Santiago Johanna M, Keffer David J, Counce Robert M
Department of Chemical Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
Langmuir. 2006 Jun 6;22(12):5358-65. doi: 10.1021/la052903h.
We performed a series of experiments designed to elucidate the effects of the presence of sodium dodecyl sulfate (SDS) surfactant and an applied electrical field on the wetting behavior in a system containing a sessile droplet of phenylmethyl polysiloxane (PMPS) oil on a polished stainless steel surface submersed in aqueous solution. The voltage difference ranged from -3 to +3 V, which is at least 3 orders of magnitude smaller than from comparable recent work. We report the measured equilibrium contact angle of the droplet as a function of surfactant concentration and field strength. We then modeled the system. We solved the Laplace equation to obtain the 3D field within our system. We expanded the three surface tensions (oil droplet-aqueous solution (oa), oil droplet-metal surface (os), and aqueous solution-metal surface (as)) in a Taylor series with respect to surfactant concentration and local field strength. We use these three surface tensions in Young's equation to obtain the theoretical contact angle of the organic droplet. We demonstrate that the large changes in contact angle due to the simultaneous presence of small concentrations of surfactant and small voltage differences can be accounted for by changes in the oa and as surface tensions.
我们进行了一系列实验，旨在阐明十二烷基硫酸钠（SDS）表面活性剂的存在以及外加电场对一个系统中润湿行为的影响，该系统包含一滴苯基甲基聚硅氧烷（PMPS）油在浸没于水溶液中的抛光不锈钢表面上形成的固着液滴。电压差范围为-3至+3V，这比近期类似工作中的电压差至少小3个数量级。我们报告了测量得到的液滴平衡接触角随表面活性剂浓度和场强的变化情况。然后我们对该系统进行了建模。我们求解拉普拉斯方程以获得系统内的三维场。我们针对表面活性剂浓度和局部场强，将三种表面张力（油滴 - 水溶液（oa）、油滴 - 金属表面（os）以及水溶液 - 金属表面（as））展开为泰勒级数。我们在杨氏方程中使用这三种表面张力来获得有机液滴的理论接触角。我们证明，由于同时存在低浓度表面活性剂和小电压差而导致的接触角的大幅变化，可以通过oa和as表面张力的变化来解释。
