CFD evaluation of drop retraction methods for the measurement of interfacial tension of surfactant-laden drops
CFD evaluation of drop retraction methods for the measurement of interfacial tension of surfactant-laden drops
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DOI：
10.1016/j.jcis.2003.09.030
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发表时间：
2004-04-01
影响因子：
9.9
通讯作者：
Macosko, CW
中科院分区：
文献类型：
--
作者：
Velankar, S;Zhou, H;Macosko, CW
液滴回缩法是测量不混溶聚合物之间界面张力的常用方法。实验表明，当液滴表面存在表面活性剂时，两种不同的液滴回缩方法（嵌入纤维回缩 (IFR) 和变形液滴回缩 (DDR)）会给出不一致的结果。这些不一致被认为是由于表面活性剂的稀释以及表面活性剂沿液滴表面的界面浓度梯度造成的。该物理图像针对牛顿矩阵中牛顿滴的简单情况进行了量化，界面处存在不溶性、非扩散性表面活性剂。在计算流体动力学模拟中，液滴通过剪切基体而变形，然后缩回。人们发现稀释和界面张力梯度效应在回缩的早期阶段特别大，使得 IFR 不适合测量表面活性剂负载界面的界面张力。发现表面活性剂稀释和梯度的影响甚至在回缩的后期仍然存在，导致 DDR 方法显着低估平衡界面张力。当液滴粘度低于基质粘度时，会发生最大的低估。 (C) 2003 Elsevier Inc. 保留所有权利。
Drop retraction methods are popular means of measuring the interfacial tension between immiscible polymers. Experiments show that two different drop retraction methods, imbedded fiber retraction (IFR) and deformed drop retraction (DDR), give inconsistent results when a surfactant is present on the surface of the drop. These inconsistencies are deemed to be due to dilution of the surfactant and due to gradients in interfacial concentration of surfactant along the drop surface. This physical picture is quantified for the simple case of a Newtonian drop in a Newtonian matrix, with an insoluble, nondiffusive surfactant at the interface. The drop is deformed in computational fluid dynamics simulations by shearing the matrix, and then allowed to retract. Dilution and interfacial tension gradients effects are found to be especially large at the early stages of retraction, making IFR unsuitable for measuring the interfacial tension of surfactant-laden interfaces. The effects of surfactant dilution and gradients are found to persist even at late stages of retraction, causing the DDR method to underestimate the equilibrium interfacial tension significantly. The largest underestimates occur when the drop viscosity is lower than the matrix viscosity. (C) 2003 Elsevier Inc. All rights reserved.