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

Abstract

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.

A Microfluidic Device for Automated High Throughput Detection of Ice Nucleation of Snomax®

“…A negative vinyl mask was printed (CAD art services), and the mold for the polydimethylsiloxane (PDMS) devices was prepared in the UMN MNC cleanroom using the following modified photolithography process: Solid state SUEX sheets (DJ Microlaminates, Sudbury, MA, USA) were bonded to standard 4” silicon wafers at 70 °C in a thermal laminator. The sheets act as negative photoresists, and standard photolithographic processes previously described [ 41 ] were used following this modification to develop the channel pattern on the wafer. The sheets were used to ensure height uniformity as spin coating was seen to cause slight alterations in the height across the long flow channel.…”

“…standard 4" silicon wafers at 70 °C in a thermal laminator. The sheets act as negative photoresists, and standard photolithographic processes previously described [41] were used following this modification to develop the channel pattern on the wafer. The sheets were used to ensure height uniformity as spin coating was seen to cause slight alterations in the height across the long flow channel.…”

“…Recent advances in droplet microfluidic technology have allowed generation and study of phase changes of nano- to picoliter droplets for aerosol science applications [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. These devices range from microfluidic droplet generators for off-chip analysis [ 42 , 46 ], and on-chip analysis with static arrays of droplet traps [ 45 , 47 ] to flow-through channel based devices [ 43 , 48 ].…”

Single-particle Raman spectroscopy for studying physical and chemical processes of atmospheric particles

“…However, most studies are based on experimental results at room temperature or 298 K. Further exploration with respect to the effect of low temperature on the properties of the particles and multiphase sulfate chemistry is still warranted. Employing a temperature-controlled cold-plate flow-cell-Raman system for deposited single particles (Wheeler et al, 2015;Mael et al, 2019;Roy et al, 2020), investigations of temperature-dependent reaction kinetics can be easily achieved. Temperature control in a small levitation chamber is also more convenient than in a flow tube or smog chamber.…”

Comment on acp-2021-423

“…Employing a temperature-controlled cold plate flow cell -Raman system for deposited single particles (Roy et al, 2020;Mael et al, 2019;Wheeler et al, 2015), investigations of temperaturedependent reaction kinetics can be easily achieved. Temperature control in a small levitation chamber is also more convenient than in a flow tube or smog chamber.…”