aliginate in combined fouling. In other word, there are antagonistic effects during combined fouling because the charge functional groups of two above foulants are negative and increase electrostatic repulsion between two foulants and also foulant-membrane. The flux reduction increased with increasing ionic strength, foulant concentrations, and with lower pH. This observation implies the importance of interaction between various foulants for deeper understanding of fouling phenomena. The membrane fouling was largely dependent on organic properties and fractions. © 2009 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.desal.2009.05.021
  • Functional coatings for anti-biofouling applications by surface segregation of block copolymer additives
    Berndt, E. and Behnke, S. and Dannehl, A. and Gajda, A. and Wingender, J. and Ulbricht, M.
    Polymer 51 (2010)
    Temperature responsive or bactericidal coatings with poly(n-butyl methacrylate) (PBMA) as bulk material and surface segregated poly(n-butyl acrylate)- block-poly-(N-isopropylacrylamide) (PBA- b-PNIPAAm) or poly(n-butyl acrylate)- block-quaternized poly(2-(dimethylamino)ethyl methacrylate) (PBA- b-PDMAEMAq) as additive were prepared via sequential solvent evaporation of polymer solutions in a solvent mixture. The degree of enrichment at the air surface of the coating and the functionality were examined for different molecular weight additives with different block ratios obtained via Atom Transfer Radical Polymerization (ATRP). The design of the block copolymers with an anchor block (PBA) which is compatible with the bulk polymer (PBMA) and water-compatible functional blocks (PNIPAAm and PDMAEMAq) along with the selection of suited solvent mixtures based on pre-estimation of the selective solubility and sequential evaporation via the Hansen solubility parameters and vapor pressures, respectively, were found to work very well. A small fraction of water in the solvent mixture had been crucial to obtain surface segregation of the functional block, e.g., a PNIPAAm surface with temperature-switchable wettability. Reversible temperature dependent wettability and long term stability of the functionalization, based on contact angle data, were obtained for an optimized PBA- b-PNIPAAm additive. Surface charge density, estimated from dye binding and zeta potential measurements, and killing efficiency against Staphylococcus aureus were investigated for PBA- b-PDMAEMAq as additive. Both block copolymer additives were found to dominate the surface properties and the functionality of the PBMA coating. © 2010 Elsevier Ltd.
    view abstract10.1016/j.polymer.2010.10.002
  • Grafted glycopolymer-based receptor mimics on polymer support for selective adhesion of bacteria
    Yang, Q. and Strathmann, M. and Rumpf, A. and Schaule, G. and Ulbricht, M.
    ACS Applied Materials and Interfaces 2 (2010)
    A sugar-containing monomer (2-lactobionamidoethyl methacrylate, LAMA) was grafted on a polypropylene (PP) microfiltration membrane surface by UV-induced graft copolymerization. The degree of grafting can be controlled by variation of monomer concentration, UV irradiation time, and photoinitiator concentration. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to confirm the surface modification on the membranes. The water contact angle was used to evaluate the hydrophilicity change of the membrane surface before and after modification. Bacteria capture experiments showed that the membrane could selectively bind E. faecalis while adhesion of S. maltophilia was not influenced by the functionalization of PP with grafted poly(LAMA). The adhesion of E. faecalis onto poly(LAMA) grafted membrane could be inhibited by 200 mM galactose solution; however, glucose solution showed no inhibition effect. Moreover, occupying sugar residues on the membrane surface primarily by a galactose targeting lectin, peanut agglutinin, could significantly suppress the following adhesion of E. faecalis. All these results clearly demonstrate that this poly(LAMA) grafted PP membrane can selectively capture E. faecalis and that this selection is based on the interaction between galactose side groups on grafted flexible functional polymer chains on the membrane surface and galactose binding protein on the E. faecalis cell membrane. © 2010 American Chemical Society.
    view abstract10.1021/am1007276
  • Model Based Quantification of Internal Flow Distributions from Breakthrough Curves of Flat Sheet Membrane Chromatography Modules
    von Lieres, E. and Wang, J. and Ulbricht, M.
    Chemical Engineering & Technology 33 (2010)
    A novel model for quantifying radial flow distributions in flat sheet membrane chromatography modules under non-binding conditions is presented and applied for the practical analysis of two modules. The proposed model partitions the total void volume of the chromatography module into zones that are considered homogeneous with respect to flow velocity. The corresponding solute concentrations are time variant, but also spatially homogeneous within each zone. The model is mathematically represented and analytically solved as a network of continuously stirred tank reactors (CSTR). An additional plug flow reactor (PFR) is connected in series with the CSTR network in order to account for a time-lag that is not associated with the system dispersion. The capability of the model to describe experimental breakthrough data is compared to the frequently applied standard model for extra-membrane system dispersion, which consists of a single CSTR in series with a PFR. Non-binding conditions are deliberately chosen for studying the impact of module geometries on breakthrough curves separately from chromatographic membrane performance. The commercial CIM module and a custom designed cell (Scell) are studied with acetone and lysozyme as test tracers at varied flow rates and for various membrane pore sizes under non-binding conditions. In all studied cases, the proposed model fits the measured breakthrough curves better than the standard model. Moreover, the minimal number of radial flow zones that are required to accurately describe observed breakthrough curves and the estimated flow fractions through these zones provide valuable information for the analysis and optimization of internal module designs.
    view abstract10.1002/ceat.200900614
  • Surface modification of polypropylene microfiltration membrane via entrapment of an amphiphilic alkyl oligoethyleneglycolether
    Guo, H. and Ulbricht, M.
    Journal of Membrane Science 349 (2010)
    For surface hydrophilic and antifouling modification of polypropylene (PP) microfiltration membrane, the novel method for entrapment of the amphiphilic modifier octaethyleneglycol monooctadecylether (C18E8) was investigated in detail. The effects of the modification conditions on PP membrane and polymer structure were characterized by gas flow/pore dewetting, nitrogen adsorption/BET analysis, scanning electron microscopy and X-ray diffraction; surface properties were evaluated by ATR-FTIR spectroscopy and static water contact angle; filtration performance as well as antifouling property were investigated by water flux measurement, trans-membrane zeta potential, static and dynamic protein adsorption experiments. Furthermore, a stability study of the modified membrane was performed to offer a comprehensive understanding of this physical entrapment strategy. It can be concluded that both outer surface and inner pore walls of PP membrane were covered with oligoethylene glycol after entrapment modification by C18E8, with only very slight changes of membrane pore and polymer structures. Correspondingly, PP membrane surface hydrophilicity and antifouling performance were evidently improved. It was also found that the entrapped modifier has a tendency to leach out of the PP membrane in water at room temperature. However, after 8 weeks changes became very small, and the modified PP membrane surface still exhibited significant hydrophilicity and antifouling properties. © 2009 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.memsci.2009.11.062
  • The effects of (macro)molecular structure on hydrophilic surface modification of polypropylene membranes via entrapment
    Guo, H. and Ulbricht, M.
    Journal of Colloid and Interface Science 350 (2010)
    Entrapment of a variety of ethyleneoxide-containing substances from nonpolar solutions into polypropylene (PP) microfiltration membrane surface for hydrophilic modification was studied. The results from gravimetric weight gain, surface characterization by contact angle measurements and ATR-IR spectroscopy, water flux measurements and protein adsorption revealed that poly(ethylene glycol)s (PEGs) were ineffective, while many nonionic amphiphilic substances, especially some tri-block copolymers of poly(ethyleneoxide) (PEO) and poly(propylene oxide) (PPO) were very effective for PP surface modification. The relationship between modifier structure and architecture and entrapment behavior was investigated by studying the micellization of the amphiphilic modifiers in nonpolar solutions via pyrene-probe fluorescence and 1H NMR spectroscopy. We observed that the balanced structure of nonionic tri-block (macro)molecules tended to promote the formation of reverse micelles. For the most efficient polymeric modifiers, the lowest reverse critical micelle concentration (RCMC) had been observed. We conclude that a block copolymer structure and architecture promoting the self-association in the nonpolar solvent is the basis for a high modification efficiency, and that reverse micelles are involved in the entrapment modification performed at concentrations above RCMC. A different mechanism has been deduced for amphiphilic modifiers with low molar mass. This work provides more comprehensive insights in surface entrapment as a easy to perform physical surface modification method for polymeric materials. © 2010 Elsevier Inc.
    view abstract10.1016/j.jcis.2010.06.032
  • Tuning the ultrafiltration properties of anti-fouling thin-layer hydrogel polyethersulfone composite membranes by suited crosslinker monomers and photo-grafting conditions
    Peeva, P.D. and Pieper, T. and Ulbricht, M.
    Journal of Membrane Science 362 (2010)
    Anti-fouling composite membranes were prepared via photo-initiated " grafting-from" of the hydrophilic monomer poly(ethylene glycol) methacrylate on commercial polyethersulfone ultrafiltration membranes. A fine adjustment of the sieving properties of the modified membranes could be achieved by addition of suited crosslinker monomers in appropriate ratio to the reaction mixture. In this study, two crosslinkers were used: N,N'-methylene bisacrylamide (MBAA) and pentaerythritol triallyl ether (PETAE). Systematic variations of UV intensity and UV irradiation time in combination with varied monomer mixtures have been performed. The resulting membranes have been characterized with respect to degree of functionalization, contact angle and zeta potential as well as water flux and protein ultrafiltration performance with bovine serum albumin and myoglobin, yielding data for solute rejection and permeability loss due to membrane fouling. A minimum degree of functionalization was necessary to achieve fouling resistance, and especially in this range, the effects of the two crosslinker monomers were largely different. Crosslinking with the " two-armed" MBAA yielded denser hydrogel layers on the porous base membrane and, consequently, enhanced protein rejection with increasing crosslinker ratio. In contrast, on the same membrane pore size, hydrogel layers crosslinked with the " three-armed" PETAE yielded a more open barrier structure and the protein rejection decreased with increasing crosslinker ratio. Overall, this study delivered fundamental results for the preparation of high performance composite membranes with enhanced selectivity and anti-fouling properties for ultrafiltration. © 2010 Elsevier B.V.
    view abstract10.1016/j.memsci.2010.07.016
  • grafting (chemical)

  • hydrogels

  • membranes

  • polymers

  • surfaces

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