Virial Coefficients and Demixing of Athermal Nonadditive Mixtures

Abstract

We compute the fourth virial coefficient of a binary nonadditive hard-sphere mixture over a wide range of deviations from diameter additivity and size ratios. Hinging on this knowledge, we build up a y expansion [B. Barboy and W. N. Gelbart, J. Chem. Phys. 71, 3053 (1979)] in order to trace the fluid-fluid coexistence lines which we then compare with the available Gibbs-ensemble Monte Carlo data and with the estimates obtained through two refined integral-equation theories of the fluid state. We find that in a regime of moderately negative nonadditivity and largely asymmetric diameters, relevant to the modelling of sterically and electrostatically stabilized colloidal mixtures, the fluid-fluid critical point is unstable with respect to crystallization.

Virial coefficients, thermodynamic properties, and fluid-fluid transition of nonadditive hard-sphere mixtures

“…Of course, when nonadditivity is introduced, the five approximations differ from each other. Figures 1-6 show the comparison of the values of the composition-independent fourth virial coefficients, as given by the five theoretical proposals considered in this paper, with the recent data of Pellicane et al 17,24 One can immediately see that in the cases of B 1112 and B 1222 the best overall performance is the one of the nlMIX1 theory, followed closely by Hamad's approximation. Also worth noting is that the mMIX1 theory already does a very good job, especially for the smaller size ratios, while the original MIX1 theory gives the poorest agreement.…”

“…First, the theoretical predictions of the composition-independent fourth virial coefficients have been tested against new available Monte Carlo data. 17 In the cases of B 1112 and B 1222 , the best overall agreement with the Monte Carlo values are obtained with the nlMIX1 theory, followed by Hamad's proposal. As for B 1122 , none of the theories does well at high asymmetry and nonadditivity, the discrepancies being especially important in the case of Hamad's approximation.…”

Population Inversion of a NAHS Mixture Adsorbed into a Cylindrical Pore

“…NAHS pair potential has been successfully applied to the study of the morphology of composite polymer particles 30 , the solubility of molecu-lar additives in different solvents 31 , the microstructure of micelles 32 , and for the description of gas-gas phase transition at high pressure observed in mixtutes of rare gases 33 . Here we use the NAHS as a simple way of modelling affinity between particles of the same species and phobicity for particles of a different one 22,23,24,34,35,36,37 , such as, for example, a colloidal phase of oil interacting with a water soluble polymer. The model distinguishes between two species (A and B) by defining a closest approach distance between two particle of species i and j, σ ij , as follows:…”

Fourth virial coefficients of asymmetric nonadditive hard-disk mixtures

“…Later, a unified framework for some of the most important theories (including some generalizations) of the equation of state of d-dimensional nonadditive hard-core mixtures was presented. 35 The framework was used for d = 3 to compare the results of the different approaches with simulation data for the fourth virial coefficients that had recently been derived 36 and with simulation data for the compressibility factor. It was also used to examine the issue of fluid-fluid demixing.…”