Fabrication of Ellipsoidal Mesostructures in Block Copolymers via a Step-Shear Deformation
Fabrication of Ellipsoidal Mesostructures in Block Copolymers via a Step-Shear Deformation
复制标题
通过阶梯剪切变形制备嵌段共聚物中的椭圆体介观结构
DOI：
10.1021/acs.macromol.7b02060
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发表时间：
2018
期刊：
影响因子：
5.5
通讯作者：
M. Müller
中科院分区：
文献类型：
--
作者：
D.-W. Sun;M. Müller
椭球体由于其形状相关、各向异性的特性而引起了人们的持久关注。在一些应用中，例如光子晶体，需要椭球填充的位置和取向顺序。我们提出了一种通用、简便和高效的策略，通过阶跃剪切变形在嵌段共聚物中制备位置和取向有序的软椭球晶体。从共聚物材料热力学稳定、平衡的球形中间相出发，阶跃剪切变形提供了瞬时的各向异性刺激，将球形微区变形为椭球体，同时拉伸了大分子构象。随后，在固定应变下，分子应力松弛到平衡，此时获得的椭球体的形状和取向由堆积受挫决定。由于残余分子应力很小，在没有外应力的情况下，通过滑移引起的晶格驰豫被延长，即具有位置和取向有序的软椭球晶体是伪亚稳态的。我们的策略还允许椭球的低体积分数(与胶体系统相比)。用平均场中单链(SCMF)模拟和自洽场理论(SCFT)计算验证了所得椭球的赝亚稳性。通过改变阶跃剪切应变的大小和嵌段共聚物的组成，可以独立地控制椭球形结构域的非球度和取向。我们的研究为制备软的、位置有序和取向有序的椭球晶体提供了一个新的概念，在工程功能材料中具有潜在的应用前景。
Ellipsoids have attracted abiding attention because of their shape-dependent, anisotropic properties. In some applications, e.g., photonic crystals, both positional and orientational order of the ellipsoidal packing are required. We propose a versatile, facile, and efficient strategy to fabricate positionally and orientationally ordered crystals of soft ellipsoids in block copolymers via a step-shear deformation. Starting from the thermodynamically stable, equilibrium spherical mesophase of the copolymer material, the step-shear deformation provides an instantaneous, anisotropic stimulus to deform the spherical domains into ellipsoids and simultaneously stretches the macromolecular conformations. Subsequently, at fixed strain, the molecular stress relaxes to an equilibrium where the shape and orientation of the obtained ellipsoids are dictated by the packing frustration. Since the residual molecular stress is minuscule, the lattice relaxation via slippage in the absence of external stress is protracted, i.e., the crystal of soft ellipsoids with positional and orientational order is pseudometastable. Our strategy also allows for low volume fractions of ellipsoids (compared to colloidal systems). Both single-chain-in-mean-field (SCMF) simulations and self-consistent field theory (SCFT) calculations are employed to demonstrate the pseudometastability of the obtained ellipsoids. Varying the magnitude of the step-shear strain and the composition of the block copolymer, we can control the asphericity and orientation of the ellipsoidal domains independently. Our study provides a new concept for fabricating soft, positionally and orientationally ordered crystals of ellipsoids with potential applications in engineering functional materials.