Mutual and self-diffusion in fluids undergoing strong shear.

Abstract

We derive a Green-Kubo relation for the mutual diffusion tensor (MDT) of a binary fluid mixture subject to a strong Couette shear field. We calculate the MDT of a Lennard-Jones (LJ) mixture and the self-diffusion tensor (SDT) of a pure LJ fluid as functions of state point and strain rate. The qualitative dependence of the diffusion tensors upon these variables is explained in greater detail by analyzing the velocity and mass current autocorrelation functions. Finally, we compare the zero-color field color conductivity with the SDT. For nonzero shear rates we find that the color conductivity and the SDT are different, confirming the prediction by Evans, Baranyai, and Sarman [Mol. Phys. (to be published)], according to which these two transport coefficients should only be related at zero shear rate.