Electrical resistivity of carbon black loaded polyethylene modified by ion implantation
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Vladimir Hnatowicz and Jifi Kvitek Institute of Nuclear Physics, Academy of Sciences of Czech Republic, 250 68 Rez, Czech Republic (Received 22 June 1993; accepted 14 October 1993)
Different properties of the mixtures of polyethylene with carbon black modified by the implantation of Sb + ions were studied. Chemical changes of polymer were examined by IR- and UV-visible spectroscopy. Sheet resistivity as a function of sample temperature was studied. Depth profiles of implanted Sb atoms and incorporated oxygen were determined by the Rutherford backscattering technique. The percolation threshold of unimplanted mixtures is found at 4.5 and 5 wt. % of carbon black. As a result of ion implantation, the polymer is oxidized and conjugated double bonds are produced. The mixtures with carbon black concentration above percolation threshold exhibit metal-like conductivity. For the mixtures below percolation threshold, the measurements of resistivity versus temperature dependence indicate semiconductor type conductivity and charge transport via a variable range-hopping mechanism.
I. INTRODUCTION
II. EXPERIMENTAL
Electrically conductive carbon black is one of the often studied and applied additives for plastics, namely for elastomers. The increased interest in the carbon black loaded materials is connected with their good mechanical properties and with the possibility to change easily their resistivity in rather broad intervals by simply changing the carbon black additive concentration. These properties make carbon black loaded polymers attractive for usage in electrical and electronic devices.1 The mixtures with high resistivity may be used, e.g., for protection of communication cables, low-loss conventional apparatus, and optical fibers. Mixtures with a low resistivity, on the other hand, are used for elimination of static electricity charging of clothing, carpeting, satellite antenna bushing, etc., in cases where common measures are not sufficient. It is well known that the electrical resistivity of the mixtures depends on the type and the concentration of carbon black additive and also on the degree of its dispersion in polymer matrix.2'3 The resistivity is also affected by other factors such as temperature, pressure, orientation, and possibly by macromolecule crosslinking.4'5 In polymers modified by ion implantation, a significant increase of electrical conductivity is observed.6'7 The structure and the electrical resistivity of polyethylene samples loaded with carbon black to different concentrations and implanted with 150 keV Sb + ions are examined as functions of the carbon black concentration, implanted dose, and temperature.
All experiments were performed on polyethylene (PE) with the molecular weight of 180000 and the density of 0.945 g • cm" 3 . As a carbon black (CB) conducting agent, Chezcarb EC-A was added into the mixture in wt. %. Samples in the form of 15 /xm thick foils or 1.5 mm thick sheets were implanted at room temperature with 150 keV Sb + ions to doses from 1 X 10 1 2 -2 X 1015 cm" 2 . Thin samples
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