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Rub a balloon on your head, and your hair will stand on end. Nearly everyone has done it, or at least seen it. But even though static electricity was first observed by the ancient Greeks, scientists still don’t know why rubbing certain materials together generates an electrical charge. Now, they may have the answer.
Unlike the electric current flowing through a power line, static electricity stays put. That’s because this type of electricity (also known as triboelectricity) typically builds up in materials that don’t conduct a charge very well, like rubber or plastic, which causes it to get stuck. These insulators accumulate a static charge when rubbed together.
In a new study, researchers happened to be looking into another electrical phenomenon called flexoelectricity and wondered whether it might explain how friction generates static electricity. The flexoelectric effect is the spontaneous appearance of electrical fields during continuous but inconsistent flexing or bending at the nanoscale, like haphazardly running your finger along the teeth of a plastic comb.
At this tiny scale, even smooth objects are riddled with protruding bits and bobs. The team found that when two objects rub together, these tiny protrusions bend, and, because of the flexoelectric effect, this causes static electricity to accumulate, they report today in Physical Review Letters. The new explanation also clarifies why insulators made of the same material still generate voltage when rubbed together. This confounded scientists who thought the accumulation of static charge might come down to inherent differences between the two materials rubbed together.
Plastics do a particularly good job of generating static electricity, the results suggest. This new understanding could help engineers optimize materials to produce more static electricity and harness it to do things like charge wearable technology. The findings could also help improve safety in places like oil refineries where even a spark can cause a catastrophic explosion.