The Surface of Ice under Equilibrium and Nonequilibrium Conditions
The Surface of Ice under Equilibrium and Nonequilibrium Conditions
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DOI：
10.1021/acs.accounts.8b00615
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发表时间：
2019-03
影响因子：
18.3
通讯作者：
Yuki Nagata;T. Hama;E. Backus;M. Mezger;D. Bonn;M. Bonn;G. Sazaki
中科院分区：
文献类型：
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作者：
Yuki Nagata;T. Hama;E. Backus;M. Mezger;D. Bonn;M. Bonn;G. Sazaki
冰的预融，通常被称为准液体层（QLL），是冰的润滑，冰吸收气体和气溶胶生长的关键。尽管其明显的重要性，从微观到宏观尺度的冰预融的深入了解还没有获得。通过回顾使用分子动力学（MD）模拟，和频产生（SFG）光谱学，激光共焦差分干涉显微镜（LCM-DIM）获得的数据，我们提供了一个统一的观点，实验观察到的准液体（QL）状态的变化。特别是，我们解开三种不同类型的QL状态的无序层，QL-液滴，和QL-膜，并讨论它们的性质。最上面的冰层在能量上是不稳定的，因为最上面的界面H2O分子失去了氢键，在冰-空气界面处产生了无序层。这种无序层均匀地分布在冰面上。无序层的性质在从−90 °C到体熔点的宽温度范围内变化。结合MD模拟和SFG测量显示，最顶层的冰表面在−90 °C左右开始无序，通过一个过程，最顶层的水分子与三个氢键转化为双氢键物种。当温度进一步升高时，第二层在-16 °C左右开始变得无序。这种无序化不是以渐进的方式发生，而是以双层接双层的方式发生。当温度达到-2 °C时，更复杂的结构，QL-液滴和QL-膜，出现在冰面的顶部。与无序层相反，这些QL-液滴和QL-膜是不均匀分布的。我们发现，这些QL-液滴和QL-膜出现仅在过饱和/欠饱和蒸汽压条件下，作为部分和pseudopartial润湿状态，分别。精确控制压力的实验表明，在气冰平衡条件下的水蒸气压附近，无法观察到QL液滴和QL膜，这意味着QL液滴和QL膜仅在非平衡条件下出现，而不是在平衡条件下形成的无序层。这些发现与许多与冰面有关的现象有关。例如，我们解释了最上面的冰面的无序如何控制冰面的光滑度，从而允许滑冰。进一步的重点是在冰面上的气体吸收机制。最后，我们注意到尚未解决的问题和未来的挑战有关的冰预融。
Conspectus The ice premelt, often called the quasi-liquid layer (QLL), is key for the lubrication of ice, gas uptake by ice, and growth of aerosols. Despite its apparent importance, in-depth understanding of the ice premelt from the microscopic to the macroscopic scale has not been gained. By reviewing data obtained using molecular dynamics (MD) simulations, sum-frequency generation (SFG) spectroscopy, and laser confocal differential interference contrast microscopy (LCM-DIM), we provide a unified view of the experimentally observed variation in quasi-liquid (QL) states. In particular, we disentangle three distinct types of QL states of disordered layers, QL-droplet, and QL-film and discuss their nature. The topmost ice layer is energetically unstable, as the topmost interfacial H2O molecules lose a hydrogen bonding partner, generating a disordered layer at the ice–air interface. This disordered layer is homogeneously distributed over the ice surface. The nature of the disordered layer changes over a wide temperature range from −90 °C to the bulk melting point. Combined MD simulations and SFG measurements reveal that the topmost ice surface starts to be disordered around −90 °C through a process that the topmost water molecules with three hydrogen bonds convert to a doubly hydrogen-bonded species. When the temperature is further increased, the second layer starts to become disordered at around −16 °C. This disordering occurs not in a gradual manner, but in a bilayer-by-bilayer manner. When the temperature reaches −2 °C, more complicated structures, QL-droplet and QL-film, emerge on the top of the ice surface. These QL-droplets and QL-films are inhomogeneously distributed, in contrast to the disordered layer. We show that these QL-droplet and QL-film emerge only under supersaturated/undersaturated vapor pressure conditions, as partial and pseudopartial wetting states, respectively. Experiments with precisely controlled pressure show that, near the water vapor pressure at the vapor-ice equilibrium condition, no QL-droplet and QL-film can be observed, implying that the QL-droplet and QL-film emerge exclusively under nonequilibrium conditions, as opposed to the disordered layers formed under equilibrium conditions. These findings are connected with many phenomena related to the ice surface. For example, we explain how the disordering of the topmost ice surface governs the slipperiness of the ice surface, allowing for ice skating. Further focus is on the gas uptake mechanism on the ice surface. Finally, we note the unresolved questions and future challenges regarding the ice premelt.