Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637.
Department of Materials, Eidgenössische Technische Hochschule (ETH) Zürich, CH-8093 Zürich, Switzerland.
Proc Natl Acad Sci U S A. 2022 Jun 14;119(24):e2121405119. doi: 10.1073/pnas.2121405119. Epub 2022 Jun 8.
Nonequilibrium interfacial thermodynamics has important implications for crucial biological, physical, and industrial-scale transport processes. Here, we discuss a theory of local equilibrium for multiphase multicomponent interfaces that builds upon the "sharp" interface concept first introduced by Gibbs, allowing for a description of nonequilibrium interfacial processes such as those arising in evaporation, condensation, adsorption, etc. By requiring that the thermodynamics be insensitive to the precise location of the dividing surface, one can identify conditions for local equilibrium and develop methods for measuring the values of intensive variables at the interface. We then use extensive, high-precision nonequilibrium molecular dynamics (NEMD) simulations to verify the theory and establish the validity of the local equilibrium hypothesis. In particular, we demonstrate that equilibrium equations of state are also valid out of equilibrium, and can be used to determine interfacial temperature and chemical potential(s) that are consistent with nonequilibrium generalizations of the Clapeyron and Gibbs adsorption equations. We also show, for example, that, far from equilibrium, temperature or chemical potential differences need not be uniform across an interface and may instead exhibit pronounced discontinuities. However, even in these circumstances, we demonstrate that the local equilibrium hypothesis and its implications remain valid. These results provide a thermodynamic foundation and computational tools for studying or revisiting a wide variety of interfacial transport phenomena.
非平衡界面热力学对于关键的生物、物理和工业规模的输运过程具有重要意义。在这里，我们讨论了一种适用于多相多组分界面的局部平衡理论，该理论建立在吉布斯首次引入的“sharp”界面概念基础上，允许描述诸如蒸发、冷凝、吸附等非平衡界面过程。通过要求热力学对分割面的精确位置不敏感，可以确定局部平衡的条件，并开发测量界面上强度变量值的方法。然后，我们使用广泛的、高精度的非平衡分子动力学（NEMD）模拟来验证理论并确立局部平衡假设的有效性。特别是，我们证明了平衡状态方程在非平衡状态下也是有效的，并且可以用于确定界面温度和化学势（s），这些参数与克劳佩龙和吉布斯吸附方程的非平衡推广相一致。我们还举例说明，即使在远离平衡的情况下，温度或化学势差不必在界面上均匀，而是可能表现出明显的不连续性。然而，即使在这些情况下，我们也证明了局部平衡假设及其含义仍然有效。这些结果为研究或重新研究各种界面输运现象提供了热力学基础和计算工具。
