Fluorescence studies of polymer adsorption. 2. A simple model describing adsorbed polymer rearrangement

Abstract

A simple model is developed to describe the structure of isolated tracer chains adsorbed from solution onto a planar surface when challenged with displacing polymer. We assume that a tracer polymer adsorbing on a planar surface can be modeled as a Gaussian chain and that the rearrangement of tracer chains on the surface is affected only by a field due to displacing chains. From a modified diffusion equation, we obtain an approximate analytic expression describing the rearrangement. The effects of tracer and displacer molecular weight and displacer concentration on the rearrangement are examined. The rearrangement of tracer chains in this study is described in terms of the change in mean square end-to-end distance, which is related to the fluorescence observable, the excimer to monomer intensity ratio (Ze/Im)T. he hydrophobic attraction between pyrene ends and the displacement of tracer chains are taken into account, and the predictions are compared with the experimental fluorescence data obtained previously. The model gives qualitative agreement with the fluorescence observations. The quantitative discrepancy at elevated displacer concentrations may be due to nonequilibrium entrapment of some tracer chains by the higher molecular weight displacers.