Dielectrorheology of Aspect-Ratio-Tailored Carbon Nanotube/Polyethylene Composites under Large Deformations: Implications for High-Temperature Dielectrics

In this work, advanced custom-synthesized carbon nanotube (CNT)-based polymer nanocomposites were designed and prepared for electrical applications, with an innovative strategy in terms of catalyst preparation. The physical structures of the CNTs were fine-tuned by varying synthesis time to investigate the effect of aspect ratio on the electrical and rheological properties of the nanocomposites with state-of-the-art dielectro-nonlinear-rheological spectroscopy. The network structures of the nanotubes within the polymer matrix were studied utilizing a wide range of characterization techniques (e.g., linear rheology, electrical conductivity, dielectric properties, and electromagnetic interference shielding effectiveness). The results showed distinct differences in the microstructural features of the samples upon changing the aspect ratio of the CNTs. Then, for the first time, a correlation was developed between rheological and electrical properties with respect to deformation, under small, medium, and large amplitude oscillatory shear (SAOS, MAOS, and LAOS, respectively) flows. Dielectrorheological results depicted that the electrical properties of the nanocomposites containing longer CNTs are strain invariant while their rheological behaviors are highly sensitive to deformation. However, nanocomposites with shorter CNTs followed an opposite trend, which means there is a high dependency of electrical properties and a low sensitivity of rheological behavior to deformation. The output stress waveforms and Lissajous–Bowditch plots confirmed the aforementioned results. Our results disclose the importance of the physical properties of the nanomaterials on the performance of the high-temperature dielectrics and reveal that nanocomposites containing higher aspect ratio nanomaterials provide a more stable dielectric response when subjected to large deformations.