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Water Condensation on Graphite Studied by Elastic Helium Scattering and Molecular Dynamics Simulations

机译:弹性氦散射研究石墨上的水凝结及分子动力学模拟

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摘要

Formation of water/ice layers on graphite has been studied in the temperature range from 90 to 180 K by elastic helium scattering, light scattering, and molecular dynamics simulations. Combined helium- and lightscattering experiments show that an ice film that wets the graphite surface is formed at surface temperatures of 100-140 K, whereas three-dimensional ice structures are formed at 140-180 K. Desorption of adsorbed water molecules competes with water incorporation into the ice film, and the ice formation rate is strongly temperature dependent. At 150 K, ice-layer formation takes place at the same time scale as layer reconstruction, and its properties are sensitive to the water deposition rate. The experimental results are compared with kinetics models, and the Johnston-Mehl-Avrami-Kolmogorov model is concluded to well describe the ice-layer formation kinetics in the whole temperature range. Molecular dynamics simulations of water-cluster formation on graphite at 90-180 K show that water molecules and small clusters are highly mobile on the surface, which rapidly results in the nucleation of large and less mobile clusters on the surface. Clusters formed at low temperature tend to have the most molecules in direct contact with the uppermost graphite layer, while multilayer cluster structures are preferred at high temperatures. The results are discussed and compared with earlier studies of water ice formation on solid surfaces.
机译:通过弹性氦散射,光散射和分子动力学模拟,研究了在90至180 K的温度范围内在石墨上形成水/冰层的情况。氦气和光散射的联合实验表明,在100-140 K的表面温度下会形成一层润湿石墨表面的冰膜,而在140-180 K的温度下会形成三维冰结构。吸附的水分子的解吸与水的引入竞争进入冰膜后,冰的形成速度与温度密切相关。在150 K时,冰层的形成与层重建的时间尺度相同,并且其性质对水的沉积速率敏感。将实验结果与动力学模型进行比较,得出Johnston-Mehl-Avrami-Kolmogorov模型,以很好地描述整个温度范围内的冰层形成动力学。石墨在90-180 K上形成水团簇的分子动力学模拟表明,水分子和小团簇在表面上具有很高的移动性,从而迅速导致表面上较大和较少移动的团簇成核。在低温下形成的团簇倾向于具有最多的分子与最上层的石墨层直接接触,而在高温下优选多层团簇结构。对结果进行了讨论,并与早期在固体表面形成水冰的研究进行了比较。

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