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Research Progress on Photoswitchable Surface Topography of Liquid Crystalline Polymer
Yu-Fan JI, Feng CAI, Hai-Feng YU
Chinese Journal of Applied Chemistry    2021, 38 (10): 1226-1237.   DOI: 10.19894/j.issn.1000-0518.210381
Abstract   (661 PDF (4128KB)(637)  

Light-responsive liquid crystalline polymer has been widely used in the study of micro/nanostructures on the surface because of its self-organization and photoresponsive properties. Complex and diverse topographical deformation with different orientation modes and order parameters in various systems is important for applications in the fields of optics, biology and mechanics. The key to achieving the manipulation of surface topography lies in a deep understanding and grasp of the mechanism behind phenomena: From the perspective of the liquid crystal director, when the order parameter decreases, molecules will shrink in the direction of the director and expand in the direction perpendicular to the director. The lateral shear stress generated by the difference in molecular orientation between adjacent domains can be used to construct a type of micro/nanostructure. As for the free volume of liquid crystalline polymer, it can be generated by ultraviolet light irradiation and the density of the film will decrease. In the dynamic process of the reversible trans-cis-trans isomerization of azobenzene, macroscopic surface reliefs will be formed. Another principle is light-induced polymer mass transport. The light intensity distribution, polarization state of the light field, and the wavefront of the beam all have an impact on the directional mass transport of the material. Last but not least, light can change the stability of the surface. The anisotropic shrinkage of the film during photopolymerization can be used to produce wrinkles, and the surface wrinkling of the film can be manipulated by stress release. Therefore, based on the four different mechanisms of light-induced topographical deformation, the research processes in the development of light-controlled surface topography are reviewed. Accordingly, the possible future directions in this field are outlooked, and some guidelines for further research on the surface topography control and functional applications of liquid crystalline polymer are provided.


Fig.4 (A,B) Surface reliefs resulting from linearly (A) and circularly (B) polarized beams 49 ; (C) Scheme of the influence of q value on spiral pattern; (D,E) Optical micrograph and AFM image of the pattern of q=10 (D) and q= -10 (E) L-G beam. All the scale bars are 1 μm 51 ; (F,G) Manipulation of surface topography using dichroic dye (F) and dichroic initiator (G) during polymerization
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