Electroviscous forces on a charged particle suspended in a flowing liquid

The force on a charged solid particle (of general shape) suspended in a flowing polar fluid (e.g. an aqueous electrolyte solution) in the presence of a solid bounding wall (of general shape) is obtained for the situation in which the electrical double-layer thickness is very much smaller than the particle size (and the distance between particle and wall). The very general results so obtained are applied to the sedimentation of a charged spherical particle in an unbounded polar fluid (with no walls present) for which the drag force is found to be in complete agreement with Ohshima et al. (1984). However, there is disagreement between the present results and those obtained in a number of published papers owing to incorrect assumptions being made in the latter as to what physical mechanism gives rise to the dominant contribution to the electroviscous force on the particle.