HYDRODYNAMIC STUDIES OF ADSORBED DIBLOCK COPOLYMERS IN POROUS MEMBRANES

Extension and surface coverage of adsorbed poly(2-vinylpyridine)/polystyrene (PVP/PS) diblock copolymers were studied by measuring their effect on convective transport in the pores of wellcharacterized mica membranes. When PVP/PS is adsorbed to a mica membrane from toluene, the PVP block anchors the diblock to the surface and the PS block imitates a terminally attached chain extending from the pore wall. The hydrodynamic thickness of the polymer layer in toluene was measured, and using a Debye-Brinkman model for the hydrodynamic interaction of the polymer segments with the fluid, it was concluded that the hydrodynamic thickness is a good measure of the polymer layer extension. This conclusion was further supported by agreement between the hydrodynamic thickness in toluene and the chain extension estimated from published force-distance measurements on the same diblock samples and by a constant hydrodynamic thickness over a range of shear rates (103-104 s-1). The polymer layer was collapsed by replacing toluene with the nonsolvent heptane, and the hydrodynamic thickness measurements in heptane were used to estimate the surface coverage. Reversibility of the extension of the polymer layer to changes in solvent quality, from toluene to heptane to toluene, was observed. © 1990, American Chemical Society. All rights reserved.