Mixing selectivity in bicomponent, bipolar aggregation

The selectivity of aggregation in mixtures of two charged aerosols containing chemically dissimilar nanoparticles is studied by means of a newly developed direct simulation Monte Carlo method. This method allows to trace changes in complex multidimensional systems, in this case describing particle size, charge and aggregate composition. A new procedure was developed for estimating the effective collision diameter of an aggregate composed of primary particles of any size. Three model systems were studied: polydisperse aerosols with initially bipolar charge distribution, unipolarly charged polydisperse aerosols and quasi-monodisperse oppositely charged aerosols. The study is focused on the aggregate composition's dependence on the initial size and charge distribution. It was found that the use of bipolarly charged aerosols does not increase the selectivity of mixing whereas unipolarly, oppositely charged aerosols reach more rapidly a more homogeneous distribution of components within the aggregates. In the last case, the addition of one more elementary charge to the particles roughly doubles the fraction of bicomponent, 1 : 1 mixed nanoaggregates and accelerates the process. (C) 2001 Elsevier Science Ltd. All rights reserved.