Size dependent polarities in tribocharged dust aggregates.

It is long known that particles of the same material but with different sizes charge with different polarities in mutual collisions. In most cases, the smaller grains become negative. Here, we study tribocharging of (sub-)mm dust aggregates in the course of microgravity experiments by determining the charges of particles through their motion within an electric field.

Violation of triboelectric charge conservation on colliding particles.

In microgravity experiments, we quantified the net charge on systems of two identical, 434-μm-diameter glass spheres before and after a collision. We find that charge conservation is significantly violated. Independent of the sign of the total charge, the systems regularly lose some of their net charges, that is, they slightly discharge.