physica s s p status solidi b 1956 V. Levin et al.: The cluster architecture of carbon in polymer nanocomposites ß

A set of epoxy resin-based composites filled with 0.25 – 2.0 wt.% of commercially available exfoliated graphite (EG) and thick graphene (TG), prepared by suspending EG particles in cyclohexane, and submitting the suspension to a series of grinding and ultrasonic dispersion steps, was produced. The microstructure of such epoxy-graphite composites has been studied by the impulse acoustic microscopy technique. According to acoustic microscopy data, exfoliated graphite microparticles have been well dispersed in the epoxy matrix. TG nanoflakes demonstrated persistent tendency to clustering and formation of agglomerates. The addition of graphite particles in small amount (0.25 – 2.0 wt.%) did not influence the bulk elastic properties of epoxy-graphite composite materials. Being extremely lightweight, 0.003 g cm−3, EG had a lower percolation threshold than TG, at the level of 1-1.5 wt.% against 2.1-3.2 wt.%, respectively. As a result, epoxy composites filled with 1.0-2.0 wt.% EG provided high electromagnetic (EM) interference shielding both at microwave and THz frequencies. In contrast, no significant influence of TG loading was observed at low weight fraction (up to 2 wt.%) on the EM performance of epoxy composites.

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The impulse acoustic microscopy method was applied to observe the bulk microstructure and to measure sonic velocities and elastic moduli in the carbon nanocomposite specimens prepared by a traditional method and with the use of a vacuum mixer. It is shown that carbon nanoparticles tend to cluster and form micron‐sized aggregates. The impulse acoustic microscopy technique makes it possible to visualize a non‐uniform distribution of carbon nanofillers over the specimen bulk. Both nanotube and nanoplatelets conglomerates are visible most likely due to the air containing. Results of the elastic measurements demonstrate homogeneity of elastic properties over the material bulk and a weak dependence of sonic velocities and elastic moduli on the filler content. Reduction of the air content and enhancement of elastic properties are observed when increasing the nanofiller content and employing the vacuum mixing technology in nanocomposite fabrication. POLYM. ENG. SCI., 57:697–702, 2017. © 2017 Society of Plastics Engineers