Mixtures of associating spherical and chain molecules

Recently, we have investigated the effect of molecular association on the critical and phase coexistence properties of fluids with various off-centre attractive sites. The individual molecules are first represented by hard-sphere repulsive core6 with square-well attractive sites, and a simple van der Waals mean-fleld term is also added to account for the dispersion forces. The equations can be extended to associating mixtures of spherical molecules with off-centre attraction sites. In the limit of complete bonding, chains of hard-spheres are formed. Expressions for mixtures of associating spherical molecules, pure hard-sphere chains and mixtures of chains, are reviewed. These equations are then used to study the effect of chain length on the phase equilibrium properties of non-associating chains. Quantitative comparisons of the theoretical results with experimental data are shown for the critical points of the n-alkane homologous series.