SURFACE FORCE AND NEUTRON-SCATTERING STUDIES ON ADSORBED POLY(2-VINYLPYRIDINE)-B-POLYSTYRENE

A low molecular weight, highly asymmetric block copolymer of polyvinyl pyridine-polystyrene has been adsorbed on silica particles suspended i n toluene solution and examined using small-angle neutron scattering ( SANS). The results are compared with theoretical calculations based on the Evers-Scheutjens-Fleer model. The same polymer has been adsorbed on mica in the surface force apparatus. It is shown that both the exte nded length of the polymer in toluene and the amount adsorbed are in g ood agreement with previous scaling predictions in the literature. Cha nging the solvent is complicated in the particulate system as floccula tion is induced by theta or below-theta solvents. However, the SANS da ta clearly show the shrinking of the polymer in the poorer solvents an d the increase in volume fraction close to the surface. The scaled len gths of highly asymmetric block copolymers can be rationalized in term s of the breakdown of the uniformly wetting anchor film (but it is poi nted out that slow adsorption kinetics could give rise to the same sca ling).