Kinetic-diffusion-controlled adsorption and desorption kinetics on planar surfaces

The adsorption and desorption kinetics of water-soluble associative polymers with different molecular weights on the silicon wafers were studied by ellipsometry. The parameters characterizing the adsorption and desorption processes such as (a) the maximum amount of adsorbate adsorbed, Gamma(infinity), (b) the equilibrium constant, K-(p), (C) the activation energy of adsorption, (-Delta H), (d) the rate constants for adsorption and desorption processes, K-ad, K-des, (e) the coefficient of diffusion, D-o, (f) the activation energy of the effective diffusion, Q, and (g) the time needed to attain the equilibrium states for the adsorption and desorption processes were calculated from the experimental ellipsometric data. It is shown that the adsorption kinetics for mixtures over a wide range of concentrations is governed by: (I) the kinetic adsorption at the interface, (II) the kinetic adsorption at the interfaces as well as simultaneous diffusion, and/or (III) diffusion. The existence of regimes (I), (II), and (III) for adsorption and desorption kinetics are justified by using the experimental data for the adsorption and desorption kinetics of water-soluble associative polymers with different molecular weights of 12, 62, and 120 kg/mol. (C) 1998 Academic Press.