Mechanism of charge generation by high-speed water nanodroplets impinging on metal surfaces

This study explores the mechanism of charge generation when high-speed water nanodroplets impact metal surfaces. Using a condensation-based nanodroplet generator, we measured the electric potential and current upon droplet collisions with various metals. Results showed a clear dependence on metal type, with charge polarity and magnitude following a descending trend from positive to negative: Pb > Al > Fe > Cu > Sn. The observed trends correspond strongly with the triboelectric series, indicating that triboelectric charging is the primary charge generation mechanism. Other factors, such as electrochemical reactions, thermoelectric effects, wettability, and pre-existing droplet charge, showed limited influence. These findings not only address a fundamental gap in the understanding of droplet-induced electrification at the nanoscale but also lay the groundwork for advanced applications in charge-controlled nanodroplet technologies.