Precision measurement of tribocharging in acoustically levitated sub-millimeter grains

Contact electrification of dielectric grains forms the basis for a myriad of physical phenomena. However, even the basic aspects of collisional charging between grains are still unclear. In this talk, we present a new experimental method [1], extending a prior approach [2] based on acoustic levitation, which allows us to controllably and repeatedly collide two sub-millimeter grains head-on and measure the evolution of their electric charges. This is the first collisional tribocharging experiment to provide complete electric isolation of the grain-grain system from its surroundings. We use this method to measure collisional charging rates between pairs of grains for three different material combinations: polyethylene-polyethylene, polystyrene-polystyrene, and polystyrene-sulfonated polystyrene. The ability to directly and noninvasively collide particles of different constituent materials, chemical functionality, size, and shape opens the door to detailed studies of collisional charging in granular materials.
[1] A. Kline et al., arXiv: 1910.09669 (2019)
[2] V. Lee et al., Physical Review Materials 2, 035602 (2018)