Static electricity's secrets lie on the surface

“Static electricity” is among the most commonly experienced physical phenomena. Though associated with pocket lint and children rubbing balloons on hair, it plays crucial roles across nature. In clouds, charge exchange between microscopic ice crystals leads to electrical discharge on kilometer scales—i.e., lightning. Bees foraging through flowers exchange charge with, and therefore attract, pollen, enabling plant reproduction. In protoplanetary disks, charged dust particles experience electrostatic attractions that accelerate the earliest stages of rocky planet formation.

Despite this broad relevance, we know little about why contacting objects exchange charge. Our ignorance has two causes. First, ubiquity gives the false impression that the effect “must already be understood,” discouraging scientific pursuit. Second, as anyone who has pursued it knows, it is an absolutely brutal problem. Issues as simple as making clean contacts derail projects. Handling of samples introduces unwanted charging and leakage. Two objects can exchange charge one way initially, only to reverse polarity. Even identical materials exchange charge, despite the absence of any obvious symmetry-breaking parameter.

In this talk, I will present our work searching for the symmetry-breaking parameter in nature’s most common materials, oxides. Using acoustic levitation, we achieve hands-free contacts and charge measurement with spheres and plates of the same material. Even when samples are prepared as identically as possible, they still exchange charge as if they were different materials. With an array of surface-sensitive techniques, we discover that the secret lies on the surface. Every sample acquires a history-dependent “cocktail” of atmospheric adsorbates, which breaks symmetry and drives charge. Our results identify the crucial parameter that causes charging in settings ranging from desert sands to volcanic plumes, while simultaneously revealing why “static electricity” has been so difficult to tame.