Digital flow rate sensor based on isovolumetric droplet discretization effect by a three-supersurface structure

Minute droplets play a growingly important role in the fields of manufacturing and measurement for the ability of being miniscule liquid carries. A digital microfluidic flow rate sensor, which works by counting the number of droplets generated between two electrodes, is designed and fabricated in this article. The droplets with equal volume ranging from nanoliter to microliter are generated by a three-supersurface structure (TSS), and the droplet volume is directly related to the size of gap in the TSS, which means that the resolution of the flow rate sensor can be simply tuned by changing the gap. A theoretical model is presented to reveal the mechanism of the isovolumetric discretization effect, showing that the superhydrophobicity/superhydrophilicity of the TSS’s three surfaces plays the most important role in the isovolumetric droplet discretization. Both numerical simulation and experimental results demonstrate that the droplets can keep uniform size at different flow rates under 200 μL/min, indicating a potential application of the digital flow rate sensor for low rate metering in microfluidic devices.