ABSTRACT
The aim of this chapter is to present a Fermi-like description for the adsorption of charged or neutral particles at a surface. This theory accounts, in a natural way, for the saturation phenomenon found in real samples. In fact, the Fermi-like distribution-owing to the exclusion principle-naturally takes into account the occupation of the adsorption sites without the need to consider steric potentials with artificial cut-offs. For this reason, the saturation in the coverage of the surface by the adsorbed particles can be found also in the perfect gas approximation. Furthermore, this approach removes some limitations of the classical one, based on a Maxwell-Boltzmann (MB) description. As an application, the steady state distribution of ionic impurities in a sample of an isotropic fluid, whose limiting surfaces are supposed to adsorb positive charged particles, is investigated having as the classical counterpart the theory developed in the first part of Chapter 8. The fundamental equations of the problem can be numerically solved, thus permitting the determination of the electrical potential distribution in the sample, and the full thickness dependence of the surface density of adsorbed charges. In the “classical limit” the results of the MB approach are recovered.
