Double layer capacity studies of adsorption at mercury-solution interfaces effects of expanding and receding surfaces stability of oriented langmuir monolayers

Abstract

Double layer capacity measurements were performed on aqueous solutions of n-octyl alcohol, n-nonanoic acid, and n-butyric acid with a pendant mercury drop electrode capable of expansion or recession. No appreciable differences of double layer capacity were observed whether the mercury drop was formed by expansion or by recession. Temporary differences are probably due to different rates of approach to equilibrium rather than to structural differences. A Langmuir isotherm is applicable for n-nonanoic acid at concentrations below two-thirds of saturation. Beyond that concentration there is evidence of multilayer adsorption. Compressed, oriented Langmuir monolayers of palmitic acid on mercury-coated platinum are found to reach the same equilibrium state as bare mercury-coated platinum. The double layer capacity of an oriented monolayer of palmitic acid is 4.3 μf. /cm 2. at the potential of maximum adsorption, as measured against 0.1 M NaClO 4.