Low-Temperature Raman Imaging of Component Distribution in Micron-Size Droplets
Low-Temperature Raman Imaging of Component Distribution in Micron-Size Droplets
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微米级液滴成分分布的低温拉曼成像
DOI：
10.1021/acsearthspacechem.1c00412
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发表时间：
2022
影响因子：
3.4
通讯作者：
Vikesland, Peter J.
中科院分区：
文献类型：
--
作者：
Huang, Qishen;Vikesland, Peter J.
大气液滴由于其不同的混合状态和相而表现出异质性。冰核形成是一种常见且随机的大气过程，可能会增强各个液滴之间的差异。在这项研究中，我们通过拉曼成像在 293 K 和 223 K 下记录硫酸盐、冰晶和金纳米粒子 (AuNP) 的空间图，研究了微米级液滴内化学部分的分布。我们在 293 K 下的硫酸铵 (AS) 溶液和液滴中以及在 223 K 下的过冷 AS 液滴中观察到硫酸盐在空间上均匀分布。从冰晶中排出的空间富集的硫酸盐出现在冷冻溶液中。有趣的是，一部分冻结的液滴表现出空间丰富的硫酸盐分布，而其他液滴则均匀地冻结。初始 AS 浓度越高，分布越均匀的液滴百分比越高。我们根据收集的光学图像的亮度将液滴区分为过冷或冻结。使用 AS 液滴的拉曼图像，我们确定 >93% 的过冷液滴均匀分布，而 >90% 的冷冻液滴由于冰成核而在空间上富集。我们认为，过冷液滴内的局部冰成核和完全冻结的液滴内的玻璃形成是造成剩余液滴的主要因素（~10%）。不同的成分分布反映了冰成核的随机性质。我们还研究了功能化 pH 感应 AuNP 在冷冻 AS 液滴内的分布，并观察到与 AS 分布或冰成核位点不同的 AuNP 的独立分布。与室温光谱相比，AuNPs 拉曼光谱的相对峰值强度在 223 K 时发生变化，这表明在 223 K 时 AuNPs 附近冰晶的形成改变了功能化纳米颗粒的光谱行为。
Atmospheric droplets exhibit heterogeneity due to their distinct mixing states and phases. Ice nucleation is a common and stochastic atmospheric process that potentially enhances differences between individual droplets. In this study, we investigated the distribution of chemical moieties within micron-size droplets by recording spatial maps of sulfate, ice crystals, and gold nanoparticles (AuNPs) via Raman imaging at 293 and 223 K. We observed a spatially even distribution of sulfate in ammonium sulfate (AS) solutions and droplets at 293 K, and in supercooled AS droplets at 223 K. Spatially enriched sulfate, expelled from ice crystals, appeared in frozen droplets and bulk solution at 223 K. Interestingly, a fraction of the frozen droplets exhibited spatially enriched sulfate distributions, while others froze evenly. A higher percentage of more evenly distributed droplets were found for higher initial AS concentrations. We differentiated the droplets as supercooled or frozen according to the brightness of the collected optical images. Using the Raman images of the AS droplets, we determined that >93% of the supercooled droplets were evenly distributed, while >90% of the frozen droplets were spatially enriched due to ice nucleation. We suggest that localized ice nucleation, within supercooled droplets, and glass formation, within completely frozen droplets are the major factors contributing to the remainder of the droplets (∼10%). The different component distributions reflect the stochastic nature of ice nucleation. We also investigated the distribution of functionalized pH-sensing AuNPs within frozen AS droplets and observed an independent distribution of AuNPs that differed from either the AS distribution or the ice nucleation sites. The relative peak intensity of the Raman spectrum of AuNPs changed at 223 K compared to its room temperature spectrum, which suggests that the formation of ice crystals in the vicinity of AuNPs at 223 K altered the spectral behavior of the functionalized nanoparticles.
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DOI：
--
发表时间：
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期刊：
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影响因子：
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DOI：
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