Applications of fluctuation transport theory

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Abstract
It is shown that linearized theories of fluctuation transport cannot be self‐consistently applied to most dynamic light‐scattering experiments on particles whose characteristic nearest‐neighbor spacing is comparable to or larger than the reciprocal of the scattering wave vector. The electrophoretic mobility of concentration fluctuations in protein–counterion solutions without excess salt is shown to have the opposite sign of the protein mobility and to increase through zero as a function of added salt. Effects of coupling between charge and concentration fluctuations are considered, and the magnitude of these effects on the fluctuation mobility is estimated for solutions of bovine serum albumin. Several dramatically anomalous experimental effects are predicted, and relevant published reports of dynamic‐light‐scattering determinations of fluctuation diffusion coefficients and electrophoretic mobilities are compared with the predictions of fluctuation transport theory.