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

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${\mathrm{Cl}}_4$-$p$, $p^{\prime }$-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→isotropic phase transition is controlled primarily by excluded-volume effects and the overall strength of the intermolecular attractions in the system.