An Equation for the Surface Pressure of Long Chain Electrolytes Taking lnterionic and Vander Waals Attractions into Consideration

Starting from an equation similar to that proposed by Volmer and Frumkin for the surface pressure of neutral long chain molecules, an equation has been derived for the surface pressure of long chain electrolytes at oil/water interface taking electrostatic repulsion and interionic attraction into consideration. The equation may be written as follows 

π=2n₀kT In \(({A{} \over A-A_0})\)+(exp ^(A-A₀)a/A-1) n₀kT In +\({n_0kT{} \over 2}\) ln f

where n= \({1{} \over A}\) represents the number of long chain ions adsorbed per unit area of the interface, f their mean activity coefficient and A₀= \({1{} \over n_0}\) the other terms have their usual significance. Experimental evidence available in the literature has been cited in support of this equation.