Equal G analysis of ternary liquid-crystalline systems

Abstract

The equal Gibbs energy analysis of binary liquid-crystalline systems can predict, to a high degree of accuracy, the phase diagram of the binary system. We extend this analysis to ternary systems. Two systems of homologous dialkyloxy-azoxybenzenes were studied. In particular we studied the mixtures 6-1-5 and 6-4-5, where the number denotes the number of carbon atoms in the terminal alkyl chain. The experimental temperature-composition phase diagrams were determined by differential scanning calorimetry and by optical microscopy using a ternary contact method as well as individual compositions. Both the crystal-nematic and nematic-isotropic phase regions were studied. The first mixture is highly non-ideal, whereas the second is almost ideal. The form used for the excess Gibbs energy was

This particular form, where x, y and (1 - x - y) are the molar fractions of the three components and A_ijk are the interaction parameters, either binary or ternary, looks at the origins of the excess Gibbs energies from the view of the three binary systems and a ternary perturbation. A method of treating ternary solid solution-liquid phase equilibria is introduced and discussed. The success of the method and the relative magnitudes and meanings of the parameters are discussed.