Research Progress on Photoswitchable Surface Topography of Liquid Crystalline Polymer

doi:10.19894/j.issn.1000-0518.210381

Chinese Journal of Applied Chemistry ›› 2021, Vol. 38 ›› Issue (10): 1226-1237.DOI: 10.19894/j.issn.1000-0518.210381

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Research Progress on Photoswitchable Surface Topography of Liquid Crystalline Polymer

Yu-Fan JI, Feng CAI, Hai-Feng YU()

School of Materials Science and Engineering，and Key Laboratory of Polymer Chemistry and Physics of Ministry of Education，Peking University，Beijing 100871，China

Received:2021-07-30 Accepted:2021-08-26 Published:2021-10-01 Online:2021-10-15
Contact: Hai-Feng YU
About author:yuhaifeng@pku.edu.cn
Supported by:
National Natural Science Foundation of China(51773002)

Abstract

Abstract:

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.

Key words: Light-responsive, Liquid crystalline polymer, Surface topography control, Functional application

CLC Number:

O631

Yu-Fan JI, Feng CAI, Hai-Feng YU. Research Progress on Photoswitchable Surface Topography of Liquid Crystalline Polymer[J]. Chinese Journal of Applied Chemistry, 2021, 38(10): 1226-1237.

Figures/Tables 6

Fig.1 （A） The change induced by the decreased order parameter；（B） Photo-isomerization of azobenzene；（C） The formation process of surface relief gratings；（D） Two instability modes of bilayer membrane

Fig.2 （A） LCN containing chiral nematic and homeotropic orientation. After ultraviolet （UV） illumination， the chiral nematic areas expand perpendicular to the plane of the film while the homeotropic areas contract in the perpendicular direction；（B） LCN including fingerprint patterns. Images from interferometer measurements showing the surface topography before and during UV irradiation［40］； Topographical deformation of LCN coatings with （C） rigid glass and （D） a compliant polymer layer as the substrate［41］

Fig.3 （A） Illustration of the reduced LCN density after UV illumination with photomasks due to the generation of free volume；（B） Under the illumination of 365 and 455 nm light， surface topographical deformation is increased［21］；（C） Design box for maximizing the optomechanical response under two-light illumination with arbitrary wavelengths［45］

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

Fig.5 Optical microscopic images of the surface topography without （A） and with （B） 436 nm linearly polarized light irradiation；（C） Scheme of the macroscopic wrinkle formation of the PDMS surface by the UV-curable LCP film containing azobenzene-containing photoinitiator［56］； Optical microscopic images of wrinkle topography under UV illumination when uniaxial compression is parallel （D） and perpendicular （E） to the line pattern［57］；（F） Multiple cycles of stimulus-induced wrinkling， light-induced tuning and erasing in the optically wrinkling system［58］

Fig.6 （A） Schematic illustration of the fabrication of complex hierarchical multilevel structures；（B） Structural color images of imprinted nanopatterns［65］；（C） Schematic process of the surface topography change on the light-responsive LCE coatings and phase contrast images of NIH-3T3 cells on patterned LCN in hexagonally arranged pillars of 0.2 μm height and a circular pattern with a height of 0.3 μm. Scale bars are 50 μm［67］；（D） Cell orientation on confocal-induced pDR1m patterns including the geometry along the sides， on the vertex， on concentric rings and on array of dots. Scale bars are 10 μm［68］；（E） AFM images of surface topography of the HH-perpendicular structure which is UV photostationary state and locally exposed to green light. Surface waving happens under the continuous UV illumination and alternative green light［69］；（F） Schematic illustration of the switch of adhesion via light-triggered topographical deformation and 3D digital holographic microscopic images of the surface topographical inversion during the light stimulation process［70］

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Research Progress on Photoswitchable Surface Topography of Liquid Crystalline Polymer

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