State For Hard-sphere Mixtures Research Articles

Partial molar volume of tertiary amines in methanol at T = 298.15 K. Solvation, shape and specific interactions

Limiting partial molar volumes for six tertiary amines in methanol were obtained from accurate experimental density data at 298.15K. Data analysis has been performed using the “non H-bonded methanol” approach and a model obeying the accurate Mansoori et al. equation of state for hard sphere mixtures. Volumetric contributions for the specific interaction between the lone pair of electrons of the amine group and the methanol have been obtained. Aliphatic hydrocarbons were used as reference compounds to account for the destruction of the methanol structure and non-polar solute-solvent interaction. Three types of differently shaped aliphatic hydrocarbons were considered aiming at analyzing the effect of the solute structure. Specific interactions between tertiary amines and methanol could then be derived. Hydrocarbons which are homomorphic forms of the amines were chosen as reference.

Empirical expressions of the pair correlation functions at contact and equation of state of the liquid hard-sphere mixtures at large size ratio

The virial–pressure equation of state of hard-sphere mixtures in the colloidal limit obtained from ad hoc expressions of the contact values of the pair correlation functions and the related question of the fluid–fluid phase separation are revisited. The sensitivity of the location of the binodal to the exponential behaviour of the contact value of the big spheres pair correlation function and its size ratio dependence are analyzed by considering a model for the mean force potential that is used to parameterise the contact value. Agreement with simulation data or accurate integral equations theories is improved when compared with previous approaches based on the virial–pressure equation of state.

The equation of state of soft repulsive spherical molecules

A non-perturbational method is proposed by which the compressibility factors of ensembles of soft repulsive spheres can be estimated. A distribution function for the effective collision diameter is derived from the Maxwell velocity distribution. This distribution function is used in connection with an equation of state for hard-sphere mixtures to calculate the thermodynamic properties of soft repulsive spheres. The predicted compressibility factors are compared to the results of the Weeks-Chandler-Andersen perturbation theory and Monte Carlo simulation. The new method, which does not require explicit information about radial distribution functions, agrees reasonably well with the simulation results.