The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, People's Republic of China.
The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, People's Republic of China.
Spectrochim Acta A Mol Biomol Spectrosc. 2018 Jul 5;200:179-185. doi: 10.1016/j.saa.2018.04.027. Epub 2018 Apr 14.
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.
通过单光束光镊研究了不同相对湿度 (RH) 下单个醋酸镁 (MgAc) 气溶胶颗粒的吸湿性和挥发性，并用腔增强拉曼光谱对折射率 (RI) 和形态进行了表征。观察到了醋酸 (HAc) 在 MgAc 液滴中的凝胶形成和挥发。由于形成非晶态凝胶结构，在 RH < 50%的时间尺度上，水在液滴中的置换被显著阻碍，时间长达 140000s。提出了在 RH < 10%时的不同相变来解释凝胶形成后明显的失水。为了比较不同体系中 HAc 的挥发，将 MgAc 和乙酸钠 (NaAc) 液滴保持在几个不同的稳定 RH 下长达 86000s。在 RH ≈ 74%时，由于 HAc 的挥发，MgAc 液滴中形成了氢氧化镁 (Mg(OH)) 夹杂物，并且在拉曼光谱中，MgAc 液滴的 whispering gallery modes (WGMs) 在 50000s 后熄灭。相比之下，在 RH ≈ 70%时，86000s 后，NaAc 液滴处于良好混合的液态，含有可溶性氢氧化钠 (NaOH)。在这种状态下，NaAc 液滴的 RI 增加，并且 WGM 的猝灭不可观察到。
