Percolation threshold, conductive hybrids

Figure 5.3 also shows that there is no linear relationship between the quantity of filler content and conductivity. At a low filler content, the conductivity of the matrix polymer is dominant. With increasing fibre content, the contacts between the fibres increase and the specific conductivity escalates in a small window. The critical concentrations of volume required for this escalation - called the percolation threshold - range between 20-25 vol% for both the metal/thermoplastic hybrid material, and the polymer exclusively filled with copper. Above this concentration, the metal network becomes more dense to an extent where conductivity can be increased only marginally [3,16-18]. 

Let us briefly consider the conducting properties of hybrid nanocomposites. Conducting properties are manifested only with particular inorganic component to polymer ratios in which cmrent-conducting channels of fractal metal-containing clusters are formed in a polymeric matrix for one reason or other. The highest conductivity is achieved when the composite is converted into a network of interrelated current-conducting chains. This is where a percolation structure is achieved. To put it differently, critical concentrations of the filler (p (the percolation threshold) exist above which (9 > 9 ) the conductivity sharply increases. 

The introduction of AuNPs into PS/SWCNT composites has not shown to significantly alter the ultimate conductivity of these composites. In the case of only one studied hybrid system made from PSS-stabilized SWCNTs decorated with AuNPs, the addition of the gold particles to the PS/SWCNT composite seems to slightly reduce the percolation threshold. But in all other systems, no effect of the addition of AuNPs... 

A theoretical smdy showed that it is not necessary to build a conductive network with a high-aspect-ratio filler alone [109] and that the percolation threshold of CPCs is sensitive to the part of high-aspect-ratio filler in a system that contains hybrid fillers with different dimensions [111]. A number of studies on CPCs with two mixed carbon-filler-filled have been reported. The percolation thresholds of these systems are often close or below the average value of the systems that are filled with... 

This concept is illustrated in Fig. 13.17. The measurements were taken from epoxy primers containing either non-conductive as-received aluminium flake or a conductive PPy/Al flake hybrid pigment from reaction 1. Before EIS measurements were taken, the samples were immersed in dilute Harrison s solution for 3 h. Notice that for the conductive PPy/Al flake primer, there is a large drop in impedance between a PVC of 30% and 35% while this same drop is not observed for the as-received flake until a PVC of 45%. The drop observed at the lower PVC for the conductive pigment would be indicative of the percolation threshold while the impedance drop observed at the higher PVC for the non-conductive pigment would be more closely associated with the CPVC. Also it is important to note that at a PVC of 35%, the impedance of the PPY/Al flake hybrid primer drops below the impedance observed for bare aluminium 2024. This is indicative of some interaction between the aluminium and PPy at the interface between the aluminium substrate and the coating. 

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