Droplets, Membranes and Interfaces; MPI for Dynamics and Self-organization, Am Fassberg 17, 37077 Goettingen, Germany.
Lab Chip. 2014 Mar 21;14(6):1099-106. doi: 10.1039/c3lc51143j.
We demonstrate the control of droplet sizes by an ac voltage applied across microelectrodes patterned around a flow-focusing junction. The electrodes do not come in contact with the fluids to avoid electrochemical effects. We found several regimes of droplet production in electric fields, controlled by the connection of the chip, the conductivity of the dispersed phase and the frequency of the applied field. A simple electrical modelling of the chip reveals that the effective voltage at the tip of the liquid to be dispersed controls the production mechanism. At low voltages (≲ 600 V), droplets are produced in dripping regime; the droplet size is a function of the ac electric field. The introduction of an effective capillary number that takes into account the Maxwell stress can explain the dependance of droplet size with the applied voltage. At higher voltages (≳ 600 V), jets are observed. The stability of droplet production is a function of the fluid conductivity and applied field frequency reported in a set of flow diagrams.
我们通过在流聚焦结周围图案化的微电极上施加交流电压来演示液滴尺寸的控制。这些电极不与流体接触，以避免电化学效应。我们发现，在电场中有几种液滴产生的模式，这些模式受芯片的连接、分散相的电导率和施加场的频率控制。对芯片的简单电模型表明，在要分散的液体尖端的有效电压控制着生产机制。在低电压（≲600 V）下，液滴以滴状模式产生；液滴尺寸是交流电场的函数。引入考虑了麦克斯韦应力的有效毛细管数可以解释液滴尺寸与施加电压的关系。在更高的电压（≳600 V）下，观察到射流。液滴产生的稳定性是一组流动图中报告的流体电导率和施加场频率的函数。
