AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Interpreting Heterogeneous Nucleation Probability Measurements: Molecule-Level Cluster Properties and Unusual Temperature Dependence
ROBERT MCGRAW, Paul M. Winkler, Paul E. Wagner, Brookhaven National Laboratory
Abstract Number: 399 Working Group: Aerosol Physics
Abstract In this study we analyze the unusual temperature dependence seen in the heterogeneous nucleation of water vapor on silver (Ag) nano seeds [Kupc et al. (2013), Aerosol Sci. Technol. 47, i]. Molecular-level cluster properties are obtained from the measurements in the following sequence: direct determination of critical nucleus molecular content, from the 1st nucleation theorem; determination of microscopic contact angle, from the Kelvin relation, seed particle size, and critical nucleus molecular content; direct determination of adsorbed cluster energy, from the 2nd nucleation theorem; and model-based determination, using classical heterogeneous nucleation theory, of the temperature derivative of the microscopic contact angle from adsorbed cluster energy.
The fundamental connection between contact angle derivative and cluster energy is shown to provide an important clue as to the origin of unusual temperature dependence, which we describe here in terms of the molecular-level cluster properties. For example, it is shown analytically that increasing microscopic contact angle with temperature is a necessary condition for unusual temperature dependence. Exceedingly good agreement between laboratory measurements and classical heterogeneous nucleation theory (Fletcher theory) was found in studies of the heterogeneous nucleation of tungsten oxide nano-particles in the presence of water vapor [Winkler et al. (2008), Science 319, 1374]. In the present study we extend Fletcher theory to accommodate the analysis of cluster energy, which is needed to make contact with the 2nd nucleation theorem. Consistent agreement between contact angles from the Kelvin relation, which are obtained independently of one another at several different temperatures, and the microscopic contact angle derivative, obtained from the 2nd nucleation theorem and adsorbed cluster energy, provides new and independent evidence of the surprising utility of Fletcher theory in the nano-regime.