Programmable Milli-Microfluidics via Oxide-Mediated Continuous Electrowetting of Liquid Metal Droplets

Interfacial oxide layers on gallium-based liquid metal (LM) have traditionally been regarded as obstacles to stable electrohydrodynamic actuation. Here, we demonstrate that such oxides can be leveraged to achieve programmable flow field control. By introducing a Faradaic depolarization model that accounts for interfacial redox reactions, we resolve the long-standing discrepancy between theoretical predictions and experimental observations in continuous electrowetting (CEW). We reveal that oxide coverage dictates flow direction and pattern under identical electrical inputs, enabling full reversal of jet flows without changing the driving signals. Experimentally, four distinct flow regimes are identified under impulsed and unbiased AC excitations, showing excellent agreement with our model. Moreover, we demonstrate oxide-mediated flow operations such as bubble-free pumping, reconfigurable fluidic logic, and sustained performance exceeding 19 h. This work establishes an encoding framework for small-scale pumps capable of multi-mode and long-term operation, enabling on-demand flow field programming and paving the way for intelligent milli-microfluidic systems in adaptive thermal management and autonomous lab-on-a-chip devices.