The present work reveals results on the network formation of graphene nanoribbon (GNR) synthesized using a nonoxidative technique from multiwalled carbon nanotube (MWCNT). MWCNT and GNR presented comparable powder conductivity and dispersion state in a poly­(vinylidene fluoride) (PVDF) matrix. This enabled us to purely discern the effect of geometrical features of the nanofillers on network formation by comparing the rheological and electrical percolation in the PVDF matrix. Unique features of the rheological response of PVDF/GNR nanocomposites, such as abrupt transition to a solid state, were interpreted according to a network structure activated by the formation of primary and secondary entanglements between adsorbed and bulk polymer chains. However, MWCNT nanocomposites presented a rheological behavior consistent with a strongly flocculated network structure formed through the direct tube–tube contacts and mechanical entanglements. Poor broadband electrical conductivity of the GNR nanocomposites compared to their MWCNT counterparts confirmed our conclusion from the rheological results.

Results of the present study demonstrate the potential of graphene nanoribbon to induce giant synergistic effects in the broadband dielectric properties of multiwalled carbon nanotube/​graphene nanoribbon/​polyvinylidene fluoride (MWCNT/​GNR/​PVDF) nanocomposites. The nanocomposites were prepared using a melt-mixing technique at various nanofiller total contents and MWCNT/​GNR weight ratios. Rheology coupled with AC conductivity measurements of the nanocomposites unearthed highly superior capability of MWCNT to neighbor or interlace compared to GNR; i.e., the MWCNT has higher ability to participate in a percolative network. Broadband dielectric spectroscopy demonstrated superior dielectric properties for MWCNT/​GNR/​PVDF ternary (hybrid) nanocomposites compared to the MWCNT or GNR binary nanocomposites. For instance, at 1.5 wt % and 1000 Hz, the ternary nanocomposite with an MWCNT/​GNR ratio of 3:1 presented a real permittivity and dissipation factor of 41.4 and 0.91, surpassing the binary MWCNT nanocomposite with a real permittivity and dissipation factor of 39.3 and 86.7, respectively. We attribute this synergistic effect to the poor interlacing ability of GNRs, as secondary conductive nanofillers, acting as extra nanoelectrodes. In fact, the role of GNRs as extra nanoelectrodes in conjunction with their poor propensity to bridge MWCNTs led to effective nanocapacitor structures with low energy loss.

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Poly(vinylidene fluoride) (PVDF) was melt-mixed with custom-synthesized multiwalled carbon nanotubes (CNTs) at various loadings to create polymer nanocomposites for electrical applications. The custom-made CNTs were finetuned using chemical vapor deposition technique over a broad range of temperatures, i.e., from 550 to 950°C at 100°C intervals. Characterization revealed that synthesis temperature had a huge impact on the structural features of CNTs and, consequently, on CNT network formation within the polymeric matrix. Oscillatory amplitude sweep test indicated that nanocomposites with poor conductive network showed a multistep yielding in the nonlinear regime; i.e., the storage modulus dropped to an intermediate plateau and then decreased significantly. Conversely, the PVDF/CNT 650 (CNT synthesized at 650°C) nanocomposite with the highest conductivity demonstrated a gradual single-step yielding process. Physical interpretations and structure−property relationships were expounded based on intra-and intercycle quantitative nonlinear viscoelastic parameters, which showed strongly dissipative nonlinearity at intermediate deformations for poorly conductive nanocomposites (PVDF/ CNT 850 and PVDF/CNT 950 ). Multiple gap-size rheometry of the nanocomposites confirmed that the dissipative feature of poorly dispersed polymer nanocomposites originates from disruption of the bridges of nanofillers spanning the rheometer gap, i.e., aggregated structures experiencing the rheometer plates confinement effect. Moreover, for the first time, we showcased the effect of confinement of nanofiller aggregates on intracycle viscoelastic response of polymer nanocomposites in both mediumand large-amplitude oscillatory shear regions.

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