Shah Virenkumar, Broseta Daniel
Laboratoire des Fluides Complexes, UMR 5150, Université de Pau et des Pays de l'Adour, BP1155, 64013, Pau Cedex, France.
Langmuir. 2007 Dec 4;23(25):12598-605. doi: 10.1021/la701893z. Epub 2007 Oct 31.
We propose an accurate method to predict interfacial tension between water and nonpolar fluids by using Cahn gradient theory. The only necessary elements are (i) a water contact energy function and (ii) an equation of state (EoS) for the nonpolar fluid, chosen here as the Peng-Robinson EoS. The contact energy, a function of the fluid (adsorbate) surface density, is related to interfacial tension (IFT) by means of the Gibbs adsorption equation. Examining a large number of IFT data, we observe that the water contact energy is a universal function of adsorbate's surface density when proper scaling variables are used: it depends neither on adsorbate nor on temperature. A corresponding-states principle appears to govern the interfacial behavior between water and any nonpolar compound that is sparingly soluble in water. A predictive method (without any adjustable parameter) is therefore available for estimating IFT between water and any nonpolar fluid, whether the fluid is in supercritical or in subcritical states. The method performs well when the adsorbate is sparingly soluble in water, but slightly overestimates IFTs when the adsorbate's solubility in water is significant (e.g., CO2 and H2S). A similar behavior should also hold for interfaces involving a solid substrate.
我们提出了一种利用卡恩梯度理论预测水与非极性流体之间界面张力的精确方法。唯一必要的要素是：（i）水接触能函数；（ii）非极性流体的状态方程（EoS），这里选择彭 - 罗宾逊状态方程。接触能是流体（吸附质）表面密度的函数，通过吉布斯吸附方程与界面张力（IFT）相关。通过研究大量的界面张力数据，我们观察到，当使用适当的标度变量时，水接触能是吸附质表面密度的通用函数：它既不依赖于吸附质，也不依赖于温度。对应态原理似乎支配着水与任何微溶于水的非极性化合物之间的界面行为。因此，有一种预测方法（无需任何可调参数）可用于估算水与任何非极性流体之间的界面张力，无论该流体处于超临界状态还是亚临界状态。当吸附质微溶于水时，该方法表现良好，但当吸附质在水中的溶解度较大时（例如二氧化碳和硫化氢），会略微高估界面张力。对于涉及固体基质的界面，也应该有类似的行为。
