Anomalies in the self-diffusion coefficient near the critical point

Abstract

In this paper we calculate the contribution Ds to the self-diffusion coefficient D0 from the coupling of solute motion to solvent density fluctuations in an infinitely dilute near-critical binary mixture using the methods of fully renormalized kinetic theory in the disconnected approximation. The expression for Ds is found to be similar to mode-coupling expressions for diffusion coefficients in dense or supercooled liquids. As a function of the solvent density ρ, and along the critical isotherm, D0 exhibits an anomalous decrease in the vicinity of the critical point that originates in the vanishing of Ds according to the scaling relation Ds∼(ρ−ρc)2, where ρc is the critical density. An analogous decrease in D0 has recently been observed in the simulations of Drozdov and Tucker [J. Chem. Phys. 114, 4912 (2001)] on a neat liquid of Lennard-Jones particles, and has been ascribed to local density inhomogeneities in the medium.