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

Abstract

SYNOPSISThe adsorption and desorption kinetics of water-soluble associative polymers with different molecular weights on crystals of titanium dioxide [Ti0,(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 a t the interface, (2) the kinetics of adsorption and desorption a t the interfaces as well as simultaneous diffusion in the adsorbed layer, and/or ( 3 ) diffusion in the adsorbed layer.The existence of regimes (I), (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 a t different polymer concentrations. 0 1995 John Wiley & Sons, Inc.

Adsorption Kinetics of Amphipathic Polystyrene-block-polybutadiene onto Silicon Wafer and Polystyrene Planar Surfaces

“…The difference between the averaged values, Γ av ( t ), for two or three independent runs was no more than 10%. The average adsorbed layer thickness, d ad layer , and the average refractive index, n ad layer , of the adsorbed layer were found simultaneously by using the following equations. , where Re(δ) and Im(δ) are the real and imaginary parts of the phase shift, respectively, λ is the wavelength of light (λ = 632.8 nm), θ sol is the angle of incidence of the He−Ne laser beam, and n ad layer and n sol are the refractive indices (average values) of the adsorbed layer and the polymer solutions, respectively. First, the values of d ad layer and n ad layer from eq 1 are calculated by using ellipsometric data (Δ and ψ) for the model shown in Figure .…”