Measurement of Charge Transfer to Aqueous Droplets in High Voltage Electric Fields
Measurement of Charge Transfer to Aqueous Droplets in High Voltage Electric Fields
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DOI：
10.1021/acs.langmuir.7b03375
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发表时间：
2017-12-12
期刊：
影响因子：
3.9
通讯作者：
Ristenpart, William D.
中科院分区：
文献类型：
--
作者：
Elton, Eric S.;Tibrewala, Yash;Ristenpart, William D.
在实验和工业应用中，当它们接触电极时由水性液滴获得的电荷是一个关键参数，其中电场用于操纵液滴运动和聚结。由于不清楚的原因，许多研究人员发现，水性液滴获得的正电荷明显多于负电荷。用于确定液滴电荷的现有技术通常依赖于流体动力平衡，该流体动力平衡取决于作用在液滴上的拖曳力的准确表征。在这里，我们提出了一种替代的方法来测量液滴电荷通过直接测量的电流。当液滴接近电极时，观察到电流逐渐增加，随后当液滴进行明显接触时出现大脉冲。我们解释的瞬态电流信号的RLC电路的自然响应和Shockley-Ramo理论描述的感应电流的叠加。观察到的电流的非线性回归的理论模型允许提取的液滴电荷，独立于任何假设的力平衡的液滴。我们证明，回归的电流信号产生的电荷值，平均在4%以内的通过力平衡测量的电荷。我们使用计时库仑法来研究电荷如何随施加的电势而变化，并且我们证明了接触平面电极的去离子水滴平均获得比负电荷多69%的正电荷。
The electric charge acquired by aqueous droplets when they contact an electrode is a crucial parameter in experimental and industrial applications where electric fields are used to manipulate droplet motion and coalescence. For unclear reasons, many investigators have found that aqueous droplets acquire significantly more positive than negative charge. Extant techniques for determining the droplet charge typically rely on a hydrodynamic force balance that depends on accurate characterization of the drag forces acting on the droplet. Here we present an alternative methodology for measuring the droplet charge via direct measurement of the electric current. As the droplet approaches the electrode the current is observed to gradually increase, followed by a large pulse when the droplet makes apparent contact. We interpret the transient current signals as the superposition of the natural response of an RLC circuit and an induced current described by the Shockley Ramo theory. Nonlinear regression of the observed current to the theoretical model allows for the droplet charge to be extracted, independent of any assumptions about the force balance on the droplet. We demonstrate that regression of the current signal yields charge values that are on average within 4% of charges measured via a force balance. We use the chronocoulometric methodology to investigate how the charge varies with the applied potential, and we demonstrate that deionized water droplets contacting planar electrodes acquire on average 69% more positive charge than negative charge.