Surface Characteristics that Drive Heterogeneous Ice Nucleation

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With support from the Environmental Chemical Sciences Program in the Division of Chemistry, Professor Miriam Freedman and her graduate and undergraduate students at Pennsylvania State University will study the freezing behavior of atmospheric particles, or aerosols. Aerosols catalyze the formation of clouds in the atmosphere, which can be composed of liquid water, ice, or a mixture of these phases. Ice particles in clouds can form by the freezing of aqueous droplets below -38 degrees C, or ice can form on the surface of an ice-nucleating particle (INP) at warmer temperatures. How particles nucleate ice on a molecular level is not well understood. To investigate the surface features that promote the ice nucleation process, the approach used in this project is to work with materials in which the surface can be infinitely tuned and probed. The goal of this project is to provide a framework for understanding which surface features are important for ice nucleation and the relative importance of these different features. This project is important for atmospheric scientists developing models of cloud formation. In addition, this project is of interest to the physical chemistry community because it deals with phase transitions, catalysis, and surfaces. Ice nucleation experiments are ideal for the inclusion of undergraduate researchers, often leading to publications with undergraduate coauthors. Results from these studies will be incorporated into undergraduate course lectures. Students performing this work will also be engaged in public outreach to families as well as continuing education for members of the wider community.This project characterizes the ice nucleation behavior of inorganic systems as well as organic and biological systems. Similarities are hypothesized between mineral, organic, and biological ice nucleating particles (INPs) in terms of how structure determines the ice nucleation behavior. For inorganic systems, the role of functional groups and surface composition will be characterized using functionalized gold nanoparticles, porous metalosilicates, and spinels. In terms of organic and biological systems, this project aims to characterize the role of hydrogen bonding on ice nucleation through studies of virgin and aged microplastics, ice-nucleating bacteria and their isolated proteins, and poly(vinyl alcohol)/poly(vinyl acetate) with different degrees of hydrolysis. Experiments will be performed primarily using immersion freezing, which is a dominant pathway for ice nucleation in the atmosphere.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.