chapter  6
44 Pages

ELECTROKINETIC PHENOMENA AND ELECTROCHEMICAL SEPARATION METHODS

We saw in chapter 5 that at the interface between a charged solid phase and an electrolyte solution, there is a volumic distribution of excess charge in solution that can be modelled using the Gouy-Chapman theory. We have so far considered electrolyte solutions next to polarised metals or semi-conductors, but interfaces of interest also include for example: ∑ the surfaces of metal oxides in solution, such as those illustrated in Figure 6.1,

for which the surface charges depend on the pH of the solution ∑ soft interfaces formed by self-assembled layers e.g. soap bubbles, lipid bio-

membranes ∑ the surface of ion exchange resins, etc. Electrokinetic phenomena are associated with the movement of an electrolyte solution near a charged solid, and in fact four types can be distinguished. Electro-osmosis is the phenomenon associated to the movement of an electrolyte solution near a charged interface under the influence of an electric field parallel to the surface. Electro-osmosis has many applications, one of the most recent being electrophoresis in a silica capillary.