Engineering of a Microfluidic Platform for Investigation of Immersion Freezing in the Atmosphere

The West Texas A&M University Microfluidic Static Droplet Array (WT-MFSDA) platform was developed for studying atmospheric ice nucleation, specifically immersion freezing. It combines a microfluidic device with interconnected droplet parking traps and a unique hand pipetting method to create an array of nanoliter-sized droplets containing ice-nucleating particles (INPs). A commercialized cooling unit facilitates the visualization and characterization of freezing events in individual droplets. Each droplet is carefully isolated and covered with a thin mineral oil film, enhancing measurement reliability by eliminating artifacts due to surface contact, mass transfer, and evaporation. The WT-MFSDA platform allows simulation and investigation of immersion freezing in water and INP-involved suspensions at temperatures below -35 °C, with cooling rates relevant to atmospheric cloud updraft velocities. Temperature uncertainty is controlled within ± 0.3 °C. Platform performance is verified using well-known bulk powder INP surrogates, such as illite NX, Snomax, and microcrystalline cellulose. The results from nanoliter freezing assays in WT-MFSDA are compared and validated against other freezing assays and published data. A calorimetry analysis of single droplet freezing is conducted to understand thermodynamics, kinetics, and exothermic energy release during the liquid-to-solid phase transition. Future plans include testing freezing properties of high-latitude soil dust samples from the North Slope of Alaska region using WT-MFSDA and integrating research and teaching activities by training students, and expanding laboratory exercises to classrooms. The advanced ice nucleation capabilities of WT-MFSDA enable enhanced science teaching in atmospheric ice nucleation research.