Liquid Crystalline Anisotropic Gels Based on Azobenzene-Containing Networks

Abstract

A method is described using optical alignment of azobenzene groups to prepare liquid crystalline anisotropic gels. We demonstrate that anisotropic gels with uniform liquid crystal orientation can be obtained by performing thermal polymerization of a homogeneous mixture composed of a nonreactive nematic liquid crystal BL006 and a reactive nonmesogenic diacrylate monomer bearing azobenzene groups while the mixture is exposed to linearly polarized light. Infrared dichroism measurements show that this liquid crystal orientation is recoverable upon repeated cycles of heating the sample into the isotropic phase followed by cooling it to the nematic phase. In this method, the optical alignment of azobenzene monomer and, as a result, of liquid crystal molecules before and during the polymerization replaces the surface alignment or electric and magnetic fields, which are usually used to prepare anisotropic gels. Anisotropic gels were obtained from two diacrylate monomers that lead to networks having azobenzene groups as part of main chain and side groups.