Droplet rotation in a microfluidic loop channel driven by three-phase pressure modulation without embedded pneumatic valves

Abstract

Continuously rotating a single microdroplet within a circular loop channel keeps the droplet in motion while holding it within a fixed field of view. Existing approaches to droplet rotation, however, typically rely on multi-layer devices equipped with pneumatic control valves, which complicate both fabrication and operation. In this study, we present a method, free of embedded pneumatic valves, in which a single droplet is rotated in a circular loop microchannel by applying three pressure waveforms, analogous to the driving currents of a three-phase synchronous motor, to three radially arranged control channels. The operating principle is formulated using this motor analogy, and an equation of motion is derived that explicitly accounts for the time delays arising from the pressure pumps and the feedback loop. Computational fluid dynamics simulations and experiments consistently show that the measured optimal lead angle closely matches the theoretical prediction of 90° across a range of system parameters, including tubing length. The proposed framework simplifies the integration of loop-based droplet manipulation into existing lab-on-a-chip devices and provides a practical design guide for controlling such systems.