Structure and texture of anisotropic nematic gels.

Abstract

Anisotropic nematic gels are prepared via in situ polymerization of diacrylate monomers in an oriented nematic liquid crystal (LC) matrix. The structure of the gels is studied from micrometer to nanometer scales by optical microscopy, small angle neutron scattering, and theta/2theta light scattering. A strong anisotropy is evidenced at all scales without electric field for both mesogenic and nonmesogenic monomers. The gel network can be pictured as an ordered but strongly distorted and polydisperse structure with two characteristic sizes: the mean size of the polymer objects and a correlation length between these objects, corresponding to the mean-size of the LC domains, which are estimated from neutron and light scattering results to be of the order of some tens of nanometers and some micrometers, respectively. Moreover, a sheet-like structure of the polymer network is evidenced. When an electric field is applied, one part of the LC switches while the other part remains anchored to the polymer network. The electric field dependence of the volume fraction of anchored LC is estimated from the analysis of the light scattering data. We emphasize systematic correlations between structure and electro-optical properties of the gels.