title: 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/m(2), or ∼100 charges/μm(2)) 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.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
authors.forename: Siowling
authors.initials: S
authors.lastname: Soh
authors.forename: Sen Wai
authors.initials: SW
authors.lastname: Kwok
authors.forename: Helena
authors.initials: H
authors.lastname: Liu
authors.forename: George M
authors.initials: GM
authors.lastname: Whitesides
mesh_terms: D009757:Nylons / Q000737:chemistry*; D011138:Polytetrafluoroethylene / Q000737:chemistry*; D012117:Resins, Synthetic / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D009757:Nylons; D012117:Resins, Synthetic; D011138:Polytetrafluoroethylene; C010102:delrin