Effects of intermacromolecular interactions on diffusion. I. Two-component solutions

Abstract

The effect on the diffusion coefficient of nondissipative interactions between diffusing macromolecules is evaluated for two-component solvent-macromolecule solutions. For linear concentration gradients, the generalized Stokes-Einstein relation is obtained from purely microscopic arguments. Application of these results to a model solution of hard spheres demonstrates new effects of conformational change on the mutual diffusion coefficient. For spatially sinusoidal concentration gradients, such as those observed by quasielastic light scattering spectroscopy, the mutual diffusion coefficient is shown to have an intrisic dependence on the wavelength of the gradient. Consideration of a dilute solution of charged macromolecules illustrates the wavelength dependence of the mutual diffusion coefficient.