Theoretical Study of Nematic to Isotropic Transition in Porous Media

Abstract

Experimental observations show that the N-I transition temperature (TNI) for liquid crystals embedded in solid porous materials is lower compared to that of the bulk liquid crystals and TNI is reduced linearly with the inverse pore diameter. To explain this, various theoretical studies have been proposed. We propose to use the mean field approach. We modify the Maier-Saupe mean field theory to include the disordering effects of porosity as a disordering surface potential. A molecule near the surface is assumed to feel the mean field potential (the Maier-Saupe type) and also the surface induced potential. We calculate the values of the nematic order parameter and hence find the TNI for different pore diameters. The weighted average of the order parameter is calculated considering the cylindrical symmetry of the pores. Our calculations on the variation of TNI with pore diameter agree with experimental data. Also, the calculated values of specific heat peak decrease with decrease in pore radius, in agreement with experimental trends.