10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


Mass Accommodation and the Condensation Rate for Nanoclusters

Huan Yang, Eirini Goudeli, CHRISTOPHER HOGAN JR., University of Minnesota

     Abstract Number: 253
     Working Group: Aerosol Physics

Abstract
In modeling particle growth in the gas phase, the condensation rate for nanoparticles is most commonly calculated with a hard-sphere derived equation, in which the condensation rate coefficient scales with the square root of the temperature (i.e. the free molecular condensation rate equation). However, molecular scale clustering reactions, in which two vapor molecules/atoms collide and bind to one another to form a condensed phase entity, often have rates which decrease with increasing temperature. As condensational growth proceeds from the molecular scale to the particle scale, the condensation rate coefficient therefore must undergo a shift from molecular scale behavior (decreasing with temperature) to particle scale behavior (increasing with temperature). Using molecular dynamics trajectory calculations combined with classical collision rate theory, we have examined the evolution of the condensation rate coefficient and the degree of mass accommodation (binding efficiency) for homogeneous condensation onto gold and magnesium nanoclusters (composed of 6-50 atoms). Interestingly we find that for each cluster, above a critical temperature, there is a transition in the condensation rate coefficient; below the critical temperature its derivative is positive with temperature, and above it its derivative with respect to temperature can become negative. Critical temperatures, particularly for the smallest clusters, are found to be well below the melting temperature of the cluster, and at the critical temperature clusters are still stable over the time scales of simulations. We additionally examine high speed atom-nanocluster collisions, which do not lead to binding/condensation, but instead lead to cluster dissociation.