Nagata Yuki, Hama Tetsuya, Backus Ellen H G, Mezger Markus, Bonn Daniel, Bonn Mischa, Sazaki Gen
Max Planck Institute for Polymer Research , Ackermannweg 10 , 55128 Mainz , Germany.
Institute of Low Temperature Science , Hokkaido University , Sapporo 060-0819 , Japan.
Acc Chem Res. 2019 Apr 16;52(4):1006-1015. doi: 10.1021/acs.accounts.8b00615. Epub 2019 Mar 29.
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 HO 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.
冰预融层，通常称为准液态层（QLL），对于冰的润滑、冰对气体的吸收以及气溶胶的生长至关重要。尽管其重要性显而易见，但尚未从微观到宏观尺度深入了解冰预融层。通过回顾使用分子动力学（MD）模拟、和频产生（SFG）光谱以及激光共聚焦微分干涉对比显微镜（LCM-DIM）获得的数据，我们提供了一个关于实验观察到的准液态（QL）状态变化的统一观点。特别是，我们区分了无序层、QL液滴和QL膜这三种不同类型的QL状态，并讨论了它们的性质。最顶层的冰层在能量上是不稳定的，因为最顶层的界面HO分子失去了一个氢键伙伴，在冰-空气界面处产生了一个无序层。这个无序层在冰表面均匀分布。无序层的性质在从-90°C到体熔点的很宽温度范围内都会发生变化。MD模拟和SFG测量相结合表明，最顶层的冰表面在-90°C左右开始无序化，过程是最顶层具有三个氢键的水分子转变为具有两个氢键的物种。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，而是以双层逐双层的方式发生。当温度达到-2°C时，更复杂的结构，即QL液滴和QL膜，出现在冰表面顶部。与无序层不同，这些QL液滴和QL膜分布不均匀。我们表明，这些QL液滴和QL膜仅在过饱和/欠饱和蒸气压条件下分别作为部分润湿和假部分润湿状态出现。精确控制压力的实验表明，在气-冰平衡条件下的水蒸气压力附近，观察不到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，与在平衡条件下形成的无序层相反。这些发现与许多与冰表面相关的现象有关。例如，我们解释了最顶层冰表面的无序化如何控制冰表面的滑爽性，从而实现滑冰。进一步关注的是冰表面的气体吸收机制。最后，我们指出了关于冰预融层尚未解决的问题和未来的挑战。
