Boundary conditions at the liquid-liquid interface in the presence of surfactants.
Boundary conditions at the liquid-liquid interface in the presence of surfactants.
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DOI：
10.1021/la101025h
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发表时间：
2010-05
期刊：
影响因子：
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通讯作者：
Y. Hu;Xianren Zhang;Wenchuan Wang
中科院分区：
文献类型：
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作者：
Y. Hu;Xianren Zhang;Wenchuan Wang
本文研究了在低剪切速率条件下，在有无表面活性剂存在的情况下，两种不互溶液体界面的流动边界条件。模拟结果表明，表面活性剂的存在大大改变了边界条件。类似于液-固边界，在不混溶的液-液界面处的几个边界条件，包括滑移、无滑移和锁定边界条件，被观察到取决于界面表面活性剂浓度。滑移边界条件仅在表面活性剂浓度为零或更低时实现。锁定边界条件观察时，表面活性剂浓度足够大，形成一个充分发展的单层，而无滑移条件发生的系统与中间值的表面活性剂浓度。滑移、无滑移和锁定边界条件分别产生正、零和负滑移长度。我们还研究了在不同界面活性剂浓度下，边界滑移对剪切速率的依赖性。与不含表面活性剂的体系相比，由于表面活性剂的存在，滑移随剪切速率的增加速度减慢，滑移长度的线性关系变为非线性关系。模拟结果还表明，剪切速率也影响表面活性剂的分布。特别是当表面活性剂浓度足够高以形成完全发育的单分子膜时，较高的剪切速率将使单分子膜破裂。
In this work, we studied the flow boundary conditions for the interface between two immiscible liquids under the condition of low shear rates in the presence or absence of surfactants. Our simulation results indicate that the boundary conditions are substantially changed by the presence of surfactants. Similar to the liquid-solid boundary, several boundary conditions at immiscible liquid-liquid interfaces, including slip, no-slip, and locking boundary conditions, are observed depending on the interfacial surfactant concentration. The slip boundary condition is achieved only at zero or lower surfactant concentration. The locking boundary condition is observed when the surfactant concentration is large enough to form a fully developed monolayer whereas the no-slip condition occurs for systems with intermediate values of surfactant concentration. The slip, no-slip, and locking boundary conditions yield the positive, zero, and negative slip lengths, respectively. We also investigated the dependence of boundary slip on shear rate at different interfacial surfactant concentrations. Compared to the systems without surfactants, the increase in slip with shear rate slows down because of the presence of surfactants, and consequently, the linear dependence of slip length changes to a nonlinear dependence. Simulation results also indicate that the shear rate also affects the surfactant distribution. In particular, when the surfactant concentration is high enough to form a fully developed monolayer, the higher shear rate would make the monolayer rupture.