SELF-CONSISTENT-FIELD THEORY FOR POLYMER ADSORPTION - MOLECULAR VOLUME EFFECTS

In this work, we develop a self-consistent field model for homopolymer adsorption as a special case of a general theoretical formulation rep orted previously (H. J. Ploehn, Macromolecules, 27 (1994) 1617). The m odel treats polymer molecules as chains of continuously-distributed, i dealized segments, thereby avoiding the artificiality of lattice discr etization. The continuum formulation properly accounts for polymer sti ffness by allowing polymer segments and solvent molecules to have diff ering molar volumes. We find that the polymer molecular weight, solven t quality, and surface adsorption energy influence the polymer density distribution and adsorbed amount in ways that are consistent with exp erimental observations. Varying the ratio of solvent and polymer molar volumes alters the polymer adsorbed amount by changing the balance of local mixing enthalpy and entropy. Using no adjustable parameters, th e predicted variation of adsorbed amount with polymer molecular weight agrees well with some published experimental results. We observe unsa tisfactory agreement when both the polymer molecular weight and its so lution concentration are high.