Polarization Controlled Photomechanical Behaviors of Polydomain Azobenzene Liquid Crystalline Polymer Networks

We report the polarization controlled photomechanical behaviors of azobenzene liquid crystalline polymer networks (azo-LCNs) as a function of crosslink density and temperature. High modulus, glassy polydomain azo-LCNs were synthesized by copolymerizing RM257 and 2-azo, initiated by 1 wt{\%} of the inorganic photoinitiator Irgacure 784. Crosslinking density of azo-LCNs increases from 2.09 mol/dm$^{3}$ to 7.24 mol/dm$^{3}$ with curing time from 1-120 min. Storage modulus and loss tangent of azo-LCNs also increase with crosslinking density. All azo-LCNs are glassy at room temperature. To increasing temperature, E' begins to decrease through T$_{g}$ to a level dependent on the crosslinking density, and eventually reaching a rubbery plateau region. Interestingly, the bidirectional (forward and reverse) bending angles of the polydomain azo-LCN cantilevers at equilibrium decrease with increasing temperature and crosslinking density. Absorption and bending behaviors of the azo-LCNs with various thicknesses, concentrations and molecular structure of azobenzene monomer will be discussed.