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Confined Crystallization within Cylindrical P3EHT Block Copolymer Microdomains

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journal contribution
posted on 09.08.2017, 14:18 by Emily C. Davidson, Rachel A. Segalman
Confinement of crystallites within block copolymer microdomains is a promising approach to study conjugated polymer crystallization due to interfacial chain tethering and defined geometries. The nanoscale organization of crystallites is often critical to determining the charge transport properties of conjugated polymers. Here, a poly­(3-(2′-ethyl)­hexyl­thiophene)-block-poly­(methyl acrylate) (P3EHT-b-PMA) system is leveraged to study the impact of confinement within cylindrical microdomains. The crystalline P3EHT permits accessible melting temperatures and robust formation of traditional microphase-separated morphologies, while the rubbery PMA allows the local deformations required to permit P3EHT crystallization. Crystallites form with chains perpendicular to the diblock interface, causing domain expansion; TEM reveals that this is accommodated in the cylindrical geometry via local deformation. Complementary SAXS/WAXS of aligned diblocks shows preferential orientation of the alkyl chain stacks down domains. Furthermore, cylindrically confined P3EHT demonstrates a smaller window of thermal control over crystalline perfection via isothermal crystallization conditions than homopolymer P3EHT or block copolymer P3EHT in lamellar confinement. This work demonstrates that postcrystallization annealing is an alternative route to generating uniformly high quality crystallites in cylindrically confined P3EHT. These results are important for considering routes to optimizing and controlling crystallinity in nanoscale confined geometries.