Studies on the electrical double layer

Abstract

The differential capacityC of the dropping mercury electrode in contact with nonionic surface active agent solutions was measured by the method described in part 1. The nonionic surface active agents used were the condensation products of lauryl alcohol and ethylene oxides, and the indifferent electrolyte was either 1 N sodium sulphate or chloride. The experimentalC vs.E curves, whereE is the polarizing potential with reference to the electrocapillary maximum, showed anodic and cathodic peaks atE ≅ + 0.25 and − 1.5 V, respectively. The height of these peaks was, in accordance with theLorenz andMockel theory, an increasing function of the surface active agent concentrationc. The monolayer adsorption was clearly indicated by the capacity suppression over the zero polarization range, the monolayer becoming complete atc=10−4 ∼ 10−5 M. The electrochemical free energy of adsorption obtained was an increasing function of the mole numberx of the ethylene oxide in the surface active agent molecule. Whenx was small, the adsorbability was strongly influenced by the indifferent electrolyte, and was higher in the presence of the chloride than the sulphate. Whenx was higher than ca. 30, the effect of the indifferent electrolyte on the adsorbability appeared to diminish.