Liquid crystalline anisotropic gels prepared from optical alignment:: Polymer network formed in the isotropic phase

Anisotropic gels were prepared through the induction of a long-range liquid crystal (LC) orientation by the action of an anisotropic polymer network formed in the isotropic phase. The method uses a mixture composed of a nonreactive nematic Liquid crystal and a reactive diacrylate monomer bearing azobenzene groups. When thermal polymerization is carried out in the isotropic phase while the mixture is exposed to linearly polarized light, an anisotropic polymer network can be obtained as a result of the optical alignment of either the azobenzene monomer or the azobenzene moieties on the network. By holding the irradiation, the anisotropy of the network is preserved in the isotropic phase, and upon cooling, the network is able to induce a long-range LC orientation in the nematic phase. Subsequent heating of the sample into the isotropic phase, with irradiation turned off, can no longer randomize the azobenzene network, which leads to the LC orientation recovery once the sample is cooled to the nematic phase. The orientation recovery is complete or partial depending on the concentration of azobenzene monomer, the nematic LC used, and the polymerization temperature.