Directed Self-Assembly of Block Copolymers into Twin BCC-Sphere: Phase Transition Process from Aligned Hex-Cylinder to BCC-Sphere Induced by a Temperature Jump between the Two Equilibrium Phases

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• 作者：Norihiro Sota ; Kenji Saijo ; Hirokazu Hasegawa ; Takeji Hashimoto ; Yoshiyuki Amemiya ; Kazuki Ito
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：March 26, 2013
• 年：2013
• 卷：46
• 期：6
• 页码：2298-2316
• 全文大小：1898K
• 年卷期：v.46,no.6(March 26, 2013)
• ISSN：1520-5835

文摘

We explored in situ a 鈥渄irected鈥?self-assembly of block copolymers into a twinned body-centered cubic sphere (bcc-sphere) with a special orientation via the order鈥搊rder phase transition from a specially aligned hexagonal cylinder (hex-cyl) by using time-resolved synchrotron small-angle X-ray scattering and transmission electron microscopy. We elucidated that the hex-cyl with its cylinder axis and {11} lattice plane aligned respectively parallel to the OX axis and the OXZ plane was epitaxially transformed into the twin bcc-sphere with its twin axis 111 and twin plane {112} having respectively the 鈥渄irected orientation鈥?parallel to the OX axis and the OXZ plane. We found that the directed self-assembly involves a three-step nucleation growth (NG) process as follows. Step I corresponds to a pretransition process, where hex-cyl undergoes the cooperative and periodic undulation of the cylinders with their pinching or bulging points being spatially arranged with the 鈥渂cc symmetry鈥?which is attained in bcc-sphere after completion of the transformation (designated as 鈥渦ndulated hex-cyl鈥?. Moreover, the undulation fluctuations modes found to have the degeneracy in the form of the undulations with bcc-symmetry A and those with bcc-symmetry A鈥?which have the twin relationship to each other. Step II involves NG of two types of bcc-sphere (designated as A- and A鈥?sphere which have a mirror symmetry with respect to the {112} plane parallel to the OXZ plane) formed with an equal statistical weight in the matrix of the undulated hex-cylinder; Grains of bcc-sphere grow at the expense of the matrix phase at a faster growth rate parallel to 111 axis than normal to it. Step III involves impingements of bcc-sphere A and A鈥?with their twin planes {112} as their grain boundaries and with their twin axes 111 parallel to the OXZ plane and the OX axis, respectively. Thus, the volume-filling A- and A鈥?spheres accompanied by spatial rearrangements toward a more perfect bcc-sphere are inevitably directed to form twin bcc-sphere composed of bcc-sphere A and A鈥?