Influence of Anchor Block Size on the Thickness of Adsorbed Block Copolymer Layers

We present surface force data on three different polystyrene/poly(2-vinylpyridine) block copolymers (PS/P2VP) with a fixed size of the nonadsorbing PS block but widely varying sizes of the adsorbing P2VP block. With respect to the sizes of the two blocks, they range from moderately to highly asymmetric. The equilibrium force profiles are almost overlapping, which means that the variation in layer thickness is very small over a large range of anchor block size. This finding is in disagreement with the predictions of simple scaling models for polymer brushes. However it agrees with findings from neutron reflectivity data on a comparable series of PS/P2VP block copolymers. We also find agreement with recent neutron reflectivity experiments on poly(dimethylsiloxane)/polystyrene and with self-consistent field calculations on selectively adsorbed block copolymers.