In search of a predictive molecular-based model of nematic solutions

The athermal model of a binary rectangular-parallelepiped fluid, continuous in translations and discrete in orientational distribution, is used for calculations of infinite dilution activity coefficients, γ∞, of nonmesogenic solutes dissolved in nematic and isotropic phases of model nematogens. The particles having D2h symmetry were chosen so as to model molecules of meta- and para-xylenes (nonmesogens) and the first five homologues of 4,4′-alkyloxyazoxybenzenes (nematogens). The calculations of γi∞ (i=m,p denotes isomers of xylene) for various values of the relative temperature, t*, have explicated different characters of the functions γi∞(t*) for the isotropic and nematic phases. The ratio γm∞/γp∞ is less than 1 and practically constant in the isotropic phase, whereas in the nematic phase it holds that γm∞/γp∞>1, the ratio increasing with a decrease in t*. These features agree with experimentally established regularities and confirm the significance of the effect of the particle biaxiality in interpreting the separation of structural organic isomers with the aid of nematic sorbents.