Multifunctional liquid crystal polymer networks. Azobenzene-based monoacrylate molecules impart a photothermal effect to polymer networks

Stimuli-responsive liquid crystal polymer networks (LCPNs) consisting of azobenzene are mostly studied based on ultraviolet (UV)-induced photochemical isomerization. However, depending on the molecular structure and the degree of UV absorption of azobenzene molecules, the photothermal effect can induce stimuli-responsiveness of azobenzene-based LCPN. In this report, an azobenzene-based monoacrylate (AM) monomer that can be easily introduced into an LCPN is designed and synthesized to develop a multifunctional LCPN that exhibits a photothermal effect. An AM LCPN is successfully fabricated with AM, LC monomer, and thiol groups, and the fabricating process is systematically optimized by controlling the ratio of each component. The thermal, mechanical, and structural behaviors of the AM LCPN are confirmed through various experimental analyses, and the shape memory properties are quantitatively and qualitatively verified via dynamic mechanical analysis and photographs. Thanks to the azobenzene molecules present, the AM LCPN exhibits a photothermal effect under UV exposure, which is demonstrated by macroscopic and spectroscopic experiments. Alignment and self-healing experiments indicate that the AM LCPN can be applied to fields requiring orientation or self-healing property.