Contact Electrification Of Polymers Research Articles

Effect of Redox Atmosphere on Contact Electrification of Polymers.

The Triboelectric Nanogenerator has demonstrated broad applications in energy, environmental, and electronic fields, as well as huge potential in the mechanism study of contact electrification, since 2012. Herein, we employed a Triboelectric Nanogenerator working in vertical contact-separation mode to study the electrification performance of the polymer under redox atmosphere. The results show that the electron-withdrawing ability of the polymer is weakened with increasing O3 concentration. Considering that O3 is typically one of the strongest oxidants, we further studied the electrification performance under H2, CO, and O2 atmosphere. It is found that the electron-withdrawing ability was predictably weakened under O2 atmosphere similar to the case of O3. On the contrary, the electron-withdrawing ability was enhanced under H2 and CO atmosphere. Accordingly, a theoretical mechanism involving the highest occupied surface state level is proposed to explain the effect of redox atmosphere on contact electrification. These results clarify that contact electrification can be varied by redox agents. Conversely, it also suggests the possibility to manipulate the redox reactions through the modification of contact electrification.

Transient aspects of plasma luminescence induced by triboelectrification of polymers

Transient electric gas discharges that occur around sliding interfaces during contact electrification of polymers were studied at millisecond timescales and with micrometre resolution. Deduced vibrational temperatures indicate cold plasma resulting from positive corona discharge. At millisecond timescales, previously unseen rapid discharge events are observed, and modelling suggests that these result from streamer development, triggered by electron emission from the polymer surface. Those which occur over a period of several seconds are shown to be caused by competition between charge generation and the formation of polymer films. The findings explain the interplay between charging and plasma generation and their dependence on wear processes.

The Contact Electrification of Polymers and the Depth of Charge Penetration

Measurements of contact electrification have been made on polymer films charge by repeated contacts to mercury. In these studies the saturation surface potential of monodisperse polystyrene has been measured as a function of film thickness, and we show that charges appear to be trapped within about 30 nm of the surface. In a related series of experiments, using an electron beam to inject into the free surface of polystyrene film we, find that the electron range is several μm. A reason for this large difference in charge penetration distance is presented.

Low-Energy Electronic States Related to Contact Electrification of Pendant-Group Polymers: Photoemission and Contact Potential Difference Measurement

Low-energy electronic states, 3-6 eV below the vacuum level, relevant to contact electrification of pendant-group polymers were investigated by means of photoemission and contact potential difference (CPD) measurements under atmospheric conditions. As a result, it was shown that the thresholds of photoemission of the polymers are related to their highest occupied molecular orbital (HOMO) levels derived from modified neglect of diatomic overlap (MNDO) molecular orbital calculation, and that the thresholds exist near the energy corresponding to their work function inferred from CPD measurement. Furthermore, it was found that the contact electrification of the polymers is related to their threshold of photoemission. These results are interpreted in terms of a molecular ion model proposed by Duke et al. [Phys. Rev. B 18 (1978) 5717].

Contact electrification of chemically modified surfaces

We have studied charge transfer from a variety of metals to solution-cast samples of polyvinyl-alcohol chemically treated to introduce superficial halogens (F, Cl, Br and I). Even though surface analysis shows that only a fraction of the hydroxyl groups are converted to halogen we find that the chemical treatments change the sign of the charge transfer from positive to negative; moreover, the charge transfer becomes much less dependent on metal work function as a result of the chemical treatment. Just such changes are expected if it is supposed that the Cl treatment (for example) converts the surface of the polymer from polyvinylalcohol to polyvinylchloride, and our experiments thus provide striking support for the opinion, expressed by many workers, that the contact electrification of polymers is intimately connected with their chemical composition. Chemical modification of a thin surface layer may provide a controlled means of adjusting the contact charging properties of a polymer with minimum disturbance of desirable bulk properties.

Contact electrification of polymers: A quantitative model

An explicit model of contact-charge exchange in polymers is proposed in which the steady-state exchanged charge resides in intrinsic molecular-ion states. The eigenvalue spectra of these states are inferred from metal/polymer contact-charge measurements using a theoretical formalism constructed for this purpose. This model of metal/polymer contact-charge exchange is extended to encompass the description of polymer/polymer contact-charge exchange as well. Utilizing the metal/polymer contact-charge-exchange spectra as input data, the model predicts correctly both the sign and order of magnitude of measured contact-charge exchange between polystyrene and copolymers of styrene and methyl methacrylate.

Contact electrification of polymers

Measurements of the charge produced by rolling or sliding contact between a metal or polymer sphere and a dielectric sheet have been carried out under controlled conditions. The dependence of charge on air pressure was studied. Charge decay and mobilities were estimated. The metal work-function had no effect on charge transfer. The polymer materials was of great importance, polar polymers charging positively with respect to both metals and non-polar polymers. The relation between charge per unit length and the square root of the normal contact force was found, and the time constant for charge transfer was evaluated.