The dispersion state of multilayer graphene sheets in polymers has a strong impact on the properties of the nanocomposite, and is driven by the processing parameters of the dispersion method. Herein, multilayer graphene sheet/vinyl ester nanocomposites were manufactured using a three‐roll mill. The roller gaps and number of processing cycles were varied to study their effect on the dispersion state and their relationship with the effective electromechanical properties of the nanocomposites. It was found that reducing the roller gaps and increasing the number of processing cycles yields smaller (up to 7.4 μm in diameter) and more densely packed (up to ~1500 agglomerates/mm2) agglomerates. Nanocomposites manufactured with the three‐roll mill contain agglomerates up to 75% smaller and more densely packed than those manufactured with an ultrasonic tip. Electrical conductivity was higher for moderately‐sized, homogeneously distributed agglomerates (23 μm in diameter) with a high areal density (~920 agglomerates/mm2), while smaller agglomerates reduced electrical conductivity. Smaller agglomerates increased the mechanical properties but decreased the piezoresistive sensitivity. The agglomerate density proved to be a key factor governing the piezoresistive sensitivity, with a lower number of agglomerates per unit area promoting higher gauge factors.
The construction, characterization and control of an electric oven dedicated to the study of thermoresistive polymer nanocomposites is presented. The oven is designed with a heating plate capable of reaching 300 • C with a resolution of 0.3 • C and an area of uniform temperature of 3.8 cm × 2.5 cm. The temperature is regulated by means of a discrete proportional-integral-derivative controller. A heat transfer model comprising three coupled non-linear differential equations is proposed to predict the thermal profiles of the oven during heating and cooling, which are experimentally verified. The oven is used for thermoresistive characterization of polymer nanocomposites manufactured from a polysulfone polymer and multiwall carbon nanotubes.
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