Charge Distribution Inversion for Supermicrometer Particles via Differential Mobility Analysis and Optical Particle Spectrometry

Abstract

Charge control of particles has long been of use for applications in laser printing, electrophotography, and electrostatic powder coating. Effective charge control is difficult, however, without an accurate understanding of particle charge state distributions. Traditional methods of charge state characterization, including the use of an average charge value, or the employment of instruments like electrodynamic balances or spectrometers, fail to robustly capture a charge distribution.This work presents a novel approach to particle charge state characterization, using aerosol instrumentation to assess full charge state distributions for supermicrometer particles. While there are preexisting methods to discern aerosol charge state distributions, such as the Tandem Differential Mobility Analyzer approach, they are generally applied only for low charge, submicrometer particles. The method proposed here combines a Differential Mobility Analyzer (DMA) with a laser-based optical particle spectrometer capable of measuring supermicrometer-sized particle concentrations. Before selection based on electrical mobility by the DMA, particles collide with ions generated in a custom unipolar corona ionizer and become highly charged relative to what is achieved in an equilibrium charge distribution. The particles’ high charge state allows them to traverse the DMA despite their large diameter. The results of this work represent the possibility to expand the applications of aerosol instrumentation into additional fields, including for use with micropowder characterization in the printing industry.