The Surface of Shear and Viscoelectric Effect

The surface of shear is the location within the electrical double layer at which the various electrokinetic phenomena measure the potential. We saw in Chapter 11 how the double layer extends outward from a charged wall. The potential at any particular distance from the wall can, in principle, be expressed in terms of the potential at the wall and the electrolyte content of the solution. In terms of electrokinetic phenomena, the question is How far from the interface is the surface of shear situated and what implications does this have on the relation between measured zeta potential and the surface potential  

the very existence of a surface of shear implies some interesting behavior within the fluid phase of the system under consideration. In our discussion of all electrokinetic phenom- 

8a Viscoelectric Effect and Its Influence on Electrophoretic Mobility and Zeta Potential 

How must the expressions derived in the sections above be modified to take into account the variation in rj and the finite distance over which it increases The answer is that rj — the viscosity within the double layer —must be written as a function of location. Our objective in discussing this variation is not to examine in detail the efforts that have been directed along these lines. Instead, it is to arrive at a better understanding of the relationship between f and the potential at the inner limit of the diffuse double layer and a better appreciation of the physical significance of the surface of shear. 

Measurements of the viscosity of organic liquids in the presence of an electric field reveal that there is an increase in viscosity in high electric fields that is described by the expression 

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