Electrophoresis, Electro-osmosis, and Streaming Potentials

Electrically charged particles tend to move under the influence of an electric field. Once again as a first approach to this problem we may set the electrical force acting on a particle carrying unit charge equal to the negative of the differential of the electrical potential, tp. If the particle carries a charge q, then the force is 

When the particle is in a state of steady motion, the two opposing forces are equal so that 

Now the electrical potential (f) at the surface of a sphere of radius a and carrying a charge q is  

For very small particles in dilute solution where the radius of the double layer (l/tf) is large so that Ka — 0, the correction factor f Ka) — 1.0 and equation (6.45) still applies. However, for large particles in more concentrated solution where Ka — (in 

In addition to the above theoretical problems in interpreting electrophoretic data there is also an important experimental 

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The above relationship shows that zeta potenticd is a little lower than the Stem potential and this is because it Is located further out from the surface of the macromolecule. The zeta potential of any colloidal solution can be calculated by electrokinetic measurements like electrophoresis, electro-osmosis and streaming potential. Though the methods are different, all lead to the same calculated value of the zeta potential for any particular system. All the methods involve the relative motion of the two surfaces in contact. 

Electrokinetic phenomena, namely electrophoresis, electro-osmosis and streaming potential are discussed in Vol. 1 at a fundamental level. These effects arise because of charge separation at the interface that is induced for example by application of an electric field. The plane at which the liquid starts to move is defined as the shear plane and the potential at this plane is defined as the electrokinetic or zeta potential. A schematic picture is given that describes the shear plane and zeta potential. The latter is mostly assumed to be equal to the Stern potential and in the absence of specific adsorption it can be equated to the surface potential, which is the parameter... 

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