Probing Contact‐Electrification‐Induced Electron and Ion Transfers at a Liquid–Solid Interface

TLDR

Contact electrification has been studied for decades, and while electron transfer explains solid–solid interactions, the mechanism for liquid–solid interfaces remains controversial. The study systematically investigates contact electrification between various liquids and PTFE film to clarify the liquid–solid electrification mechanism. The authors measured surface charge densities and ion adsorption on PTFE during CE with liquids, revealing electron transfer as the dominant process. CE between deionized water and PTFE generates surface charges (~1 nC cm⁻²), an order of magnitude higher than ion‑transfer predictions, indicating electron transfer dominates; higher ion concentrations suppress this transfer, and oil–PTFE experiments confirm electron transfer in the absence of ions, reshaping the conventional view of electric double‑layer formation at liquid–solid interfaces.

Abstract

As a well-known phenomenon, contact electrification (CE) has been studied for decades. Although recent studies have proven that CE between two solids is primarily due to electron transfer, the mechanism for CE between liquid and solid remains controversial. The CE process between different liquids and polytetrafluoroethylene (PTFE) film is systematically studied to clarify the electrification mechanism of the solid-liquid interface. The CE between deionized water and PTFE can produce a surface charges density in the scale of 1 nC cm-2 , which is ten times higher than the calculation based on the pure ion-transfer model. Hence, electron transfer is likely the dominating effect for this liquid-solid electrification process. Meanwhile, as ion concentration increases, the ion adsorption on the PTFE hinders electron transfer and results in the suppression of the transferred charge amount. Furthermore, there is an obvious charge transfer between oil and PTFE, which further confirms the presence of electron transfer between liquid and solid, simply because there are no ions in oil droplets. It is demonstrated that electron transfer plays the dominant role during CE between liquids and solids, which directly impacts the traditional understanding of the formation of an electric double layer (EDL) at a liquid-solid interface in physical chemistry.