The Electrical Aspects of Interfaces

It is clear that determination of the change of interfacial tension with solute concentration in dilute solutions provides a way to find the surface excess of the solute. This method has been successfully applied to many two-component systems involving molecules. Application to electrolyte solutions is more complicated but is discussed further below. Before doing so, more details about the electrical aspects of interfaces are outlined. 

The inner potential is further subdivided into the outer potential / and the surface potential that is, 

The outer potential is due to the free or excess charge on the surface of phase a and can be measured experimentally. The surface potential is due to the dipolar distribution of charge at the interface due to the unequal adsorption of ions and orientation of molecular dipoles. It cannot be measured experimentally. Since these quantities are defined with respect to the process of bringing a charged species from infinity into the phase, the surface potential is positive when the positive end of the dipolar charge points toward the center of the solution and the negative end toward charge-free infinity. 

The method of measuring the outer potential of phase a can be described on the basis of a conceptual experiment in which a test charge is brought up to the phase, which bears a net charge q. Assuming that the phase is an isolated sphere of radius r, the potential experienced by the test charge is 

When the outer potential of phase a is zero, it is convenient to define another quantity, namely the real potential. Recalling that the electrochemical potential for species i in phase a is given by 

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Emphasis has been placed on the electrical aspects of interfaces in this chapter. This is especially important in examining the properties of electrolyte solutions at... 

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