Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom.
Thomas Young Centre, University College London, London WC1E 6BT, United Kingdom.
Proc Natl Acad Sci U S A. 2019 Feb 5;116(6):2009-2014. doi: 10.1073/pnas.1817135116. Epub 2019 Jan 22.
When an ice crystal is born from liquid water, two key changes occur: () The molecules order and () the mobility of the molecules drops as they adopt their lattice positions. Most research on ice nucleation (and crystallization in general) has focused on understanding the former with less attention paid to the latter. However, supercooled water exhibits fascinating and complex dynamical behavior, most notably dynamical heterogeneity (DH), a phenomenon where spatially separated domains of relatively mobile and immobile particles coexist. Strikingly, the microscopic connection between the DH of water and the nucleation of ice has yet to be unraveled directly at the molecular level. Here we tackle this issue via computer simulations which reveal that () ice nucleation occurs in low-mobility regions of the liquid, () there is a dynamical incubation period in which the mobility of the molecules drops before any ice-like ordering, and () ice-like clusters cause arrested dynamics in surrounding water molecules. With this we establish a clear connection between dynamics and nucleation. We anticipate that our findings will pave the way for the examination of the role of dynamical heterogeneities in heterogeneous and solution-based nucleation.
当冰晶从液态水中形成时，会发生两个关键变化：（）分子有序化，（）分子的流动性随着它们进入晶格位置而降低。大多数关于冰核形成（以及一般的结晶）的研究都集中在理解前者上，而对后者的关注较少。然而，过冷水中表现出迷人而复杂的动力学行为，最显著的是动力学非均匀性（DH），即相对移动和不移动的粒子在空间上分离的区域共存的现象。引人注目的是，DH 与冰核形成之间的微观联系尚未在分子水平上直接揭示。在这里，我们通过计算机模拟来解决这个问题，模拟结果表明：（）冰核形成于液体的低流动性区域，（）在任何类似冰的有序化之前，分子的流动性会先经历一个动力学潜伏期，（）类似冰的团簇会导致周围水分子的动力学停滞。这就建立了动力学与成核之间的明确联系。我们预计，我们的发现将为考察动力学非均匀性在多相和溶液成核中的作用铺平道路。
