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 σ* 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 σ 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.