THE MUTUAL DIFFUSION-COEFFICIENT FOR THE VAN-DER-WAALS BINARY MIXTURE OF TYPE-I

In the framework of the mean-field kinetic variational theory, the explicit dependence of the mutual diffusion coefficient of the van der Waals binary mixture with composition and interaction parameters is obtained. The different kinds of behavior shown by this coefficient can be classified according to the scheme of van Konynenburg and Scott devised to describe the global phase diagram of this model mixture. A numerical study to understand the concentration dependence of the mutual diffusion coefficients for mixtures of type I is presented here, in terms of molecular masses, sizes, and interaction parameters. Moreover, the behavior of the mutual diffusion coefficient of the van der Waals mixture is compared with that of a hard-sphere mixture. In addition, a comparison is made between our calculations and experimental data of binary systems classified as belonging to type I: H2O/D2O, hexane/heptane, toluene/hexane, and benzene/hexane. From the explicit model presented here, one can obtain semiquantitative explanations of the role played by the variables that determine the concentration dependence of the mutual diffusion coefficient.