Photonic liquids

Andre Gröschel, University of Duisburg Essen, Duisburg, Germany

Photonic materials exhibit bright structural colours originating from coherent photon scattering from structural periodicities with length scales of half of the wavelength of light. They are found in many natural systems, inspiring approaches for the formation of synthetic photonic crystals. Since there are no pigments involved, structural colours do not bleach and are able to respond to stimuli, e.g., for sensing applications. Typically, structural colours are observed for solid lattices that satisfy the stringed requirements for high symmetry and positional order. In addition, components to create the lattices are either grown in nature or constructed with top down methods. With the exception of extraordinarily large core−shell virus particles, photonic crystals have so far not been engineered with synthetic particles that are themselves intrinsically self-assembled from the bottom-up. This presentation gives an overview of recent developments to create on average positional order to be able to observe the photonic effect in viscous mobile phases and even liquids. Above all, the lattices are built from particles that are intrinsically self-assembled themselves. The mobile lattice is a hierarchical construct starting from few nanometre block copolymer chains that assemble into block copolymer micelles with size of few dozen nanometres, and finally, into lattices with several 100 nm period. The final material is stimuli responsive, can be produced in large quantities and shows high selectivity towards reflected wavelengths as narrow as 1 nm. Given the extensive libraries of existing block copolymers, many more examples of block copolymer photonics with diverse properties are expected.

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