We have already derived a few models for evaluating (Energy per unit surface area) using some approximations in the previous chapters. Let us consider the Gouy-Chapman model for a symmetric electrolyte. So, the expression for  now becomes,

where,

If the two surfaces have unequal potentials, and  (viz and ), the expression for GEL becomes:

It is important to note that the Electrostatic repulsion (G^EL) decreases, and k^-1 increases as the solute concentration increases (n_o). As we'll see later this decrease in repulsion favors coagulation of colloidal particles.

For the Van-der Waals attraction term (for flat plates) we know that,

where  is the Hamaker constant for the system.

Therefore, the total energy could be written as:

(10.1)