Micromechanical scribing and indentation behavior of injection-molded polymeric carbon nanotube (CNT) nanocomposites

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Polymeric carbon nanotube (CNT) nanocomposites have unique mechanical, electrical, and thermal properties. Anisotropy can be induced depending on the alignment of the CNT fillers within polymeric composites, which is known to affect material properties. In order to investigate the effects of CNT alignments in micromechanical scribing using a single crystal diamond tool, a microindenter–scriber system was developed. Multiwalled carbon nanotube–polystyrene (MWCNT–PS) samples with varying CNT concentrations were prepared through a microinjection molding process, where the injection enables the partial alignment of CNTs in the flow direction through high shear stress. A mechanistic scribing force model was proposed based on the material properties that could be obtained using the microindentation techniques. Scribing experiments were performed in the parallel and perpendicular directions to the CNT alignment. Forces in three axes were measured and analyzed to identify three unknown parameters—the shearing, plowing, and adhesion friction coefficients. The resulting coefficients for scribing perpendicular to the CNT alignment showed distinguishable trends from scribing parallel to the CNT alignment as the CNT loadings increased. Their linear trends in relation to the material properties identified from indentation techniques can be used to predict microscribing parameters and resulting cutting forces, in combination with the proposed mechanistic model.