Arrangement Of Carbon Nanotubes Research Articles

Catalyzing oxygen reduction by morphologically engineered ZIF-derived carbon composite catalysts in dual-chamber microbial fuel cells

From the past decades, microbial fuel cells (MFCs) have evolved as a green alternative to produce electrical energy from organic matter degradation. Cathode modification significantly enhances the overall MFC performance. In this work, we report on ZIF-8 and carbon nanotubes (CNTs) derived catalyst materials as cathode for MFC. The catalysts were prepared via high-temperature pyrolysis at 900 °C and were physically characterized by various analytical techniques. All the catalyst materials carry tubular arrangements of CNTs covering the ZIF-8 crystals and exhibit highly micro-mesoporous texture. The electrocatalytic activity for oxygen reduction reaction (ORR) was studied in 0.1 M phosphate buffer at a catalyst loading of 0.2 mg cm−2. The FeCo-N-C@900 catalyst showed the highest ORR activity with half-wave potential of 0.71 V vs RHE and limiting current density of −5.62 mA cm−2 at 1900 rpm. When tested in MFC, FeCo-N-C@900 coated cathode delivered the maximum power density of 1557 mW m−2 (comparable to Pt/C catalyst reaching Pmax of 1681 mW m−2) with chemical oxygen demand (COD) removal efficiency of 87.3%. The Next generation DNA sequencing analysis revealed the accumulation of various exoelectrogenic bacterial strains i.e., Bacillus, Desulfovibrio, Comamonadaceae sp. etc. commonly found in anaerobic biomass and showing the successful enrichment of the biofilm responsible for oxidizing organic matter at the anode. The present study illustrates the potential of transitional metal-doped ZIF-8 and CNTs composite electrocatalysts for enhancing the power output of MFC with generating promising power and current densities.

Understanding the Mechanism of the Structure-Dependent Mechanical Performance of Carbon-Nanotube-Based Hierarchical Networks from a Deformation Mode Perspective.

Carbon nanotube (CNT)-based networks have wide applications, in which structural design and control are important to achieve the desired performance. This paper focuses on the mechanism behind the structure-dependent mechanical performance of a CNT-based hierarchical network, named a super carbon nanotube (SCNT), which can provide valuable guidance for the structural design of CNT-based networks. Through molecular dynamic (MD) simulations, the mechanical properties of the SCNTs were found to be affected by the arrangement, length and chirality of the CNTs. Different CNT arrangements cause variations of up to 15% in the ultimate tensile strains of the SCNTs. The CNT length determines the tangent elastic modulus of the SCNTs at the early stage. Changing the CNT chirality could transform the fracture modes of the SCNT from brittle to ductile. The underlying mechanisms were found to be associated with the deformation mode of the SCNTs. All the SCNTs undergo a top-down hierarchical deformation process from the network-level angle variations to the CNT-level elongations, but some vital details vary, such as the geometrical parameters. The CNT arrangement induces different deformation contributors of the SCNTs. The CNT length affects the beginning point of the CNT elongation deformation. The CNT chirality plays a crucial role in the stability of the junction's atomic topology, where the crack propagation commences.

Flexible Piezoresistive Polystyrene Composite Sensors Filled with Hollow 3D Graphitic Shells.

The objective of this research was to develop highly effective conductive polymer composite (CPC) materials for flexible piezoresistive sensors, utilizing hollow three-dimensional graphitic shells as a highly conductive particulate component. Polystyrene (PS), a cost-effective and robust polymer widely used in various applications such as household appliances, electronics, automotive parts, packaging, and thermal insulation materials, was chosen as the polymer matrix. The hollow spherical three-dimensional graphitic shells (GS) were synthesized through chemical vapor deposition (CVD) with magnesium oxide (MgO) nanoparticles serving as a support, which was removed post-synthesis and employed as the conductive filler. Commercial multi-walled carbon nanotubes (CNTs) were used as a reference one-dimensional graphene material. The main focus of this study was to investigate the impact of the GS on the piezoresistive response of carbon/polymer composite thin films. The distribution and arrangement of GS and CNTs in the polymer matrix were analyzed using techniques such as X-ray diffraction and scanning electron microscopy, while the electrical, thermal, and mechanical properties of the composites were also evaluated. The results revealed that the PS composite films filled with GS exhibited a more pronounced piezoresistive response as compared to the CNT-based composites, despite their lower mechanical and thermal performance.

Dewetting assisted self-assembly of carbon nanotube into circular nanorings

In this article, we demonstrate how the instability of a polymeric thin film, when cast either as a mobile underlying support-layer of a bilayer assembly, as a mixture, or as a template, affects the self-assembly and arrangement of carbon nanotube (CNT) nanoparticles dispersed over/with it. The interplay of the different forces, like centrifugal, dewetting, Marangoni, electrostatic, assist the mobile nanoparticles in arranging themselves into circular ring-like structures. The congruence of the length scales of the self-assembled circular ring and the dewetted length scales of the thin polystyrene film reveals that the influence of dewetting dynamics is majorly responsible for the incipience of ring formations. However, the absence of coarsening and complete stoppage of movement of the rings towards the particulate region, reveals the presence of electrostatic repulsion. The nanoparticles not involved in circular-ring-self-assembly formation are driven by Marangoni force and engender nano-scratches over the polymeric surface. CNTs of smaller lengths deposit in the particulate zone where also, beyond a particular aspect ratio, the nanotubes are found to bend into circular rings. The bending of the carbon nanotubes is an energetically favored self-organization process controlled by the shape formation energy. When the underlying dewetted polystyrene surface acts as a template, the assembled CNT forms a circular ring-like interconnected relief structure. The circular rings of CNTs formed throughout the PS surface, fabricated by the dewetting of the mixture method, can be used to identify trace amounts of oil from an oil–water mixture by selective adsorption. The different self-assembled ring structures of CNTs are realized only for a specific concentration range of CNTs. The nanotubes assemble into random bundles/blobs devoid of any definite structures above this concentration.

Progress on carbon nanotube filled polymer-based thermal conductive composites

<p indent="0mm">In the 5G era, the effective thermal management has become more demanding due to the ever-rising integration of electronic devices. High thermal conductivity materials play a crucial role in the field of thermal management, for example, thermal interface materials (TIMs) are used to fill the gap between the electronic chip and the heat sink to improve thermal transfer. In recent years, polymers have become a popular choice for thermal conductive materials because of their light, economical and excellent insulation and processability. To improve the thermal conductivity of materials, inorganic fillers with high thermal conductivity are generally composited with polymers. With the merits of high thermal conductivity, desirable chemical stability, carbon nanotubes (CNTs) are considered to have broad application potential in thermal conductive composites. Simple composition methods failed to increase thermal conductivity of composite materials to expected levels due to the large interfacial thermal resistance between CNTs and polymers and the disorderly distribution of CNTs in polymers. Therefore, reasonable design of polymer composites filled with CNTs is the key to achieving high thermal conductivity. This review mainly introduces the application of CNTs in thermal conductive polymer composites. Based on the existing theoretical research on thermal conductivity of composites and the application of molecular dynamics, more feasible strategies for improving the thermal conductivity of polymer composites filled with CNTs have been proposed. The approaches that improve the thermal conductivity of composites are mainly introduced from three aspects. (1) The intrinsic thermal conductivity of CNTs is an important factor affecting the thermal conductivity of polymer-based composites. CNTs and their macroscopic bulk materials both have excellent thermal conductivity. However, the thermal conductivity test results of the macroscopic materials of CNTs (such as CNTs fibers, arrays, and films) showed that the thermal conductivity of the macroscopic materials of CNTs was much smaller than that of single CNTs due to impurities, defects and inter-tube contact thermal resistance. Studies have shown that purification of CNTs and reduction of intertubular contact thermal resistance can improve the intrinsic thermal conductivity of CNTs. (2) From a microscopic perspective, phonons, the quantized energy of lattice vibration, are the main mechanism of heat conduction in most carbon fillers and polymers. Phonon scattering occurs in the process of phonon transfer, including the scattering between phonons and the scattering at the interface caused by defects and impurities, resulting in thermal resistance. The bonding strength of fillers and polymer interfaces are the crucial factors affecting the transmission of phonons. Hence, the thermal conductivity of composites could be effectively enhanced by surface treatment of CNTs, including covalent functionalization and non-covalent functionalization. Studies have shown that the functionalization can enhance the interfacial interaction between CNTs and polymers, while improving the dispersion of CNTs in polymers. (3) According to the thermal conduction network theory, the key to improving the thermal conductivity is whether the fillers can form a large number of continuous thermal conduction paths in the polymers and maintain a stable existence. However, high CNTs content usually affects the comprehensive properties of composites. To solve this problem, the arrangement and distribution of CNTs in the polymer should be improved to construct more heat conduction pathways, which can achieve high thermal conductivity at a low filling content. Here we introduce some effective methods, including the synergy effect, field orientation and the construction of 3D network structures. In this review, the characteristics and improvement effects of different technical approaches are summarized, which provides a reference for the research and application of CNT-filled polymer-based composites with high thermal conductivity. Finally, the future development prospects of carbon nanomaterial-filled polymer composites are discussed from perspectives of theoretical research, experimental design and engineering application.

Enhanced Thermal Conductivity via In Situ Constructed CNT Aerogel Structure in Composites

AbstractPolymer‐based thermal conductivity composite plays an important role in the thermal management of electronic devices to ensure normal operation. Carbon nanotubes (CNT) are effective thermally conductive fillers to improve the heat transfer efficiency of composites. However, the controlled arrangement of CNT in composites is still a huge challenge for improving their thermal conductivity. To address this issue, CNT aerogel with a regular structure is in situ constructed as a heat transfer pathway based on the catalytic conversion of zeolitic imidazolate framework (ZIF‐67) aerogel. Benefiting from the network structure of aerogel, the in‐plane thermal conductivity of composites not only reach 1.1 W m–1 K–1 at 7.35 vol% filler, but also exhibit a small fluctuation with the increase of temperature. The composites open previously unexplored preparation avenues toward electronic packing thermal management materials.

FEM micromechanical modeling of nanocomposites with carbon nanotubes

Abstract Mechanical properties of carbon nanotube (CNT)-based nanocomposites are broadly discussed in the literature. The influence of CNT arrangements on the elastic properties of nanocomposites based on the finite-element method (FEM) and representative volume element (RVE) approach is presented here. This study is an application of RVE modeling in the characterization of elastic behavior of CNT polymer nanocomposites. Our main contribution is the analysis of the impact of a nanotube arrangement on the elastic properties of nanocomposite to comprehensively determine the material constants. While most of the articles are focused on one distribution, not all material constants are determined. Our FEM analysis is compared with micromechanical models and other results from the literature. The current work shows that nanotube arrangements lead to different results of elastic properties. The analytical micromechanical models are consistent with the numerical results only for axial Young’s modulus and Poisson’s ratio, whereas other elastic constants are lower than the numerical predictions. The results of these studies indicate that FEM can predict nanocomposite mechanical properties with good accuracy. This article is helpful and useful to comprehensively understand the influence of CNT arrangements on the elastic properties of nanocomposites.

Molecular dynamics-based multiscale nonlinear vibrations of PMMA/CNT composite plates

Poly (methyl methacrylate) (PMMA)/carbon nanotube (CNT) composite plates have been extensively used in aviation and aerospace fields. During intended service life, the PMMA/CNT composite structure is prone to severe vibration, which leads to the formation of cracks and the fracture of structures. In order to achieve vibration attenuation, it requires a fundamental understanding of the vibration behavior of composite structures. Here, a molecular dynamics (MD) based multiscale approach is developed to analyze the nonlinear vibration behavior of PMMA/CNT composite plate. Molecular simulations are performed to capture the mechanical properties of the composite and constituents, including longitudinal, transverse, and shear moduli of single-walled CNT (SWCNT) segment, PMMA matrix, and PMMA/SWCNT nanocomposite. The MD simulation results are substituted into the extended rule of mixtures to derive the related efficiency parameters, which are used as the fundamental inputs in a meshless approach to predict the nonlinear vibration of macroscale functionally graded (FG)-based composite plates. According to the macroscale simulation, it is found that the arrangement of CNTs has a significant influence on the nonlinear vibration of FG-based composite plates. The developed multiscale approach provides an efficient paradigm of investigating the macroscopic behavior of composite structure in consideration of the mechanical response from microscopic constituents.

In situ polymerization of functionalized multiwalled-carbon nanotubes/epoxy resin composite fibers using a non-solvent technique

The aim of this study was to produce carbon nanotubes (CNTs)/polymer composite fibers by wet spinning without any solvent. The functionalized multiwalled-carbon nanotubes (F-MWNTs)/epoxy resin was synthesized by in situ polymerization method. Epoxy resin, F-MWNTs, and curing agent were mixed and injected by a syringe pump. The effects of operating parameters including the percentage of CNTs and the extrusion velocity of the syringe pump on the dispersion and alignment of F-MWNTs in the cross-section of F-MWNTs/polymer composite fibers were investigated. The composite fibers were characterized by tensile strength analysis, scanning electron microscopy (SEM), and electrical conductivity analysis. The experimental results showed that a decrease (30 ml/h to 15 ml/h) in extrusion velocity increased the electrical conductivity of composite fibers by more than 3%. This behavior was attributed to the higher alignment of F-MWNTs and improved conducting pathways along the composite fiber axis, as observed by SEM. In addition, by reducing extrusion velocity (30 ml/h to 15 ml/h), the tensile strength of composite fibers was enhanced just over twofold due to the better arrangement of CNTs which can be attributed to the further retention time of composite fibers and the pressure of the walled-needle. Moreover, the higher the processing time of spinning, the lower electrical conductivity of the fibers is which might be due to the higher coagulation of fibers.

Directly Grown Aligned Carbon Nanotubes As a Novel Microporous Layer for Proton Exchange Membrane Fuel Cells

Proton Exchange Membrane Fuel Cells (PEMFC) convert electrochemical energy into electricity. Nevertheless, the system still needs to be improved in order to be economically relevant. In that purpose, it is needed to produce more current for a reduced use of materials. Working on developing new materials for PEMFCs, managing both high gas diffusion and adequate water transport, is necessary to achieve these goals. One of the most important materials used in the fuel cell is the gas diffusion layer (GDL). A microporous layer (MPL) is generally deposited on top of the gas diffusion layer to improve gas transport and water management, and thus enhance the cell performances and stability.Carbon nanotubes interest as a MPL or as catalyst support has already been demonstrated in several works [Kannan (2009); Tang (2011); Xie (2015)]. In the literature, most of works about CNTs as microporous layers are using bulk carbon nanotubes integrated in a carbon black MPL. A few works are displacing a different microporous layer structure where carbon nanotubes are obtained by direct growth and are forming a foam around the gas diffusion layer fibers. In this work, a layer made of vertically aligned CNTs was grown in-situ on the fibers of a gas diffusion layer by a hot filaments assisted chemical vapor deposition (HFCVD). It has been possible to successfully grow aligned CNTs on different commercial supports. Functional properties of the GDL with CNTs were characterized with SEM imaging, contact angle and electrical conductivity measurements. A variety of growth time, filaments temperature, chamber temperature and gas flows have been tested. These parameters influence the carbon nanotubes length, thickness, and the CNTs forest density. At last, electrochemical characterizations were conducted in a differential single cell. This cell allows a better homogeneity of flows on the surface. Several cell configurations were studied: gas diffusion layer with carbon nanotubes on the anode, on the cathode, and on both electrodes, either in dry conditions (no condensed water) or wet conditions (with condensed water). Polarization curves have been measured to study the electrochemical phenomena leading to the variation of performances of the various cell configurations. Impedance spectroscopy has been done to measure the overall cell resistance and its intrinsic composition such as the protonic resistance or the transport resistance.SEM imaging has shown that the CNTs layers are distributed all along the carbon fibers of the GDL, also inside the GDL pores. The overall structure strictly differs from conventional microporous layers as well as other CNT-made MPLs in the literature. 10-25 µm-long multiwall carbon nanotubes with a diameter ranging between 7-10nm were obtained. CNTs as a microporous layer gives better performances (10% in dry conditions, 25% in wet conditions) than commercial MPLs. Contact angle measurements indicates that the obtained gas diffusion media (GDL+MPL) is hydrophilic, which also differs from commercial hydrophobic GDLs. Although carbon nanotubes are individually expected to be hydrophobic, the CNT forest structure and its combination with the former GDL porosity have a different property. The measurement of electrical resistance of the global fuel cell with a commercial MPL or with CNT layers shows that carbon nanotubes don’t provide a better electrical transport.Electrochemical measurements gave access to the fuel cell performance in operating conditions. The results have been compared to the reference SGL 29BC and to the Department of Energy expectations for the fuel cell performances for the next years. In dry state, GDL with CNTs work as well as the reference gas diffusion media. In wet conditions, a dramatic improvement is obtained, especially at low current density. These results are all the more interesting as the gas diffusion layer with carbon nanotubes is hydrophilic, but can compete with the hydrophobic commercial GDLs. The arrangement of carbon nanotubes might also be important as it is aligned in the direction of gas flows and water flows in the fuel cell.In closing, the results of this work show the need to develop nanostructured materials for energy applications. Carbon nanotubes proved their interest as a material for fuel cells. Even with a hydrophilic and a strictly different structure of microporous layer, the fuel cell performances with carbon nanotubes compete with the best commercial reference results. This could lead to a better understanding of the flows phenomena in fuel cells on one side, and of the predominant factors inhibiting a dramatic improvement of the PEMFCs performances. Figure 1

Creep performance of CNT-based nanocomposites: A parametric study

Epoxy materials have been widely applied in various applications ranging from nanoscale structures, such as microelectronic devices, to macroscale components in aerospace and building constructions. The structural stability under constant loadings is a major concern for polymeric materials during long-term service. The incorporation of carbon nanotubes (CNTs) into epoxy matrix has been considered to enhance creep resistance in recent decades. Substantial improvement of CNT-based nanocomposites largely relies on optimized design of material microstructures, and such manipulation requires comprehensive understanding of creep behavior in CNT-epoxy nanocomposites. In addition, effective arrangement of CNTs in epoxy matrix for enhancement in creep resistance needs a systematic study of related parametric effects. In this work, the effects of CNT length, CNT weight fraction and CNT dispersion state on the creep response of nanocomposites are investigated using molecular dynamics simulations. The creep deformation of nanocomposites including creep strain and system dynamics are found to decrease with the increasing length, weight fraction and good dispersion state, showing the contribution of the additional CNTs towards the resistance in time-dependent deformation. These results suggest that the CNT-epoxy nanocomposites with superior creep resistance can be achieved in the design by optimizing the CNT-associated parameters.

Multiscale Composites: Assessment of a Feasible Manufacturing Process

A very interesting field of research on advanced composite materials is the possibility to integrate new functionalities and specific improvements acting on the matrix of the composite by means of a nanocharged resin. In this way, the composite becomes a so-called “multiscale composite” in which the different phases change from nano to macro scale. For example, the incorporation of nanoscale conductive fillers with intrinsically high electrical conductivity could allow a tailoring of this property for the final material. The properties of carbon nanotubes (CNT) make them an effective candidate as fillers in polymer composite systems to obtain ultralight structural materials with advanced electrical and thermal characteristics. Nevertheless, several problems are related to the distribution in the matrix and to the processability of the systems filled with CNT. Existing liquid molding processes such as resin transfer molding (RTM) and vacuum-assisted resin transfer molding (VARTM) can be adapted to produce carbon fiber reinforced polymer (CFRP) impregnated with CNT nanofilled resins. Unfortunately, the loading of more than 0.3-0.5% of CNT can lead to high resin viscosities that are unacceptable for such kind of processes. In addition to the viscosity issues that are related to the high CNT content, a filtration effect of the nanofillers caused by the fibrous medium may also lead to inadequate final component quality. This work describes the development of an effective manufacturing process of a fiber-reinforced multiscale composite panel, with a tetra-functional epoxy matrix loaded with carbon nanotubes to increase its electrical properties and with GPOSS to increase its resistance to fire. A first approach has been attempted with a traditional liquid infusion process. As already anticipated, this technique has shown considerable difficulties related both to the low level of impregnation achieved, due to the high viscosity of the resin, and to the filtration effects of the dispersed nanocharges. To overcome these problems, an opportunely modified process based on a sort of film infusion has been proposed. This modification has given an acceptable result in terms of impregnation and morphological arrangement of CNTs in nanofilled CFRP. Finally, the developed infiltration technique has been tested for the manufacture of a carbon fiber-reinforced panel with a more complex shape.

Semi-exact solution for nonlinear dynamic analysis of graded carbon nanotube-reinforced beam with graded shape memory wires

In this study, the nonlinear dynamical response of a graded carbon nanotube-reinforced beam with graded shape memory wire has been investigated regarding the instantaneous variations of martensite volume fraction and therefore material nonlinearity along the beam. The boundary conditions of the beam are considered as the clamped-clamped. Carbon nanotubes and shape memory wires have been arranged in various distributions of UD, and FG – A along the thickness of the beam. The governing differential equation of the beam is obtained by the use of Brinson’s relation to describe the behavior of the shape memory wire, considering Von Karman nonlinear strain and utilizing Hamilton's principle. The obtained nonlinear equation is solved using the semi-exact solution. For this purpose, Galerkin’s method was first used to isolate the spatial derivatives from the time derivatives and then the obtained equation was solved using Runge-Kutta method. A comparative study has been conducted between the present study and the reference paper to confirm the presented model. This comparison study shows an appropriate agreement between the results of this research and the previous studies. In this research, the influence of the certain parameters such as the considering the nonlinear effects, the volume fraction of carbon nanotube, the type of carbon nanotube distribution, the volume fraction of shape memory wire, and the type of its arrangement on the vibrational behavior of the beam and its loss factor is investigated. Some results show that, in case of the vibration of the beam by the initial excitement, the higher density of carbon nanotubes in the mid-layers and the higher density of the shape memory wires in the outer layers of the beam lead to the higher amount of loss factor. Also, the percentage of the reduction in the loss factor which occurs due to the reduction of the volume fraction of the shape memory wire is almost the same in the beams with different distribution and arrangement of carbon nanotubes and shape memory wire.

High temperature quasistatic and dynamic mechanical behavior of interconnected 3D carbon nanotube structures

Carbon nanotubes (CNTs) are one of the most appealing materials in recent history for both research and commercial interest because of their outstanding physical, chemical, and electrical properties. This is particularly true for 3D arrangements of CNTs which enable their use in larger scale devices and structures. In this paper, the effect of temperature on the quasistatic and dynamic deformation behavior of 3D CNT structures is presented for the first time. An in situ high-temperature nanomechanical instrument was used inside an SEM at high vacuum to investigate mechanical properties of covalently interconnected CNT porous structures in a wide range of temperature. An irreversible bucking at the base of pillar samples was found as a major mode of deformation at room and elevated temperatures. It has been observed that elastic modulus and critical load to first buckle formation decrease progressively with increasing temperature from 25 °C to 750 °C. To understand fatigue resistance, pillars made from this unique structure were compressed to 100 cycles at room temperature and 750 °C. While the structure showed remarkable resistance to fatigue at room temperature, high temperature significantly lowers fatigue resistance. Molecular dynamics (MD) simulation of compression highlights the critical role played by covalent interconnections which prevent localized bending and improve mechanical properties.

Dependence of carbon nanotube array-silicon interface thermal conductance on array arrangement and filling fraction

Carbon nanotube (CNT) is a promising candidate of thermal interface material for micro/nano-scale devices due to its ultra-high axial thermal conductivity. However, low interface thermal conductance between CNT and other materials restricts its effectiveness in the thermal management. We use non-equilibrium molecular dynamics (NEMD) method to investigate the factors that possibly influence the interface thermal conductance between vertical CNT array and silicon substrate. The dependence of the interface thermal conductance on the arrangement of CNT (aligned and crossed), filling fraction (0.14–0.70), CNT diameter (6.88–35.75 Å), temperature (200–400 K), and van der Waals force among the CNTs are studied in detail. From the simulation results, the enhancement of the interface thermal conductance difference caused by CNT-array filling fraction in this work reaches to 91%, and that value caused by the arrangement of CNT on silicon is as high as 84%. The mechanism of heat transport across the interface between CNT array and silicon substrate is discussed by comparing the vibrational densities of states (VDOS) of atoms from both sides under different conditions.

Role of hierarchical morphology of helical carbon nanotube bundles on thermal expansion of polymer nanocomposites

Abstract

Hybrid carbon nanotubes and conductive carbon black in natural rubber composites to enhance electrical conductivity by reducing gaps separating carbon nanotube encapsulates

Filled natural rubber (NR) vulcanizates were prepared with three types of carbon based filler, namely carbon nanotubes (CNT), conductive carbon black (CCB), and CNT/CCB hybrid filler. The formations of fillers in the NR matrix were investigated from the morphology during vulcanization, the Payne effect, and filler dispersion. Furthermore, the wetting ability was estimated based on temperature scanning stress relaxation (TSSR). It was found that the NR-CNT composite showed higher interfacial energy than the NR-CCB composite. This improved the arrangement of CNT in the CNT/CCB hybrid filled NR vulcanizates. Also, a significant increase was found in the optimal conductivity of the hybrid composites with 5 phr CNT and 7.5 phr CCB. This might be attributed to high electron tunneling when the CNT encapsulates are bridged by CCB aggregates. The CNT/CCB combination significantly reduced the inter-particle gaps from ∼6 to ∼2nm, giving very low percolation threshold concentration at which three-dimensional filler networks form. In addition, statistical analysis by ANOVA revealed that the filler type and loading are the principal factors contributing to the relative conductivity of composites, both below and above the percolation threshold.

Three-dimensional micromechanical analysis of the CNT waviness influence on the mechanical properties of polymer nanocomposites

The effects of carbon nanotube (CNT) waviness on the elastic characterizations of polymer nanocomposites are investigated using a three-dimensional unit cell-based micromechanical model. The most important advantages of this model are its accuracy, simplicity, and efficiency. Both random and regular CNT arrangements can be included in the modeling. The wavy CNTs are modeled as sinusoidal solid CNT fibers while at any location along the length of CNT, the CNT is considered as transversely isotropic material. The polymer and interphase formed due to non-bonded interaction between a CNT and the polymer are assumed to be homogeneous and isotropic as well. Results show that the effect of CNT waviness is not important for the effective coefficients \(C_{11}\), \(C_{12}\), and \(C_{13}\) of the nanocomposites. CNT waviness plays a critical role in determining the effective coefficients \(C_{22}\), \(C_{23}\), \(C_{33}\), and \(C_{44}\) of the nanocomposites. Also, it is found that the CNT waviness slightly affects the effective values of \(C_{55}\) and \(C_{66}\). The effects of volume fraction of CNT and interphase on the mechanical properties of the nanocomposite are examined. Comparison of the present model results shows very good agreement with other available micromechanical analysis and experiment. As comparing with the finite element method, the present model requires much less computational time for obtaining the effective properties of the nanocomposites. Consequently, the results emphasize that all four important parameters, i.e., CNT behavior and waviness, CNT random arrangement, and interphase contributions, should be precisely included in the modeling to predict a more realistic outcome.

КОМПОЗИТ НА ОСНОВЕ ДИОКСИДА ЦИРКОНИЯ, МОДИФИЦИРОВАННОГО УГЛЕРОДНЫМИ НАНОТРУБКАМИ: СТРУКТУРА И МЕХАНИЧЕСКИЕ СВОЙСТВА

Results of experimental investigation of mechanical properties of synthesized composite “zirconium oxide - multiwalled carbon nanotubes” are presented in this paper. Ceramic composite was produced on the basis of hydrothermal synthesis from zirconium salt solution with dispersed carbon nanotubes followed by critical point drying of hydrogel and thermal treatment of obtained aerogel. Zirconium oxide/carbon nanotubes aerogel fragments were then sintered in order to obtain bulk sample in the form of tablet by hot pressing technique. Mechanical properties of composite were investigated with microindentation system NanoTest. Experiments on single loading with different values of maximum applied load in range 100...500 mN were conducted. Elastic modulus and hardness of the composite were calculated from experimental indentation curves with standard Oliver-Pharr model. Energy dissipated into the material during indentation and energy of elastic recovery during unloading stage were calculated as areas under corresponding parts of indentation curves. It was found that composite microhardness is a power law function of indentation depth, whereas elastic modulus linearly decreases with increasing indent depth. Synthesized composite exhibits huge fraction of energy dissipated into material which increases with increasing load/indentation depth. Moreover, for all investigated values of maximum applied loads there were no cracks in the edges of indentation trace. The obtained results have shown that synthesized composite is highly effective in suppressing the cracks growth. Aforementioned regularities of mechanical behavior of composite can be linked with its phase composition as well as with presence and arrangement of carbon nanotubes in ceramic matrix.

The effect of choline-based ionic liquid on CNTs' arrangement in epoxy resin matrix

This work focuses on the effect of ionic liquids (ILs) on the arrangement of carbon nanotubes (CNTs) in CNTs–epoxy composites. Electrical conductivity experiments on epoxy–CNTs–ILs suggested that, compared to Ethaline, Oxaline and Reline, Glyceline had a more distinguishable effect on the CNTs' arrangement in the epoxy–CNTs–Glyceline (CG) composites based on scanning electron microscope results. The electrical conductivity of CG composites was improved by increasing the weight content of Glyceline up to 50 times that of CNTs (Gly/CNTs=50), and for weight ratios higher than 50, a downward trend was observed. According to the proposed model, the increase in electrical conductivity seems to be a result of the formation of liquid vesicles which push the CNTs closer outside the Glyceline vesicles. Conversely, the drop in the electrical conductivity can be due to the enlargement of the vesicles, which dissolve CNTs and reduce their content in the epoxy. In addition, the tensile strength of CG composites increased by ratio of Gly/CNTs=10 followed by a significant drop thereafter.Thermal stability of the CG composites was seen to decrease as Glyceline content is increased in the composite. This reduction was attributed to the early decomposition of Glyceline vesicles present inside the epoxy matrix.