Electrokinetic Phenomena and the Saxen Relations

Electrokinetic phenomena are due to the coupling between electrical current and matter flow. Consider two chambers, 1 and 2, separated by a porous wall. If a voltage V is applied between the two chambers (Fig. 16.4), a current will flow until a pressure difference Ap is established at the steady state. This pressure difference is called the electroosmotic pressure. Conversely, if a fluid flow J from one chamber to another is achieved by a piston, an electric current I, called the streaming current, flows through the electrodes. As before, the thermodynamic description of these effects begins with the expression for the entropy production under the conditions specified above. In this case we essentially have 

In these equations the superscripts refer to the two chambers Zk is the ion number of the component k, F is the Faraday constant, and 4 is the electrical potential. For a relatively small difference in the pressure between the two chambers, since = Vk, the partial molar volume, we may write 

Experimentally, the following quantities can be measured The streaming potential 

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