Triboelectric charge saturation on multiple particles in air and vacuum

Abstract

Triboelectric charging is the transfer of charge between two materials on contact. It occurs in numerous technologies, yielding problems and opportunities. Charge transfer on contact is complex and depends on contact properties such as material composition and contact area, as well as environmental factors including humidity, temperature, and air pressure. It has been shown that there is a reduction in charge saturation on many particles in close proximity, but no explanation has been definitively verified. Here we show that dielectric breakdown of air is the primary cause of triboelectric charge saturation on single and multiple electrically insulating particles. We combine computational simulations with experiments under controlled humidity and temperature, and at air pressures ranging from atmospheric down to vacuum (10-4 mbar). We find the charge saturation on particles increases below 0.1 mbar as expected. Our results show that the combined electric field contribution of multiple charged particles causing dielectric breakdown of air leads to a reduction in saturation charge per particle as the number of particles is increased. Furthermore, these results show that it is possible to completely remove charge from particles by maintaining a low pressure environment, yielding opportunities for improved industrial powder flows and dust mitigation from surfaces.