Garrido José Matías, Quinteros-Lama Héctor, Piñeiro Manuel M, Mejía Andrés, Segura Hugo
Departamento de Ingeniería Química, Universidad de Concepción, POB-160 C Concepción, Chile.
Departamento de Física Aplicada, Facultade de Ciencias, Universidade de Vigo, E-36310 Vigo, Spain.
J Chem Phys. 2014 Jul 7;141(1):014503. doi: 10.1063/1.4885348.
This work focuses on the application of a two-way approach, where Molecular Dynamics (MD) simulations and the Square Gradient Theory (SGT) have been used for describing the phase and interface behavior of binary and ternary Lennard-Jones (LJ) mixtures, along a condition of three-phase equilibrium. The unequivocal correspondence between MD and SGT has been achieved by using the global phase diagram of binary mixtures composed by equally sized Lennard-Jones molecules, from which representative molecular parameters for Type-I, Type-II, and Type-III systems have been determined. The so selected binaries have been used then to scale the behavior of a ternary mixture characterized by complex phase equilibrium patterns. For the case of the theoretical SGT approach applied to the Lennard-Jones equation of state was used for predicting phase equilibrium and interfacial properties. In addition the corresponding MD simulations of these macroscopic properties have been conducted for the LJ potential by using equivalent molecular parameters and conditions than in the theoretical approach. Excellent agreement has been observed between the predictions obtained from theory and simulations. Particularly, our results concerning the characterization of the three phase line of a binary Type-III mixture indicate that the bulk liquid (α) and the bulk gas (G) regions are sharply separated by a bulk liquid region (β) for all the explored temperature, pressure, and concentration conditions. The structural analysis of these bulk phases reveals that a secondary liquid phase (β) perfectly wets the liquid-gas interface (α-G), as previously found for Type-II mixture [A. Mejía and L. F. Vega, J. Chem. Phys. 124, 244505 (2006)]. The exploration along the three-phase line for the ternary mixture shows good agreement between SGT and MD. Particularly, we observed the specific influence of a third component in the phase and interface behavior. From all the previous results, we conclude that the SGT applied to an EoS with appropriate mixing rules produces reliable predictions of the properties of ternary mixtures.
这项工作聚焦于一种双向方法的应用，其中分子动力学（MD）模拟和平方梯度理论（SGT）已被用于描述二元和三元 Lennard-Jones（LJ）混合物在三相平衡条件下的相行为和界面行为。通过使用由等尺寸 Lennard-Jones 分子组成的二元混合物的全局相图，实现了 MD 和 SGT 之间明确的对应关系，从中确定了 I 型、II 型和 III 型系统的代表性分子参数。然后，所选择的二元体系被用于缩放具有复杂相平衡模式的三元混合物的行为。对于应用于 Lennard-Jones 状态方程的理论 SGT 方法，用于预测相平衡和界面性质。此外，通过使用与理论方法等效的分子参数和条件，对这些宏观性质进行了相应的 MD 模拟。理论预测和模拟结果之间观察到了极好的一致性。特别是，我们关于二元 III 型混合物三相线特征的结果表明，在所有探索的温度、压力和浓度条件下，体相液体（α）和体相气体（G）区域被一个体相液体区域（β）清晰地分隔开。这些体相的结构分析表明，一个次级液相（β）完美地润湿了液 - 气界面（α - G），正如之前在 II 型混合物中所发现的那样 [A. Mejía 和 L. F. Vega，《化学物理杂志》124，244505（2006）]。对三元混合物三相线的探索表明 SGT 和 MD 之间具有良好的一致性。特别是，我们观察到了第三组分在相和界面行为中的特定影响。从所有先前的结果来看，我们得出结论，应用于具有适当混合规则的状态方程的 SGT 能够可靠地预测三元混合物的性质。
