Temperature-Dependent Phase Transitions of Aqueous Aerosol Droplet Systems in Microfluidic Traps

• Published in: ACS earth and space chemistry Vol. 4; no. 9; pp. 1527 - 1539
• Main Authors: Roy, Priyatanu, Mael, Liora E, Makhnenko, Iaroslav, Martz, Robert, Grassian, Vicki H, Dutcher, Cari S
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.09.2020
• Subjects: temperature-dependent; model aerosols; liquid−liquid phase separation; organic to inorganic ratio; dehydration rate; separation relative humidity; microfluidics
• ISSN: 2472-3452; 2472-3452
• DOI: 10.1021/acsearthspacechem.0c00114

Well-mixed atmospheric aqueous aerosol droplets containing multiple chemical species can undergo processes such as liquid–liquid phase separation (LLPS) and crystallization depending on the ambient temperature and relative humidity (RH). So far, only a handful of single droplet studies have examined the effect of temperature in conjunction with the organic to inorganic ratio (OIR) on the separation RH for LLPS. In this work, we present a temperature-controlled microfluidic static trap approach to study the LLPS and efflorescence phenomenon in multiple ternary systems in a quasi-equilibrium manner. Ammonium sulfate or sodium chloride is used as the inorganic phase and 3-methylglutaric acid (3-MGA), poly­(ethylene glycol), poly­(propylene glycol), or poly­(ethylene glycol) diacrylate is used as the organic phase. Results show a clear trend in droplets containing 3-MGA with either salt of the initial LLPS and efflorescence events occurring at higher RH at lower temperatures, while this trend is less obvious for the other organics. The organic to inorganic ratio (OIR) of the system also affected the type of first phase transition, which can be either LLPS or efflorescence. Finally, the rate of RH change also had an impact on the temperature dependence of the formation of either anhydrous or dihydrous crystals of sodium chloride upon efflorescence. These results help inform the effects of temperature, OIR, and rate of RH change on the phase state of aqueous aerosol droplets containing multiple species.