This is a nice surprise: MIT researchers made the unexpected discovery that when two or more water droplets merge and jump away from a superhydrophobic  surface, the droplets carry an electric charge.
How does it work? First, you need the right kind of superhydrophobic surface. Next, add humid air. As droplets condense and form on the superhydrophobic surface, they assemble into a layer of paired positive and negative charges. When the drops coalesce and spring from the surface, it happens so quickly that the charge separates. Part of the charge remains on the surface, and the rest is carried away by the droplets.
Because water jumps away from superhydrophobic surfaces, an immediate application for such surfaces is condensers. Condensers are used in most electricity-generating power plants, which means that overall plant efficiency can improve.
But that’s not all:
By placing two parallel metal plates out in the open, with one surface that has droplets jumping, and another that collects them…you could generate some power – just from condensation from the ambient air. All that would be needed is a way of keeping the condenser surface cool, such as water from a nearby lake or river. You just need a cold surface in a moist environment. (Nenad Miljkovic)
Here’s the best 22 seconds of charged droplet video you’ll see today. In the video you can clearly see how the droplets are drawn toward a negatively charged electrode.
Electricity from humid air – how exciting is that?
Read more at web.mit.edu: Droplets get a charge out of jumping
- Superhydrophobic: extremely difficult to make wet. Superhydrophobic surfaces repel water to a degree that droplets roll off the surface instead of flattening and “sticking.” ↩