P. Nikitas et A. Pappalouisi, THE SURFACE-POTENTIAL SHIFT UPON ADSORPTION AT THE AIR SOLUTION AND THE UNCHARGED HG SOLUTION INTERFACES, Journal of electroanalytical chemistry [1992], 385(2), 1995, pp. 257-263
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.