利用非理想超临界流体混合物的模拟阐明分压、挥发度与索雷特效应之间的联系
Connection between partial pressure, volatility, and the Soret effect elucidated using simulations of non-ideal supercritical fluid mixtures
AI总结：
本文通过分子动力学模拟提出并验证了非理想流体混合物中索雷特效应的化学贡献源于组分分压对温度与密度梯度的响应差异，并利用新参数 $γ_{s}^{S}$ 将索雷特系数与相对挥发度关联，为通过分蒸气压测量间接确定索雷特系数提供了可能。
摘要：
在近期模拟工作的基础上，本文通过对双组分流体混合物的分子动力学（MD）模拟证明，双组分非理想流体混合物中索雷特效应的化学贡献来源于各组分分压对温度和密度梯度的响应方式存在差异。通过回顾液体混合物蒸气压测量中活度与拉乌尔定律偏差之间的联系，获得了进一步的认识。定义了一个新参数 $γ_{s}^{S}$，其定义方式类似于活度系数，用于表征与“理想”行为的偏差。随后表明，差值 $γ_{2}^{S}-γ_{1}^{S}$ 能够预测索雷特系数的符号，并与其大小相关。因此，我们将索雷特效应与流体混合物各组分的相对挥发度联系起来：挥发性较高的组分在低密度、高温区域富集，而挥发性较低的组分在高密度、低温区域富集。由于 $γ_{s}^{S}$ 与活度系数密切相关，这表明有可能利用分蒸气压的测量来间接确定索雷特系数。本文提出，此处获得的见解具有相当的普遍性，应适用于广泛的材料体系。本文还尝试理解这些结果如何应用于其他材料体系，包括固体中的间隙原子以及通过空位机制发生互扩散的多组分固体。
英文摘要：
Building on recent simulation work, it is demonstrated using molecular-dynamics (MD) simulations of two-component fluid mixtures that the chemical contribution to the Soret effect in two-component non-ideal fluid mixtures arises due to differences in how the partial pressures of the components respond to temperature and density gradients. Further insight is obtained by reviewing the connection between activity and deviations from Raoult's law in the measurement of the vapor pressure of a liquid mixture. A new parameter $γ_{s}^{S}$, defined in a manner similar to the activity coefficient, is used to characterize differences deviations from ``ideal'' behavior. It is then shown that the difference $γ_{2}^{S}-γ_{1}^{S}$ is predictive of the sign of the Soret coefficient and is correlated to its magnitude. We hence connect the Soret effect to the relative volatility of the components of a fluid mixture, with the more volatile component enriched in the low-density, high-temperature region, and the less volatile component enriched in the high-density, low-temperature region. Because $γ_{s}^{S}$ is closely connected to the activity coefficient, this suggests the possibility that measurement of partial vapor pressures might be used to indirectly determine the Soret coefficient. It is proposed that the insight obtained here is quite general and should be applicable to a wide range of materials systems. An attempt is made to understand how these results might apply to other materials systems including interstitials in solids and multicomponent solids with interdiffusion occurring via a vacancy mechanism.
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