Self-diffusion in multi-component glass-forming systems

Self-diffusion in multi-component glass-forming systems including fragile and strong glasses is studied from a unified viewpoint. A simple analytic form of long-time self-diffusion coefficient DSL is proposed. The equations for the mean-square displacements recently derived for two types of systems, (S) suspensions of colloids and (M) molecular systems, from a first principle by employing the Tokuyama–Mori projection-operator method are used to define DSL in each type formally, both of which are uniquely determined by the correlation function of the fluctuating forces. Analyses of the correlation functions in two types in terms of many-body interactions thus lead in type (M) to DSL(λ)≃κ−1(λc/λ)(1−λ/λc)2, where λ is a control parameter, such as an inverse temperature and a volume fraction. Here κ is simply written in terms of the potential parameters and λc an adjustable parameter to be determined. The predictions for λ dependence of DSL in multi-component glass-forming systems are in excellent agreement with available experimental data and simulation results in equilibrium states.