Bono Shinji, Kinugasa Hiroki, Kajita Hiroki, Konishi Satoshi
Research Organization of Science and Technology, Ritsumeikan University, Shiga, 525-8577, Japan.
Ritsumeikan Advanced Research Academy, Kyoto, 604-8502, Japan.
Sci Rep. 2024 Sep 12;14(1):21326. doi: 10.1038/s41598-024-72089-5.
This study investigates a novel microfluidic mixing technique that uses the resonant oscillation of coalescent droplets. During the vertical contact-separation process, solutes are initially separated as a result of the combined effects of diffusion and gravity. We show that the application of alternating current (AC) voltage to microelectrodes below the droplets causes a resonant oscillation, which enhances the even distribution of the solute. The difference in concentration between the top and bottom droplets exhibits frequency dependence and indicates the existence of a particular AC frequency that results in a homogeneous concentration. This frequency corresponds to the resonance frequency of the droplet oscillation that is determined using particle tracking velocimetry. To understand the mixing process, a phenomenological model based on the equilibrium between surface tension, viscosity, and electrostatic force was developed. This model accurately predicted the resonance frequency of droplet flow and was consistent with the experimental results. These results suggest that the resonant oscillation of droplets driven by AC voltage significantly enhances the diffusion of solutes, which is an effective approach to microfluid mixing.
本研究探讨了一种利用聚并液滴共振振荡的新型微流体混合技术。在垂直接触-分离过程中，由于扩散和重力的综合作用，溶质最初会被分离。我们表明，向液滴下方的微电极施加交流（AC）电压会引起共振振荡，从而增强溶质的均匀分布。顶部和底部液滴之间的浓度差异呈现频率依赖性，并表明存在一个导致浓度均匀的特定交流频率。该频率对应于使用粒子跟踪测速法确定的液滴振荡共振频率。为了理解混合过程，建立了一个基于表面张力、粘度和静电力平衡的唯象模型。该模型准确预测了液滴流的共振频率，与实验结果一致。这些结果表明，交流电压驱动的液滴共振振荡显著增强了溶质的扩散，这是一种微流体混合的有效方法。
