Measurement of the interaction force profiles between block copolymers of poly(2-vinylpyridine)/poly(t-butylstyrene) in a good solvent

Direct measurements of the interaction forces F( D) between two atomically smooth solid (mica) surfaces immersed in toluene have been performed as a function of surface separation. Interaction profiles were also measured following adsorption of the AB block copolymer poly(2-vinylpyridine)/poly(t-butylstyrene) and incubating the surfaces overnight in these solutions. Toluene is a poor solvent for poly(2-vinylpyridine) and a good solvent for poly(t-butylstyrene) implying that on adsorption the poly(t-butylstyrene) chain will extend away from the mica surface, i.e. act as a stabilizing chain. Three molecular weight poly(t-butylstyrene) chains ( M w = 4700, 15 100, 30 700) anchored by poly(2-vinylpyridine) have been studied. The pure toluene results showed an attraction between the surfaces at distances ⩽ 10 nm in agreement with our earlier findings 13. Following overnight incubation of the surfaces in the copolymer solutions long range repulsive interactions were observed which increased approximately exponentially with decreasing surface separation. The form of the force profile and the dependence of the distance of onset of interaction with the molecular weight of the stabilizing chain are compared with theoretical predictions from scaling theory. Good agreement is found for the dependence of the adsorbed layer thickness with molecular weight, however scaling ideas do not describe the form of the force profile.