Contact Electrification at Dielectric Polymer Interfaces: On Bond Scission, Material Transfer, and Electron Transfer

Triboelectric nanogenerators (TENGs) are revolutionizing mechanical-to-electrical energy harvesting. TENGs harvest energy through the polymer-polymer contact electrification (PCE) mechanism, driven by nanoscale processes at the contact interface. Currently, when discussing PCE there are two distinct schools of thought on which nanoscale interactions drive charging at the contact interface; 1) electron transfer, where orbital overlap leads to charge tunneling between polymers; or 2) mass (material) transfer, where polymer chain entanglement and intermolecular bonding leads to heterolytic bond scission. Here, a combination of in silico and benchtop experiments is used to elucidate the relative role of electron and mass transfer in PCE. In silico experiments show that covalent bond scission in a polymethylmethacrylate/polytetrafluoroethylene system occurs at 348 kcal mol-1, prior to electron cloud overlap, where the highest occupied molecular orbital and lowest unoccupied molecular orbital of the system remain separated by 163 kcal mol-1. Benchtop experiments show PCE-generated charges cannot be simply discharged via electrical grounding, indicating the formation of bound surface charge from mass transfer. The calculations and contact-electrification tests provide strong evidence to support mass transfer being the leading mechanism driving PCE. Contact electrification between dielectric polymers is a fundamental mechanism that underpins electrostatic phenomena and mechanical energy harvesters. Herein, a perspective on the two most commonly proposed mechanisms, mass (material) transfer, and electron transfer, are compared via simulations and experiments providing a path to engineer future electrostatic surfaces.image