Contact-Electrification between Two Identical Materials: Curvature Effect

Abstract

It is known that contact-electrification (or triboelectrification) usually occurs between two different materials, which could be explained by several models for different materials systems (Adv. Mater. 2018, 30, 1706790; Adv. Mater. 2018, 30, 1803968). But contact between two pieces of the chemically same material could also result in electrostatic charges, although the charge density is rather low, which is hard to understand from a physics point of view. In this paper, by preparing a contact-separation mode triboelectric nanogenerator using two pieces of an identical material, the direction of charge transfer during contact-electrification is studied regarding its dependence on curvatures of the sample surfaces. For materials such as polytetrafluoroethylene, fluorinated ethylene propylene, Kapton, polyester, and nylon, the positive curvature surfaces are net negatively charged, while the negative curvature surfaces tend to be net positively charged. Further verification of the above-mentioned trends was obtained under vacuum (∼1 Pa) and higher temperature (≤358 K) conditions. Based on the received data acquired for gentle contacting cases, we propose a curvature-dependent charge transfer model by introducing curvature-induced energy shifts of the surface states. However, this model is subject to be revised if the mutual contact mode turns into a sliding mode or more complicated hard-pressed contact mode, in which a rigorous contact between the two pieces of the same material could result in nanoscale damage/fracture and possible species transfer. Our study provides a primitive step toward understanding the basics of contact-electrification.

Fiber/Fabric‐Based Piezoelectric and Triboelectric Nanogenerators for Flexible/Stretchable and Wearable Electronics and Artificial Intelligence

“…Although it is one of the most frequently experienced effects in our daily life, the nature of the charge carriers and their transfer mechanisms behind triboelectrification or contact electrification are still puzzled or more precisely under debate. Recently, Xu and co‐workers and Lin et al have conducted some theoretical studies in order to deeply explore the triboelectrification behaviors. It is found that the electron transfer instead of ion transport is the dominant process of triboelectrification.…”

“…Due to the thermionic emission effect, electrons are thermally excited and transferred from a hotter part to a cooler one. The CE behaviors between identical materials have also been investigated . Charge transfer between similar materials can be observed from curved surfaces rather than flat structures.…”

Robust Triboelectric Nanogenerator with Ratchet‐like Wheel‐Based Design for Harvesting of Environmental Energy

“…A sponge layer is placed under the electrode layer (that underneath the PTFE layer) to have a better contact between the triboelectric layers. It is worth mentioning that PTFE is attached to the sector‐shaped plate of the movable part to achieve a better performance of the sub‐triboelectrification unit as the convex PTFE film can more easily obtain electrons than the flat film . The curvature of the sector plate is equal to that of the fixed plate (Figure S1a, Supporting Information).…”

“Self‐Matched” Tribo/Piezoelectric Nanogenerators Using Vapor‐Induced Phase‐Separated Poly(vinylidene fluoride) and Recombinant Spider Silk

“…Interestingly, the same tendency could happen on the PET‐PET‐based TENG. Normally, TENG using the same material as paired layers cannot generate significant triboelectric output because of the identical electron work function in both layers (same surface potential) and similar curvature‐induced energy shifts in the surface states . However, if we matched the PVDF with PET in different polarized directions to induce an opposite electron potential, a conspicuous output voltage of 41 V could be detected, suggesting that PVDF could change the PET surface electron states effectively.…”

“…Nevertheless, most TPNGs consisting of the tribo and piezoelectric components are based on direct energy superposition. The intrinsic electron‐cloud‐potential‐well coupling effect of TENG is often overlooked . It is known that the contact and separation of the two pairing tribo‐materials generate triboelectrification (or contact electrification).…”