Effects of intermacromolecular interactions on diffusion. II. Three-component solutions

The effect on the diffusion coefficient of nondissipative interactions between diffusing macromolecules is considered for three-component solutions containing solvent and two species of macromolecules. The spectrum of light scattered quasielastically from a system containing two species of interacting Brownian molecules is calculated. Treatment of a dilute minimum-salt protein solution as a three-component system indicates a possible way of performing light scattering measurements on charged species which do not scatter light. Extension of the techniques of paper I of this series to include the effect of interspecies interactions clarifies the relation between the tracer and mutual diffusion coefficients as these have been defined by different authors. This extension also provides a criterion for phase separations in three-component solutions.