ON THE NATURE OF THE NONANOIC ACID MONOLAYER ADSORBED AT THE HG/AQUEOUS SOLUTION INTERFACE - INFLUENCE OF CONFORMATIONAL FREEDOM IN BULK AQUEOUS-SOLUTION

The adsorption of the nonanoic acid at the electrified Hg/aqueous solution interface is studied by means of capacity and surface tension measurements. Comparison of the experimental Gamma(max) value with the calculated more favoured solvated conformation suggests that the acid is adsorbed in a partially coiled conformation. The adsorption free energy here determined, together with previously reported values found in the literature concerning other saturated acids and alcohols, is compared with reactivity and calculated molecular descriptors. The collected evidence suggests that the hydrophobic nature of the acid is responsible for the adsorption, while the electric field/molecule interaction, occurring at the electrified interface, governs the desorption. Lastly, some experimental (capacitive transients, effect of the temperature on the tensammetric curves) and theoretical findings are discussed which indicate that the adsorbed acid monolayer should be regarded as a usual, in the field of adsorption at electrodes, disordered network. Thus excluding the occurrence of a two-dimensional phase transition involving the formation of a 2D solid-like film.