Epitaxial Phase Transformation between Cylindrical and Double Gyroid Mesophases
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Epitaxial Phase Transformation between Cylindrical and Double Gyroid Mesophases Lei Zhu,1 Lu Sun,1 Jianjun Miao,1 Li Cui,1 Qing Ge,2 Roderic P. Quirk,2 Chenchen Xue,2 Stephen Z. D. Cheng,2 Benjamin S. Hsiao,3 Carlos A. Avila-Orta,3 Igors Sics,3 and Marie E. Cantino4 1
Polymer Program, Institute of Materials Science and Department of Chemical Engineering, University of Connecticut, Storrs, CT 06269-3136 2 Maurice Morton Institute and Department of Polymer Science, University of Akron, Akron, OH 44325 3 Chemistry Department, State University of New York at Stony Brook, Stony Brook, NY 11794 4 Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269 ABSTRACT Complex phase transformation between the hexagonal cylinder (Hex) and double gyroid (G) phases in a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer was investigated using two-dimensional (2D) synchrotron small-angle X-ray scattering (SAXS), and transmission electron microscope (TEM). The PS-b-PEO sample contained a small population of another bicontinuous cubic phase having an Im3 m symmetry. These two bicontinuous cubic phases (G and Im3 m ) had the same unit cell dimensions. Under a large-amplitude reciprocating shear, the bicontinuous cubic phases transformed into a “single-crystal”-like Hex phase. When annealed at 150 °C for 40 min, the Hex phase partially transformed into well-oriented twinned structures of the G and Im3 m phases without significant loss of orientation in 2D SAXS measurements. Epitaxial phase transformation relationships between the Hex/G and Hex/ Im3 m phases were identified. The mechanism of the Hex → G transformation was examined by TEM. INTRODUCTION
Similar to amphiphilic surfactants and lipids, diblock copolymers are capable of self-organizing into long-range ordered mesophases on nanometer length scales [1], which makes them attractive in the development of nanotechnology and nanofabrication. [2] The phase transformations between the double gyroid (G) phase and neighboring phases have received extensive attention since Charvolin and co-workers [3,4] studied the epitaxial relationships in the transformations between the G ↔ lamellar (L) and G ↔ cylindrical (Hex) phases in nonionic surfactants. [5] In a G ↔ L transformation, the [100]L became the [121]G, and vice versa. In a G ↔ Hex transformation, the [100]Hex transformed to the [ 1 21 ]G and the cylinder axes [001]Hex became the [111]G direction, and vice versa. In the epitaxial phase transformations, the two phases matched not only in orientation, but in the periodicity as well, e.g., the d100, L ≈ d211, G and d100, Hex ≈ d211, G. Other than the G phase, a new bicontinuous cubic morphology was recently reported for block copolymer/organically modified ceramic (ormercer) nanocomposites, namely, the P phase or so-called “Plumber’s Nightmare” [6] phase having an Im 3 m symmetry. [7-9] In this work, we report our preliminary results on complex phase transformations between the Hex and bicontinuous cubic phases (i.e., G and Im 3 m
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