The nematic to isotropic transition of a liquid crystal in porous media

An experimental study of the effect of disorder on the nematic to isotropic (N–I) transition of a liquid crystal is reported. Differential scanning calorimetry is used to monitor the N–I transition of p-azoxyanisole in a series of controlled pore glasses. An increase and a decrease in the N–I transition temperature is observed with varying pore sizes. The direction of the temperature shift depends on the pore size. The observed increase in the transition temperature can be attributed to surface induced ordering, while the observed decrease can be explained as a result of the interruption of the orientational correlation of the liquid crystalline order due to confinement in pores. These results agree, qualitatively, with Monte Carlo results showing that quenched disorder can lower the transition temperature, round and lower the heat capacity peak, and change the order of the transition.