Carbon Nanotubes In Polymer Matrices Research Articles

Fracture toughness enhancement of fuzzy CNT-glass fiber reinforced composites with a combined reinforcing strategy

Low interlaminar mechanical properties is the foremost drawback of glass fiber reinforced composites (GFRPs). Hierarchical nanoparticles on fibers (e.g. carbon nanotubes (CNTs)) can improve interlaminar properties of composites with negligible weight increase because of excellent mechanical properties, and low density. Interlaminar properties of composites can be enhanced with the well-dispersed CNTs in polymer matrices as it facilitates load transfer from matrix to fibers. This paper investigates the mechanical properties of CNT-reinforced GFRPs. Two reinforcing strategies were studied as dispersion of CNTs in epoxy matrix and direct growth of CNTs onto glass fibers (GFs), simultaneously. The former is referred to as nanotube-reinforced composites (NRCs) while the latter is known as fuzzy architectures. Furthermore, the combination of NRCs and fuzzy glass fibers (F-GFs), also known as fuzzy nano-reinforced composites (F-NRCs), is used to fabricate composites and identify the reinforcing capabilities through both methods. Mechanical properties are investigated by Mode-I fracture toughness and unidirectional (UD) composite tensile tests. Even though NRCs and F-NRCs yield similar enhancements in the propagation fracture toughness as 113% and 119%, respectively, the tensile strength of F-NRCs is decreased by 24% due to heat treatment during the CNT synthesis.

Uniaxial Stretching-Induced Alignment of Carbon Nanotubes in Cross-Linked Elastomer Enabled by Dynamic Cross-Link Reshuffling.

The fascinating properties of carbon nanotubes (CNTs) make them highly promising in fabricating polymer composites. Yet, the property enhancements of polymer/CNTs composites remain far behind the theoretical predictions. A critical issue to resolve this dilemma is to align CNTs in polymer matrices. Thus far, the state of art approaches to create CNT alignment either require complicated preparation processes and specific apparatuses, or is limited to thermoplastic polymers. Here, inspired by the network rearrangement ability of vitrimer in the solid state, we bring forth a facile methodology to align CNT in covalently cross-linked polymers by uniaxially stretching dynamic. Specifically, dynamic boronic ester bond-cross-linked epoxidized natural rubber/CNTs vitrimer composites with randomly dispersed CNTs are prepared, which are able to rearrange the network topologies and release stress at elevated temperatures through boronic ester transesterifications. The alignment of CNTs is performed by the uniaxial stretching of the composites and subsequent cross-link reshuffling at elevated temperatures, which results in anisotropic composites with remarkably enhanced mechanical properties and reduced electrical conductivity along the stretching direction. Furthermore, the mechanical properties of the composites can be readily adjusted by changing the applied strain, relaxation time and temperature due to the modulated CNT alignment degree. With this example, we envisage that this work offers a conceptual and facile approach to align anisotropic fillers in covalently cross-linked polymers.

Stress transfer in nanocomposites enabled by poly(methyl methacrylate) wrapping of carbon nanotubes

Good dispersion and interfacial interaction of carbon nanotubes in polymer matrices are important to effectively achieve mechanical reinforcement in nanocomposites. Previously, it was shown that poly(methyl methacrylate) (PMMA) helically wraps around single wall carbon nanotubes (SWNTs), and thus prevents SWNT bundling. In this work, influence of PMMA-wrapped SWNTs on tensile properties of PMMA/SWNT composites and stress transfer from the matrix to the nanotubes were studied. The tensile modulus and tensile strength of the PMMA-wrapped SWNT nanocomposite buckypapers made by vacuum filtration are 5.9 and 3.7 times that of the SWNT buckypaper without PMMA wrapping, respectively. Stress transfer in SWNTs was determined by monitoring G′ Raman band shift during nanocomposite film tensile deformation. Results showed that during tensile deformation, PMMA-wrapped SWNTs in the nanocomposite buckypapers experienced up to 1 GPa stress, while negligible stress was observed in the SWNT buckypaper without PMMA wrapping. Solvent-cast nanocomposite films under tensile deformation, and with SWNT loading between 0.1 and 10 wt%, PMMA-wrapped SWNTs experience stress as high as 3.1 GPa, while nanocomposites made without PMMA wrapping experience only about half of this stress value. The improved tensile properties are a result of improved CNT dispersion and enhanced interfacial stress transfer achieved via PMMA wrapping of SWNTs. A new Raman band peak was observed at 2276 cm−1 in PMMA-wrapped nanocomposites. Dynamic mechanical properties of various nanocomposites were also studied and reported.

Joint effect of the tube sizes and Fe-filling process on microwave dielectric properties of carbon nanotubes

To explore the effect of tube sizes and filling process on dielectric properties of carbon nanotubes (CNTs), CNTs with various diameters and lengths were applied to synthesize Fe-filled CNTs through wet-chemical method. The permittivities of the composites of CNTs and paraffin rely on the dispersion state (agglomeration) of CNTs in polymer matrices. During the filling process, CNTs with diverse tube parameters and dispersibility experienced different structural transformations, and different iron oxides (either Fe3O4 or Fe2O3) particles (depending on the dispersibility of CNTs) were observed adhering to walls of CNTs after filling. The discrepancies along with the dispersibility of CNTs per se alter the order of the permittivity (from high to low) within samples. The smallest agglomerates and the largest permittivity were obtained for CNTs with diameters of 10–20 nm and lengths of 10–30 μm, both before and after the filling of CNTs. The role that the shape parameters played in the dielectric properties during the whole filling process was analyzed. The frequency-dependent permittivity spectrum was also examined and it obeyed Jonscher’s universal dielectric relaxation law.

Characterization of Doubled Walled Carbon Nanotubes using Finite Element Method

composites will be developed using carbon nanotubes (CNTs). When compared with the conventional carbon fibers, CNTs in polymer matrices enhance the stiffness and strength of composites. The work is focused on the Double walled carbon nanotubes (DWCNTs) to investigate the mechanical properties. Modulus of elasticity is considered to analyze the behavior of CNTs by adopting the Finite element model (FEM). The experiments conducted on both armchair and zig- zag Nanotubes. By considering the length and radius of the inner and outer tubes of CNTs, the developed stress with the applied load, strain and young's modulus and its response to the load applied is estimated using FEM. The influence of external vibrations on the CNTs considerably minimized with significant stiffness constant (K) of the CNTs. The results obtained are supportive to analyze the behavior of CNTs. KeywordsDWCNTs, FEM, Stress, strain, young's modulus.

A 2D percolation-based model for characterizing the piezoresistivity of carbon nanotube-based films

Carbon nanotubes (CNTs) have attracted considerable attention due to their unique electrical, mechanical, and electromechanical properties. In particular, thin films formed by embedding CNTs in polymer matrices have been shown to exhibit strain-sensitive electromechanical properties, which can serve as an alternative to traditional strain sensors. Although numerous experimental studies have characterized their electrical properties and piezoresistivity, it remains unclear as to what nano-scale mechanisms dominate to govern nanocomposite electromechanical properties. Therefore, the objective of this study is to create a two-dimensional (2D) percolation-based numerical model to understand the electrical and coupled electromechanical behavior of CNT-based thin films. First, a percolation-based model with randomly dispersed straight nanotubes was generated. Second, the percolation and unstrained electrical properties of the model were evaluated as a function of CNT density and length. Next, uniaxial tensile–compressive strains were applied to the model for characterizing their electromechanical response and piezoresistivity. In addition, the effects of different intrinsic strain sensitivities of individual nanotubes were also considered. The results showed that bulk film strain sensitivity was strongly related to CNT density, length, and its intrinsic strain sensitivity. In particular, it was found that strain sensitivity decreased with increasing CNT density. While these strain sensitivity trends were consistent for different intrinsic CNT gage factors, the results were more complicated near the percolation threshold. These results were also compared to other experimental research so as to understand how different nano-scale parameters propagate and affect bulk film response.

Agglomerated carbon nanotube-induced growth of piezoelectric 3D nanoarchitectures assembled from hollow 1D nanowires of poly (vinylidene fluoride) at high pressure

Abstract Carbon nanotubes (CNTs) intrinsically tend to bundle and/or aggregate, and various techniques were explored to improve the dispersibility of CNTs in polymer matrices during the preparation of a variety of CNT/polymer based composites. However, herein we report the entangling nature of CNTs can be utilized for the rapid formation of unique piezoelectric three dimensional (3D) nanoarchitectures of poly (vinylidene fluoride) (PVDF). The controllable growth of the 3D nanostructures, assembled from hollow one dimensional (1D) PVDF nanowires, was achieved by the high-pressure crystallization of a binary CNT/PVDF based composite, in which CNT agglomerations were not destroyed during the fabrication process. This was attributed to the cooperation effect of the agglomerated CNTs served as hard-template and the physical interactions of macromolecular chains at high pressure as self-assembly driving forces. The present study provides a facile and effective approach to construct functional 3D nanostructures in situ, and the hybrid structures, consisting of CNTs and piezoelectric PVDF nanowires, may permit niche applications in a self-powering nanosystem that harvests its operating energy from the environment.

A new approach to determine rheological percolation of carbon nanotubes in microstructured polymer matrices

We demonstrate the rheological percolation of carbon nanotubes (CNTs) in microstructured polymer matrices. Polymer/CNT composites are fabricated from polycarbonates with different molecular weights to diversify the microstructures, which vary with the polymer radius of gyration and entanglements. We propose a model for the dispersion of CNTs in polymer matrices, which explains the electrical and rheological properties. The percolation theory represented by a power–law relation cannot account for the rheological percolation of CNTs in this work. Therefore, we investigate the crossover points to provide a quantitative indication of the rheological percolation threshold of nanofillers in polymer matrices. For the first time, the rheological percolation threshold is determined experimentally with this definition. The effects of molecular weight and shear viscosity of the medium on the percolation of CNTs are demonstrated separately.

Graphene‐Functionalized Carbon Nanotubes for Conducting Polymer Nanocomposites and Their Improved Strain Sensing Properties

Functionalization of carbon nanotubes (CNTs) is essential for the dispersion of CNTs in polymer matrices due to their inherence. However, conventional functional groups are insulating in nature, thereby destroying the basic structure of the CNTs and their electrical conductivity due to the harsh and long‐period acid treatments. Hence, a new method of functionalization is essential. In this article, a poly(vinyliedene fluoride) (PVDF) composite comprising graphene wrapped CNTs as a conducting filler is described. A strain‐gauge factor of ≈20 at low strain levels (0.1%) is with a 3 wt% graphene wrapped CNT hybrid in PVDF, which overwhelms conventional metal foil strain gauges as well as functionalized CNT or functionalized graphene based polymer composites for strain sensing. image

Characterization of dispersion of carbon nanotubes in polymer matrices

ABSTRACTDispersions of carbon nanotube polymer composites were characterized by Raman mapping.Single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), multi-walled nanotubes (MWNTs), and XD-grade carbon nanotubes (XD-CNTs) were dispersed in a vinyl ester (VE) resin using an ultrasonic probe at a fixed frequency. SWNTs were functionalized with succinic acid peroxide (SAP) to enhance dispersion. Increasing ultrasonication energy was found to improve the distribution of carbon nanotubes (CNTs) and decrease the size of ropes, whereas excessive amounts of energy were found to result in damage. The quality of dispersion was verified through optical microscopy and scanning electron microscopy (SEM).

Polymer/Carbon Nanotube Composites

The unique geometry and extraordinary mechanical, electrical, and thermal conductivity properties of carbon nanotubes (CNTs) make them ideal candidates as functional fillers for polymeric materials. In this paper we review the advances in both thermoset and thermoplastic CNT composites. The various processing methods used in polymer/CNT composite preparation; solution mixing, in-situ polymerization, electrospinning, and melt blending, are discussed. The role of surface functionalization, including ‘grafting to’ and ‘grafting from’ using atom transfer radical polymerization (ATRP), radical addition–fragmentation chain transfer polymerization (RAFT), and ring-opening metathesis polymerization (ROMP) in aiding dispersion of CNTs in polymers and interfacial stress transfer is highlighted. In addition the effect of CNT type, loading, functionality and alignment on electrical and rheological percolation is summarized. We also demonstrate the effectiveness of both Raman spectroscopy and oscillatory plate rheology as tools to characterize the extent of dispersion of CNTs in polymer matrices. We conclude by briefly discussing the potential applications of polymer/CNT composites and highlight the challenges that remain so that the unique properties of CNTs can be optimally translated to polymer matrices.

Preparation and characterization of multi‐walled carbon nanotubes/polymer gradient composite films

AbstractBACKGROUND: Recently, much work has focused on the efficient dispersion of carbon nanotubes (CNTs) throughout a polymer matrix for mechanical and/or electrical enhancement. However, there are still only few reports about gradient distribution of CNTs in polymer matrices. In the work reported here, CNTs embedded in a polymer film with a gradient distribution were successfully obtained and studied.RESULTS: For composite films with gradient distributions of CNTs, the upper surface behaves as an intrinsic insulator, while the lower one behaves as a semiconductor, or even as a conductor. It is also found that with an increase of 1 wt% CNTs, the resistance of the bottom surface decreases by 2–3 orders of magnitude, as compared with pure polyarylene ether nitrile; furthermore, when the proportion of CNTs increases up to 5 wt%, the resistance of the bottom surface shows only very little change. As a result, sufficient matrix conductivity of the bottom surface could be achieved at a lower filler concentration with CNTs in a gradient distribution. Meanwhile, the thermal stability, glass transition temperature and tensile properties of the matrix are maintained.CONCLUSION: There is considerable interest in such gradient composite films, which could be applied in the electrical engineering, electronics and aerospace fields, for their excellent mechanical properties, thermal stability and novel electrical properties. Copyright © 2008 Society of Chemical Industry

Preparation and Characterization of Carbon Nanotube/Polyacrylonitrile Composites

The incorporation of carbon nanotubes in polymer matrices should lead to composites with unique properties. It is thus tempting to use NT for mechanical reinforcement and to obtain new materials with unusual mechanical properties. However, the ultimate performance of such materials is expected to depend strongly on their ability to transfer load from the host matrix to the nanotubes. The authors here report a method to prepare polyacrylonitrile-based composites with well-dispersed multiwalled carbon nanotubes (MWNT). It turns out that carbon nanotube/polyacrylonitrile composite films can be obtained with a good dispersion of the MWNTs in the polymeric matrix and without alteration of their respective structure.