Preprints
https://doi.org/10.5194/acp-2020-1299
https://doi.org/10.5194/acp-2020-1299

  06 Jan 2021

06 Jan 2021

Review status: this preprint is currently under review for the journal ACP.

Observations on hygroscopic growth and phase transitions of mixed 1, 2, 6-hexanetriol/(NH4)2SO4 particles: Investigation of liquid-liquid phase separation (LLPS) dynamic process and mechanism and secondary LLPS

Shuai-Shuai Ma, Zhe Chen, Shu-Feng Pang, and Yun-Hong Zhang Shuai-Shuai Ma et al.
  • The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing, 100081, China

Abstract. Atmospheric aerosols consisting of organic and inorganic components may undergo liquid-liquid phase separation (LLPS) and liquid-solid phase transitions during ambient relative humidity (RH) fluctuation. However, the knowledge of dynamic phase evolution processes for mixed organic-inorganic particles is scarce. Here we present a universal and visualized observation on LLPS, efflorescence and deliquescence transitions as well as hygroscopic growth of mixed 1, 2, 6-hexanetriol/ammonium sulfate (AS) particles with different organic-inorganic mole ratios (OIR = 1:4, 1:2, 1:1, 2:1 and 4:1) with the high time resolution (0.5 s), using an optical microscope with a video camera. The optical images suggest that an inner AS solution phase is surrounded by an outer organic-rich phase after LLPS for all mixed particles. The LLPS mechanism for particles with different OIRs differs, meanwhile, multiple mechanisms may dominate successively in individual particles with a certain OIR, somewhat inconsistent with earlier observations by literature. More importantly, another phase separation in inner AS solution phase, defined as secondary LLPS here, is observed for OIR = 1:1, 1:2 and 1:4 particles. The secondary LLPS may be attributed to the formation of more concentrated AS inclusions in the inner phase, and becomes more obvious with decreasing RH and increasing AS mole fraction. Furthermore, the changes in size and amount of AS inclusions during LLPS are quantitatively characterized, which further illustrate the equilibrium partitioning process of organic and inorganic components. The experimental results have significant implications for revelation of complex phase transitions of internally mixed atmospheric particles and evaluation of liquid-liquid and liquid-solid equilibria in thermodynamic models.

Shuai-Shuai Ma et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on acp-2020-1299', Maofa Ge, 22 Feb 2021 reply
    • AC1: 'Reply on CC1', Yunhong Zhang, 12 Mar 2021 reply
  • RC1: 'Comment on acp-2020-1299', Anonymous Referee #1, 16 Apr 2021 reply

Shuai-Shuai Ma et al.

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Data of "Observations on hygroscopic growth and phase transitions of 1, 2, 6-hexanetriol/(NH4)2SO4 mixed particles: Investigation of liquid-liquid phase separation (LLPS) dynamic process and mechanism and secondary LLPS" Shuai-Shuai Ma, Zhe Chen, Shu-Feng Pang, and Yun-Hong Zhang https://doi.org/10.5281/zenodo.3958966

Shuai-Shuai Ma et al.

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Short summary
LLPS, efflorescence and deliquescence of aerosol particles can be observed visually and determined quantitatively. Different LLPS mechanisms may dominate successively in mixed organic-inorganic particles. The formation of more concentrated inorganic inclusions may cause secondary LLPS. Furthermore, high inorganic factions may result in an inorganic salt crust enclosing the separated organic phases.
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