Contact Charge Electrophoresis: Experiment and Theory
Contact Charge Electrophoresis: Experiment and Theory
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DOI：
10.1021/acs.langmuir.5b00342
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发表时间：
2015-04-07
期刊：
影响因子：
3.9
通讯作者：
Bishop, Kyle J. M.
中科院分区：
文献类型：
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作者：
Drews, Aaron M.;Cartier, Charles A.;Bishop, Kyle J. M.
接触电荷电泳（CCEP）使用稳定的电场来驱动导电颗粒和液滴在两个或多个电极之间的连续振荡运动。这些快速振荡可以通过低功率直流电压进行整流，以指导微流体环境中物体的运动。在这里，我们将微流控系统中CCEP的高精度实验测量与平行电极之间导电粒子运动的同等详细的理论预测进行了比较。我们使用一个简单的毛细管微流控平台，结合了高速成像和精密电测量，能够同步获取粒子位置和粒子运动产生的电流。实验结果与理论模型的结果进行了比较，理论模型依赖于斯托克动力学方法来准确描述控制粒子运动的静电和流体动力学问题。我们发现理论和实验之间有显著的一致性，这表明粒子运动可以通过经典静电学和低雷诺数流体力学的结合来精确地捕捉。在此协议的基础上，我们为粒子接近电极表面接触时发生的电荷转移过程提供了新的见解。特别地，我们发现粒子不会与电极发生机械接触，而是通过薄润滑膜的放电在有限的表面分离处发生电荷转移。我们讨论了这些发现对粒子充电及其后续动力学的影响。
Contact charge electrophoresis (CCEP) uses steady electric fields to drive the continuous, oscillatory motion of conductive particles and droplets between two or more electrodes. These rapid oscillations can be rectified to direct the motion of objects within microfluidic environments using low-power, dc voltage. Here, we compare high precision experimental measurements of CCEP within a microfluidic system to equally detailed theoretical predictions on the motion of a conductive particle between parallel electrodes. We use a simple, capillary microfluidic platform that combines high-speed imaging with precision electrical measurements to enable the synchronized acquisition of both the particle location and the electric current due to particle motion. The experimental results are compared to those of a theoretical model, which relies on a Stokesian dynamics approach to accurately describe both the electrostatic and hydrodynamic problems governing particle motion. We find remarkable agreement between theory and experiment, suggesting that particle motion can be accurately captured by a combination of classical electrostatics and low-Reynolds number hydrodynamics. Building on this agreement, we offer new insight into the charge transfer process that occurs when the particle nears contact with an electrode surface. In particular, we find that the particle does not make mechanical contact with the electrode but rather that charge transfer occurs at finite surface separations of >0.1 mu m by means of an electric discharge through a thin lubricating film. We discuss the implications of these findings on the charging of the particle and its subsequent dynamics.