Impact of Initial Charge Conditions on the Slide Electrification of Droplets

Contact electrification and electrostatic induction are the core mechanisms behind solid-liquid (SL) triboelectric nanogenerators (TENGs), which have garnered interest for powering microscale devices. However, the fundamental understanding underpinning charge transfer within SL-TENGs remains relatively poor, limiting their optimized material selection and device design. In this study, water droplets and poly(tetrafluoroethylene) (PTFE) are used as a model system to examine how the initial charge conditions of either the droplet or PTFE influence contact electrification and SL-TENG output performance. PTFE films were subjected to various pretreatments, including charge neutralization by plasma, pre-triboelectrification, and cleaning with polar and nonpolar solvents. Water droplets were either electrically grounded or subjected to charge injection via plasma ions. Experimental characterization and modeling revealed that the initial charge state of PTFE films greatly affects the SL-TENG output performance. Water, and other organic liquids, could not only lead to the appearance of negative charges on PTFE (aligning with the standard liquid-solid electrification model) but also neutralize these charges. This study demonstrates the importance of controlling the initial charge conditions to improve the performance stability of SL-TENG devices.