Electrification of granular systems of identical insulators

TL;DR

This paper explains how geometry-driven electron transfer causes size-dependent charging in granular insulator systems, aligning with experimental observations of particles acquiring opposite charges based on size.

Contribution

It introduces the first quantitative charging model for identical insulators in granular systems, explaining size-dependent electrification through simple geometric considerations.

Findings

Model predictions agree with experimental measurements.

Electron transfer from larger to smaller particles explains observed charge polarity.

Provides a unified explanation for size-dependent charging phenomena.

Abstract

Insulating particles can become highly electrified during powder handling, volcanic eruptions, and the wind-blown transport of dust, sand, and snow. Measurements in these granular systems have found that smaller particles generally charge negatively, while larger particles charge positively. These observations are puzzling, since particles in these systems are generally chemically identical, and thus have no contact potential difference. We show here that simple geometry leads to a net transfer of electrons from larger to smaller particles, in agreement with these observations. We integrate this charging mechanism into the first quantitative charging scheme for a granular system of identical insulators, and show that its predictions are in agreement with measurements. Our theory thus seems to provide an explanation for the hitherto puzzling phenomenon of the size-dependent charging of granular systems of identical insulators.