Nematic–isotropic transition in bounded thin films

Abstract

The thickness dependence of the nematic–isotropic transition of a liquidcrystalline thin film bounded by strongly ordering or disordering substrates has been studied through birefringence measurements. In accordance with the thermodynamic Kelvin equation, the transition temperature was found to shift from the bulk transition point by up to a few 10^–1 K upward or downward, depending on whether the substrate was ordering or disordering, as the film thickness was decreased below 100nm. The observed temperature dependence of the order parameter presents a good agreement with the Sheng–Poniewierski–Sluckin mean field theory for both types of substrates, For the ordering substrate, in particular, the present data strongly suggest, still not conclusively enough though, the presence of a critical thickness below which the nematic–isotropic transition is no longer discontinuous.