Ogawa Rei, Kusudo Hiroki, Omori Takeshi, Smith Edward R, Joly Laurent, Merabia Samy, Yamaguchi Yasutaka
Department of Mechanical Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan.
Department of Mechanical Systems Engineering, Tohoku University, 6-6-01 Aramaki Aoba-ku, Sendai 980-8579, Japan.
J Chem Phys. 2024 Dec 14;161(22). doi: 10.1063/5.0238862.
In this study, we carried out equilibrium molecular dynamics (EMD) simulations of the liquid-liquid (LL) interface between two different Lennard-Jones components with varying miscibility, where we examined the relation between the interfacial tension and the free energy to completely isolate the two liquids using both a mechanical and thermodynamic approach. Using the mechanical approach, we obtained a stress distribution around a quasi-one-dimensional EMD system with a flat LL interface. From the stress distribution, we calculated the LL interfacial tension based on Bakker's equation, which uses the stress anisotropy around the interface, and measured how it varied with miscibility. The second approach uses thermodynamic integration by enforcing quasi-static isolation of the two liquids to calculate the free energy. This uses the same EMD systems as the mechanical approach, with both extended dry-surface and phantom-wall (PW) schemes applied. When the two components were immiscible, the mechanical interfacial tension and isolation free energy were in good agreement. When the components were miscible, the values were significantly different. From the result of PW for the case of completely mixed liquids, the difference was attributed to the additional free energy required to separate the binary mixture into single components against the osmotic pressure prior to the complete detachment of the two components. This provides a new route to obtain the free energy of mixing.
在本研究中，我们对两种具有不同混溶性的不同 Lennard-Jones 组分之间的液-液（LL）界面进行了平衡分子动力学（EMD）模拟，在此过程中，我们使用力学和热力学方法研究了界面张力与完全分离两种液体所需的自由能之间的关系。使用力学方法，我们在具有平坦 LL 界面的准一维 EMD 系统周围获得了应力分布。根据应力分布，我们基于 Bakker 方程计算了 LL 界面张力，该方程利用界面周围的应力各向异性，并测量了其随混溶性的变化。第二种方法是通过强制两种液体的准静态隔离来进行热力学积分以计算自由能。这使用了与力学方法相同的 EMD 系统，并应用了扩展干表面和虚壁（PW）方案。当两种组分不混溶时，力学界面张力和隔离自由能吻合良好。当组分可混溶时，这些值有显著差异。从完全混合液体情况下的 PW 结果来看，这种差异归因于在两种组分完全分离之前，将二元混合物逆渗透压分离成单一成分所需的额外自由能。这为获得混合自由能提供了一条新途径。
