ADSORPTION OF POLY(2-VINYLPYRIDINE) POLY(STYRENE) BLOCK COPOLYMERS FROM TOLUENE SOLUTIONS

We have studied the adsorption of diblock copolymers of poly(2-vinylpyridine) (PVP)-poly-(styrene) (PS) from toluene solutions onto oxidized silicon and mica substrates. Adsorbed amounts for copolymers of various molecular weight and composition were measured by scintillation counting from tritium-labeled adsorbed layers and by X-ray photoemission spectroscopy. We find a dimensionless surface density sigma* to be a unique function of a copolymer block size asymmetry ratio. Within this correlation, we see two regimes of behavior. For copolymers of moderate asymmetry, the surface density sigma is influenced more strongly by the molecular weight of the adsorbing PVP block. These results agree well with a model by Marques et al. For copolymers with large PS blocks (high asymmetry), the surface density is determined primarily by the molecular weight of the PS block. Angle-resolved XPS measurements on dry adsorbed layers indicate a layered structure with PS segments preferentially located at the top surface. These results are supported by contact angle measurements on the dry adsorbed layers.