Modelling the observed oscillations in the adsorption kinetics of propyltrimethoxysilane on iron and aluminium oxide surfaces

The growth kinetics of surface films of propyltrimethoxysilane (PTMS) deposited on aluminium and iron oxide surfaces exhibit oscillatory adsorption, This phenomenon involves non-linear oscillations in surface coverage of the adsorbate, as measured by x-ray photoelectron spectroscopy (XPS), as a function of exposure time and solution concentration. In this paper, a mathematical model is presented to describe the experimentally observed time-dependent behaviour. The oscillatory nature of the adsorption can be modelled by a superposition of adsorption and desorption processes. The model quantitatively describes the rate and non-linearity of these processes. Using this model, the influence of the substrate upon the various adsorption processes is described quantitatively. A model for the physical origins of the three processes is presented. Copyright (C) 2000 John Wiley & Sons, Ltd.