BROWNIAN-MOTION OF ROD-SHAPED COLLOIDAL PARTICLES SURROUNDED BY ELECTRICAL DOUBLE-LAYERS

Using photon correlation spectroscopy, translational diffusion coefficients of electrostatically stabilized rod-shaped colloidal particles (tobacco mosaic virus, TMV) have been determined. The diffusion constant is that of a neutral rod at high and low electrolyte concentrations, but is reduced by a few percent when the electrical double layer thickness is comparable to the radius of an equivalent sphere. The reduction in diffusion constant depends both on the charge on the rod and the sizes of the ions in the double layer. The experimental findings are in qualitative agreement with a theory of Vizcarra-Rendon et al., indicating that at the salt concentrations used, TMV behaves like a model colloidal particle. The effective charge on the individual TMV particles is obtained as a fitted parameter, and an estimate of the zeta potential of the TMV particles is also made.