Meso‐ and Microscopic Motions in Photoresponsive Liquid Crystalline Polymer Films

Abstract

Photoresponsive azobenzene-containing systems ranging from molecular to macroscopic material levels have greatly been increasing their significance in materials chemistry. This review focuses on the studies on light induced or triggered motions in azobenzene liquid crystalline (LC) polymer films at mesoscopic and microscopic levels. Due to the cooperative nature of liquid crystalline materials, highly efficient photoalignment and photo-triggered migrating motions are realized in mostly repeated manners. Here, recent advances in surface-grafted LC polymer brushes, LC block copolymer films, and LC polymer films that exhibit mass migrations are overviewed. Such newly emerged photoresponsive systems are expected to provide new possibilities and applications in polymer thin film technologies.

New strategies and implications for the photoalignment of liquid crystalline polymers

“…97 In surface tethered films with sufficiently high two-dimensional density, the azobenzene mesogens were preferentially oriented parallel to the substrate. 19,96 This unique orientation was confirmed by ultravioletvisible absorption spectroscopy and grazing angle incidence X-ray diffraction measurements. Similar to the cases of side-on polymer films, surface-grafted LC azobenzene chains are beneficial for efficient light absorption and in-plane photoalignment.…”

“…In the years since, considerable data have been accumulated, and several reviews on this topic are now available. 5,19,[120][121][122][123][124] The orientations of azobenzene mesogenic groups and MPS cylinder domains have been found to be dependent on the film thickness. For poly(ethylene oxide) (PEO)-b-PAz (Figure 10), a critical thickness was determined to be 70 nm.…”

“…Photochromic reactions have frequently been incorporated in LC media because of their repeatability for controlling material properties. This approach has provided various types of smart, light-responsive materials 1 exhibiting surface-mediated photoalignment of LC materials, [2][3][4][5][6] photoinduced phase transitions, [7][8][9][10][11][12] photoorientation/addressing of polymer thin films, [13][14][15][16][17][18] photoinduced mass migrations, [19][20][21][22][23][24][25][26][27][28] phototactic sliding motions, [29][30][31] photo-driven motions and morphology of monolayers, [32][33][34][35] and macroscopic photomechanical deformations. [36][37][38][39][40][41][42][43][44][45][46] Photoalignment research and technology started in 1988 with the discovery of the reversible alignment control of nematic LCs by the photoisomerization of azobenzene on a substra...…”

SRG Inscription in Supramolecular Liquid Crystalline Polymer Film: Replacement of Mesogens

“…The trans/cis photoisomerization cycle of Az under an interference laser illumination or patterned photo-illumination locally softens the Az polymers and induce lateral motions of the film materials. [1][2][3][4][5][6][7]. The resultant undulations correspond to the patterns of incident light modulations including both intensity [6,7] and polarization [1][2][3][4]8].…”

Stimuli-responsive photonic polymer coatings

“…Usually, the materials for such coatings are based on liquid crystalline (LC) polymers or hydrogels and solvent gels (Scheme 1). [17][18][19] Small changes in the molecular order of LC materials can lead to large dimensional changes (Scheme 1a). 20,21 Volumetric and dimensional changes in gels are based on differences in swelling and shrinkage due to the adsorption or desorption of a solvent (Scheme 1b).…”