Entropy change in the two-dimensional phase transition of adenine adsorbed at the Hg electrode/aqueous solution interface

Abstract

The combined effect of temperature, bulk concentration and applied potential, on the stability of the condensed phase of adenine adsorbed at the mercury/aqueous solution interface, is rationalized assuming that the occurrence of a 2D phase transition involves only two distinct adsorbed phases. The chemical potential, µ, which drives the equilibrium at the phase transition, is expressed by means of an equation which accounts explicity for the electric field–adsorbed molecule interaction. The approach enables the standard entropy variation of the overall process to be determined. The findings are consistent with the ordered nature of the adsorbed phase, with which the appearance of a low and constant capacity region in the capacity vs. potential curves is associated. The standard entropy variation for the 2D ‘flat → perpendicular (solid-like)’ phase transition is estimated and discussed.