Adsorption isotherms for neutral organic compounds-a hierarchy in modelling: Part V. Models for the inner layer potential difference in the presence of dipolar adsorption

Abstract

The relations for the inner layer potential difference (E) in the presence of adsorbed organic molecules are derived for three hierarchial models, m terms of molecular constants like permanent dipole moments, polarizabilities, etc It is shown how the experimentally observed patterns of the E vs. θ plots (linear in all ranges of σ^M, non-linear in one or both regions of σ^M, etc ) can be understood in a semi-quantitative manner from the simplest model in our hierarchy, viz the two-state site parity version Two-state multi-site and three-state (site parity) models are also analysed and the slope (∂E/∂θ),,_M tabulated for these also. The results for the Esin-Markov effect are denved for all the models and compared with the earlier result of Parsons. A comparison with the GSL phenomenologlcal equation is presented and its molecular basis, as well as the hmltatlons, is analysed. In partxcular, two-state multa-slte and three-state (site panty) models yield E-σ^M relations that are more general than the "umfied" GSL equation The posslblhty of vaewlng the compact layer as a "composite medium" with an "effective dlelectnc constant" and obtaimng novel phenomenological descriptions is also indicated.