Timung Seim, Chaudhuri Joydip, Borthakur Manash Pratim, Mandal Tapas Kumar, Biswas Gautam, Bandyopadhyay Dipankar
Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam, India.
Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam, India.
Electrophoresis. 2017 Jun;38(11):1450-1457. doi: 10.1002/elps.201600311. Epub 2016 Nov 28.
We report a facile and noninvasive way to disintegrate a microdroplet into a string of further miniaturized ones under the influence of an external electrohydrodynamic field inside a microchannel. The deformation and breakup of the droplet was engendered by the Maxwell's stress originating from the accumulation of induced and free charges at the oil-water interface. While at smaller field intensities, for example less than 1 MV/m, the droplet deformed into a plug, at relatively higher field intensities, e.g. ∼1.16 MV/m, a pair of droplets having opposite surface charge was formed. The charged droplets showed an interesting periodic bridging and breakup during their translation motion across the channel. For even higher field intensities, for example more than 1.2 MV/m, the entire droplet underwent dielectrophoresis toward one of the electrodes before experiencing a strong attractive force from the other electrode to deform into a shape of a Taylor cone. With progress in time, mimicking the electrospraying phenomenon, the cone tip periodically ejected a string of miniaturized water droplets to form a microemulsion inside the channel. The frequency and size of the droplet ejection could be tuned by varying the applied field intensity. A water droplet of ∼214 μm diameter could continuously eject droplets of size ∼10 μm or even smaller to form a microemulsion inside the channel.
我们报道了一种简便且无创的方法，可在微通道内外部电流体动力学场的影响下，将微滴分解为一串进一步小型化的微滴。液滴的变形和破裂是由麦克斯韦应力引起的，该应力源于油水界面处感应电荷和自由电荷的积累。在较小的场强下，例如小于1 MV/m时，液滴变形为栓塞；而在相对较高的场强下，例如约1.16 MV/m时，会形成一对具有相反表面电荷的液滴。带电液滴在其穿过通道的平移运动过程中表现出有趣的周期性桥接和破裂现象。对于更高的场强，例如超过1.2 MV/m时，整个液滴在受到另一个电极的强大吸引力而变形为泰勒锥形状之前，会向其中一个电极进行介电泳。随着时间的推移，模仿电喷雾现象，锥尖会周期性地喷出一串小型化的水滴，在通道内形成微乳液。液滴喷射的频率和大小可以通过改变施加的场强来调节。直径约214μm的水滴可以连续喷出尺寸约10μm甚至更小的水滴，在通道内形成微乳液。
