高岭石上的冰形成：分子动力学模拟的见解,The Journal of Chemical Physics

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高岭石上的冰形成：分子动力学模拟的见解
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2016-12-02 16:48:12 , DOI: 10.1063/1.4968796
Gabriele C. Sosso ₁ , Gareth A. Tribello ₂ , Andrea Zen ₁ , Philipp Pedevilla ₁ , Angelos Michaelides ₁

Affiliation

冰的形成影响着我们日常生活的许多方面以及诸如冷冻疗法和冷冻保存之类的重要技术。异物几乎总是通过非均质的冰核作用来帮助水冻结，但是该过程的分子细节仍然未知。实际上，即使使用最先进的实验技术，也很难获得对在不同基材上形成冰的微观机制的了解。同时，由于水-基质相互作用的复杂性以及表征成核事件的长时间尺度，非均质冰成核的原子模拟经常面临非同寻常的挑战。这里，我们研究了非均质冰核形成的分子动力学模拟的几个方面，其中将粘土矿物高岭石作为一种典型的冰核材料，这在大气科学中具有重要意义。我们通过种子分子动力学模拟表明，高岭石的羟基化（001）面上的冰核化仅通过六角形冰多型的形成而进行。临界核尺寸是在相同的过冷条件下均质成核所获得的临界核尺寸的两倍。先前的发现表明，高岭石表面的柔韧性可以在分子动力学模拟中改变冰成核的时间尺度。但是，我们在这里证明，具有相同弹性（或非弹性）的高岭石表面在结冰方面可能会导致截然不同的结果，根据是否考虑了粘土的表面松弛。我们表明，松弛时很小的结构变化会极大地改变高岭石的能力，从而为在水-高岭石界面上形成水分子的六边形覆盖层提供模板，因此这种松弛决定了这种矿物的成核能力。

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Ice formation on kaolinite: Insights from molecular dynamics simulations

The formation of ice affects many aspects of our everyday life as well as important technologies such as cryotherapy and cryopreservation. Foreign substances almost always aid water freezing through heterogeneous ice nucleation, but the molecular details of this process remain largely unknown. In fact, insight into the microscopic mechanism of ice formation on different substrates is difficult to obtain even if state-of-the-art experimental techniques are used. At the same time, atomistic simulations of heterogeneous ice nucleation frequently face extraordinary challenges due to the complexity of the water-substrate interaction and the long time scales that characterize nucleation events. Here, we have investigated several aspects of molecular dynamics simulations of heterogeneous ice nucleation considering as a prototypical ice nucleating material the clay mineral kaolinite, which is of relevance in atmospheric science. We show via seeded molecular dynamics simulations that ice nucleation on the hydroxylated (001) face of kaolinite proceeds exclusively via the formation of the hexagonal ice polytype. The critical nucleus size is two times smaller than that obtained for homogeneous nucleation at the same supercooling. Previous findings suggested that the flexibility of the kaolinite surface can alter the time scale for ice nucleation within molecular dynamics simulations. However, we here demonstrate that equally flexible (or non flexible) kaolinite surfaces can lead to very different outcomes in terms of ice formation, according to whether or not the surface relaxation of the clay is taken into account. We show that very small structural changes upon relaxation dramatically alter the ability of kaolinite to provide a template for the formation of a hexagonal overlayer of water molecules at the water-kaolinite interface, and that this relaxation therefore determines the nucleation ability of this mineral.

更新日期：2016-12-03

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