Abstract Surfactant-laden liquid/liquid interfaces mediate numerous chemical processes, from commercial applications of microemulsions to chemical separations. Classical molecular dynamics simulation is a prevalent method for studying microscopic and thermodynamic properties of such interfaces. However the extent to which these features can be reliably predicted, and the variations in predicted behavior, depend upon the force field parameters employed. At present, the impact of force fields upon simulated properties is relatively understudied. Yet recent advances to sampling and analysis algorithms are increasing the interpretation of simulation data and therefore understanding force field dependence is increasingly relevant. In this study, the impact of the force field of the surfactant tri-n-butyl phosphate (TBP), as well as that of water, is investigated at a water/(n-hexane + surfactant) interface. Empirical charge scaling was employed to modulate the hydrophilicity of the surfactant. As anticipated, the relative hydrophilicity of TBP influences a number of properties, including the adsorbed concentrations of TBP at the interface, and macroscopic properties that result from hydrogen bonding interactions, such as interfacial tension and width. The dynamic properties of solvents at the interface are strongly modulated by the variation in hydrogen bond strength caused by different charge scalings of the TBP model. This includes the residence times of water at the interface, where stronger water-TBP hydrogen bonding causes long-lived residences. Interestingly, there are a number of features that are relatively insensitive to the TBP hydrophilicity. In one important case, the concentration of water-bridged TBP dimers was only impacted by the least hydrophilic model. As these dimeric species are the building block of surface protrusions that lead to water transport across the interface, this implies that collective organizational patterns and surface structures that derive from multiple driving forces (e.g., TBP hydrophilicity and organic solvent free energies of solvation) are less sensitive to individual force field parameters. Further, we note that competitive interactions can “cancel” the effects of changing TBP charge on interfacial properties. One example is the orientation and hydrogen bonding structure of interfacial water, where the direct TBP-water hydrogen bonding competes against the indirect TBP-induced interfacial roughness. In combination, these observations may assist future simulation studies in calibrating surfactant models to, or interpreting results of, a broad range of dynamic, structural and thermodynamic properties.

中文翻译：

---

表面活性剂力场对液/液界面性质的影响

摘要含有表面活性剂的液/液界面介导了许多化学过程，从微乳液的商业应用到化学分离。经典分子动力学模拟是研究此类界面的微观和热力学性质的普遍方法。然而，可以可靠地预测这些特征的程度以及预测行为的变化取决于所采用的力场参数。目前，力场对模拟特性的影响研究相对较少。然而，采样和分析算法的最新进展正在增加对模拟数据的解释，因此理解力场依赖性越来越重要。在这项研究中，表面活性剂磷酸三正丁酯 (TBP) 以及水的力场的影响，在水/（正己烷 + 表面活性剂）界面进行研究。采用经验电荷缩放来调节表面活性剂的亲水性。正如预期的那样，TBP 的相对亲水性会影响许多特性，包括界面处 TBP 的吸附浓度，以及氢键相互作用导致的宏观特性，例如界面张力和宽度。界面处溶剂的动态性质受 TBP 模型不同电荷缩放引起的氢键强度变化的强烈调节。这包括水在界面上的停留时间，其中更强的水-TBP 氢键会导致长期停留。有趣的是，有许多特征对 TBP 亲水性相对不敏感。在一个重要的案例中，水桥接 TBP 二聚体的浓度仅受最不亲水模型的影响。由于这些二聚体物质是导致水跨界面传输的表面突起的组成部分，这意味着源自多种驱动力（例如，TBP 亲水性和有机溶剂自由溶剂化能）的集体组织模式和表面结构较少对单个力场参数敏感。此外，我们注意到竞争性相互作用可以“取消”改变 TBP 电荷对界面特性的影响。一个例子是界面水的取向和氢键结构，其中直接的 TBP-水氢键与间接的 TBP 诱导的界面粗糙度竞争。结合，