Interfacial adsorption with molecular reorientation

This work presents the results of a theoretical study of semi-infinite linear diffusion of single geometrically anisotropic molecular species to a stationary planar interface and monolayer adsorption at the interface assuming reorientation of the initially flat adsorbed molecules to perpendicular position. A modified Flory–Huggins isotherm including lateral molecular interaction was used in the study of adsorption kinetics with different models of molecular reorientation. The connection between the structural changes of the adsorbed monolayer induced by reorientation of the initially flatly adsorbed molecules and the corresponding subtle, but the experimentally accessible changes in the fractional electrode coverage is established and investigated. It is shown that depending on the rate constants of the reorientation process, the change in the fractional interface coverage can range from barely noticeable to a very pronounced, manifested as a pit in the fractional coverage curve. The possible implications for the experimental detection of reorientation are discussed. The presented theoretical predictions are compliant with the recent experimental findings.