Specific adsorption at the mercury/sulpholane interface

Abstract

The electrical double layer at the mercury/sulpholane interface has been studied by capacity and electrocapillary measurements at 30°C. KPF₆ is weakly adsorbed from sulpholane solution. Measurements using this salt in sulpholane + water mixtures show that sulpholane is oriented with the positive end of its dipole towards the mercury. Sulpholane is preferentially adsorbed from these mixtures at all accessible charges on the mercury, and more strongly so than at the air/solution interface. CIO^–₄ ion is more strongly adsorbed from pure sulpholane giving a capacity curve having a “hump” that is slightly temperature dependent. The adsorption isotherms fit a virial equation with charge-dependent two-dimensional second virial coefficient. A model of the inner layer structure leads to an estimate of the mean dielectric constant of the inner layer of about 7.