Application of the Flory–Huggins theory to nematic-isotropic phase equilibria

Abstract

The Flory–Huggins relations for chemical potentials in a mixture are used to predict temperature–composition phase diagrams for a binary nematic + solute system or a mixture of two nematics. The validity of this simple treatment rests on there being the same degree of long range order present in the nematic phase whenever there is a nematic–isotropic equilibrium. Data on the depression of the nematic–isotropic transition by the solute at infinite dilution give the heat of transition of the pure nematic and the ratio of the limiting activity coefficients for the solute in the nematic and isotropic phases. These quantities are not generally obtainable from data measured at usual finite solute concentrations. A procedure is given which uses a calorimetric value of the heat of transition to correct phase equilibrium data to infinite dilution yielding the ratio of activity coefficients.