Investigation by optical evanescent waves of the structure of adsorbed polymer layers in good solvents

Abstract

The adsorption of poly(methylmethacrylate) chains from toluene onto a clean flat sapphire surface at 20 °C has been studied by evanescent wave induced fluorescence. In a first step we have demonstrated that the EWIF data yield the surface excess, Γ, and the mean thickness, Z, of the adsorbed layer without any model assumption. The values of Γ and Z, obtained for two samples of different molecular weight are in good agreement with independent results obtained by ellipsometry and small-angle neutron scattering. A determination of the complete concentration profile has been attempted by fitting the data to various theoretical models. From this analysis it seems difficult to decide between the exponential model and the scaling model. The time variation of the surface excess, Γ, is identical to previously published data, while the kinetics of Z reveal an unusual behaviour which can be explained in terms of polymer dynamics within the adsorbed layer.