From charge distributions to gravity-free interactions: a two front approach to understanding granular tribocharging

Charlista: Nicolás Mujica - DFI, FCFM, U. de Chile

Resumen: Experiments have shown that particles of the same material exchange electrical charge during collisions, yet the underlying charge exchange mechanism is still not well understood. The fact that particles can become highly charged as a result of this effect has significant consequences for many settings, both in nature and industry, such as thunderstorms in volcanic eruptions, particle aggregation during planet formation, and the clogging of fluidized industrial granular beds. Toward understanding these systems, great efforts have been made on two fronts. On the first, the focus has been to develop precise in situ measurements for particle charge, e.g. to determine ensemble distributions or measure exchange in individual collisions. In the second, the aim has been  to understand how charged grains interact, e.g. aggregation, orbits, and clustering.

In this talk, I will review our recent experimental results that make significant advances on both of the fronts. In particular, we have developed experimental setups and protocols that allow us to: (1) obtain charge distributions with unparalleled accuracy for large ensembles of particles in the sub millimeter range. These distributions are non-Gaussian, which indicate the existence of memory effects in the huge number of charge exchanges that occur in a large ensemble of grains. In addition, we have developed a minimal model that reproduces in many aspects our experimental findings; and (2) witness with exquisite detail the electrostatic interactions of charged particles in a gravity free environment: Keppler-like orbits are determined in a 3D tracking experiment, where certain anomalies are detected at particle collisions, which we interpret as signatures of charge exchanges. Our results make simultaneous progress in the primary two directions required for understanding how charged grains affect systems ranging from volcanic eruptions to fluidized beds.