Investigation of gel formation and volatilization of acetate acid in magnesium acetate droplets by the optical tweezers.

Author(s) Lv, X.J.; Wang, Y.; Cai, C.; Pang, S.F.; Ma, J.B.; Zhang, Y.H.
Journal Spectrochim Acta A Mol Biomol Spectrosc
Date Published 2018 Jul 05

Hygroscopicity and volatility of single magnesium acetate (MgAc) aerosol particles at various relative humidities (RHs) are studied by a single-beam optical tweezers, and refractive indices (RIs) and morphology are characterized by cavity enhanced Raman spectroscopy. Gel formation and volatilization of acetate acid (HAc) in MgAc droplets are observed. Due to the formation of amorphous gel structure, water transposition in droplets at RH < 50% is significantly impeded on a time scale of 140,000 s. Different phase transition at RH < 10% is proposed to explain the distinct water loss after the gel formation. To compare volatilization of HAc in different systems, MgAc and sodium acetate (NaAc) droplets are maintained at several different stable RHs during up to 86,000 s. At RH ≈ 74%, magnesium hydroxide (Mg(OH)) inclusions are formed in MgAc droplets due to the volatilization of HAc, and whispering gallery modes (WGMs) of MgAc droplets in the Raman spectrum quench after 50,000 s. In sharp contrast, after 86,000 s at RH ≈ 70%, NaAc droplets are in well-mixed liquid states, containing soluble sodium hydroxide (NaOH). At this state, the RI of NaAc droplet is increased, and the quenching of WGMs is not observable.

DOI 10.1016/j.saa.2018.04.027
ISSN 1873-3557
Citation Spectrochim Acta A Mol Biomol Spectrosc. 2018;200:179185.

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