Many microfluidic devices employ techniques that manipulate droplet motion for applications like sorting, manufacturing, or precisely controlling chemical reactions at a small scale. The video above shows the oscillations of a droplet on an inclined surface as it is perturbed with an electric field. (Video credit and submission: K. Nichols)
Tag: electrohydrodynamics
The Floating Water Bridge
The interaction of electric fields and fluids can lead to some unexpected results. Here we see the formation of a water bridge formed between two beakers of demineralized water across which a large voltage difference (~15kV) is applied. The bridge is stable for separation distances up to about 2 cm. In order to achieve this feat, the water is overcoming two destabilizing forces: gravity, which bends the bridge, and capillary action, which makes the liquid bridge thin until it breaks into droplets. According to the authors, both forces are countered by induced polarization forces at interface; in short, the electrical field around the liquid causes the positive and negative charges in the liquid to separate, thereby polarizing the liquid. This separation of charges then creates normal stresses along the surface of the water that oppose the gravitational and capillary forces trying to break the bridge. (Video credit: A. Marin and D. Lohse)