Novel nanosized crystals of aquocyanophthalocyaninatocobalt (III) (Phthalcon 11) were used as a conductive filler in crosslinked epoxy materials. The crosslinked composite materials had a very low percolation threshold (u c % 0.9 vol %). The relationship between the volume conductivity and the filler fraction follows the scaling law of the percolation theory and suggests that the conducting particle networks were formed by random percolation of primary aggregates. The occurrence of the low u c can be explained by the presence of a fractal Phthalcon 11 particle network formed from fractal aggregates during crosslinking. The position of the percolation threshold and the volume conductivity of these crosslinked materials were found to depend heavily on the processing conditions applied. These dependencies are explained in terms of specific particle-matrix interactions and the particle-particle interactions and by taking into account different mechanisms of particle network formation. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] 2006
Phthalcon-11 (aquocyanophthalocyaninatocobalt (III)) forms semiconducting nanocrystals that can be dispersed in epoxy coatings to obtain a semiconducting material with a low percolation threshold. We investigated the structure-conductivity relation in this composite and the deviation from its optimal realization by combining two techniques. The real parts of the electrical conductivity of a Phthalcon-11/epoxy coating and of Phthalcon-11 powder were measured by dielectric spectroscopy as a function of frequency and temperature. Conducting atomic force microscopy (C-AFM) was applied to quantify the conductivity through the coating locally along the surface. This combination gives an excellent tool to visualize the particle network. We found that a large fraction of the crystals is organized in conducting channels of fractal building blocks. In this picture, a low percolation threshold automatically leads to a conductivity that is much lower than that of the filler. Since the structure-conductivity relation for the found network is almost optimal, a drastic increase in the conductivity of the coating cannot be achieved by changing the particle network, but only by using a filler with a higher conductivity level.
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