Slippage at adsorbate-electrolyte interface. Response of electrochemical quartz crystal microbalance to adsorption

The electrochemical quartz crystal microbalance (EQCM) was used to study ad sorption of pyridine on gold from aqueous and butanol solutions. It was fou nd that the effect of specific adsorption on the frequency shift could not be explained in terms of a mass change in the adsorbed layer that rigidly c oupled to the oscillating surface. In order to explain our observations we suggest a model, which accounts for two important features of adsorption at solid-electrolyte interfaces: (a) an adsorbate replaces a certain amount o f solvent molecules from the interfacial layer, and (b) adsorption may lead to a finite slippage at the adsorbed layer-solution interface. Relationshi ps between the slip length and the microscopic properties of the interfacia l layer are discussed, and a dependence of the slip length on surface exces ses is suggested. The treatment of experimental data makes it possible to d etermine the slip length as a function of surface excesses, for pyridine ad sorption on gold from aqueous and butanol solutions. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.