a) b - École Polytechnique de Montréal

threshold concentrations are obtained in semi-crystalline systems compared to amorphous
polymers due to geometrical restriction of the conductive pathway(Narkis & Vaxman, 1984).
• Polymer Blend Morphology
Another approach to reduce the percolation threshold of conductive fillers relies on the selective
localization of conductive phase particles in multiphase polymeric materials in one of the phases
or better yet at the interface of binary co-continuous blends(Gubbels et al., 1995). A percolation
threshold of 0.5 vol.% of carbon black was reported by compression molding of a mixture of
carbon black and polystyrene powders(Klason & Kubát, 1975). Although the carbon black
particles do not penetrate the polystyrene phase and remain essentially located at the interface
between polystyrene particles, this method suffers from poor mechanical properties and
reproducibility. Gubbels et al.(Gubbels, Blacher, et al., 2002; Gubbels, Jerome, et al., 2002)
succeeded in fabricating a multiphase material with low percolation of carbon black particles in
polymers by selectively localizing carbon black percolation threshold of conducting polymer
lowers owing to double percolated structure(Levon, Margolina, & Patashinsky, 2002; Sumita et
al., 1992). The percolation threshold of the poly(ethylene-co-vinyl acetate) (EVA)/high density
polyethylene (HDPE)/ carbon black (CB) blend is at a significantly lower carbon content than
the individually filled HDPE or EVA(Foulger, 1999). Similar results were obtained for
polypropylene/nylon/CB(Tchoudakov, Breuer, Narkis, & Siegmann, 1996).
The effect of the PE continuity fraction on the CB content is illustrated in Figure 2-22. Double
percolation is at the origin of this situation(Calberg et al., 1999):
1) Percolation of the polymer phases and thus of their interface.
2) Percolation of the conducting particles in one phase or at the interface.
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