Effects of a surfactant monolayer on the measurement of equilibrium interfacial tension of a drop in extensional flow.
Effects of a surfactant monolayer on the measurement of equilibrium interfacial tension of a drop in extensional flow.
复制标题
表面活性剂单层对拉伸流中液滴平衡界面张力测量的影响。
DOI：
10.1016/j.jcis.2009.02.004
复制
发表时间：
2009-05-15
影响因子：
9.9
通讯作者：
Eggleton, Charles D.
中科院分区：
文献类型：
--
作者：
Gonzalez-Mancera, Andres;Gupta, Vijay Kumar;Jamal, Mustapha;Eggleton, Charles D.
采用边界积分法研究了表面活性剂单分子层浓度对瞬态液滴变形法测量界面张力的影响。乳化液滴与表面活性剂单层建模与朗缪尔状态方程最初在平衡突然受到轴对称拉伸流，直到达到稳态变形。然后去除外部流，并模拟液滴在静止状态下缩回到球形平衡形状。分析液滴对外加流的瞬态响应，得到特征响应时间。忽略初始和最终阶段，回缩过程可以通过具有特征时间的指数衰减来近似。为了研究变形和表面活性剂分布对特征弛豫时间的耦合效应，增加了每个模型液滴上的外部流的强度。通过改变内部粘度和平衡表面活性剂浓度，从表面活性剂游离状态（清洁）到接近最大填充极限的高浓度，来考虑不同的模型液滴。从模拟的液滴动力学在延伸和收缩中获得的特征时间被用来确定采用线性理论的表观表面张力。在延伸下，表观表面张力低于预定的平衡表面张力。该误差随平衡表面活性剂浓度的增加而单调增加，接近最大填充极限时发散。在回缩中，表观表面张力低于预定的平衡表面张力，非单调地依赖于平衡表面活性剂浓度。中等表面活性剂浓度的错误是最高的，并减少接近最大包装限制。结果表明，随着粘度比的减小，表面张力与表观表面张力之差增大。在规定的表面张力和由线性理论预测的表观表面张力之间可以看到高达40%的差异。
The effect of surfactant monolayer concentration on the measurement of interfacial surface tension using transient drop deformation methods is studied using the Boundary Integral Method. Emulsion droplets with a surfactant monolayer modeled with the Langmuir equation of state initially in equilibrium are suddenly subjected to axisymmetric extensional flows until a steady-state deformation is reached. The external flow is then removed and the retraction of the drops to a spherical equilibrium shape in a quiescent state is simulated. The transient response of the drop to the imposed flow is analyzed to obtain a characteristic response time, . Neglecting the initial and final stages, the retraction process can be closely approximated by an exponential decay with a characteristic time, . The strength of the external flow on each model drop is increased in order to investigate the coupled effect of deformation and surfactant distribution on the characteristic relaxation time. Different model drops are considered by varying the internal viscosity and the equilibrium surfactant concentrations from a surfactant free state (clean) to high concentrations approaching the maximum packing limit. The characteristic times obtained from the simulated drop dynamics both in extension and retraction are used to determine an apparent surface tension employing linear theory. In extension the apparent surface tension under predicts the prescribed equilibrium surface tension. The error increases monotonically with the equilibrium surfactant concnetration and diverges as the maximum packing limit is approached. In retraction the apparent surface tension under predicts the prescribed equilibrium surface tension depends non-monotonically on the equilibrium surfactant concentration. The error is highest for moderate surfantant concentrations and decreases as the maximum packing limit is approached. It was found that the difference between the prescribed surface tension and the apprent surface tension increased as the viscosity ratio decreased. Differences as large as 40% were seen between the prescribed surface tension and the apparent surface tension predicted by the linear theory.
登录
查看更多内容
影响因子：
9.9
作者：
Eggleton, CD;Stebe, KJ
通讯作者：
Stebe, KJ
影响因子：
9.9
作者：
Velankar, S;Zhou, H;Macosko, CW
通讯作者：
Macosko, CW
影响因子：
3.7
作者：
Zinchenko, AZ;Rother, MA;Davis, RH
通讯作者：
Davis, RH
影响因子：
3.9
作者：
Hansen, Finn Knut
通讯作者：
Hansen, Finn Knut
影响因子：
4.6
作者：
Pawar, Y;Stebe, KJ
通讯作者：
Stebe, KJ