Absorption vs. redox reduction of Pd2+ and Cu2+ on triboelectrically and naturally charged dielectric polymers

Abstract

It has recently been reported that Teflon and polyethylene (PE) if rubbed by polymethylmethacrylate (PMMA) or Nylon as well as non-rubbed PMMA and Nylon induce “redox” reactions, including those of the reduction of Pd⁺² and Cu⁺² ions. On this basis, it was deduced that these dielectric materials may hold ≅10¹³–10¹⁴ of “hidden” electrons cm⁻², a value at least three orders of magnitude higher than the charge that a dielectric surface can accumulate without being discharged in air. The “hidden” electrons were termed “cryptoelectrons”. In variance to these reports, we offer here an alternative interpretation. Our model is supported by X-ray photoelectron spectroscopy, contact angle and vibrating electrode (modified Kelvin probe) measurements performed on representative examples. Rubbing of the polymers was found to transfer polymer fragments between the rubbed surfaces altering their physical properties. The transferred polymer fragments promote adsorption of Cu²⁺ and Pd²⁺ ions. It was found that Teflon and PE rubbed with PMMA and Nylon, and non-rubbed PMMA and non-rubbed Nylon do not induce “redox” reactions of Cu²⁺ and Pd²⁺ ions but adsorb these ions on their surfaces. Furthermore, the earlier reported reduction of Pd²⁺ to Pd⁰ by electrons, as detected by catalytic activity of Pd⁰ in a Cu-plating bath, can be alternatively explained by reduction of adsorbed Pd²⁺ by the reducing agents of the bath itself. Based on these findings, we support the hypothesis that charging of dielectric polymers is due to ions or free radicals rather than electrons and there is no evidence to invoke a hypothesis of “cryptoelectrons”.