Non-Langmuir Adsorption on Planar Surfaces: Nonlinear Theory and Experiment

A theory of non-Langmuir kinetics of polymer molecules on planar surfaces in the framework of the kinetic-conformational-diffusive-controlled model has been developed. It is shown that an overshoot in both the equilibrium adsorption and the adsorption kinetics may be explained using the conformational kinetics of polymer molecules on planar surfaces with the term depending on the surface polymer concentration. From the experimental data, equations were derived to calculate the equilibrium constant, K0(p), the conformational parameter beta characterizing the conformational process, the thickness of the adsorbed layer, dad.layer, the weight fraction of polymers in the adsorbed layer, Wtplat, the activation energy of adsorption, (-DeltaH), the diffusion coefficient, D(theta), the activation energy of diffusion in the adsorbed layer, Q, the relaxation time tconf characterizing the conformational process, and the time needed to attain the equilibrium state for the adsorption process. The adsorption of poly(dimethylsiloxane) on an oxide surface of silicon has been investigated by ellipsometry. Overshoots in both the equilibrium adsorption and the adsorption kinetics of poly(dimethylsiloxane) on an oxide surface of a silicon were observed. Copyright 1997 Academic Press. Copyright 1997Academic Press