Dr. Frank Katzenberg

Biomaterials & Polymer Science
TU Dortmund University

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  • Improvement of high voltage direct current material properties upon tailoring the morphology of crosslinked polyethylenes
    Niedik, C.F. and Jenau, F. and Maricanov, M. and Segiet, D. and Tiller, J.C. and Katzenberg, F.
    Polymer Crystallization (2021)
    Crosslinked linear low-density polyethylene (XLPE) is the most common polymeric cable insulation material for high-voltage applications with a high number of operating hours in high voltage alternating current (HVAC) systems. High voltage direct current (HVDC) power transmission and polymeric cable systems play a major role in the future and raise, besides numerous systemic benefits, challenges in the design of material properties. The main issue is injection and trapping of space charges in insulation materials under DC-fields. The objective of this work is to increase knowledge of the interplay between microstructure and material performance of XLPE under DC by tailoring its morphology beyond the capabilities of “common crystallization kinetics” upon constrained crystallization at certain elongations. It was found that the tailored oriented morphology influences the energetic depth of traps and a significant reduction of space charge density occurs. Moreover, the optimized oriented morphology leads to a significant reduction of field enhancement for field strengths ELaplace ≥ 20 kV mm−1 compared to unoriented XLPEs with spherulitic morphology. It is shown that this way of morphology tailoring results in a considerable, material dependent reduction of field exposure by a factor of 4, which promises a significant improvement in the electrical life time of polymeric insulation material used. Polymer Crystallization© 2021 The Authors. Polymer Crystallization published by Wiley Periodicals LLC.
    view abstract10.1002/pcr2.10208
  • Insights in the Thermal Volume Transition of Poly(2-oxazoline) Hydrogels
    Segiet, D. and Stockmann, A. and Sadowski, J. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics (2021)
    Polymers with a lower or an upper critical solution temperature (LCST or UCST) can precipitate in a very narrow temperature range. Cross-linking of such polymers and adding them to suited solvent results in smart gels that are capable of greatly changing their dimensions with changing temperature. This transition occurs very often in a broad temperature range, which limits the applicability of smart materials. To shed some light into the design of thermo-responsive hydrogels with a narrow phase transition, poly(2-ethyl-2-oxazoline) (PEtOx), poly(2-isopropyl-2-oxazoline), and statistical copolymers of 2-butyl-2-oxazoline and 2-ethyl-2-oxazoline, respectively, are synthesized and the concentration-dependent cloud point temperatures (Tcp) of the free polymers in aqueous media are determined in relation to the thermo-responsive swelling behavior of the respective hydrogels. A narrow thermal transition of the hydrogels can only be achieved when the Tcp of the free polymers in water is independent on the concentration. Aqueous salt solutions can render even PEtOx into a concentration independent LCST polymer. However, this salt effect does not work for hydrogels. © 2021 The Authors. Macromolecular Chemistry and Physics published by Wiley-VCH GmbH
    view abstract10.1002/macp.202100157
  • Small-Angle X-Ray Scattering Measurements on Amphiphilic Polymer Conetworks Swollen in Orthogonal Solvents
    Benski, L. and Viran, I. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics 222 (2021)
    Amphiphilic polymer conetworks (APCNs), which combine two different polymer nanophases, have a broad range of applications that involve their unique potential to separately swell one of these nanophases in a selective solvent. Little is known about the structural changes of such APCNs upon swelling in dependence on the topology. Here, conetworks composed of poly(2-ethylhexyl acrylate) crosslinked by poly(2-methyl-2-oxazoline) (PMOx) are investigated with small-angle X-ray scattering in dry and swollen state using the orthogonal solvents water and toluene. The data clearly show that the structural changes induced by swelling are strongly dependent on the topology of the APCNs. While water leads to fusion of PMOx phases resulting in larger structures than found in the dry APCN, toluene is only swelling the hydrophobic phases without structural changes. © 2020 The Authors. Macromolecular Chemistry and Physics published by Wiley-VCH GmbH
    view abstract10.1002/macp.202000292
  • Investigation of the swelling behavior of hydrogels derived from high-molecular-weight poly(2-ethyl-2-oxazoline)
    Segiet, D. and Jerusalem, R. and Katzenberg, F. and Tiller, J.C.
    Journal of Polymer Science 58 (2020)
    Thermoresponsive hydrogels are of great importance as smart materials. They are usually composed of cross-linked polymers with a lower critical solution temperature (LCST). Although much is known about networks of poly(N-isopropylacrylamide), all other polymers are somewhat neglected. In this work, the temperature-dependent swelling behavior of differently cross-linked thermoresponsive poly(2-ethyl-2-oxazoline) (PEtOx) hydrogels were investigated with regard to varying parameters of the network composition. It was found that the degrees of swelling of the hydrogels converge for a certain polymer/solvent system at a distinct temperature independent of its degree of cross-linking. Furthermore, this temperature correlates with the LCST of the respective starting PEtOx. Its net chain molecular weight Mc only affects the maximum degree of swelling and thus, the swelling–deswelling rate of the hydrogel. The fundamental structure/property relations found in this study could be useful to predict the behavior of other thermoresponsive hydrogels. © 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc.
    view abstract10.1002/pol.20190267
  • Realizing a shape-memory effect for synthetic rubber (IR)
    Segiet, D. and Neuendorf, L.M. and Tiller, J.C. and Katzenberg, F.
    Polymer 203 (2020)
    In this work, two different approaches were followed to realize a shape-memory effect for synthetic rubber (IR). Firstly, we explored the influence of stearic acid (StA) on the shape-memory effect (SME) of IR. It was found that small concentrations of StA cause an intrinsic’ shape-memory effect of IR by significantly increasing the melting temperature of the strain-induced crystals. Secondly, we blended IR with the biocompatible poly(2-ethyl-2-oxazoline) (PEtOx) prior to crosslinking. We obtained an ‘extrinsic’ SME with trigger temperature well above room temperature. Moreover, the prepared IR/PEtOx networks showed characteristics of an amphiphilic polymer conetwork. Both methods were found to be capable of making IR a protein-free and efficient, and in the case of IR/PEtOx also water-triggerable SMP that can be applied for biomedical purposes. © 2020 Elsevier Ltd
    view abstract10.1016/j.polymer.2020.122788
  • Shape memory effect, shock- And energy-absorption capability of critically cross-linked syndiotactic polypropylene
    Katzenberg, F. and Tiller, J.C.
    Materials Today: Proceedings 16 (2019)
    Critical cross-linking, a light cross-linking right at the borderline between thermoplastic and elastomer, was applied to syndiotactic polypropylene (sPP) to gain at least a shape memory effect for storing preferably high strains. Beside the expected shape memory effect with maximum storable strains of 550%, critically cross-linked syndiotactic polypropylene (x-sPP) exhibits further amazing properties. For example, amorphous x-sPP is one of a few “cold programmable” shape memory polymers. At room temperature, it is easily deformable by hand and forms strain-induced crystals, which stabilize it at strains of up to 340%. Thermal triggering of cold-programmed x-sPP exhibits a triple-shape memory effect with an intermediate shape that depends on the heating rate applied for triggering. Thus, cold-programmed x-sPP is capable of reacting to a temperature increase by adapting its shape change according to the applied heating rate. Since a material with such property can be used e.g. to predict a system failure when used in a defined environment, we called it “predictive material”. Since amorphous x-sPP is easily deformable, transforms itself from a compliant, elastomeric into a rigid, semi-crystalline state upon stretching to large elongations and retains the latter after removing the stretching force, we explored its suitability as a shock- and energy absorber. To this end, thin safety lines of x-sPP were prepared and tested by falling weight experiments to determine characteristic physical quantities such as maximum impact force, maximum jerk (first derivative of the deceleration) and energy absorption capability. It was found that x-sPP is excellently suited for cushioning the impact force, vibration and chatter, which occur when a safety line abruptly tightens after the free fall in a falling weight experiment. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Shape Memory Applications, Research and Technology 2018.
    view abstract10.1016/j.matpr.2019.05.336
  • Shock- and Energy-Absorption Capability of Cold-Programmable Shape Memory Polymers
    Raidt, T. and Santhirasegaran, P. and Hoeher, R. and Tiller, J.C. and Katzenberg, F.
    Macromolecular Chemistry and Physics 220 (2019)
    In this work, the shock- and energy-absorption capability of cold-programmable shape memory polymers is evaluated. To this end, thin safety lines are prepared from different materials (critically cross-linked syndiotactic polypropylene, shape memory natural rubber, natural rubber, and Dyneema) and tested by falling weight experiments to determine characteristic physical quantities such as maximum impact force, maximum jerk (first derivative of the deceleration), and energy absorption capability. Critically cross-linked syndiotactic polypropylene is the best suited of all tested materials for cushioning the impact force, vibration, and chatter, which occur when a safety line abruptly tightens after the free fall in a falling weight experiment. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/macp.201800274
  • Thermo-/moisture-responsive shape-memory effect of poly(2-ethyl-2-oxazoline) networks
    Segiet, D. and Raidt, T. and Özdem, H. and Weckes, S. and Tiller, J.C. and Katzenberg, F.
    Journal of Polymer Science, Part B: Polymer Physics 57 (2019)
    In this work, poly(2-ethyl-2-oxazoline) (PEtOx) is crosslinked to realize a moisture- and thermo-responsive shape-memory polymer. The obtained PEtOx networks exhibit excellent shape-memory properties with storable strains of up to 650% and recovery values of 100% over at least 10 shape-memory cycles. The trigger temperature (Ttrig) of 68 °C of a PEtOx network at a relative humidity (RH) of 0% decreases with increasing moisture and equals room temperature at an RH of 40%. Thus, programmed PEtOx networks trigger sensitively on a certain temperature/moisture combination and, further, can be programmed as well as triggered at room temperature exclusively by varying humidity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1053–1061. © 2019 Wiley Periodicals, Inc.
    view abstract10.1002/polb.24859
  • Tunable swelling kinetics of shape-memory poly(2-ethyl-2oxazoline)-networks
    Segiet, D. and Tiller, J.C. and Katzenberg, F.
    Materials Today: Proceedings 16 (2019)
    Thermally programmed PEtOx-networks are capable of storing fully recoverable strains of up to 640% and mechanical energies of up to 0.56 J g-1, which is 74% of the work applied for programming. Furthermore, it was found that thermally programmed and solvent triggered PEtOx-networks exhibit swelling degrees of up to 38 depending on the kind of solvent (e.g. water, ethanol, chloroform and DMF). Interestingly, the swelling rate significantly depends on the thermally programmed strain of the PEtOx-network. Programming the PEtOx-network above a critical strain results in immediate disruption. However, programming to a degree below the critical strain allows control over the swelling kinetic of the network. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Shape Memory Applications, Research and Technology 2018.
    view abstract10.1016/j.matpr.2019.05.340
  • Crosslinking of Semiaromatic Polyesters toward High-Temperature Shape Memory Polymers with Full Recovery
    Raidt, T. and Schmidt, M. and Tiller, J.C. and Katzenberg, F.
    Macromolecular Rapid Communications (2018)
    In this work, high-temperature shape memory polymers are realized by end-group crosslinking of the semiaromatic polyesters polyethylene terephthalate as well as polybutylene terephthalate. Both networks exhibit trigger temperatures distinctly higher than 200 °C and excellent shape memory properties such as storable strains of 200%, full fixity of the applied strain in the temporary shape, and full recovery of the permanent shape. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/marc.201700768
  • Investigating the crystallinity of Poly(butylene)terephthalate (PBT): Correlation between THz TDS measurements and X-ray scattering data
    Sommer, S. and Raidt, T. and Engel, A. and Balzer, J.C. and Fischer, B.M. and Katzenberg, F. and Tiller, J.C. and Koch, M.
    International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz (2017)
    We present angle-resolved terahertz time-domain spectroscopy (THz TDS) measurements of poly(butylene) terephthalate (PBT) and compare the results to x-ray scattering measurements. This comparison confirms that the THz TDS measurements can be correlated to the crystal structure. Further, the THz TDS measurements give insights into the binding energies of the crystal bounds. © 2017 IEEE.
    view abstract10.1109/IRMMW-THz.2017.8066927
  • Investigations on "near perfect" poly(2-oxazoline) based amphiphilic polymer conetworks with a crystallizable block
    Schmidt, M. and Raidt, T. and Ring, S. and Gielke, S. and Gramse, C. and Wilhelm, S. and Katzenberg, F. and Krumm, C. and Tiller, J.C.
    European Polymer Journal 88 (2017)
    Amphiphilic polymer conetworks (APCNs) of near perfect structure were prepared by cross-linking defined poly(2-oxazoline)-based block copolymers. To this end, ABA triblock copolymers with poly(2-methyloxazoline) (PMOx) as A block and poly(2-heptyloxazoline) (PHepOx) as B block in different compositions and with different cross-linkable end groups were prepared and crosslinked. The resulting amphiphilic polymer conetworks were characterized with atomic force microscopy (AFM) and small as well as wide angle X-ray scattering (SAXS/WAXS). The results show that the PHepOx block crystallizes in the APCNs if the content is larger than 19. vol.%, but shows no thermal signature in the differential scanning calorimetry if the polymer content is below 68. vol.%. Further, the size of the polymer phase is the same in a composition range of 38-58. vol.% PHepOx. The phase size was confirmed by AFM. The found very regular interconnected structure over a wide range of compositions seems to be the generic structural motive in APCNs and is also formed when inserting a crystallizable polymer block. © 2016 Elsevier Ltd.
    view abstract10.1016/j.eurpolymj.2016.09.046
  • Multiaxial Reinforcement of Cross-Linked Isotactic Poly(propylene) upon Uniaxial Stretching
    Raidt, T. and Hoeher, R. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Materials and Engineering 302 (2017)
    Isotactic poly(propylene) (iPP) is one of a few polymers that show homoepitaxy, i.e., the formed crystals act as nuclei for so-called daughter crystals that are formed nearly perpendicular to the backbones of the primary crystallized mother crystals. Lightly cross-linked isotactic poly(propylene) (x-iPP) offers the opportunity to form nearly all mother crystals in stretching direction and simultaneously allow formation of daughter crystals. Since crystals in polymers act as reinforcement along chain direction, this unique behavior allows multiaxial reinforcement in iPP induced only by stretching in one direction. In this study the influence of applied uniaxial strain is explored on the resulting multiaxial crystal orientations and Young's moduli parallel, perpendicular as well as under an angle of 45° to the stretching direction of the sample. It is shown that the occurring multiaxial orientations strongly depend on applied strain during crystallization and cause significantly improved Young's moduli parallel as well as perpendicular to the prior stretching direction while that under an angle of 45° is slightly decreasing. The here described technique to obtain multiaxially oriented morphologies is not restricted to thin films but can be efficiently applied also to bulk samples. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/mame.201600308
  • Heating Rate Sensitive Multi-Shape Memory Polypropylene: A Predictive Material
    Hoeher, R. and Raidt, T. and Katzenberg, F. and Tiller, J.C.
    ACS Applied Materials and Interfaces 8 (2016)
    Here we report on a novel type of smart material that is capable of specifically responding to the changing rate of an environmental signal. This is shown on the example of lightly cross-linked syndiotactic polypropylene that reacts to a temperature increase by adapting its shape change according to the applied heating rate. In general, a material with such properties can be used to predict a system failure when used in a defined environment and is therefore called "predictive material". © 2016 American Chemical Society.
    view abstract10.1021/acsami.6b04177
  • Ionically Cross-Linked Shape Memory Polypropylene
    Raidt, T. and Hoeher, R. and Meuris, M. and Katzenberg, F. and Tiller, J.C.
    Macromolecules 49 (2016)
    An ionically cross-linked syndiotactic polypropylene (ix-sPP) was synthesized by subsequent grafting of maleic anhydride (MA) to the polymer followed by compounding with ZnO. The polymer network was investigated by X-ray scattering, transmission electron microscopy, and various thermal and mechanical analyses. The optimized polymer network with 1 wt % MA grafting and 20 wt % ZnO exhibits a crystal melting temperature of 125 °C and rubber elastic behavior up to 203 °C and becomes a viscous polymer melt at higher temperatures. This process is fully reversible. Further, ix-sPP is an exceptionally stable ionic polymer network that matches the stability of the respective covalently cross-linked polymer in terms of shape memory properties. Additionally, the ionic cross-linking affords thermoplastic processability and shape memory assisted self-healing. © 2016 American Chemical Society.
    view abstract10.1021/acs.macromol.6b01387
  • Shape memory natural rubber
    Katzenberg, F. and Tiller, J.C.
    Journal of Polymer Science, Part B: Polymer Physics 54 (2016)
    Charles Goodyear discovered the vulcanization of natural rubber (NR) 170 years ago and transferred the gooey natural compound into the first representative of an entirely new class of materials; the elastomers. Thenceforth, NR was intensively explored and was used for countless products to date. All the more surprising, it was found recently that NR exhibits superior and unexpected properties whenever it is cross-linked to a degree smaller than 0.4% which is fairly below the commonly used 1%-2%. This article gives a brief overview on the exceptional properties of lightly cross-linked NR, named shape memory natural rubber (SMNR), including the cold programmable shape memory effect, storing of extremely large strain, energy and cold, and its capability to sense and memorize environmental parameters. © 2016 Wiley Periodicals, Inc.
    view abstract10.1002/polb.24040
  • THz-Spectroscopy on High Density Polyethylene with Different Crystallinity
    Sommer, S. and Raidt, T. and Fischer, B.M. and Katzenberg, F. and Tiller, J.C. and Koch, M.
    Journal of Infrared, Millimeter, and Terahertz Waves 37 (2016)
    The different crystallinity states of high density polyethylene (PE-HD) are investigated using THz time-domain spectroscopy by exploiting the complex permittivity at a frequency range from 0.5 up to 3.5 THz. We found that samples with different crystallinity can be distinguished by comparing the material specific refractive index (n) or rather the linked complex part of the permittivity (∈ ′ ′). Correlating the calorimetrically determined degrees of crystallinity with the absolute values of the refractive index and the specific absorption peak at 2.18 THz, respectively, suggests in both cases a linear correlation. © 2015, Springer Science+Business Media New York.
    view abstract10.1007/s10762-015-0219-8
  • VOC Sorption in Stretched Cross-Linked Natural Rubber
    Gushterov, N. and Doghieri, F. and Quitmann, D. and Niesing, E. and Katzenberg, F. and Tiller, J.C. and Sadowski, G.
    Industrial and Engineering Chemistry Research 55 (2016)
    Sorption of volatile organic compound (VOC) vapors in natural rubber (NR) was measured at 20 °C using a magnetic suspension balance. Experiments were performed with non-cross-linked NR, as well as NR cross-linked with dicumyl peroxide. Stretching the cross-linked NR samples leads to crystal formation and therefore to a constraint to volume swelling of the amorphous domains. To investigate the influence of NR stretching and therefore of crystal formation on the VOC sorption, measurements of nonstretched NR were compared to data for cross-linked NR samples stretched with different extension ratios. Analysis of the VOC sorption data revealed a reduced VOC sorption in the stretched NR compared to fully amorphous, nonstretched NR. The sorption data were modeled using the perturbed-chain statistical associating fluid theory (PC-SAFT) accounting for network elasticity by an additional Helmholtz-energy contribution. Influence of crystallinity content on VOC solubility in stretched NR was finally accounted for following a recently proposed approach and thus accounting for an additional contribution to pressure in the amorphous phase as a result of constraint imposed by crystalline domains. Comparison of modeling results with measured solubility for several VOCs in NR confirmed the overall consistency of the modeling approach used. © 2016 American Chemical Society.
    view abstract10.1021/acs.iecr.6b01710
  • Altering the trigger-behavior of programmed shape memory natural rubber (SMNR) by solvent vapor
    Quitmann, D. and Dibolik, M. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Materials and Engineering 300 (2015)
    Lightly cross-Linked natural rubber was found to have a tunable trigger-Temperature through programming procedure. Solvent vapor has a further impact on the trigger-Behavior of programmed SMNR. For exploring thiswe used the 1st derivative of the temperature dependent thickness increase to get insights in the trigger-Behavior. Additionally subsequently applied solvent vapor treatment allows reversibly changing TTrig as well as the maximum trigger-Rate vmax and thus the whole trigger-Process. The variation of solvent vapors or subsequently applied solvent combinations results in a novel way to alter the trigger-Behavior after programming. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/mame.201400224
  • Chemical cross-linking of polypropylenes towards new shape memory polymers
    Raidt, T. and Hoeher, R. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 36 (2015)
    In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross-linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x-iPP is stable for many cycles, x-sPP ruptures after the first shape-memory cycle. It is shown by wide-angle X-ray scattering (WAXS) experiments that cross-linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals. Shape memory polypropylene is prepared by cross-linking of syndiotactic as well as isotactic polypropylene (iPP). Cross-linked iPP is a shape-memory polymer with excellent stored strain, fixity-, and recovery-ratios. Wide angle X-ray scattering (WAXS) experiments reveal that the crystals in programmed x-iPP show a microstructure with mother and daughter crystals. In contrast to previous reports, the amount of daughter crystals exceeds that of the mothers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/marc.201400727
  • Programming of shape memory natural rubber for near-discrete shape transitions
    Quitmann, D. and Reinders, F.M. and Heuwers, B. and Katzenberg, F. and Tiller, J.C.
    ACS Applied Materials and Interfaces 7 (2015)
    Typical shape memory polymers are hot-programmed and show a shape transition over a broad temperature range of 10 K and more. Cold-programmed shape memory natural rubber (SMNR) recovers more than 80% of its original shape within 1 K. The trigger point can be increased upon aging the stretched SMNR over several weeks without losing the narrow trigger range. This process can be accelerated by treatment of the stretched SMNR with nonaffine solvent vapors. Affine solvent vapors of low concentrations afford higher trigger points than that achieved by aging. This way, even higher cross-linked natural rubber can be cold-programmed. © 2014 American Chemical Society.
    view abstract10.1021/am507184c
  • Shape-memory PVDF exhibiting switchable piezoelectricity
    Hoeher, R. and Raidt, T. and Novak, N. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 36 (2015)
    In this study, a material is designed which combines the properties of shape-memory and electroactive polymers. This is achieved by covalent cross-linking of polyvinylidene fluoride. The resulting polymer network exhibits excellent shape-memory properties with a storable strain of 200%, and fixity as well as recovery values of 100%. Programming upon rolling induces the transformation from the nonelectroactive α-phase to the piezoelectric β-phase. The highest β-phase content is found to be 83% for a programming strain of 200% affording a d33 value of -30 pm V-1. This is in good accordance with literature known values for piezoelectric properties. Thermal triggering this material does not only result in a shape change but also renders the material nonelectroactive. Cross-linking of polyvinylidene fluoride results in a polymer network that combines excellent shape-memory properties with a switchable piezoelectricity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/marc.201500410
  • Viel mehr als nur Gummi
    Katzenberg, F. and Tiller, J.C.
    Nachrichten aus der Chemie 63 (2015)
    view abstract10.1002/nadc.201590205
  • Environmental memory of polymer networks under stress
    Quitmann, D. and Gushterov, N. and Sadowski, G. and Katzenberg, F. and Tiller, J.C.
    Advanced Materials 26 (2014)
    Generally reversible stimuli-responsive materials do not memorize the stimulus. In this study we describe an example in which stretched and constrained semi-crystalline polymer networks respond to solvent gases with stress and simultaneously memorize the concentration and the chemical nature of the solvent itself in their microstructure (see figure). This written solvent signature can even be deleted by temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/adma.201305698
  • Recoverable strain storage capacity of shape memory polyethylene
    Hoeher, R. and Raidt, T. and Rose, M. and Katzenberg, F. and Tiller, J.C.
    Journal of Polymer Science, Part B: Polymer Physics 51 (2013)
    Shape memory polymers (SMPs) are an important class of smart materials. So far the focus of such polymers was to find suited triggers for various application fields. Thus, the potential of most of these macromolecular networks regarding their maximally storable strain capability was not explored. In this study, the polyethylenes HDPE, LDPE, and ethylene-1-octene (EOC) were systematically investigated with respect to their strain storage potential. To achieve maximum strains, the polymers were chemically cross-linked in such a way that they are at the borderline between thermoplastics and elastomers. All investigated polymers showed higher strain storage than literature reported systems and exhibited excellent shape memory parameters. The highest stored strain was found for networks of EOC with fully recoverable 1400%. Interestingly, this value could not be enlarged by using EOCs with higher molecular weight, which is probably due to increasing content of entanglements as confirmed by Mooney-Rivlin. Copyright © 2013 Wiley Periodicals, Inc.
    view abstract10.1002/polb.23301
  • Shape-memory natural rubber: An exceptional material for strain and energy storage
    Heuwers, B. and Beckel, A. and Krieger, A. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics 214 (2013)
    Shape-memory polymers (SMPs) are smart, responsive materials with numerous potential applications. Based on previously introduced shape-memory natural rubber (SMNR), which shows exceptional properties such as strain storage of 1000%, cold storage, cold programmability, and mechanical and thermal triggers tunable both during and after programming, different SMNRs regarding their shape-memory parameters are investigated. Furthermore, their energy-storage capability and their mechanical properties are explored. SMNRs show fixity ratios of up to 94% and excellent recovery ratios of up to 100% whereas strains even above 1000% can be stored. Energies of up to 4.88 J g-1 can be stored with efficiencies of up to 53.30%. Further, the Young's modulus of SMNR can be switched by two orders of magnitude upon triggering or programming. The energy-storage capability and shape-memory parameters of shape-memory natural rubber (SMNR) are investigated. SMNRs are able to store large strains (up to 1000%) and energies (up to 4.88 J g-1) with recovery ratios of up to 100%. Furthermore, the Young's modulus of SMNR can be switched by two orders of magnitude upon triggering or programming. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/macp.201200649
  • Solvent-sensitive reversible stress-response of shape memory natural rubber
    Quitmann, D. and Gushterov, N. and Sadowski, G. and Katzenberg, F. and Tiller, J.C.
    ACS Applied Materials and Interfaces 5 (2013)
    We found that constrained shape memory natural rubber (SMNR) generates mechanical stress when exposed to solvent vapor. When the solvent vapor is removed, the material reprograms itself. This process is reversible and the stress answer is proportional to the solvent vapor concentration. Further, the stress answer is specific to the solvent. © 2013 American Chemical Society.
    view abstract10.1021/am400660f
  • Stress-induced stabilization of crystals in shape memory natural rubber
    Heuwers, B. and Quitmann, D. and Hoeher, R. and Reinders, F.M. and Tiemeyer, S. and Sternemann, C. and Tolan, M. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 34 (2013)
    In contrast to all known shape memory polymers, the melting temperature of crystals in shape memory natural rubber (SMNR) can be greatly manipulated by the application of external mechanical stress. As shown previously, stress perpendicular to the prior programming direction decreases the melting temperature by up to 40 K. In this study, we investigated the influence of mechanical stress parallel to prior stretching direction during programming on the stability of the elongation-stabilizing crystals. It was found that parallel stress stabilizes the crystals, which is indicated by linear increase of the trigger temperature by up to 17 K. The crystal melting temperature can be increased up to 126.5 °C under constrained conditions as shown by X-ray diffraction measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/marc.201200594
  • Tunable multiple-shape memory polyethylene blends
    Hoeher, R. and Raidt, T. and Krumm, C. and Meuris, M. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Chemistry and Physics 214 (2013)
    Shape memory polymers (SMPs) are an important class of smart materials. Usually, these polymers can be switched between two shapes. Recently, the possibility of switching more than two shapes was introduced for SMPs with relatively low strain storage capability. In this work, a lightly cross-linked polyethylene blend comprising 80 wt% EOC, 15 wt% LDPE, and 5 wt% HDPE is prepared in order to obtain a tunable multiple-shape memory polymer with high strain storage capacity. It is found that depending on the programming procedure, this SMP obtains a dual-, triple-, or quadruple-shape memory effect, with well-defined intermediate temporary shapes (retraction < 0.5% K -1) over a significantly broad temperature range (up to 30 K), large storable strains (up to 1700%), and nearly full recovery of all shapes (&gt;98.9%). A lightly cross-linked blend of different polyethylenes (EOC, LDPE, and HDPE) is prepared to gain a network exhibiting a tunable multiple-shape memory capability. The achieved material shows depending on the programming procedure a dual-, triple-, or quadruple-shape memory, with well-defined intermediate temporary shapes (retraction less then 0.5% K-1) over a significantly broad temperature range (up to 30 K), stored strains of up to 1700%, and excellent-shape memory properties. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/macp.201300413
  • Stress-induced melting of crystals in natural rubber: A new way to tailor the transition temperature of shape memory polymers
    Heuwers, B. and Quitmann, D. and Katzenberg, F. and Tiller, J.C.
    Macromolecular Rapid Communications 33 (2012)
    Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature Ttrig(σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/marc.201200313
  • Superheated rubber for cold storage
    Katzenberg, F. and Heuwers, B. and Tiller, J.C.
    Advanced Materials 23 (2011)
    Highly stretched rubber cools down upon relaxation. A natural rubber material that stores high elongations up to 1000% strain upon strain-induced crystallization at room temperature is reported. The strain recovered and, with this, the stored "cold" is released only by a thermal or athermal trigger. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/adma.201100408
  • Tensile creep measurements of glassy VOC-loaded polymers
    Mueller, F. and Heuwers, B. and Katzenberg, F. and Tiller, J.C. and Sadowski, G.
    Macromolecules 43 (2010)
    The paper describes a new apparatus to measure tensile creep curves of polymer/volatile organic compound (VOC) systems, especially designed for measurements of small VOC loadings in glassy polymers. For the first time creep curves for glassy polymer/VOC systems are recorded. The measurements were performed for the system polystyrene/toluene at different toluene loads up to wtoluene = 0.13 and at temperatures of 30, 50, and 70 °C. It was found that increasing VOC mass fractions qualitatively influence the mechanical properties of a polymer in the same way like increasing temperature does. Since at isothermal conditions these properties are affected by the glass transition of the system, this information for the polystyrene/toluene mixtures was used to modify and to verify the correlation of Kelly and Bueche to predict the glass-transition temperature of polymer/solvent systems. © 2010 American Chemical Society.
    view abstract10.1021/ma101782d
  • nanotechnology

  • polymers

  • shape memory effect

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