Theory of the Streaming Potential

Abstract

BOOTH¹ has recently pointed out the unsatisfactory nature of the existing theory of electrokinetics, and suggested modifications to the commonly used equations of Helmholtz² and Smoluchowski³, with particular reference to the phenomenon of electrophoresis. I have devoted some attention to the theory of the streaming potential difference set up in the plane of flow when an electrical double layer, existing at an immobile interface in an ionic liquid, is sheared. This potential difference will tend to resist the flow of the liquid owing to the electrical retarding force acting on the ions of the double layer. It has been shown^4,5 that in narrow channels this electrical resistance to flow, or ‘electroviscous resistance', can assume considerable importance, with the result that the apparent viscosity of a liquid in such channels may be increased several fold, depending on the values of the electrokinetic potential of the double layer, the specific conductivity of the liquid in the channel, and the dielectric constant. Various workers^6–8 have reported the qualitative observation of such an effect, and a quantitative experimental examination of the subject has been commenced in this laboratory.