The effect of dust charge variation, due to ion flow and electron   depletion, on dust levitation
  Using a fluid model, the plasma densities, electron temperature and ion Mach number in front of a powered electrode in different plasma discharges is computed. The dust charge is computed using OML theory for Maxwellian electrons and ions distributed according to a shifted-Maxwellian. By assuming force balance between gravity and the electrostatic force, the dust levitation height is obtained. The importance of the dust charge variation is investigated. 
Victor Land, Angela Douglass, Ke Qiao, Lorin Matthews and Truell Hyde
physics.plasm-ph