Abstract
This study seeks to unravel the effect of carbon nanotube’s physical and chemical features on the final electrical and rheological properties of polymer nanocomposites thereof. Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized over two different types of catalysts, i.e., Fe and Ni, employing chemical vapor deposition. Utilizing this technique, we were able to synthesize N-CNTs with significantly different structures. As a result, remarkable differences in the network structure of the nanotubes were observed upon mixing the N-CNTs in a polyvinylidene fluoride (PVDF) matrix, which, in turn, led to drastically different electrical and rheological properties. For instance, no enhancement in the electrical conductivity of poorly-dispersed (N-CNT)Ni/PVDF samples was observed even at high nanotube concentrations, whereas (N-CNT)Fe/PVDF nanocomposites exhibited an insulative behavior at 1.0 wt%, a semi-conductive behavior at 2.0 wt%, and a conductive behavior at 2.7 wt%. In terms of rheology, the most substantial differences in the viscoelastic behavior of the systems were distinguishable in the medium amplitude oscillatory shear (MAOS) region. The stress decomposition method combined with the evaluation of the elastic and viscous third-order Chebyshev coefficients revealed a strong intra-cycle elastic nonlinearity in the MAOS region for the poorly-dispersed systems in small frequencies; however, the well-dispersed systems showed no intra-cycle nonlinearity in the MAOS region. It was shown that the MAOS elastic nonlinearity of poorly-dispersed systems stems from the confinement of N-CNT domains between the rheometer’s plates for small gap sizes comparable with the size of the agglomerates. Moreover, the intra-cycle elastic nonlinearity of poorly-dispersed systems is frequency-dependent and vanished at higher frequencies. The correlation between the microstructure and viscoelastic properties under large shear deformations provides further guidance for the fabrication of high-performance 3D-printed electrically conductive nanocomposites with precisely controllable final properties for engineering applications.
Highlights
Carbon nanotube (CNT) has emerged as one of the most popular nanofillers in the polymer composites industry since it can produce a dramatic improvement in final properties at low contents
It has been widely shown that a critical factor in controlling the electrical [1,2], mechanical [3,4,5], electromagnetic interference (EMI) shielding effectiveness [6], and rheological [7,8,9,10,11,12] properties of CNT/polymer nanocomposites (CPN) is the network structure of the nanotubes; monitoring the network structure formation is of high significance
The detailed characterization of Nitrogen-doped carbon nanotubes (N-CNTs) has been provided in Supporting Information, and here we summarized the results
Summary
Carbon nanotube (CNT) has emerged as one of the most popular nanofillers in the polymer composites industry since it can produce a dramatic improvement in final properties at low contents. To unravel the underpinnings of the nonlinear responses of melted CNT-based polymeric nanocomposites under MAOS and LAOS, N-CNTs with various physical structures were synthesized This systematic methodology provides us with a unique opportunity to investigate the effect of physical properties and dispersion characteristics of nanotubes on inter/intra-cycle nonlinear rheology of polymer nanocomposite, playing a crucial role in 3D-printing. It can be asserted that this study proposes a bilateral achievement: (i) employing MAOS and LAOS techniques to obtain a better understanding of the Nanomaterials 2020, 10, 1257 effect of the morphology of N-CNTs on network formation within a polymer matrix and (ii) enhanced exploration of intra-cycle viscoelastic parameters in MAOS and LAOS regions using well-defined synthesized N-CNTs and nanocomposites thereof
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