| Abstract
| - The morphology of binary blends ofpoly(styrene)−poly(2-vinylpyridine) (PS−PVP)diblockcopolymers of the type (A−B)α +(A−B)β was examined in a thin-film geometry usingneutron reflection(NR), transmission electron microscopy (TEM), and self-consistent field(SCF) calculations. Blends ofsymmetric diblock copolymers(fA,α ≈fA,β ≈ 0.5) revealed alocalization of the lower molecular weightdiblock copolymer and stretching of the higher molecular weight diblockcopolymer near the AB interfacethat is qualitatively consistent with the data of a prior study byMayes and co-workers. Blends ofasymmetric diblock copolymers of the typefA,α< 0.5 andfA,β> 0.5 having similarmolecular weights (Nα≈ Nβ) and with ∼50% overall compositionof a chemically similar block in the blend,〈fA〉 ≈ 0.5, revealedmolecular-level mixing of the two components and the formation of asingle-phase morphology. A lamellarmorphology was formed even when the individual components exhibit anonlamellar morphology in thepure melt state. In general, the morphological characteristics arewell anticipated by SCF calculations.After accounting for fluctuations at the interface, spatialdistributions of the individual components inthe blend obtained by SCF calculations were in close agreement with theNR data. For diblock copolymersnear the order−disorder transition, a χ value higher than the bulkwas necessary to fit the experimentaldata, suggesting an enhancement of ordering in the thin films near thetransition due to the presence ofthe surfaces.
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