Effect of capillary waves on the double layer capacitance of the interface between two immiscible electrolytes

The effect of capillary waves on the double layer capacitance of the interface between two immiscible electrolytes has been studied. We have found that a corrugation of the interface due to capillary waves leads to an increase in the capacitance, as compared with the Gouy–Chapman result for a flat interface. The theory offers a concept of a roughness function, R0, which determines the deviation of capacitance from the Gouy–Chapman result. R0 is a function of Debye lengths of the two immiscible electrolytes. Analytical expression for the roughness function has been derived which shows a strong dependence of R0 on the interfacial tension and the dielectric constants of contacting solutions. Predictions amenable to experimental tests have been discussed. © 1999 Elsevier Science Ltd. Al