ELECTRICAL-CONDUCTION NEAR PERCOLATION-THRESHOLD IN POLYMER COMPOSITECONTAINING CONDUCTING POLYPYRROLE-COATED INSULATING POLYMER FIBER

New types of conductor-insulator composites are prepared, in which con ducting polymer-coated insulating polymers (polyethylene in spheres, n ylon66 in iibers), whose size and shape are well controlled, are used as the conductor, and noncoated polyethylene spheres are used as the i nsulator. The dependence of electrical conductivity on the concentrati on of coated insulating polymers near the percolation threshold is stu died in detail. The percolation threshold decreased with increasing le ngth of coated nylon66 fibers. In the composite made of polypyrrole-co ated polyethylene spheres and noncoated polyethylene spheres, the crit ical exponent t is evaluated to be 2.0 +/- 0.2. In the composite made of polypyrrole-coated nylon fibers (400 mu m, 800 mu m) and noncoated polyethylene spheres, a larger value t (3.0 +/- 0.4) is obtained. The dependence of t on applied voltage is also studied. In the composites made of polypyrrole-coated nylon66 fibers, t increases with increasing applied voltage. This can be explained by taking interparticle tunnel ing conduction into consideration in the percolation model.