ABSTRACT
In the previous chapters, the analysis of the adsorption phenomenon was limited to the steady state. No time variation of the surface density of adsorbed particles or evolution of the bulk density of particles was considered. In the present chapter this aspect of the adsorption phenomenon will be treated. For this reason, a general discussion on the continuity equation, diffusion and drift currents is presented. After that, typical problems concerning the adsorption of neutral particles from the surfaces are discussed. The role of the kinetic equations at the bounding surfaces is considered in details. A simple model of a diffusion-drift phenomenon giving rise to a classical kinetic equation at the surface is proposed for neutral particles. The intrinsic times in the drift-diffusion phenomenon are investigated in the simple case where the drift field is independent of the adsorption phenomenon of neutral particles. The final part of this chapter is dedicated to presenting a dynamical analysis of the problem relevant to a liquid containing ions submitted to an external voltage. It is assumed that the external voltage is step-like. The problem is a little bit more complicated than the one considered in the first sections for the following reasons. First, the actual electric field in the sample has to be determined in a self-consistent manner by means of the Poisson equation. Second, there are two kinds of ions: the positive and the negative ones, and hence, two different continuity equations have to be solved. Third, the kinetic equations at the limiting surfaces for the two kind of ions involve different phenomenological parameters. In this general case, the equations governing the phenomenon, i.e., continuity, Poisson and equilibrium of the nematic torques, will be numerically solved.
