Comparing Photoactuation of an Azobenzene-Doped Nematic Liquid Crystal Polymer through Its Activation Mechanism: Trans–Cis–Trans Reorientation and Photoisomerization

Abstract

We compare the actuation speeds of the azobenzene-doped nematic liquid crystal polymer (azo-LCP) by examining its activation mechanisms: photoisomerization and trans−cis−trans reorientation (TCTR) (also known as Weigert effect). Both experiments and modeling are carried out in this study to compare the speed of bending and contraction acting on azo-LCP. We identify that the TCTR-based photobending of azo-LCP generated less than half the photostrain in a unit cell than that in the photoisomerization case but involves a larger azo-LCP thickness in triggering photodeformation. Because photodeformation occurs in a deeper region than that in the photoisomerization case, the TCTR-based photobending of azo-LCP exhibits a faster bending speed than the photoisomerization-based photobending of azo-LCP, even though less strain is generated in the TCTR case.

Bioinspired light-driven soft robots based on liquid crystal polymers

“…16 However, such effects has been shown to generate lower strains than more often employed trans-cis isomerization. 17 When actuated in dry environments, photomechanical photoswitches may also release heat, resulting in a combination of thermal and mechanical contributions to actuation in dry environments. Decoupling of photomechanical effects from temperature allows LCPs containing photomechanical chromophores to act as amphibious actuators, capable of functioning in both dry and aqueous environments.…”

Bio-Inspired Soft Robotics: Tunable Photo-Actuation Behavior of Azo Chromophore Containing Liquid Crystalline Elastomers

“…By applying heat to cis form, the molecule can also be relaxed to stable trans form. The photoisomerization process of azobenzene mesogens in CLCPs can result in induced molecular reorientation, and this is the source for photo-actuation [50][51][52][53][54]. The chemical structures of azobenzene chromophores (monomer and crosslinker) used to prepare photo-actuating liquid-crystalline gels (LCGs) by Ikeda et al are shown in Figure 4 [51].…”

“…The chemical structures of azobenzene chromophores (monomer and crosslinker) used to prepare photo-actuating liquid-crystalline gels (LCGs) by Ikeda et al are shown in Figure 4 [51]. Yun et al [52] studied azobenzene-doped liquid-crystal polymer (azo-LCP) prepared by "host-guest" method of fabrication process. 1,4-bis-[4-(3-acryloyloxypropyloxy)benzoyloxy]-2-methylbenzene was used as host and 4-4′-bis[6-(acryoloxy)hexyloxy]-azobenzene as guest material.…”

“…Conversely, the shape of LCP is recovered when the mesogens transform from isotropic to the nematic phase. This can be achieved by visible-light irradiation [52]. Yun et al [52] studied azobenzene-doped liquid-crystal polymer (azo-LCP) prepared by "host-guest" method of fabrication process.…”

“…This can be achieved by visible-light irradiation [52]. Yun et al [52] studied azobenzene-doped liquid-crystal polymer (azo-LCP) prepared by "host-guest" method of fabrication process. 1,4-bis-[4-(3-acryloyloxypropyloxy) benzoyloxy]-2-methylbenzene was used as host and 4-4 -bis[6-(acryoloxy)hexyloxy]azobenzene as guest material.…”