According to a news release from the Massachusetts Institute of Technology, MIT researchers have found that small water droplets that develop on a superhydrophobic surface, and then “jump” away from that surface, have an electric charge. The discovery could result in more efficient power plants, as well as a novel method of obtaining power from the atmosphere, they contend.

According to MIT postdoc Nenad Miljkovic, this discovery was an extension of earlier research conducted by the MIT team. That research revealed that under certain conditions, rather than sliding down and separating from a surface because of gravity, droplets can actually jump away from it. This takes place when water droplets condense onto a metal surface with a specific type of superhydrophobic coating and at least two of the droplets come together: they are then able to spontaneously jump from the surface due to the release of excess surface energy.

“We found that when these droplets jump, through analysis of high-speed video, we saw that they repel one another midflight,” Miljkovic said. “Previous studies have shown no such effect. When we first saw that, we were intrigued.”

In order to determine the reason for the repulsion between jumping droplets after they leave the surface, the researchers conducted a number of experiments utilizing a charged electrode. They noted that when the electrode had a positive charge, droplets were repelled by it as well as by each other; when it had a negative charge, the droplets were attracted to it. This demonstrated that the effect was the result of a net positive electrical charge developing on the drops as they jumped away from the surface.

According to Miljkovic, the charging process occurs because as droplets develop on a surface they naturally create an electric double layer (a layer of paired positive and negative charges) on their surfaces. When neighboring drops come together, which results in their jumping from the surface, that process takes place so quickly that the charge separates. “It leaves a bit of charge on the droplet, and the rest on the surface,” Miljkovic added.

The primary discovery that droplets could jump from a condenser surface offered a mechanism for improving the efficiency of heat transfer on those condensers, and thus bettering power plants’ overall efficiency. The new discovery offers a way of improving that efficiency even more: by applying the relevant charge to a nearby metal plate, jumping droplets can be yanked away from the surface, lowering the chance of their being pushed back onto the condenser by gravity or by the drag generated by the flow of the surrounding vapor toward the surface.

The discovery also implies another novel application: by locating two parallel metal plates out in the open, with one surface that has droplets jumping, and another that gathers them “you could generate some power” just from condensation from the surrounding air.