Photoinduced Bending Behaviour of Cross-linked Liquid Crystalline Polymers with High Cross-linking Densities

Highly cross-linked liquid crystalline polymer (CLCP) films with a long spacer and azobenzene chromophores (of varying concentrations and positioned differently) were prepared. The effects of various factors on the photoinduced bending behaviour of the highly CLCPs were explored. Long spacer groups and high cross-linking density resulted in considerably faster bending of the CLCP films relative to those reported in the literature that feature shorter spacer groups and smaller cross-linking densities. The azobenzene chromophores at the cross-linking points significantly influenced the photoinduced bending behaviour of the CLCP films relative to those at side chains. Furthermore, reduced concentrations of the azobenzene chromophores produced faster bending and larger photoinduced stress of the CLCP films that contained chromophores at the side chains as opposed to those incorporating chromophores at the cross-linking points. Moreover, the CLCP film with relatively low azobenzene concentration and small thickness exhibited bending in the reverse direction following maximum bending under continuous UV irradiation, thereby showing that photomobile behaviour of the material system.