Physics of Complex Fluids, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
Lab Chip. 2012 Aug 21;12(16):2832-6. doi: 10.1039/c2lc21036c. Epub 2012 May 30.
The adsorption of surface active species to liquid-liquid and to solid-liquid interfaces can have dramatic effects in microfluidics. In this paper we show how electrowetting on dielectric can be used to monitor a dynamic liquid-liquid interfacial tension (IFT) with a time resolution of O(1 s) using amplitude modulation of the AC voltage. This straightforward method, which requires less than a microlitre of sample, is demonstrated for aqueous drops containing Triton X-100 surfactant on a Teflon AF-coated substrate and with heptane as the immiscible oil ambient. Under these conditions, next to extracting the oil-water IFT (γ(ow)), also the effective water-substrate IFT difference (Δγ(ws)) can be obtained from the oil-water IFT and the Young's angle. Both γ(ow) and γ(ws) decrease over time due to adsorption. The measured dynamic oil-water IFT compares well to results of pendant drop experiments.
在微流控中，表面活性剂在液-液和固-液界面的吸附会产生显著的影响。本文展示了如何利用介电电泳来监测动态液-液界面张力（IFT），其时间分辨率可达 O(1 s)，使用交流电压的幅度调制。这种简单的方法仅需要不到一微升的样品，在含有 Triton X-100 表面活性剂的水滴滴在 Teflon AF 涂层基底上，且以庚烷作为不混溶油环境的情况下进行了演示。在这些条件下，除了提取油水 IFT（γ(ow)）外，还可以从油水 IFT 和杨氏角得到有效水-基底 IFT 差值（Δγ(ws)）。由于吸附作用，γ(ow)和γ(ws)随时间而降低。测量得到的动态油水 IFT 与悬滴实验的结果非常吻合。
