Equilibrium textures in main-chain liquid crystalline polymers

Abstract

We analyse the Schlieren textures formed by the nematic director in a thermotropic main-chain liquid crystalline polymer. After an initial coarsening, the textures reach a stable time-independent state which appears to be an equilibrium function of temperature and material parameters, with a characteristic length scale ξ of order 2 μm. In particular, we study the evolution of this domain size when the temperature approaches the nematic-isotropic transition T_ni. The texture size ξ increases towards T_ni, but decreases reversibly when the temperature decreases back into the nematic phase. We discuss possible theoretical models that may explain such an equilibrium polydomain state of nematic director and the dependence of its size on the nematic order parameter.