Tribo‐Charge Induced Wetting (TCW): A New Wettability Control Mechanism for Electric‐Free Droplet Manipulation

Electrowetting-on-dielectric (EWOD) has revolutionized digital microfluidics (DMF) by dynamically controlling surface wettability via electric fields. However, its reliance on external power, patterned electrodes, and complex circuitry limits device simplicity and portability. Here, tribo-charge driven wetting (TCW) is introduced as a fundamentally new, electric-free mechanism for active wettability control. Unlike voltage-driven control in EWOD, TCW employs surface charges generated through contact electrification to modulate surface wettability, eliminating the need for electrodes, wiring, and power supplies. Using TCW, we demonstrate a substantial contact angle modulation of Δθ = 44.4°±1.1, achieved solely by a tribo-actuator with its surface charge density of σ = -12.61 µC m^- ². Comprehensive experimental and numerical analyses reveal that TCW performance scales strongly with actuator area and charge density but is remarkably insensitive to dielectric thickness within a practical range. Leveraging these features, core DMF operations are demonstrated, including droplet transport, merging, and generation from a reservoir, all accomplished without any electric components. Droplet motion reaches speeds up to 40 mm s^-1, even across non-planar terrains. Furthermore, fingertip-controlled droplet manipulation highlights TCW's simplicity, cost-effectiveness, and user-interactivity. This work advances fundamentals of charge-driven wettability control and establishes TCW as an electric-free paradigm for active droplet control, opening new opportunities for resource-limited, lab-on-a-chip and point-of-care applications.