Abstract Classical density functional theory (DFT) is applied to study the vapor-liquid interface of associating fluids. Our classical DFT implementation uses a Helmholtz free energy functional that reduces to the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state in the bulk limit. We apply a new association functional, presented in one of our previous works, based on the weighted density approximation to calculate the interfacial tension of associating fluids and compare them with two of the most used association functionals from literature. It is found that classical DFT with the three association functionals and the current molecular parameters of PC-SAFT is not able to predict satisfactorily the interfacial tension of alkanols. Therefore, the experimental interfacial tension of alkanols and some associating fluids is included in the determination of the pure molecular parameters of PC-SAFT. With this approach the determination of interfacial tension of pure associating fluids can be greatly improved with the new parameters, but at the expense of slightly higher deviations in the vapor pressure. The new parameters are tested for the determination of vapor-liquid equilibria (VLE) and the prediction of interfacial tension of binary mixtures containing at least one associating compound. Good agreement is found between experimental data of VLE and interfacial tension of the binary mixtures and the three association functionals. Furthermore, we discuss about the limitations and capabilities of the current classical DFT implementation in the study of the vapor-liquid interface of associating fluids.

中文翻译：

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用经典密度泛函理论研究缔合流体的汽液界面

摘要 应用经典密度泛函理论（DFT）研究缔合流体的汽液界面。我们的经典 DFT 实现使用亥姆霍兹自由能函数，该函数简化为体积极限中的扰动链统计关联流体理论 (PC-SAFT) 状态方程。我们应用一种新的关联泛函，在我们之前的一项工作中提出，基于加权密度近似来计算关联流体的界面张力，并将它们与文献中最常用的两个关联泛函进行比较。发现具有三个缔合泛函的经典 DFT 和 PC-SAFT 的当前分子参数不能令人满意地预测烷醇的界面张力。所以，烷醇和一些缔合流体的实验界面张力包括在 PC-SAFT 纯分子参数的测定中。使用这种方法，纯缔合流体的界面张力的确定可以通过新参数大大提高，但代价是蒸气压的偏差略高。测试新参数用于确定气液平衡 (VLE) 和预测包含至少一种缔合化合物的二元混合物的界面张力。在 VLE 的实验数据和二元混合物的界面张力和三个关联泛函之间发现了良好的一致性。此外，