Cross-linked epoxy composites filled with intrinsically conductive phthalocyanine nanocrystals. Influence of filler amount, layer thickness, and cross-linkers used on the percolation threshold and conductivity level of the composites

Novel aquocyanophthalocyaninatocobalt(III) (Phthalcon 11) nanocrystals were used as intrinsically conducting fillers in cross-linked epoxy composites. The prepared conductive composites had a percolation threshold phi(c) between 0.9 and 9 vol%. The phi(c) appeared to be strongly dependent on layer thickness. Modeling showed that when the layer thickness was sufficiently large the phi(c) could be as low as 0.55 vol %. The occurrence of such a low and variable phi(c) was explained by the presence of a percolating Phthalcon 11 fractal particle network. Quantitative fractal analysis of these networks indicates that these networks were formed by diffusion-limited cluster-cluster aggregation of the small primary Phthalcon 11 fractal aggregates, which were already present in the Phthalcon 11 powder itself. Moreover, it was found that phi(c) and sigma(v) also strongly depended on the choice of the cross- linker used and on the chosen processing conditions for making the epoxy molecular network, such as cross-linking temperature and gel time. Rheological experiments were done, and models were proposed to explain these unexpected phenomena. The results presented here suggest that also in other thermoset matrices containing other (non) conductive nanoparticles the above-mentioned factors may have a major impact on the final particle distribution in the matrix and therefore on the final material properties of these composites.