A MOLECULAR-MODEL FOR POLYLAYER FORMATION ON ELECTRODE SURFACES

The statistical mechanical approach in studying multilayer adsorption phenomena presented in the J. Phys. Chem., 100 (1996) 15247, is extend ed to electrified interfaces. According to this approach, an adsorbed him composed of solvent and adsorbate molecules forming n layers is ma thematically equivalent to a monolayer of n + 1 components; which are the solvent molecules and columns of i (=1, 2,..., n) adsorbate molecu les. The contribution of the field-dipole interactions to the chemical potentials is calculated by assuming that the electric field is not u niform across the adsorbed layer and all the other contributions, comi ng from the distribution of the adsorbed particles over the adsorption sites and from the particle-particle and particle-adsorbent interacti ons, are calculated using lattice statistics. It is shown that the mod el developed can predict, at least qualitatively, the adsorption chara cteristics of n-heptanol, n-hexanol, n-heptanoic acid and n-hexanoic a cid on Hg when they form polylayers, the peculiar behaviour characteri sed by the appearance of just one transition potential at certain adso rption systems, like the adsorption of methyl- and dimethylpyridines o n Hg, and finally the appearance of a transition pit inside another pi t at the capacitance plots, observed in several experimental systems w ith ionic molecules or molecules of biological importance. (C) 1998 El sevier Science S.A. All rights reserved.