Photoinduced bending behavior of crosslinked liquid-crystalline polymer films with a long spacer

An acrylate monomer and diacrylate crosslinker containing a spacer of undecylene were synthesized and crosslinked liquid-crystalline polymer films with different crosslinking densities were prepared by photopolymerization of mixtures of the monomer and the crosslinker. Due to the relatively long spacer, distinct bending behavior was observed in the film with a low crosslinking density: when the temperature was lower than 90 degrees C, the film first bent away from the light source and then towards it upon the irradiation of UV light. As the temperature was raised above 90 degrees C, the film bent directly towards the light source. X-ray diffraction was used to probe the phase structures of the film at different temperatures and a plausible mechanism was presented to explain the distinct phenomenon. In addition, when the crosslinking density was increased, all the films bent directly towards the light source with faster speed, which is related to their modulus and order parameters.