Sano Motoya, Kamei Kota, Yatsuhashi Tomoyuki, Sakota Kenji
Division of Molecular Material Science, Graduate School of Science, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
Department of Chemistry, Graduate School of Science, Osaka Metropolitan University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan.
J Phys Chem Lett. 2024 Aug 15;15(32):8133-8141. doi: 10.1021/acs.jpclett.4c01819. Epub 2024 Aug 1.
Microdroplets offer unique environments that accelerate chemical reactions; however, the mechanisms behind these processes remain debated. The localization and orientation of solute molecules near the droplet surface have been proposed as factors for this acceleration. Since significant reaction acceleration has been observed for electrospray- and sonic-spray-generated aerosol droplets, the analysis of microdroplets in air has become essential. Here, we utilized whispering gallery mode (WGM) resonances to investigate the localization and orientation of dissolved rhodamine B (RhB) in a levitated microdroplet (∼3 μm in diameter) in air. Fluorescence enhancement upon resonance with the WGMs revealed the localization and orientation of RhB near the droplet surface. Numerical modeling using Mie theory quantified the RhB orientation at 68° to the surface normal, with a small fraction randomly oriented inside the droplet. Additionally, low RhB concentrations increased surface localization. These results support the significance of surface reactions in the acceleration of microdroplet reactions.
微滴提供了能加速化学反应的独特环境；然而，这些过程背后的机制仍存在争议。溶质分子在液滴表面附近的定位和取向已被认为是这种加速的因素。由于在电喷雾和声波喷雾产生的气溶胶微滴中观察到了显著的反应加速，因此对空气中微滴的分析变得至关重要。在这里，我们利用回音壁模式（WGM）共振来研究溶解在空气中悬浮微滴（直径约3μm）中的罗丹明B（RhB）的定位和取向。与WGM共振时的荧光增强揭示了RhB在液滴表面附近的定位和取向。使用米氏理论的数值模拟量化了RhB相对于表面法线成68°的取向，在液滴内部有一小部分是随机取向的。此外，低RhB浓度增加了表面定位。这些结果支持了表面反应在微滴反应加速中的重要性。
