Abstract
Conductive particle-filled polymer composites are promising materials for applications where both the merits of polymer and conductivity are required. The electrical properties of such composites are controlled by the particle percolation network present in the polymeric matrix. In this study, the electrical properties of crosslinked carbon black–epoxy–amine (CB-EA) composites with various CB concentrations are studied at room temperature as a function of the AC frequency f. A transition at critical frequency fc from the DC plateau σDC to a frequency-dependent part was observed. Conductivity mechanisms for f > fc and f < fc were investigated. By considering the fractal nature, conduction for f > fc was verified to be intra-cluster charge diffusion. For f < fc, with the assistance of conductive atomic force microscopy (C-AFM), the conduction behavior of individual clusters can be observed, revealing both linear and nonlinear I–V characteristics. By combining microtoming and C-AFM measurements, 3D reconstructed images offer direct evidence that the percolating network of these materials consists of both a low-conductivity part, in which the charge transports through tunneling, and a high-conductivity part, which shows ohmic electrical properties. Nevertheless, for these CB-EA composites, the presence of these non-ohmic contacts still leads to Arrhenius-type behavior for the macroscopic conductivity.
Highlights
Epoxy–amine resins are widely applied in various fields where easy processing, low water uptake, excellent adhesion and good corrosion protection are needed [1,2,3,4]
The conductivities as a function of frequency f for carbon black–epoxy–amine (CB-EA) composites with different carbon blacks (CB) concentrations are plotted in Fig. 1a, in which an increase in intercept values as well as an extension of the plateau for each sample can be observed with increasing CB content
The AC conductivity of carbon black–epoxy–amine (CB-EA) composites has been characterized by a crossover at frequency fc from a frequencyindependent rDC to the frequency-dependent part, on samples with CB concentration higher than 0.5 vol%
Summary
Epoxy–amine resins are widely applied in various fields where easy processing, low water uptake, excellent adhesion and good corrosion protection are needed [1,2,3,4] Such polymer systems are generally electrically insulating, having a volume resistivity from 1012 to 1015 X cm [5]. Electrons are transported via conductive pathways in these networks To deal with such disordered systems in which long-range connectivity suddenly appears, percolation theory has been extensively applied [14, 15]. A master batch with 2 vol% of CB was prepared by dispersing these particles in a bisphenol A-based epoxy resin (Epikote 828, Resolution Nederland BV) for 8 h at 6000–15000 rpm by using a disk agitator (Dispermat CA40-C1, VMA) until a homogeneous dispersion was obtained During this process, the temperature remained below 80 °C. This array of scans has been aligned in one 3D image by using a simple procedure for which a more detailed description can be found in [18]
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