Electrical double layer formation, free energy

The aim of this paper is not to add to the current debate but to present a simple graphical method of analysing the free energy of formation of the electrical double layer at the oxide/solution interface ( 1). This will provide a simple way of visualizing the complementary roles of chemical reactions or surface properties of... 

To get the interaction potential we must first evaluate the free energy of formation of the electrical double layer between two charged bodies. This is defined as the work done in charging up the surfaces. The process by which uniformly charged surfaces are charged up from a neutral reference state has been discussed by Yerwey and Overbeek [4], who have shown that the electrostatic work of charging a surface is given by the simple formula... 

If a bar of zinc is dipped into a diluted solution of zinc sulphate, some zinc ions, Zn2+, dissolve, leaving two electrons each on the metal. This causes a separation of charge, and eventually (Fig. 9.1) equilibrium is achieved. An electrical double layer forms, which consists of electrons on the metal surface, and zinc ions immediately adjacent to it. At this stage, the tendency to dissolve is exactly matched by the tendency of zinc ions to deposit, which is caused by the charge separation. This means that there is a potential difference between metal and solution, which, however, cannot be measured. If the potential difference could be measured, we would have a direct measure of the free energy of formation of hydrated zinc ions ... 

Ruckenstein (Ruckenstein and Chi, 1975 Friberg and Venable, 1983 Flanagan and Singh, 2006) explored the stability and size of microemulsion domains based on a thermodynamic approach where interactions (Van der Waals forces, electric double layer potential, and free energy and entropy of formation) were considered. He studied the dependence of the free... 

In 3 the case has been treated, where the interface bears an electrical double layer and independent of the way of formation of the double layer (polarizable interface or reversible case) the free energy can be written (see cq (24) p 122 and (29) p. 123) ... 

We recall that the first integral in Equation 23a represents the change in electrical free energy in forming the diffuse double layer. This contribution to f, the free energy of formation of the charged interface, is positive and hence represents an unfavourable component which opposes the formation of the charged interface. 

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