The light responsiveness is achieved by utilizing an azobenzene compound that isomerizes from its trans conformation to the cis conformation under exposure with UV light and thereby changing the local order of neighboring mesogenic molecular units. (Danqing Liu and Dirk J. Broer, New insights into photoactivated volume generation boost surface morphing in liquid crystal coatings, Nature Communications 2015, 6. )
1.Light switchable regular linear gratings
The polymer coating consists of alternating regions of planar helicoidal and homeotropic alignment. In the absence of UV light, the coating surface is fat attributed to the ITO imprints during the fabrication process. When exposed to UV light linear corrugations appear where the cholesteric network tends to expand perpendicular to the surface, while the homeotropic areas tend to contract along the film thickness and expand in the plane of the film.
Danqing Liu, Cees W.M. Bastiaansen, Jaap M.J. den Toonder and Dirk J. Broer, Photo-switchable surface topologies in a chiral-nematic polymer, Angewandte Chemie International Edition 2012, 51, 892-896.
Danqing Liu, Cees W.M. Bastiaansen, Jaap M.J. Toonder and Dirk J. Broer, Light-induced formation of dynamic and permanent surface topologies in chiral-nematic polymer networks, Macromolecules 2012, 45, 8005-8012.
Danqing Liu, Cees W.M. Bastiaansen, Jaap M.J. Toonder and Dirk J. Broer, Photo-responsive surface topology in chiral nematic media, Proceeding SPIE 2012, 8279 doi:10.1117/12.909899.
Danqing Liu, Dirk J. Broer, Liquid crystal network comprising a photopolymerizable monomer, European Patent application number WO 2015030572 A1, 2015
2.Light switchable Fingerprints
Chiral-nematic polymer network coatings form a “fingerprint” texture through self-assembly. The coating has a flat surface but when actuated by light in the presence of a copolymerized azobenzene compound, 3D fingerprint structures appear in the coating. The helix forms protrusions at the positions where the molecules are aligned parallel to the surface and withdraws at the positions where the orientation is perpendicular. The texture in the on-state akin to the human fingerprint.
Danqing Liu and Dirk J. Broer, Self-assembled dynamic 3D fingerprints in liquid crystal coatings towards controllable friction and adhesion, Angewandte Chemie International Edition 2014, 53, 4542-4546.
3.Light switchable polydomain
We use a self-organizing process to form polydomains of liquid crystal polymer networks in a thin coating layer adhering to a substrate. Each domain deforms differently when exposed with light thus switching the surface from flat to jagged. Video recorded by Dr. Matthew Hendrikx.
Danqing Liu, Ling Liu, Patrick Onck and Dirk J. Broer, Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating, Proceedings of the National Academy of Sciences 2015, 112, 3880-3885.
Wei Feng, Dirk J. Broer and Danqing Liu*, Combined light and electric response of topographic liquid crystal network surfaces, Advanced Functional Materials, 2019, 1901681.