Thin Film Structure of Symmetric Rod-Coil Block Copolymers

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• 作者：Bradley D. Olsen ; Xuefa Li ; Jin Wang ; Rachel A. Segalman
• 刊名：Macromolecules
• 出版年：2007
• 出版时间：May 1, 2007
• 年：2007
• 卷：40
• 期：9
• 页码：3287 - 3295
• 全文大小：2187K
• 年卷期：v.40,no.9(May 1, 2007)
• ISSN：1520-5835

文摘

Poly(alkoxyphenylenevinylene-b-isoprene) (PPV-b-PI) rod-coil block copolymers demonstratenovel structures due to the rodlike PPV block. Thin films of the polymers self-assemble into lamellar microphasesupon thermal annealing with the lamellae oriented primarily parallel to the substrate. The parallel lamellae showsymmetric wetting of PI at both the substrate and vacuum interfaces. Grains of lamellae with parallel orientationare characterized by irregular polygon shapes and are bounded by defect regions where the lamellae are orientedout of the plane of the film. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that these out-of-plane lamellae are strongly oriented perpendicular to the film. The perpendicular lamellae are much straighterthan those typically observed in coil-coil block copolymers due to the high bending energy of the liquid crystallinerod nanodomains. Islands or holes form in the films, and domain spacings estimated from the island/hole heightsare equal to the bulk domain spacing. The perpendicular "defect" lamellae mediate the change in thickness requiredto transition between islands or holes and the surrounding region. Increasing film thickness results in an increasingfraction of the surface covered by perpendicular lamellae, presumably due to limited penetration of the substrateorienting field into the film. At great enough thickness total reorientation of the lamellar structure from parallelto perpendicular orientation at the vacuum interface is observed.