Photoalignment in Polysiloxane Liquid-Crystalline Elastomers with Rearrangeable Networks

Molecular alignment in liquid-crystalline elastomers with polysiloxane backbone is controlled with the aid of photoalignment and exchangeable links to enhance performance as photoactuators. The photoalignment is triggered by trans-cis-trans isomerization of azobenzene moieties, which are introduced at crosslinking points, upon irradiation with linearly polarized UV (LPUV) light under heating. The induced alignment is memorized by rearrangement of network structures through exchange reactions of covalent bonds. When irradiated with LPUV light, freestanding films show bending along with the alignment change in surface regions. Macroscopic shapes are also rememorized by exchange reactions at crosslinks. Combination of photoalignment and network rearrangement allows continuous deformation of freestanding films upon exposure to LPUV light with varying polarization directions. This approach enhances the degree of freedom in alignment control, photoactuation, and reshaping of polysiloxane-based liquid-crystalline elastomers, which are feasible as soft actuators.

Automated summary

This study demonstrates enhanced performance of liquid-crystalline elastomers as photoactuators through molecular alignment control using photoalignment and exchangeable links, allowing continuous deformation under LPUV light. The memory of macroscopic shapes through exchange reactions at crosslinks increases the degrees of freedom in alignment control, photoactuation, and reshaping.