Macromolecular Research, Vol.30, No.11, 799-810, November, 2022
Bending Behaviors in Photoresponsive Liquid Crystalline Polymer Films Derived from a Hockey Stick-Shaped Reactive Mesogen
In this study, we deal with the light-driven motion of liquid crystalline polymer (LCP) films. For an investigation of the photoresponsive properties, the LCP films were fabricated through a photocrosslinking reaction on the surface-aligned LC state of the mixtures of reactive mesogens (RMs) with appropriate mixing ratios. To maximize the photo-induced volume change of an LCP film, a hockey stick-shaped mesogenic group was introduced. Concretely, a novel hockey stick-shaped RM3 has been synthesized in addition to a conventional rod-like RM1 for surface alignment and an azobenzene-based RM2 for photoisomerization. The photo-driven bending behavior for the LCP films, fabricated RM mixture with RM3 (R90A10H5) and without RM3 (R85A10H0), have been compared. Specifically, the relationship between irradiation time and bending angle was investigated. In order to evaluate the cyclic photoresponse behavior of the two LCP films, they were repeatedly irradiated sixtimes with 365 nm and 445 nm light sources. As a result, for the trans-cis photoisomerization by 365 nm irradiation, the bending angle began to change relatively faster in the former than the latter, and reached the maximum angle relatively quickly. For the cis-trans photoisomerization by 445 nm irradiation, the bending angle began to change relatively faster in the former than the latter, and reached the minimum angle relatively quickly. As the irradiation cycle was repeated for the R85A10H5 film, which contained 5 wt% RM3, the pattern for banding motion for the trans-cis isomerization was maintained, whereas that for the cis-trans isomerization becomes faster, and such effect was gradually intensified. Therefore, we confirmed that the introduction of hockey stick-type RM3 fairly affects the bending behavior of the planar-aligned LCP film. Note that the research can provide diversity in motion by seeking complexation of bending motions and discovering novel photoresponse mechanisms by introducing new conceptual structures in the RM.
Keywords:photo-driven soft actuator;liquid crystalline polymer film;planar-surface alignment;hockey stick-shaped RM;photocrosslinking;photoisomerization of azobenzene-based RM