Electric-Field-Induced Selective Directed Transport of Diverse Droplets

Droplet directional transport is one of the central topics in microfluidics and lab-on-a-chip applications. Selective transport of diverse droplets, particularly in another liquid phase environment with controlled directions, is still challenging. In this work, we propose an electric-field gradient-driven droplet directional transport platform facilitated by a robust lubricant surface. On the platform, we clearly demonstrated a liquid-inherent critical frequency-dominated selective transport of diverse droplets and a driving mechanism transition from electrowetting to liquid dielectrophoresis. Enlightened by the Kelvin–Helmholtz theory, we first realize the directional droplet transport in another liquid phase whenever a permittivity difference exists. Co-transport of multiple droplets and various combinations of droplet types, as well as multifunctional droplet transport modes, are realized based on the presented powerful electric-field gradient-driven platform, overcoming the limitations of the surrounding environment, liquid conductivity, and intrinsic solid–liquid wetting property existing in traditional droplet transport strategies. This work may inspire new applications in liquid separation, multiphase microfluidic manipulation, chemical reagent selection, and so on.