Charged Surface with Ion Adsorption

The Helmholtz free energy of the particle surface, that is, the interface between the surface and the surrounding electrolyte solution, is given by [1-3] 

Biophysical Chemistry of Biointerfaces By Hiroyuki Ohshima Copyright 2010 by John Wiley Sons, Inc. 

Since the change in the Helmholtz free energy of the surrounding electrolyte solution caused by adsorption of N ions onto the particle surface is —Nfx, the total change F, in the Helmholtz free energy of the particle and the surrounding solution is given by 

the second term on the right-hand side, which we denote by F, 

The tension of the interface between the particle and the electrolyte solution is obtained from Eq. (5.7), namely. 

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