Re-entrant behavior of relaxation time with viscosity at varying composition in binary mixtures

In order to understand the long known anomalies in the composition dependence of diffusion and viscosity of binary mixtures, we introduce here two new models and carry out extensive molecular dynamic simulations. In these models, the two molecular species (A and B) have the same diameter and mass. In model I the inter-species interaction is more attractive than that between the pure components, while the reverse is true for model II. Simulations and also mode coupling theory calculations reveal that the models can capture a wide variety of behavior observed in experiments, most interesting among them are the non-monotonic variation of diffusion and viscosity with the composition and the re-entrant viscosity dependence of the relaxation time.