Kinetics of adsorption and desorption of water‐soluble associative polymers on planar titanium dioxide surfaces by ellipsometry

Abstract

AbstractThe adsorption and desorption kinetics of water‐soluble associative polymers with different molecular weights on crystals of titanium dioxide [TiO2(001)] have been studied by ellipsometry. The model water‐soluble associative polymers used in the kinetic study are nonionic polyurethanes based on polyethylene glycol, and have average molecular weights of 17,000, 51,000, and 100,000 with a C16H33 linear alkyl group on each end of the molecule. It is shown that the adsorption and desorption kinetics over a wide range of polymer concentrations is governed by: (1) the kinetics of adsorption and desorption of polymer chains at the interface, (2) the kinetics of adsorption and desorption at the interfaces as well as simultaneous diffusion in the adsorbed layer, and/or (3) diffusion in the adsorbed layer. The existence of regimes (1), (2), and (3) of the adsorption and desorption kinetics are justified by using the experimental data for the adsorption and desorption of water‐soluble associative polymers with different molecular weights. It is shown that the adsorption is an irreversible process for the strongly convex adsorption isotherms. Equations were derived to calculate: (a) the rate constant for polymer adsorption and desorption processes, (b) the coefficient of diffusion, (c) the activation energy of diffusion in the adsorbed layer, and (d) the time needed to attain the equilibrium states for the adsorption and desorption processes by using adsorption and desorption kinetics data with associative polymers of different molecular weights at different polymer concentrations. © 1995 John Wiley & Sons, Inc.