10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Can Nanodroplets Shatter?
YENSIL PARK, Kehinde Ogunronbi, Barbara Wyslouzil, The Ohio State University
Abstract Number: 915 Working Group: Aerosol Physics
Abstract Millimeter and micron size water droplets that freeze from the surface inward can build up enough internal pressure, due to the density mismatch, to explode. In our freezing experiment of n-alkane nanodroplets, we occasionally observe droplets that shrink far more than they should based on the expected liquid/solid density change. Furthermore, at the low temperatures involved, mass loss by evaporation should be negligible, even if the droplets reach their melt temperature.
Data from n-hexane nanodroplets is particularly intriguing. Here, nanodroplets formed in a supersonic Laval nozzle by condensation and then froze. The particles and the phase transitions were characterized using pressure trace measurements (PTM), Small Angle X-ray Scattering (SAXS) and Fourier Transform Infrared Spectroscopy (FTIR). In one case the carrier gas was pure Argon and in a second case the gas mixture contained 12 % CO2. In both cases we observed a sudden decrease in droplet size and a corresponding heat release event. In the Argon case, the average droplet radius decreased by ~ 7.5 %, and in the presence of CO2 the decrease was ~ 17.0 %. FTIR clearly confirms freezing in the pure Ar case, but not when CO2 is present. Since n-alkanes are known to freeze from the surface inward if the chain length is long enough, it may be possible that gasses expelled from the crystal structure exert enough pressure to shatter these droplets despite their small size.