Translational diffusion of hydrophobic solutes in supercritical water studied by molecular dynamics simulations
Translational diffusion of hydrophobic solutes in supercritical water studied by molecular dynamics simulations
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DOI：
10.1063/1.1607953
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发表时间：
2003-09
影响因子：
4.4
通讯作者：
Tsutomu Ohmori;Y. Kimura
中科院分区：
文献类型：
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作者：
Tsutomu Ohmori;Y. Kimura
用分子动力学模拟方法研究了疏水溶质(氧气和甲烷)在不同温度和密度下在水中的扩散过程。我们发现在中等密度区疏水溶质在水中的自扩散常数与温度的反常关系，即扩散常数几乎与温度无关。在氧气的情况下，甚至可以观察到温度依赖关系的反转。为了探讨这种反常现象的原因，我们基于广义朗之万理论，分析了摩擦力对扩散的速度自相关函数和记忆函数。疏水溶质的VACF几乎呈指数衰减，这表明Enskog理论是成立的。对记忆函数的分析表明，在密度小于663kgm−-3的温度范围内，摩擦的二元贡献随温度的降低而减小，这是产生反常现象的主要原因。
The diffusion process of hydrophobic solutes (oxygen and methane) in water at various temperatures and densities has been studied by molecular dynamics simulation. We found anomalous temperature dependence of the self-diffusion constants of hydrophobic solutes in water in the medium-density region, i.e., the diffusion constants are almost independent of the temperatures. In the case of oxygen, even the inversion of the temperature dependence is observed. To investigate the reason of this anomaly, we have analyzed the velocity auto correlation function (VACF) and memory function of the friction on the diffusion based on the generalized Langevin theory. The VACFs of hydrophobic solutes decay almost exponentially, which suggests that the Enskog theory holds. According to the analysis of the memory functions, it has been revealed that the binary contribution of the friction decreases with decreasing temperature from 973 to 647 K in the density region below 663 kg m−3, which is the main reason for the anomalou...