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a) b - École Polytechnique de Montréal

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Figure 2-19. Approaching the percolation threshold in a binary blend<br />

Thereby, continuous chains or networks of conductive material through sample are formed. An<br />

electrical charge can now pass through the conductive composite or blend via this network<br />

without encountering the low conductivity of the polymer resin. Introducing further conductive<br />

material loading beyond the percolation threshold does not greatly increase the conductivity of<br />

this material(Bhattacharya, 1986).<br />

2.3.1.1.1 Parameters Influencing the Percolation Threshold of Conductive<br />

Fillers<br />

There are several ways to <strong>de</strong>crease the percolation threshold of conductive filler concentration in<br />

polymeric matrices, which are mainly based on the use of additives, the polymer properties, the<br />

optimization of processing conditions, and the size, distribution and porosity of the<br />

filler(Smuckler & Finnerty, 1974; Verhelst, Wolthuis, Voet, Ehrburger, & Donnet, 1977).<br />

Therefore, varying these factors can cause strong <strong>de</strong>viations from the percolation theory. Several<br />

important factors influencing the percolation threshold in conductive polymer composites are as<br />

follows:<br />

• Type and Shape of Conductive fillers<br />

The shape of the particle plays a critical role in where (at what filler volume) percolation occurs.<br />

The more structured or elaborately shaped the particle, the more likely it is to contact a nearest<br />

neighbor and form a continuous network. Perfectly spherical fillers, which arguably have the<br />

least elaborate and least structured shape, can require as much as 40% loading in or<strong>de</strong>r to reach<br />

49

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