Li Zhengxin, Zeng Hongbo, Zhang Xuehua
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.
Physics of Fluids Group, Max Planck Center Twente for Complex Fluid Dynamics, JM Burgers Center for Fluid Dynamics, Mesa+, Department of Science and Technology, University of Twente, Enschede 7522 NB, The Netherlands.
Langmuir. 2022 May 31;38(21):6638-6646. doi: 10.1021/acs.langmuir.2c00516. Epub 2022 May 19.
Chemical reactions in small droplets are extensively explored to accelerate the discovery of new materials and increase the efficiency and specificity in catalytic biphasic conversion and high-throughput analytics. In this work, we investigate the local rate of the gas-evolution reaction within femtoliter droplets immobilized on a solid surface. The growth rate of hydrogen microbubbles (≥500 nm in radius) produced from the reaction was measured online with high-resolution confocal microscopic images. The growth rate of bubbles was faster in smaller droplets and near the droplet rim in the same droplet. The results were consistent for both pure and binary reacting droplets and on substrates of different wettability. Our theoretical analysis based on diffusion, chemical reaction, and bubble growth predicted that the concentration of the reactant depended on the droplet size and the bubble location inside the droplet, in good agreement with experimental results. Our results reveal that the reaction rate may be spatially nonuniform in the reacting microdroplets. The findings may have implications for formulating the chemical properties and uses of these droplets.
人们广泛探索小液滴中的化学反应，以加速新材料的发现，并提高催化双相转化和高通量分析的效率及特异性。在这项工作中，我们研究了固定在固体表面的飞升级液滴内气体逸出反应的局部速率。利用高分辨率共聚焦显微镜图像在线测量了反应产生的氢微泡（半径≥500 nm）的生长速率。在较小的液滴中以及同一液滴的液滴边缘附近，气泡的生长速率更快。对于纯反应液滴和二元反应液滴以及不同润湿性的基底，结果都是一致的。我们基于扩散、化学反应和气泡生长的理论分析预测，反应物的浓度取决于液滴大小和液滴内气泡的位置，这与实验结果高度吻合。我们的结果表明，反应速率在反应性微滴中可能在空间上是不均匀的。这些发现可能对阐明这些液滴的化学性质和用途具有启示意义。
