STRUCTURE OF ADSORBED POLYMER LAYERS - MOLECULAR VOLUME EFFECTS

A new continuum model for homopolymer adsorption is developed within t he framework of self-consistent field theory. The model differs from p revious lattice-based and continuum models in that it properly account s for polymer stiffness in the idealization of a polymer molecule as a chain of segments and it allows segments and solvent molecules to hav e differing partial molar volumes. The altered balance of mixing entha lpy and entropy has quantitative implications for the structure of ads orbed polymer layers. Beginning with a heuristic development of a free energy balance for the system, functional minimization of the free en ergy determines the appropriate form of the self-consistent field. The field appears in a modified diffusion equation which governs the spat ial distribution of polymer. This equation is solved via a regular per turbation expansion in powers of reciprocal polymer molecular weight. Retention of only the first term precludes tails but allows a semianal ytical solution. We explore the effects of varying polymer-solvent int eractions and partial molar volumes upon adsorbed layer structure, and we compare predicted polymer adsorbed masses and layer thicknesses wi th experimental values.