The Conformation of Adsorbed Polystyrene

Abstract

The properties of synthetic polymers at the solid-solution interface are relevant to the fields of adhesion, composites, coatings, and flocculation. The description of both the microscopic and macroscopic systems requires the determination of both the conformation and changes in the conformation of the polymer molecule upon interaction with a surface. A number of theoretical and experimental techniques have been employed to characterize adsorbed polystyrene and to test the theoretical models describing the system. These include investigations of: 1) the extension of the adsorbed molecule normal to the surface by ellipsometry and viscosity studies, 2) the distribution of segments of the adsorbed molecule normal to the surface by attenuated total reflection, 3) the fraction of segments of the polymer chain attached to the surface using infrared difference spectroscopy, and 4) the rates of polymer adsorption and desorption using radiotracer techniques. In general, the conformation of adsorbed polystyrene is dependent upon competition among polymer molecules for the available surface sites. At low surface concentration, the adsorbed polymer molecules show a relatively low extension and flat conformation. As the adsorption time continues, or the surface concentration increases, the molecular conformation becomes more extended. Rates of adsorption and desorption provide additional information on the adsorbed molecular conformation. The rate of adsorption is dependent on the molecular weight, solvent, and substrate. For a given molecular weight, the rate of desorption is dependent on the initial adsorbance.