Entropy Variation in the Two-dimensional Phase Transition of Anthracene Adsorbed at the Hg Electrode/Ethylene Glycol Solution Interface

The adsorption of anthracene (C14H10), at the mercury electrode/ethylene glycol(EG) solution interface, is characterized by a low and almost constant capacity (about8 μF cm−2) region (capacitive “pit” or “plateau”) in capacity vs. potential curves, uponselection of suitable values of temperature, bulk concentration and applied potential values.This result is rationalized assuming the occurrence of a 2D phase transition betweentwo distinct adsorbed phases: (i) a “disordered” phase, characterized by a flat “parallel”disposition of the aromatic moiety on the electrode surface (ii) an “ordered” phase,characterized by a “perpendicular” disposition of the aromatic moiety on the electrodesurface. The experimental evidence is rationalized by considering the chemical potential asan explicit function of the “electric field/adsorbed molecule” interaction. Such a modelisticapproach enables the determination of the relevant standard entropy variation.