Contact De-electrification of Electrostatically Charged Polymers

Abstract

The contact electrification of insulating organic polymers is still incompletely understood, in part because multiple fundamental mechanisms may contribute to the movement of charge. This study describes a mechanism previously unreported in the context of contact electrification: that is, “contact de-electrification”, a process in which polymers charged to the same polarity discharge on contact. Both positively charged polymeric beads, e.g., polyamide 6/6 (Nylon) and polyoxymethylene (Delrin), and negatively charged polymeric beads, e.g., polytetrafluoroethylene (Teflon) and polyamide-imide (Torlon), discharge when the like-charged beads are brought into contact. The beads (both with charges of ∼±20 μC/m2, or ∼100 charges/μm2) discharge on contact regardless of whether they are made of the same material, or of different materials. Discharge is rapid: discharge of flat slabs of like-charged Nylon and Teflon pieces is completed on a single contact (∼3 s). The charge lost from the polymers during contact de-electrification transfers onto molecules of gas in the atmosphere. When like-charged polymers are brought into contact, the increase in electric field at the point of contact exceeds the dielectric breakdown strength of the atmosphere and ionizes molecules of the gas; this ionization thus leads to discharge of the polymers. The detection (using a Faraday cup) of charges transferred to the cup by the ionized gas is compatible with the mechanism. Contact de-electrification occurs for different polymers and in atmospheres with different values of dielectric breakdown strength (helium, argon, oxygen, carbon dioxide, nitrogen, and sulfur hexafluoride): the mechanism thus appears to be general.

Tribo-electric charging and adhesion of cellulose ethers and their mixtures with flurbiprofen

“…As the majority of pharmaceutical materials are insulators, this process is extended, perhaps over minutes to hours, in comparison to conductive materials (Bailey, 1984;Rowley, 2001). A fundamental understanding of the phenomenon is still elusive (Soh et al, 2012), however, on the basis of existing theories, the mechanism of charge generation can be due to electron transfer, (charge is produced due to the flow of electrons between particles); ion transfer (diffusion of ions between the surface of particles); or due to material transfer (some material is rubbed off from one contacting body and attached onto the surface of another particle). Commonly, the tribo-electric charging process is a combination of these processes, although the charging behaviour of pharmaceutical materials is usually ascribed to the electron transfer theory because it provides a relatively understandable description of the charging process (Matsusaka et al, 2010).…”

Using the gravitational energy of water to generate power by separation of charge at interfaces

“…Two types of solid surfaces were used: L-shaped channels, or cylindrical tubes. After flowing water across the solid surface, we measured its charge by collecting it in a Faraday cup connected to an electrometer (model 6514, Keithley) (as discussed in a previous study; 4 see ESI,† Section 1 for more details on the experimental methods and materials used). We also determined the power output of SLIDE by measuring the potential difference across a resistor connected to the Faraday cup and to the ground.…”

Layer-by-layer films for tunable and rewritable control of contact electrification

“…The maximum amount of charge storable on a material is influenced by discharge, and discharge is -to some extent -idiosyncratic. 30 When the measured charge on the rolling sphere reached ~900 pC, discontinuities occurred in the charging curves (such as those in Fig. 2b-c).…”

“…We attribute these features to spontaneous electrical discharges through ambient air. 29,30 According to Equation 1, where E is the electric field, ε 0 is the permittivity, and r is the radius of the rolling sphere, the electric field generated by 900 pC on the surface of a sphere with a diameter of 3.2 mm would exceed the dielectric breakdown limit of air (~3 MV/m). pC/sec for the PDDA(+) fix terminated and -150 pC/sec for the PSS(-) fix terminated films.…”