The electrolyte double layer surface tension, charge density, and capacity

2 The electrolyte double layer surface tension, charge density, and capacity 

In this chapter the structure of the electrolyte double layer, and the consequences of adsorption on the electrode surface, are described. The effect of differences in structure and electronic distribution of different metals are indicated. The space-charge region in semiconductors is then discussed. Finally some properties of colloids are mentioned, given that they possess an interfacial region very similar to an electrode. 

The proportionality constant between the applied potential and the charge due to the species ordering in the solution interfacial region is the double layer capacity. The study of the double layer capacity at different applied potentials can be done by various methods. One much used is the impedance technique, which is applicable to any type of electrode, solid or liquid, and is described in Chapter 11. Another method uses electrocapillary measurements. It was developed for the mercury electrode, being only applicable to liquid electrodes, and is based on measurement of surface tension. 

The principle of electrocapillary measurements was described more than a century ago by Lippmann9. It is a null-point technique that counterbalances the force of gravity and surface tension, and highly accurate results can be obtained. 

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