Polymeric Amphiphiles at Solid-Fluid Interfaces: Forces between Layers of Adsorbed Block Copolymers

Block copolymers are macromolecular amphiphiles and as such have a wide variety of interesting interfacial behavior. We present here a case of block copolymer adsorption from solution studied by the direct measurement of forces between two adsorbed layers. The case is polystyrene (PS)-poly(2-vinylpyridine) (PVP) adsorbed on mica from toluene. Under these circumstances a layer of firmly anchored PS cilia (or loops in the case of PVP-PS-PVP tri-blocks) is assembled on the surface. Furthermore, the PS cilia adopt an extended chain configuration due to lateral crowding imposed on them by the high graft density. The long-range repulsive forces measured in toluene are direct evidence for the wellknown efficacy of this sort of macromolecule in the stabilization of colloidal dispersions. The picture of the adsorbed configuration for di-block copolymers is reasonably clear; that for tri-blocks is less so. Some thoughts are offered on new experiments and technological uses of these materials.