Alignment Memory of a Nematic Liquid Crystal and Thermal Isotropization of the Surface Adsorbed Layer06/15/2008
We use a digital image analysis of the schlieren textures to study the effect of memory of the surface anisotropy in a nematic-liquid-crystal cell and establish its relation to the surface adsorbed molecular layer. The anisotropy is induced on an isotropic glass surface by a flow of the nematic liquid. The proposed technique allows us to quantify the alignment and its changes under the effect of temperature. The temperature at which the memory of the alignment texture is lost is interpreted as the temperature of the full isotropization of the initial anisotropic surface layer adsorbed during the flow: the molecules oriented along the flow are thermally desorbed whereas newly adsorbed bulk molecules have isotropic distribution. The measured temperature dependence of the director alignment texture is used to estimate the adsorption energy of the liquid-crystal molecule onto the surface.