The case of two-dimensional phase transitions involving surfactants at the water—mercury interface

Abstract

Many organic surfactants, which are dissolved in an aqueous electrolyte in contact with a mercury electrode, adsorb in the form of compact monolayer films which are strongly stabilized by lateral attractions of the Fowler—Frumkin type. For some systems, a two-dimensional phase transition separates two distinct phases, which are characterized by different molecular orientations and may be either liquid- or solid-like monolayers. The elucidation of the nature and properties of the adsorbed layers is based on experimental results obtained at equilibrium as well as under non-steady state conditions. Adequate potential-step programmes have been used successfully to trigger either a surface solidification, which is controlled by a nucleation and growth mechanism, or a melting process which appears to emanate from line defects of the initial solid-like film.