Richard P. N. Veregin

Endor studies of carbon black and carbon black-polymer composites

Abstract Electron-nuclear double resonance (ENDOR) spectra have been obtained at the free proton frequency for a carbon black and a carbon black-polymer composite, at temperatures ranging from 130 K to 350 K. The ENDOR spectra show an unusual dependence on the saturation of the associated homogeneously broadened ESR resonance, as “non-saturating” microwave power gives rise to largest ENDOR enhancements. This behaviour is attributed to a “lineshift” ENDOR mechanism. In the composite, the polymer 1 H nuclei contribute very strongly to the ENDOR signal, and this signal shows a marked dependence on molecular motion within the polymer.

Determination of the origin of the narrow ESR signal in carbon black filled polymers

Abstract A comparison of the ESR and ENDOR signals generated during the melt blending of carbon blacks and polymers with the signals generated upon electrochemical reduction of the carbon blacks has been made. Both an oxidized and an unoxidized carbon black were used. For the oxidized black, the magnetic resonance spectra revealed a localized site on the surface which interacted with the hydrogen nuclei of the polymer. However, for the unoxidized black, a conduction ESR signal was observed which also interacted with the polymer matrix. In both cases it was concluded that the narrow ESR signal of the composite was equivalent to the electrochemically reduced signal of the carbon black. This in turn demonstrates that the narrow ESR signals observed in composites arise from electron acceptance by the carbon blacks. Finally, the possible mechanisms for this reaction are discussed.

1H and 19F ENDOR of carbon black-polymer composites

Abstract 1 H and 19 F electron-nuclear double resonance (ENDOR) spectra have been obtained for some carbon blacks carbon black-polymer composites, at temperatures ranging from 130 to 350 K. The ENDOR spectra are sensitive to the nature of the carbon black surface, the carbon black-polymer interface in the composites. In the carbon blacks D 2 O exchange shows that approximately one-half of the 1 H ENDOR signal arises from acidic protons accessible to the carbon black surface. In the composites, the contribution of the polymer 1 H nuclei to the ENDOR signal is much larger than that from the carbon black. In addition, 19 F nuclei in the polymer can also give rise to an ENDOR signal. The 1 H 19 F ENDOR signals are a novel probe of the orientation motion of the polymer at the polymer-carbon black interface, show a marked dependence on the physical properties of the composite, including the glass transition temperature, the ratio of fluorine to hydrogen in the polymer, prior heat or mechanical treatment.

Electrical Conduction in Iron Oxide Powder Coated with Polymethyl Methacrylate

Current-voltage and transient behaviours of iron oxide powder coated with polymethyl methacrylate (i.e., a model xerographic carrier) was studied by measuring current through powder piles sandwiched between two planar electrodes. A space charge limited process was identified as the major factor controlling transverse DC conduction in the coatings. Current-voltage hysteresis and the characteristic transient behaviour observed in the present structure indicate the presence of intrinsic longlifetime traps in polymethyl methacrylate, that may play a significant role in its triboelectric response.