Oxidized Mechanoradicals Drive Triboelectricity in Polytetrafluoroethylene: A First Principle Understanding

Abstract

Although triboelectricity has played a crucial role in mankind’s discovery of charges and is of high relevance in different technological fields, the underlying mechanisms remain elusive. Even the type of charge carriers transferred─electrons, ions, or material fragments─is still controversial. One of the most relevant triboelectric materials is polytetrafluoroethylene (PTFE) due to its extremely high tendency toward negative triboelectric charging. Since PTFE is a chemically very stable insulator with a large band gap, the question arises how it stabilizes charges during contact electrification. Here, we use density functional theory and GW to clarify how the charge transfer between PTFE and gold surfaces takes place. During tribological contact, PTFE suffers mechanochemical bond cleavage. However, the resulting C-centered radicals are not electron affine enough to explain negative charging. Our GW calculations suggest that more electronegative alkoxy and carboxylate defects, which form from C-centered radicals in the presence of O₂ and H₂O, are required for stable integer electron transfer. A simple model based on electrostatics and quantum-mechanical tunneling explains how charging of these defects is preserved during contact separation.