Adsorption of quaternary ammonium ions at the mercury-solution interface: Part II. Rearrangement of the adsorbed film

Abstract

A detailed explanation of the major features of the differential capacitance curves for a number of long chain quaternary ammonium halides is undertaken. The curves show both anodic and cathodic capacitance peaks, the former being ascribed to a desorption process. A variety of evidence, including frequency dispersion measurements, is advanced to show that the cathodic peaks, however, are spurious effects caused by the double layer rearranging at negative potentials. The movement of charge in the compact layer as the rearrangement takes place gives rise to a low impedance, which a simple series R-C circuit analogue interprets as a large capacitance, thus generating a peak. A model for the rearrangement has been developed which successfully explains the integral capacity behaviour, and from which an electrical analogue for the double layer may be derived to interpret the impedance behaviour at the potential of the rearrangement. This model fits the variable frequency impedance data extremely well over the audio frequency range considered (260 Hz−15 kHz), although it is restricted at a quantitative level to those compounds which most nearly form a perfect monolayer. The differential capacity curves derived from this model show no cathodic peak.