SELECTIVELY SWOLLEN FILMS OF TRIBLOCK DIBLOCK COPOLYMER BLENDS - DEPENDENCE OF SWOLLEN FILM STRUCTURE ON BLEND COMPOSITION/

Compositional variation in blends of triblock and diblock copolymer fi lms can be used to adjust the film response to a selective solvent. We investigated the relationship between blend composition and film stru cture in ordered films containing poly(styrene-b-2-vinylpyridine) (PS- P2VP) diblocks and PS-P2VP-PS triblocks. The study focuses on films po ssessing a lamellar morphology. Methanol, a strongly selective solvent for P2VP, is used to swell the films. Since methanol solvates P2VP bu t not PS, periodic multilayer structures result in which solvent-rich P2VP domains are separated by undissolved PS domains. The film structu re is characterized in the dry and swollen states with neutron reflect ivity. Although the dry state morphology dimensions are practically id entical for all samples, in the swollen state films richer in triblock swell less due to higher density of bridges interconnecting the PS do mains. Furthermore, in swollen triblock-containing samples, polymer co ncentration variations in P2VP domains are suppressed and the PS domai ns are better aligned with respect to the substrate.