Shape programming and photoactuation of interpenetrating polymer networks containing azobenzene moieties

Abstract

Crosslinked liquid-crystalline polymers (LCPs) with photochromic moieties exhibit macroscopic deformation upon irradiation with light. Controlling the 3D shapes of crosslinked LCPs leads to fabrication of photoactuators with desired structures and functions. Here, we investigate the shape memory effects and photoinduced deformation of interpenetrating polymer network (IPN) films composed of azobenzene LCP (PAzo) and poly(methyl methacrylate) (PMMA). PAzo/PMMA IPN films could be temporarily programmed into desired 3D structures with the aid of glass transition. The IPN films with temporary shapes showed high thermal stability compared to pristine PAzo films, which is ascribed to the gradual glass transition behaviour over a wide temperature range. The shape-programmed IPN samples showed various reversible deformation behaviours depending on the programmed shapes upon irradiation with UV and visible light. Furthermore, the thermal stability of temporary shapes allowed reversible photoactuation of shape-programmed samples at elevated temperatures as high as 100 °C. Formation of IPN films is a promising approach to enhance the design and functions of photoactuators consisting of crosslinked LCPs.