2-DIMENSIONAL PHASE-TRANSITION OF BENZOIC-ACID AT THE HG AQUEOUS-SOLUTION INTERFACE

The electroadsorptive behaviour of benzoic acid, investigated by means of a.c. phase selective polarography under different experimental conditions (1 mol dm-3 NaClO4, 1 mol dm-3 NaCl), shows a marked dependence on the temperature, indicating the existence of a two-dimensional phase transition 'gas-like' (disordered disposition of the adsorbed molecules) --> 'solid-like' (ordered disposition of the adsorbed molecules). The experimental results in terms of the variation induced by different temperatures on the capacity vs. potential curves are analysed, leading to the determination of a repulsive intermolecular energy, epsilon(AA), in contrast with the experimental evidence presented and with previously obtained data concerning the Frumkin interaction factor. Values of epsilon(AA) that are attractive are calculated by the atom-atom potential method, thus supporting theoretically the experimental evidence for condensation of the adsorbed benzoic acid molecules.