Influence of Component Ratio on Adsorption of Polymer Mixtures under Phase Separation of Solutions

Atomic force and ultrasonic force microscopy investigation of adsorbed layers formed by two incompatible polymers: polystyrene and poly(butyl methacrylate)

Atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) have been used to study the properties of adsorption layers formed by two incompatible polymers, polystyrene and poly(butyl methacrylate), in the course of simultaneous adsorption on the surface of silica (naturally oxidized surface of a silicon wafer). The adsorption was performed from solutions containing both of the components in a common solvent (carbon tetrachloride) in dilute and semidilute concentration regimes. It was discovered that in both cases the structure of adsorption layers has a complex mosaic structure, the details of which depend on solution composition, on the solution concentration regime, and on the ratio of the components in the adsorption layer. The observed structural inhomogeneity on the length scale of approximately 200-500 nm (distribution of segment density revealed by UFM) appears as result of thermodynamic incompatibility in the system and is conditioned by changes in the conformation states of the adsorbed macromolecules in the route of competitive adsorption of the components. The adsorbed polymer films with thicknesses of approximately 20-500 nm appeared to have fractal properties and could be characterized with fractal dimensions dependent on the ratio of the components at the interface and the adsorption conditions.