Epitaxial transition from gyroid to cylinder in a diblock copolymer melt
Epitaxial transition from gyroid to cylinder in a diblock copolymer melt
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DOI：
10.1021/ma052075z
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发表时间：
2006-03-21
期刊：
影响因子：
5.5
通讯作者：
Kawakatsu, T
中科院分区：
文献类型：
--
作者：
Honda, T;Kawakatsu, T
利用实空间动态自洽场技术，模拟了由双连续双陀螺(G)结构向六边形填充圆柱(C)结构的有序过渡过程。为了正确地模拟结构变化，我们引入了一种系统尺寸优化技术，通过该技术可以抑制人工中间结构的出现。当在G单元胞的[I I I]方向施加剪切流时，观察到C畴的成核，然后是G相和C相之间的稳定共存。我们证实了生成的C畴是外延生长的，其中G结构的{220}面与C结构的{10}面重合（所谓的外延生长），而实验研究表明{211}向{10}过渡。在剪切流作用下的稳态下，随着剪切流速度梯度方向的改变，G结构呈现出不同的分裂和重连过程。因此，从初始G相到最终C相的动力学路径不仅取决于初始和最终畴结构（外延条件）的位置和晶格常数之间的可通约性，还取决于相共存的稳定性，这取决于速度梯度的方向。
An order-order transition from a bicontinious double-gyroid (G) structure to a hexagonally packed cylinder (C) structure induced by an external flow is simulated by using real-space dynamical self-consistent field technique. To simulate the structural change correctly, we introduce a system size optimization technique by which emergence of artificial intermediate structures are suppressed. When a shear flow in [I I I] direction of the G unit cell is imposed, a nucleation of the C domains followed by a stable coexistence between the G phase and the C phase is observed. We confirm that the generated C domains grow epitaxially, where the {220} planes of the G structure coincide with the {10} planes of the C structure (so-called epitaxial growth), while the experimental studies suggest {211} to {10} transition. In a steady state under the shear flow, the G structure shows different splitting and reconnection processes when the direction of the velocity gradient of the shear flow is changed. Thus, the kinetic pathway from the initial G phase to the final C phase is determined, not only by the commensurability between the positions and the lattice constants of the initial and the final domain structures (epitaxial condition), but also by the stability of the phase coexistence that depends on the direction of the velocity gradient.