Research Center for Computational Design of Advanced Functional Materials, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan.
Department of Physics, Faculty of Science, Kyushu University, Fukuoka, Fukuoka, Japan.
Nat Commun. 2021 Sep 6;12(1):5278. doi: 10.1038/s41467-021-25586-4.
Phase transition of anisotropic materials is ubiquitously observed in physics, biology, materials science, and engineering. Nevertheless, how anisotropy of constituent molecules affects the phase transition dynamics is still poorly understood. Here we investigate numerically the phase transition of a simple model system composed of anisotropic molecules, and report on our discovery of multistep nucleation of nuclei with layered positional ordering (smectic ordering), from a fluid-like nematic phase with orientational order only (no positional order). A trinity of molecular dynamics simulation, machine learning, and molecular cluster analysis yielding free energy landscapes unambiguously demonstrates the dynamics of multistep nucleation process involving characteristic metastable clusters that precede supercritical smectic nuclei and cannot be accounted for by the classical nucleation theory. Our work suggests that molecules of simple shape can exhibit rich and complex nucleation processes, and our numerical approach will provide deeper understanding of phase transitions and resulting structures in anisotropic materials such as biological systems and functional materials.
各向异性材料的相变在物理学、生物学、材料科学和工程学中普遍存在。然而，组成分子的各向异性如何影响相变动力学仍未被很好地理解。在这里，我们通过数值模拟研究了由各向异性分子组成的简单模型系统的相变，并报告了我们的发现，即具有层状位置有序（向列有序）的核的多步成核，从仅具有取向有序（无位置有序）的类似流体的向列相。分子动力学模拟、机器学习和分子簇分析的三位一体，产生了自由能景观，明确证明了涉及特征亚稳簇的多步成核过程的动力学，这些亚稳簇先于超临界向列核，不能用经典成核理论来解释。我们的工作表明，形状简单的分子可以表现出丰富而复杂的成核过程，我们的数值方法将为各向异性材料（如生物系统和功能材料）中的相变和由此产生的结构提供更深入的理解。
