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The optimal structure-conductivity relation in epoxy-phthalocyanine nanocomposites

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Author: Huijbregts, L.J. · Brom, H.B. · Brokken-Zijp, J.C.M. · Kemerink, M. · Chen, Z. · Goeje, M.P. de · Yuan, M. · Michels, M.A.J.
Type:article
Date:2006
Publisher: American Chemical Society ACS
Institution: TNO Industrie en Techniek
Source:Journal of Physical Chemistry B, 46, 110, 23115-23122
Identifier: 239610
Keywords: Atomic force microscopy · Coating techniques · Dielectric devices · Electric conductivity · Optimization · Percolation (solid state) · Epoxy coatings · Epoxy phthalocyanine nanocomposites · Percolation threshold · Semiconducting nanocrystals · Nanostructured materials

Abstract

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.