Diblock copolymers order into a variety of periodic
morphologies when the constituent blocks
are sufficiently incompatible. Previous studies have demonstrated
that classical dispersion (spherical
and cylindrical) and lamellar morphologies, as well as complex
morphologies (e.g., gyroid*, lamellar
catenoid, and hexagonally perforated lamellae), can be selectively
accessed through either tailored
molecular synthesis or copolymer/homopolymer blends. In the
present work, control over ultimate
morphology is achieved through the use of binary copolymer blends
composed of two strongly-segregated
poly(styrene-b-isoprene) (SI) diblock copolymers of
equal molecular weights but different compositions
(one 50 wt % S and the other 85 wt % S). Blend morphologies are
examined by electron microscopy
(including three-dimensional imaging) and small-angle X-ray scattering,
and a theoretical framework is
proposed to describe strongly-segregated copolymer blends exhibiting
the lamellar morphology. Results
obtained here indicate that diblock copolymer blends of a given bulk
composition may exhibit coexisting
morphologies but in general behave as single-phase diblock copolymers
of equal molecular composition,
suggesting that such blends offer an alternative, and attractive, route
by which to generate a desired
morphology.
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