Engineering Thermodynamics, Process, and Energy Department, Delft University of Technology, 2628 CA Delft, The Netherlands.
J Chem Phys. 2009 Nov 28;131(20):204705. doi: 10.1063/1.3263124.
A Helmholtz energy functional for inhomogeneous fluid phases based on the perturbed-chain polar statistical associating fluid theory (PCP-SAFT) equation of state is proposed. The model is supplemented with a capillary wave contribution to the surface tension to account for long-wavelength fluctuations of a vapor-liquid interface. The functional for the dispersive attraction is based on a nonlocal perturbation theory for chain fluids and the difference of the perturbation theory to the dispersion term of the PCP-SAFT equation of state is treated with a local density approximation. This approach suggested by Gloor et al. [Fluid Phase Equilib. 194, 521 (2002)] leads to full compatibility with the PCP-SAFT equation of state. Several levels of approximation are compared for the nonlocal functional of the dispersive attractions. A first-order non-mean-field description is found to be superior to a mean-field treatment, whereas the inclusion of a second-order perturbation term does not contribute significantly to the results. The proposed functional gives excellent results for the surface tension of nonpolar or only moderately polar fluids, such as alkanes, aromatic substances, ethers, and ethanoates. A local density approximation for the polar interactions is sufficient for carbon dioxide as a strongly quadrupolar compound. The surface tension of acetone, as an archetype dipolar fluid, is overestimated, suggesting that a nonisotropic orientational distribution function across an interface should for strong dipolar substances be accounted for.
提出了一种基于受扰链极性统计缔合流体理论（PCP-SAFT）状态方程的不均匀流体相的亥姆霍兹能量泛函。该模型补充了一个毛细波对表面张力的贡献，以解释汽液界面的长波长涨落。色散吸引力的泛函基于链流体的非局部微扰理论，并且微扰理论与 PCP-SAFT 状态方程的色散项之间的差异用局部密度近似来处理。这种由 Gloor 等人提出的方法[Fluid Phase Equilib. 194, 521 (2002)]导致与 PCP-SAFT 状态方程完全兼容。比较了几种近似水平的色散吸引力的非局部泛函。发现一阶非平均场描述优于平均场处理，而二阶微扰项的包含并没有对结果有显著贡献。对于非极性或只有中等极性的流体，如烷烃、芳香物质、醚和乙酸盐，所提出的泛函给出了极好的表面张力结果。对于二氧化碳等强四极化合物，对极性相互作用进行局部密度近似就足够了。作为典型偶极流体的丙酮的表面张力被高估，这表明对于强偶极物质，应该考虑界面上的各向异性取向分布函数。
