Active sorting of droplets by using an ECF (Electro-conjugate Fluid) micropump

Abstract

This paper proposes an on-demand method to sort water-in-oil (W/O) droplets by using an ECF (Electro-Conjugate Fluid) micropump on a chip. ECF is a kind of functional and dielectric oil, which can generate a strong and active flow (called ECF jet) when a high DC voltage is applied to its corresponding anode & cathode in ECF. Targeting at on-demand droplets sorting, we design a new sorter including several parts: a T-junction droplet generator made of SU-8, a sorting area, an ECF micropump, and I/O ports. The ECF combined with a suitable concentration of a surfactant (Span 80) and DI (deionized) water are utilized as the continuous and the dispersed fluids, respectively. The mixture of ECF and Span 80 can also be pumped by our ECF micropump and then forms the ECF jet. The fabrication of the sorter is based on the photolithographic patterning of thick resists (KMPR and SU-8) and the electroforming. We model the ECF micropump and also analyze the sorting performance of our sorter based on the FEM analysis. To validate the sorter, we investigate the influence of two vital parameters of the strength of ECF jets and the droplet sizes on the sorter. Then, we also research the working zones (areas), throughput and sorting efficiency in terms of flow rate ratios and the applied voltages of our device.