Two-dimensional phase formation by heterocoalescence of a surface active droplet at the aqueous/mercury interface

Abstract

We propose a novel experimental technique for the characterization of the initial steps of organic monolayer formation at a fluid interface: mercury/aqueous dispersion of insoluble surfactants. The electrochemical methodology, chronoamperometry at a dropping mercury electrode, is based on suppression of the polargoraphic maximum of 10 −3 M Hg(II) in artificial seawater. Individual droplets (diameter ⩾ 1μm) of neutral and electroactive molecules (1-heptadecene, methyl oleate, squalene) transform into compact molecular layers at the mercury electrode/seawater interface. As a result, the mercury electrode surface is composed of two coexisting and immiscible domains: metallic and organically coated. On the organically coated fraction of the surface of the mercury electrode, Hg(II) reduction proceeds with a measurable nucleation and growth step forming a compact monolayer of elemental mercury on top of the organic film. The attachment of the organic film to the electrode substrate through the collision and spreading of insoluble surfactant droplets provides a convenient in situ technique for the preparation and investigation of organic or organometallic films.