Polymer Brushes and Mesogels in Selectively Swollen Lamellar Block Copolymer Films. R. Levicky^*, N. Koneripalli^*, M. Tirrell^*, S.K. Satija ⁺, P.D. Gallagher ⁺ and J.F. Ankner^SS, R. Kulasekere^SS and H. Kaiser^{SS, *}University of Minnesota, Minneapolis, Minnesota ⁺National Institute of Standards and Technology, Gaithersburg, Maryland ^SS Missouri University Research Reactor, Columbia, Missouri

The exposure of an ordered block copolymer film to a strongly selective solvent - one that is good for block A and a nonsolvent for block B - can result in a selectively swollen structure where the A domains are dissolved but the B domains remain "dry". A convenient example, scrutinized in the present study, is afforded by lamellar poly(styrene-b 2-vinylpyridine) (PS-P2VP) diblock and PS-P2VP-PS triblock films placed into direct contact with a methanol reservoir. Methanol is a good solvent for P2VP and a nonsolvent for PS. Films 0.5D, 1.5D and 2.5D thick are examined, where D represents the spatial periodicity of the block copolymer microstructure, with emphasis on 1.5D films. Neutron reflectivity is used to characterize the film structure in both solvent-swollen and dry states. The lamellar dry state structure is recovered after exposure to methanol. In the swollen state, preferential segregation of methanol to P2VP domains causes them to expand by up to ~ 600%. The presennce of P2VP bridges, such as occur in the triblock film, diminishes the swelling. Furthermore, bridging serves to maintain the undissolved PS domains conformal with respect to the substrate surface. In diblock samples the P2VP concentration profile in domains wholly internal to the film is consistent with a pair of opposing polymer brushes.