High potential, near free molecular regime Coulombic collisions in aerosols and dusty plasmas


Determination of the particle charge in aerosols and dusty plasmas requires an accurate calculation of the particle-ion collision kernel taking into account the particle-ion Coulombic coupling and ion-neutral gas molecule collisions. While the effect of Coulombic interactions of any strength is described accurately in the continuum limit and free molecular limit, an accurate physical description at intermediate collisional regimes remains elusive. Specifically, the Coulomb influenced collisions between oppositely charged particles and ions have evaded accurate theoretical description in the past. We use Langevin dynamics (LD) calculations to infer the non-dimensional collision kernel H as a function of the electrostatic potential energy to thermal energy ratio (Formula presented.) and the diffusive Knudsen number (Formula presented.) the index of ion-neutral collisionality in a finite pressure system. The LD approach yields a simple, approximate treatment of particle charging in the entire ion-neutral collision regime under the assumption that (Formula presented.) where (Formula presented.) is the mass of an ion and (Formula presented.) is the mass of the background gas molecules. We show that the Gumbel distribution accurately describes the underlying distribution of (Formula presented.) calculated using LD. The effect of high ion concentrations (at which screening of particle by free charges in space is important) on (Formula presented.) is parameterized through a non-dimensional screening length parameter (Formula presented.) Analysis of the dependence of the distribution parameters on (Formula presented.) and (Formula presented.) leads to a regression for (Formula presented.) that is valid for (Formula presented.) and (Formula presented.) plasmas. Inter-comparison of current model with select models from the literature shows that the current model and the model published by Gatti and Kortshagen (that assumes (Formula presented.)) yield similar predictions for a wide range of (Formula presented.) and (Formula presented.) Copyright © 2019 American Association for Aerosol Research.

Publication Title

Aerosol Science and Technology