Contact Electrification between Droplets and Hydrophobic Surfaces: Regulation Mechanisms of Dynamic Interfacial Behavior and Frontier Advances

Contact electrification between droplets on hydrophobic surfaces and solid–liquid interfaces is an interdisciplinary research hotspot in interface science and energy electronics, with significant application value in microfluidic manipulation, biomedicine, droplet-based triboelectric nanogenerators, and other fields. This paper systematically reviews the fundamental theories and latest research progress in this field. First, it clarifies the controversy over the carrier properties of solid–liquid contact electrification and the results of quantitative verification, details the “two-step” charge transfer mechanism and its subsequent revisions, and focuses on the core content and theoretical significance of the work-function-driven electron transfer model. On this basis, it comparatively analyzes the charge kinetic laws of two typical dynamic contact behaviors: sliding and bouncing. The net charge of sliding electrification is determined by the ion adsorption shielding effect regulated by contact time, while the bouncing electrification efficiency shows a linear positive correlation with the maximum spreading area of the droplet. Finally, it highlights the non-contact droplet pre-charging phenomenon that breaks through the boundaries of traditional theories, and explains its competitive mechanism between electrostatic field-induced polarization and negative charge jet capture. This paper points out the key scientific problems existing in the current field and provides a systematic reference for the theoretical improvement and technical application of droplet contact electrification.