Van der Waals theory of nematogenic solutions. II. Application to binary solutions with spherical solutes and rodlike solvents

Abstract

The Van der Waals theory of nematogenic solutions derived in Paper I of this series is here applied to binary mixtures with effectively spherical solute molecules and rodlike solvent molecules. Predicted temperature-mole-fraction phase diagrams are shown to be in rather good agreement with experimental data for the systems C${\mathrm{Cl}}_{4}$-$p$, ${p}^{\ensuremath{'}}$-dihexyloxyazoxybenzene (DHAB), (C${\mathrm{H}}_{3}$)$_{4}\mathrm{Sn}$-methoxybenzylidene $n$-butylaniline (MBBA), (${\mathrm{C}}_{2}$${\mathrm{H}}_{5}$)$_{4}\mathrm{Sn}$-MBBA, (${\mathrm{C}}_{3}$${\mathrm{H}}_{7}$)$_{4}\mathrm{Sn}$-MBBA, and (${\mathrm{C}}_{4}$${\mathrm{H}}_{9}$)$_{4}\mathrm{Sn}$-MBBA. On the basis of these calculations, it is argued that when a more or less spherical solute is added to a nematic mesophase, the onset of the nematic\ensuremath{\rightarrow}isotropic phase transition is controlled primarily by excluded-volume effects and the overall strength of the intermolecular attractions in the system.