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Thermoreversible, epitaxial fcc<-->bcc transitions in block copolymer solutions
Joona Bang1, Timothy P Lodge, Xiaohui Wang
1Departments of Chemistry and Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Abstract:
Uncharged block copolymer micelles display thermoreversible transitions between close-packed and bcc lattices for a range of concentration, solvent selectivity, and copolymer composition. Using small-angle x-ray scattering on shear-oriented solutions, highly aligned fcc crystals are seen to transform epitaxially to bcc crystals, with fcc/bcc orientational relationships that are well established in martensitic transformations in metals. The transition is driven by decreasing solvent selectivity with increasing temperature, inducing solvent penetration of the micellar core.