Influence of Surface Properties on Heterogeneous Ice Nucleation in Synthesized Crystalline, Porous Materials

LUCY NANDY, Katie Marak, Miriam Freedman, Pennsylvania State University

     Abstract Number: 102
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
Heterogeneous ice nucleation activity is affected by aerosol particle composition, crystallinity, pore size and surface area. However, these surface properties are not well understood with regard to how they affect cloud droplets by forming ice. Therefore, synthesized materials like zeolites and covalent organic frameworks (COFs), for which surface properties can be tuned, were studied in immersion freezing mode. The materials in powder form were dispersed in water, droplets were pipetted onto a hydrophobic glass slide, and the slide was then placed in a temperature- and humidity-controlled chamber to record the freezing events. To establish the relationship between the physical and chemical properties of the particles and efficiency of ice nucleation, materials with different compositions (e.g. Si/Al ratio for the zeolites), pore size, surface area and crystallinity were characterized using XPS, BET, and XRD. Results show that COFs with pore sizes between 2 and 3 nm exhibit the most efficient ice nucleation activity. For zeolites, the Si/Al ratio showed a strong correlation with the ice nucleation efficiency, lower ratios being more efficient. The results will be compared and discussed in the context of numerous other synthesized porous systems. From these laboratory studies, the goal is to develop a predictive model for understanding the most important surface properties that promote ice nucleation.