Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637.
Materials Science Division, Argonne National Laboratory, Lemont, IL 60439.
Proc Natl Acad Sci U S A. 2017 Sep 19;114(38):10011-10016. doi: 10.1073/pnas.1711207114. Epub 2017 Sep 5.
Liquid-crystal blue phases (BPs) are highly ordered at two levels. Molecules exhibit orientational order at nanometer length scales, while chirality leads to ordered arrays of double-twisted cylinders over micrometer scales. Past studies of polycrystalline BPs were challenged by the existence of grain boundaries between randomly oriented crystalline nanodomains. Here, the nucleation of BPs is controlled with precision by relying on chemically nanopatterned surfaces, leading to macroscopic single-crystal BP specimens where the dynamics of mesocrystal formation can be directly observed. Theory and experiments show that transitions between two BPs having a different network structure proceed through local reorganization of the crystalline array, without diffusion of the double-twisted cylinders. In solid crystals, martensitic transformations between crystal structures involve the concerted motion of a few atoms, without diffusion. The transformation between BPs, where crystal features arise in the submicron regime, is found to be martensitic in nature when one considers the collective behavior of the double-twist cylinders. Single-crystal BPs are shown to offer fertile grounds for the study of directed crystal nucleation and the controlled growth of soft matter.
液晶蓝相（BPs）在两个层次上具有高度的有序性。分子在纳米尺度上表现出取向有序，而手性则导致双扭曲圆柱在微米尺度上有序排列。过去对多晶 BP 的研究受到随机取向晶区之间晶界的存在的挑战。在这里，通过依赖化学纳米图案化表面来精确控制 BP 的成核，从而得到宏观单晶 BP 样品，其中可以直接观察到中间晶体形成的动力学。理论和实验表明，具有不同网络结构的两种 BP 之间的转变是通过晶体阵列的局部重排进行的，而双扭曲圆柱不发生扩散。在固体晶体中，晶体结构之间的马氏体转变涉及少数原子的协同运动，而不涉及扩散。当考虑双扭曲圆柱的集体行为时，人们发现，在亚微米尺度上出现晶体特征的 BP 之间的转变本质上是马氏体相变。单晶 BP 为定向晶体成核和软物质的控制生长研究提供了肥沃的土壤。
