AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Nucleation of Clusters Bridging the Scale from Molecules to Nanoparticles
PAUL E. WAGNER, Paul M Winkler, Fakultaet fuer Physik, Universitaet Wien, Vienna, Austria
Abstract Number: 48 Working Group: Invited by Conference Chair
Abstract Gas to liquid phase transitions are important processes in materials science, aerosol physics and atmospheric science. The recent decade of atmospheric observations has demonstrated particle formation by nucleation to be a frequent phenomenon in the global atmosphere. The underlying activation mechanisms of small molecular clusters are thus of vital importance. However, homogeneous as well as heterogeneous nucleation are still among the least understood phenomena in aerosol science.
New particle formation by homogeneous or heterogeneous nucleation generally proceeds via critical molecular clusters, whose sizes can be directly determined from experimental observables using the nucleation theorem. Homogeneous nucleation rate data provide information on the sizes of critical clusters down to diameters of 2 nm in satisfactory agreement with the Kelvin relation [1]. Experiments on heterogeneous nucleation in n-propanol vapour allowed for the first time to bridge the scale from molecular clusters to nanoparticles [2]. For charged seed particles an enhancement of heterogeneous nucleation and a significant charge sign preference were observed.
Recently we have activated single seed ion molecules at sizes far below the Kelvin-Thomson prediction. This unexpected behaviour has now been explained by quantitative determination of the molecular content of critical clusters [3]. We found these clusters to be significantly larger than the seed particles and in fact fairly well predicted by the Kelvin-Thomson relation. Consequently the fundamental detection limit of Condensation Particle Counters is now considerably extended down to particle diameters of about 1 nm. We have designed a new expansion type measurement system (vSANC), which will be used in joint nucleation experiments at CERN, Geneva [4].
[1] R. Strey, P.E. Wagner, Y. Viisanen, J. Phys. Chem. 98, 7748 (1994).
[2] P.M. Winkler et al., Science 319, 1374 (2008).
[3] P.M. Winkler et al., Phys. Rev. Lett. 108, 085701 (2012).
[4] J. Kirkby et al., Nature 476, 429 (2011).