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

Xi-Juan Lv; Yang Wang; Chen Cai; Shu-Feng Pang; Jia-Bi Ma; Yun-Hong Zhang

doi:10.1016/j.saa.2018.04.027

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

Spectrochim Acta A Mol Biomol Spectrosc. 2018 Jul 5:200:179-185. doi: 10.1016/j.saa.2018.04.027. Epub 2018 Apr 14.

Authors

Xi-Juan Lv¹, Yang Wang¹, Chen Cai¹, Shu-Feng Pang¹, Jia-Bi Ma², Yun-Hong Zhang³

Affiliations

¹ The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, People's Republic of China.
² The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, People's Republic of China. Electronic address: majiabi@bit.edu.cn.
³ The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, People's Republic of China. Electronic address: yhz@bit.edu.cn.

PMID: 29680496
DOI: 10.1016/j.saa.2018.04.027

Abstract

Hygroscopicity and volatility of single magnesium acetate (MgAc₂) 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 MgAc₂ 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, MgAc₂ 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)₂) inclusions are formed in MgAc₂ droplets due to the volatilization of HAc, and whispering gallery modes (WGMs) of MgAc₂ 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.

Keywords: Aerosol particles; Amorphous gel structure; Optical tweezers; Refractive index; Volatilization of acetate acid.