Surface Characteristics that Drive Heterogeneous Ice Nucleation

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The Environmental Chemical Sciences Program in the Chemistry Division funds Professor Miriam Freedman for studies of ice nucleation. At temperatures above approximately -38 degrees Celsius (or -36 degrees Fahrenheit), ice particles in the atmosphere are only formed through nucleation on aerosol particles. Here, nucleation is the first step in the formation of solid (ice) via self-assembly or self-organization of liquid. Particles differ widely in their ice nucleation activity. The aim is to measure the ice nucleation activity of many materials to develop a model that predicts which surface properties of the particles are most important for promoting ice nucleation. Because the types of particles found in the atmosphere are limited in number, man-made nanomaterials, sand, and other materials with specific surfaces are being studied. The properties of these synthesized materials can be tuned to explore the effect of different surface characteristics on ice nucleation. These studies enhance the understanding of the molecular basis of ice nucleation, which is important for industrial applications and atmospheric chemistry, specifically the research could reduce uncertainties in aerosol-cloud interactions, which are the largest uncertainty in our understanding of weather and climate. This work is of interest to the physical chemistry community because it deals with phase transitions, heterogeneous catalysis, and surface chemistry all of which are critical to industrial applications. This project provides training for undergraduate and graduate students, as well as outreach to the public through outreach events focusing on science and science policy. The ice nucleation activity of several materials is being investigated. Specifically proposed materials are amorphous silica nanoparticles, mesoporous silica, the phase change material GeTe, silver (Ag) and gold (Au) nanoparticles, salt (NaCl/KCl) mixtures, zeolites, and metal organic frameworks. The materials are selected for their ability to tune surface characteristics such as functional groups, crystallinity, crystal structure, porosity, and dopants. Both immersion and deposition mode freezing are measured in laboratory ice nucleation chambers. In addition to laboratory studies, kinematic models are used to explore the impact of heterogeneous nucleation on the properties of mixed phase and cirrus clouds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.