THE SURFACE-POTENTIAL SHIFT UPON ADSORPTION AT THE AIR SOLUTION AND THE UNCHARGED HG SOLUTION INTERFACES

A generalized expression for the potential drop across an adsorbed fil m developed in earlier work is used to interpret the adsorption potent ial shift at the free water surface and at the uncharged mercury/solut ion interface when they are composed of adsorbate and solvent molecule s. It is shown that according to the theory the inverse 1/Delta(chi) o f the adsorption potential shift should vary linearly with the inverse 1/theta of the surface coverage by the adsorbate. This prediction is verified in all the experimental systems analysed. The ratio rho = eps ilon(A)/epsilon(S), where epsilon(A) and epsilon(S) are the ''distorti onal'' dielectric constants of the adsorbed layer when theta = 1 and t heta = 0 respectively, is calculated from the intercept on the ordinat e and the slope of the linear 1/Delta X vs. 1/theta plot. It is found that p < 1 at the uncharged Hg/solution interface and p greater than o r equal to 1 at the free water surface. In order to explain this diffe rence various models of the adsorbed layer are analysed and discussed.