SIMULATION STUDIES ON MIXTURES OF POLARIZABLE DIPOLAR AND POLARIZABLENONPOLAR LINEAR-MOLECULES

In a previous paper liquid-liquid phase separation had been determined for mixtures of dipolar and non-polar two-centre Lennard-Jones molecu les of elongation L = 0.505. Here we present isobaric-isothermal molec ular dynamics simulation results for mixtures of dipolar with non-pola r molecules where either the non-polar component (I) or both component s (II) were made polarizable. The proper treatment of many-body induct ive interaction effects, especially in mixtures of polarizable non-pol ar with dipolar components, show that these inductive forces play an e ssential role in understanding the thermodynamics and phase behaviour of real polar mixtures. The state point was chosen to be T = 1.539, p = 5.617 and mu(*2) = 8, where in non-polarizable polar-non-polar mix tures phase separation had been detected previously. Excess Gibbs ener gies as a function of composition are obtained directly by the lambda- coupling method for mixtures of type I. With increasing polarizability of the nonpolar component the demixing disappears and the excess func tions show more symmetrical behaviour. The excess values for Gibbs fre e energy, enthalpy and volume have been determined directly from the s imulation data, and are given as functions of the composition of the d ipolar component. For type II mixtures excess volumes show a more symm etrical shape in comparison with type I, although the uncertainties of the simulation results are quite large.