ELECTRODYNAMIC TRAPPING OF AEROCOLLOIDAL PARTICLES - EXPERIMENTAL ANDTHEORETICAL TRAPPING LIMITS

Aerocolloidal particles have been trapped from an uncharged source aer osol using an electrodynamic balance, Graphite and soot particles were charged photoelectrically using a Xe-2 (172 nm) excimer lamp, while p articles of titanium dioxide, sodium nitrate, and diethylhexyl sebacat e (DEHS) were charged using a unipolar corona charger prior to injecti on into the chamber, It was found that the Stokesian drag force produc ed by convection in the balance chamber can destabilize the levitated microparticle when it exceeds the electrostatic force required to cent er the particle, Although the electrostatic restoring force can be inc reased by increasing either the particle charge or the ac held strengt h, charging of the particles is more difficult as the particle diamete r is decreased, which gives rise to a trapping limit, Monodisperse DEH S particles were used to determine the experimental frapping limit for unipolar charging, For the experimental apparatus used in this study, a diameter of about 1 mu m was found to be the trapping limit for DEH S. Results are compared to the theoretical trapping limit calculated b y a force balance on a particle exposed to motion of the surrounding g as. (C) 1997 Academic Press.