Energetics and near - surface structure at polymer - metal interfaces

In this work, we present a theoretical study of the energy hypersurfaces associated with the interactions of PMMA oligomers with aluminum surfaces. Based on the computed energy hypersurfaces we also present speculations regarding the chain conformations at reactive polymer interfaces. The energy hypersurfaces for the interactions of oligomers of PMMA with jellium surfaces show that the energetics are characterized by several deep configuration dependent minima that are separated from each other by barriers that are often larger than kT. This suggests that the adsorbed chains will not be able to accommodate themselves in their global minimum of free energy. In other words, long chain molecules containing reactive functional groups will adsorb in non - equilibrium conformations. Furthermore, because of the strength of the interactions we also expect that the adsorbed chains will adopt fairly flat conformations with many segments bound to the surface. This has recently also been suggested based on NMR studies of PMMA adsorbed on native aluminum oxides. Thus, our picture of the adsorbed chains is that of a collection of flat, non - equilibrium conformations. In this sense, we say that the near - surface structure of adsorbed chains at reactive interfaces is analogous to a quasi two - dimensional glass.