Ion Transport and Oscillatory Phenomena Across Adsorbed Monolayers at the Amalgam/Water and Mercurous Halide/Water Interfaces

Abstract

AbstractThis paper presents a method for the study of the transport of ions (K+, Na+, Cs+, Cl−, Br−) across adsorbed monolayers at the respective amalgam/water and mercurous halide/water interfaces. The method involves cathodic formation and anodic stripping (inverse polarography) of amalgams and in the reversed order (anodic formation) of mercury halides. Galvanostatic measurements were performed using a stationary mercury drop electrode, a platinum counter electrode and a Ag/AgCl reference electrode. Phase sensitive ac polarography was employed to determine the differential capacity of the electrical double layer in the presence of adsorbed monolayers. Adsorbed monolayers of octadecyltrimethylammonium and of eicosanyltrimethylammonium ions have different permeabilities towards the various cations; cesium ions are the most permeable. The transport of Cl− and Br− was studied across adsorbed monolayers of long chain quaternary ammonia and carboxylic acids and of polyglutamic acid at the mercurous halide/water interface. The anionic permeability depends on the type of anion, the composition of the monolayer, and the charge density of the monolayer and the interface. Ion transport is correlated with the packing in the monolayer. During the anodic stripping of potassium and sodium amalgams in the presence of octadecyltrimethylammonium chloride, and potassium, sodium and cesium amalgams in the presence of eicosanyltrimethylammonium chloride, sustained oscillations of the electrode potential were observed. The frequency varies from about 0.3 to 1.0 Hz, and depends on the current density, the duration of the anodic stripping, the composition of the monolayer, and the temperature. The amplitude of the oscillations varies from 100 to 500 mV. These oscillations involve the following processes: potential build‐up across the monolayer, monolayer rupture (hole formation), followed by hole closure. The oscillations were detected also by instabilities in the measurements of the differential capacity.