Mutual and self-diffusion in concentrated α-crystallin protein dispersions. A dynamic light scattering study

Abstract

The theory of Brownian motion has not yet reached the point where the dynamic properties of concentrated colloidal dispersions can be computed. This is mainly due to the complicated nature of many-body hydrodynamic interactions and difficulties in considering memory effects. Here we present mutual and self-diffusion coefficients for concentrated alpha-crystallin protein dispersions measured by the photon correlation technique. These measurements are compared to theoretical predictions considering only 2-body hydrodynamic interactions or screened hydrodynamic interactions without memory effects. While the limit of applicability of these theories is restricted to low concentrations, it is seen that the (long-time limit) self-diffusion follows the dispersion inverse viscosity and that mutual diffusion increases almost linearly with concentration. Although the dynamic behaviour observed may result from an accidental coincidence, similar tendencies have been reported by other authors and they could be used (with caution) as simple empirical rules for estimating diffusion coefficients in the high-concentration range.