Department of Chemical and Materials Engineering, Faculty of Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.
Lab Chip. 2020 Aug 21;20(16):2965-2974. doi: 10.1039/d0lc00571a. Epub 2020 Jul 16.
Biphasic chemical reactions compartmentalized in small droplets offer advantages, such as streamlined procedures for chemical analysis, enhanced chemical reaction efficiency and high specificity of conversion. In this work, we experimentally and theoretically investigate the rate for biphasic chemical reactions between acidic nanodroplets on a substrate surface and basic reactants in a surrounding bulk flow. The reaction rate is measured by droplet shrinkage as the product is removed from the droplets by the flow. In our experiments, we determine the dependence of the reaction rate on the flow rate and the solution concentration. The theoretical analysis predicts that the life time τ of the droplets scales with Peclet number Pe and the reactant concentration in the bulk flow c as τ∝ Pec, in good agreement with our experimental results. Furthermore, we found that the product from the reaction on an upstream surface can postpone the droplet reaction on a downstream surface, possibly due to the adsorption of interface-active products on the droplets in the downstream. The time of the delay decreases with increasing Pe of the flow and also with increasing reactant concentration in the flow, following the scaling same as that of the reaction rate with these two parameters. Our findings provide insight for the ultimate aim to enhance droplet reactions under flow conditions.
双相化学反应在小液滴中进行具有优势，例如简化了化学分析程序、提高了化学反应效率和转化率的高特异性。在这项工作中，我们通过实验和理论研究了在基底表面上的酸性纳米液滴与周围体相中的碱性反应物之间的双相化学反应的速率。通过产物被流动从液滴中移除来测量反应速率，从而导致液滴收缩。在我们的实验中，我们确定了反应速率与流速和溶液浓度的关系。理论分析预测，液滴的寿命 τ 与 Peclet 数 Pe 和体相中的反应物浓度 c 成比例，τ∝ Pec，这与我们的实验结果很好地吻合。此外，我们发现来自上游表面的反应产物可以延迟下游表面上的液滴反应，可能是由于界面活性产物在下游液滴中的吸附。延迟时间随着流动的 Pe 的增加和流动中反应物浓度的增加而减少，遵循与这两个参数的反应速率相同的标度。我们的发现为在流动条件下增强液滴反应的最终目标提供了深入了解。
