A generalized model of corrosion inhibition efficiency for multilayer adsorption

In a recent study (Kokalj, 2026), a model was developed to map multilayer surface coverage to inhibition efficiency ( η ). In that model, the corrosion protectiveness of adsorbed molecular layers beyond the first was postulated to follow a Langmuir-like dependence on the number of layers. In the present work, this model is generalized by leveraging an experimental observation that the polarization resistance of Langmuir–Blodgett monolayers increases linearly with the number of deposited monolayers beyond the first. It is shown that the previously developed model is a special case of the more general formulation presented here. Both models predict a characteristic hallmark shape in the c / η versus c plot—where c is the inhibitor concentration—featuring a bent, arching profile above the c / η = c line at low concentrations, followed by a linear regime at higher concentrations. The generalized model, however, provides further insight, indicating that the extent of this curvature increases when the contribution of the subsequent layers to inhibition efficiency is strong, or when the first adsorbed layer contributes weakly, a behavior that is consistently reproduced when the model is applied to experimental inhibition efficiency data from the literature. Yet under many conditions, the curvature remains too subtle to allow unambiguous identification of multilayer adsorption based on c / η versus c plots alone.