Measuring spontaneous charging of single aerosol particles

Charge accumulation on airborne particles and droplets plays a critical role in a variety of natural and industrial processes. It gives rise to lightning in thunder- and sandstorms and can lead to dangerous dust explosions during industrial processing. Shavlov et al. [1] suggest that the hydroxide ions and protons formed by the dissociation of water molecules are sufficient to cause charging during evaporation and condensation of droplets or surface-adsorbed water on solid particles. This hypothesis is backed up by Moreira et al. [2] who find that liquid evaporation leads to charge buildup on dielectric surfaces.

By levitating individual aerosol particles in an optical trap [3, 4] we study this proposed charging mechanism. Our setup allows for trapping of various types of solid and liquid particles in the micrometer size range. The particle’s charge is measured by applying a sinusoidal electric field and observing the resulting particle motion. The Mie scattering pattern of the particle furthermore gives information about the particle’s size and refractive index, both at equilibrium and during evaporation and condensation.

Ultimately we aim to gain detailed insights into the proposed evaporation-condensation-charging mechanism and its implications for the triboelectric effect and atmospheric electricity.

1. [1] Shavlov A. et al. (2018) J Aerosol Sci. 123 17-26.
   
   [2] Moreira K. S., et al. (2020) Adv. Mater. Interfaces 7(18) 202000884.
   
   [3] Reich O., et al. (2020) Commun. Phys. 3(1).
   
   [4] Ricci F., et al. (2022) ACS Nano 6 (16) 8677–8683.