Measurements of phase and phase change events in chemically complex aqueous droplets provide valuable information for understanding the dynamic processes in these complex micro-environments. For example, atmospheric aerosol droplets regularly undergo phase changes including liquid-liquid phase separation and crystallization. The phase and mixing state of the aerosol has profound effects on particle morphology, species uptake, equilibrium partitioning, activation to cloud condensation or ice nuclei, and optical properties. Many factors play a role in determining if a droplet will liquid-liquid phase separate, as well as its resulting orientation or morphology of the two phases, such as temperature, relative humidity, and chemical composition of the respective phases.  In this work, aqueous droplets containing sea spray aerosol samples and chemical mimics are generated in microfluidic channels and stored in passive traps until dehydration to study the influence of relative humidity and water loss on phase behavior. The solution volume of the droplet trapped changes with respect to time, and is calculated by image analysis and correlated with the concentration of the solution to determine water activities at each time interval. The research will help determine mixture liquid-liquid phase separation and efflorescence events of droplets that include presence of other dissolved components and tend to decrease the water activity. The measurements will also be used to parameterize statistical thermodynamic modeling for predictions of thermodynamic properties of aqueous aerosols as a function of relative humidity.

Thermodynamics and phase of sea spray aerosol droplets using microfluidics

2019 Fall National Meeting

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