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Solid-phase nucleation free-energy barriers in truncated cubes: interplay of localized orientational order and facet alignment†
Soft Matter ( IF 2.9 ) Pub Date : 2018-01-23 00:00:00 , DOI: 10.1039/c7sm02377d Abhishek K. Sharma 1, 2, 3 , Vikram Thapar 1, 2, 3 , Fernando A. Escobedo 1, 2, 3
Soft Matter ( IF 2.9 ) Pub Date : 2018-01-23 00:00:00 , DOI: 10.1039/c7sm02377d Abhishek K. Sharma 1, 2, 3 , Vikram Thapar 1, 2, 3 , Fernando A. Escobedo 1, 2, 3
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The nucleation of ordered phases from the bulk isotropic phase of octahedron-like particles has been studied via Monte Carlo simulations and umbrella sampling. In particular, selected shapes that form ordered (plastic) phases with various symmetries (cubic and tetragonal) are chosen to unveil trends in the free-energy barrier heights (ΔG*'s) associated with disorder to order transitions. The shapes studied in this work have truncation parameter (s) values of 0.58, 0.75, 0.8 and 1. The case of octahedra (s = 1.0) is studied to provide a counter-example where the isotropic phase nucleates directly into a (Minkowski) crystal phase rather than a rotator phase. The simulated ΔG*'s for these systems are compared with those previously reported for hard spheres and truncated cubes with s = 0.5 (cuboctahedra, CO) and s = 2/3 (truncated octahedra, TO). The comparison shows that, for comparable degrees of supersaturation, all rotator phases nucleate with smaller ΔG*'s than that of the hard sphere crystal, whereas the octahedral crystal nucleates with a larger ΔG*. Our analysis of near-critical translationally ordered nuclei of octahedra shows a strong bias towards an orientational alignment which is incompatible with the tendency to form facet-to-facet contacts in the disordered phase, thus creating an additional entropic penalty for crystallization. For rotator phases of octahedra-like particles, we observe that the strength of the localized orientational order correlates inversely with ΔG*. We also observe that for s > 0.66 shapes and similar to octahedra, configurations with high facet alignment do not favor high orientational order, and thus ΔG*'s increase with truncation.
中文翻译：
截短立方体中的固相成核自由能垒：局部取向顺序和小平面对齐的相互作用†
已经通过蒙特卡洛模拟和伞形采样研究了八面体状粒子的各向同性相中有序相的成核。特别地，选择形成具有各种对称性（立方和四边形）的有序（塑性）相的选定形状，以揭示与无序到有序跃迁相关的自由能势垒高度（ΔG *）的趋势。在这项工作中研究的形状具有0.58、0.75、0.8和1的截断参数（s）值。研究八面体（s = 1.0）的情况以提供一个反例，其中各向同性相直接成核为（Minkowski）晶相而不是旋转相。模拟的ΔG将这些系统的*与先前报道的s = 0.5（立方八面体，CO）和s = 2/3（截短八面体，TO）的硬球体和截头立方体进行了比较。比较表明，在相当的过饱和度下，所有转子相的成核比硬球晶体的ΔG *小，而八面体晶体成核的ΔG大。*。我们对八面体的近临界平移有序核的分析表明，其取向取向强烈偏向，这与在无序相中形成多面接触的趋势不相容，从而为结晶增加了熵的损失。对于八面体状粒子的转子相，我们观察到局部取向顺序的强度与ΔG *成反比。我们还观察到，对于s > 0.66形状且与八面体相似的情况，具有高小平面对齐方式的配置不利于高取向顺序，因此ΔG *随着截断而增加。
更新日期：2018-01-23
中文翻译：
截短立方体中的固相成核自由能垒：局部取向顺序和小平面对齐的相互作用†
已经通过蒙特卡洛模拟和伞形采样研究了八面体状粒子的各向同性相中有序相的成核。特别地，选择形成具有各种对称性（立方和四边形）的有序（塑性）相的选定形状，以揭示与无序到有序跃迁相关的自由能势垒高度（ΔG *）的趋势。在这项工作中研究的形状具有0.58、0.75、0.8和1的截断参数（s）值。研究八面体（s = 1.0）的情况以提供一个反例，其中各向同性相直接成核为（Minkowski）晶相而不是旋转相。模拟的ΔG将这些系统的*与先前报道的s = 0.5（立方八面体，CO）和s = 2/3（截短八面体，TO）的硬球体和截头立方体进行了比较。比较表明，在相当的过饱和度下，所有转子相的成核比硬球晶体的ΔG *小，而八面体晶体成核的ΔG大。*。我们对八面体的近临界平移有序核的分析表明，其取向取向强烈偏向，这与在无序相中形成多面接触的趋势不相容，从而为结晶增加了熵的损失。对于八面体状粒子的转子相，我们观察到局部取向顺序的强度与ΔG *成反比。我们还观察到，对于s > 0.66形状且与八面体相似的情况，具有高小平面对齐方式的配置不利于高取向顺序，因此ΔG *随着截断而增加。
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