AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Evidence for Surface Freezing in Supercooled n-Alkane Nanodroplets
VIRAJ MODAK, Harshad Pathak, Mitchell Thayer, Sherwin Singer, Barbara Wyslouzil, The Ohio State University
Abstract Number: 145 Working Group: Aerosol Nucleation: From Clusters to Nanoparticles
Abstract Crystallization from the melt is a fundamental process that plays a central role in semiconductor processing, chemical separations, pharmaceutical production and purification and material science and metallurgy. In many cases, the transition to the most stable solid phase can proceed via an intermediate metastable phase. For example, n-alkanes (C$_nH$_(n+2)) of intermediate chain length (n>15) can form a series of rotator phases. Moreover, in contrast to most other molecules that pre-melt at temperatures below the bulk melting point Tm, intermediate chain length n-alkanes (16 ≤ n ≤ 50) form an ordered surface monolayer up to 3 K above Tm. Our experiments strongly suggest that even the short chain alkanes, n-octane and n-nonane appear to freeze at the surface of supercooled liquid droplets prior to the initiation of bulk freezing. In our experiments we create liquid nanodroplets in highly non-equilibrium states in a continuous flow supersonic nozzle. We characterize the flow using axially resolved static pressure measurements, and study the droplets using spatially resolved Small Angle X-ray Scattering (SAXS) and Fourier Transformed Infrared Spectroscopy (FTIR). In addition we complement our experiments with molecular simulation studies at the united atom level to develop molecular level insight into homogeneous liquid-solid nucleation and strengthen our interpretation of the experimental results.