A model for the adsorption of poly(γ‐benzyl‐L‐glutamate) from solution onto alkali‐halide substrates

Abstract

AbstractThe isothermal adsorption of high‐and low‐molecular‐weight poly(γ‐benzyl‐L‐glutamate) (PBLG) onto (100) alkali‐halide surfaces has been studied with the intent of developing a model for the adsorption process. Data from both the solution and adsorbed phases were correlated in this study. The α‐helical conformation was maintained in solution and on the substrate for all molecular weights investigated. Fourier‐transform infrared spectroscopy proved to be a sensitive technique for conformational analysis of adsorbed PBLG films as thin as 200 Å. High‐molecular‐weight PBLG was adsorbed as an interwoven fibrous mat, homogeneously covering the entire substrate surface. This morphology was independent of the substrate. Adsorption of low‐molecular‐weight PBLG took on a lamellar morphology, often exhibiting epitaxial orientation in the substrate 〈100〉 directions. Quasielastic laser light scattering studies showed that low‐molecular‐weight PBLG had a much higher degree of aggregation in nonpolar solvents than did high‐molecular‐weight PBLG. The proposed adsorption model is essentially a modification of one suggested by Silberberg. It involves segmental adsorption of aggregates, as opposed to single macromolecules of PBLG. The unadsorbed segments of the aggregates form a concentrated interfacial region directly above the substrate. Further interaction and association of PBLG may occur in this region, thus reducing the epitaxial ordering influence of the substrate. Consequently, polymers which do not interact strongly in the concentrated interfacial region, such as polyethylene, are expected to be adsorbed epitaxially, as has been reported.