ENGINEERING A MICROFLUIDIC DEVICE FOR THE INVESTIGATION OF ATMOSPHERIC ICE NUCLEATION

Atmospheric ice-nucleating particles (INPs) promote the formation of ice particles in clouds. They usually modulate the properties of clouds, precipitation, and climate. The effect of INPs is predominant in low Arctic mixed-phase clouds. However, ambient ice nucleation in clouds is a complex process encompassing multiple freezing mechanisms. Limited knowledge about nature and the role of high-latitude INPs in the climate system is available. To fill the knowledge gap, this thesis project developed the West Texas A&M University Microfluidic Static Droplet Array (WT-MFSDA) platform for studying atmospheric ice nucleation, specifically immersion freezing. WT-MFSDA combines a microfluidic device containing interconnected droplet parking traps, a unique method of hand pipetting to create an array of INP-laden nanoliter-sized droplets, and a commercialized cooling unit for visualization and characterization of freezing events of hundreds of individual droplets. Each droplet is geometrically separated from each other and enveloped with a thin film of mineral oil. This spatial arrangement increases the reliability and reproducibility of the measurement by eliminating the artifacts due to surface contact, mass transfer, and/or evaporation. This platform is useful to simulate and investigate the immersion freezing of water and/or any INP-involved suspension down to the homogenous freezing temperature (below -35 °C) at a wide range of cooling rates from 0.01 to 30 ℃ per minute, which corresponds to atmospherically relevant cloud updraft velocities. A systematic uncertainty in terms of temperature is ± 0.3 °C. The device performance is verified with the known composition of bulk powder INP surrogates, such as illite NX, Snomax®, and microcrystalline cellulose. The results from nL-freezing assays of WT-MFSDA were compared and verified to/against the results of published immersion freezing results. The WT-MFSDA immersion freezing platform shows the potential as an affordable and handy tool for studying ice nucleation in clouds.