Dispersion Of CNTs Research Articles

On the snap-through instability of post-buckled FG-CNTRC rectangular plates with integrated piezoelectric layers

The present paper deals with postbuckling characteristics of carbon nanotube reinforced composite (CNTRC) rectangular plates with integrated piezoelectric layers subjected to in-plane compressive loads. The von Karman type of geometrical nonlinearity is taken into consideration to account for the large deformations of the plate. The dispersion of CNTs may be uniform or functionally graded and the distribution of electric potential across the thickness of piezoelectric layers is simulated by a combination of linear and sinusoidal functions. Generalized differential quadrature method is employed to discretize nonlinear stability equations, boundary conditions and Maxwell equation and then nonlinear system of equations is solved using a displacement control strategy. A comprehensive parametric study is presented to provide an insight into effects of CNT dispersion and volume fraction, geometrical parameters, type of in-plane load, boundary conditions, thickness of piezoelectric layers and external applied voltages on the postbuckling behaviors of the nanocomposite plate. It is shown that snap-through type of instability, which is known as secondary instability, occurs during postbuckling regime. It is revealed that both volume fraction and dispersion of the CNTs could affect the snap-through characteristics of the plate. It is found that snap-through instability is sensitive to thickness of the piezoelectric layers.

Fabrication and properties of CNT/Ni/Y/ZrB2 nanocomposites reinforced in situ

AbstractCarbon nanotubes (CNTs) were synthesized in situ by chemical vapor deposition of methane over nano‐ZrB2 matrix using Ni/Y catalysts. Well‐grown CNTs with tangled and long bodies and mainly composed of well‐crystallized graphite were obtained when the Ni content reaches 10 wt%. The CNT/ZrB2 nanocomposites obtained by spark plasma sintering at 1400°C exhibited full density and optimal mechanical properties. The flexural strength and fracture toughness of the nanocomposites were 1184 ± 52 MPa and 10.8 ± 0.3 MPa·m1/2, respectively. Results indicated that the dispersion of CNTs in situ can improve composite performance, rendering the mechanical properties of the CNT/ZrB2 nanocomposites synthesized in situ considerably superior to those of monolithic ZrB2 nanoceramics and CNT/ZrB2 nanocomposites synthesized using the traditional method. The toughening mechanisms included crack deflection, crack bridging, CNT debonding, pull‐out, and fracture.

Modelling mechanical behavior of cementitious material incorporating CNTs using design of experiments

One of the primary factors affecting the effectiveness of nanomaterials in enhancing cement composites properties is its ability to disperse efficiently without aggregation. To-date a number of methods have been proposed to increase the dispersion of CNTs in the mixes. Studies have shown that the response of cement-based materials to CNT addition can vary depending on the dispersion mechanism employed. Despite the need, there is no standardized methodology used to disperse CNTs, and consequently, it is hard to model the behavior. This study focused on using design of experiments (DOE) to assess the effect of dispersion protocol on the characteristics of cement-based composites. Experiments were carried out with different procedures to compare the effect of wet and dry mixing of CNTs, sonication exposure time, whisking and CNTs concentration on the mechanical properties of mortar blocks. Response Surface Methodology (RSM) was used to model the experimentally determined compressive strength. The model was further validated by comparing its predictions with other experimental scenarios. The model can be used to determine the optimum methodology to disperse CNTs in cement composites. To compare experimental data, there is a need to provide the exact details of all steps involved in a dispersion protocol that is captured by the proposed model. Following the suggested protocol for specimen preparation can ensure achieving a high level of dispersion and superior performance.

Tailoring electrical and thermal properties of polymethyl methacrylate‐carbon nanotubes composites through polyaniline and dodecyl benzene sulphonic acid impregnation

A series of composites of polymethyl methacrylate (PMMA) with polyaniline‐multiwalled carbon nanotubes (PANI‐CNTs) as filler I and dodecyl benzene sulphonic acid‐multiwalled carbon nanotubes (DBSA‐CNTs) as filler II are developed by solution mixing method. Composites are characterized for morphological, electrical, and thermal properties to study effect of two different types of additives, PANI, and DBSA. Furthermore, their influence on dispersion of CNTs is also studied. Electrical percolation behavior of both composites series is investigated through dielectric and conductivity measurements. Sharp insulators to conductor transition curves are obtained for filler I and II, with conductivity of 5.6 S cm−1 at 2 wt% of CNTs and 2 S cm−1 at 3 wt% of CNTs, respectively. High dielectric constant is observed for filler I as compared to filler II due to the formation of comparatively big clusters of filler I than II. Theoretically calculated percolation threshold was found to be 1.3 wt% for filler I and 0.8 wt% for filler II in the matrix with exponent constants 2.4 and 1.25, respectively. Thermal stability of PMMA composites, containing filler II, indicated an impressive increase by 72°C onset and 55°C in complete degradation temperature as compared to pure PMMA. POLYM. COMPOS., 39:E1052–E1059, 2018. © 2017 Society of Plastics Engineers

Effect of amine-functionalized dispersant on cure and electrical properties of carbon nanotube/epoxy nanocomposites

Abstract The efficient dispersion of carbon nanotubes, CNTs in epoxy resin is a challenging task to reach the final properties of the competent nanocomposite. In this study, the CNT/epoxy nanocomposite was fabricated by solution mixing process using an amine-functionalized dispersant. The dispersion of CNTs in organic solvent was further improved using an ultrasonic horn. According to the data obtained from UV–vis spectroscopy, a minimum ultrasonication time of 10 min is necessary to obtain proper dispersion of CNTs in organic solvent. The cure behavior of epoxy resin containing different CNT loadings was investigated by dynamic DSC thermograms. The higher CNT loading lowers the initial curing temperature and the peak temperature mainly due to high thermal conductivity of CNT. The SEM micrographs of the fractured surfaces showed the effect of dispersant on proper dispersion of CNTs in epoxy. The electrical percolation threshold was measured at about 0.5 wt% of CNT. However, the conductivity results revealed the adverse effect of dispersant on the nanocomposite electrical properties, mainly due to dispersant adsorption and hence screening the CNTs surface charges.

Microstructural evaluation and mechanical properties of Al-CNT nanocomposites produced by different processing methods

In this research, the semi-wet (SW) and slurry based (SB) methods were applied to synthesize Al-1.5 wt.%CNT nanocomposites powder. The initial 30 mm diameter compacted billets were produced through cold pressing and pressure-less sintering at 550 °C for 2 h for both types of nanocomposites. The billets were hot extruded at 400 °C to produce 10 mm diameter rods. The synthesis parameters of composites were investigated through experiments of tension, compression, FTIR, XRD, STA and Raman. The dispersion of CNTs within Al powder and fracture surface analysis was studied through FE-SEM.The yield and tensile strength of pure Al sample were measured as 90 and 136 MPa, respectively. These values were increased to 110 and 170 MPa for SW sample and improved to 152 and 203 MPa for SB product, by adding 1.5 wt.% CNT to pure Al. The strengthening effect of fibers was investigated using load transfer mechanism with fiber length less than critical value (l < lc) for SW and long fiber issue (l > lc) for SB samples. According to the fracture surface analysis, the bridging and CNTs fracture phenomena were observed in SB specimen and CNTs pull out was detected for SW sample. These results showed good agreement with strengthening efficiency of fibers (R) versus shear stress diagram including R = 25.6 in CNTs fracture and R = 13 in pull out regions. The Al4C3 interphase formation was characterized by XRD and Raman spectroscopies whereas end-contact and side-contact of carbides around CNTs were suggested as preferred sites for SB and SW products, sequentially.

Role of single‐source‐precursor structure on microstructure and electromagnetic properties of CNTs‐SiCN nanocomposites

AbstractNovel single‐source‐precursors (SSPs), namely carbon nanotube modified poly (methylvinyl) silazane (CNTs‐HTT 1800), were synthesized via amidation reaction of poly (methylvinyl) silazane (HTT 1800) with carboxylic acid functionalized carbon nanotubes (CNTs‐COOH) at the assistance of ZnCl2 catalyst, which was confirmed by means of Fourier transform infrared spectra (FT IR) and transmission electron microscopy (TEM). Besides, the TEM results unambiguously show the homogeneous distribution of the CNTs in the matrix of SSPs while serious aggregation of the CNTs in the matrix of physically‐blended‐precursor. Crack‐free monolithic silicon carbonitride modified by carbon nanotubes ceramic nanocomposites (CNTs‐SiCN) were prepared through pyrolysis of the obtained SSP green bodies at 1000°C. Due to the strong influence of polymer structure on the microstructure of final ceramics, the SSP‐derived CNTs‐SiCN nanocomposites clearly show the homogeneous distribution of the CNTs in the SiCN matrix while the physically‐blended‐precursor derived CNTs‐SiCN nanocomposites exhibit serious aggregation and entangling of the CNTs in the SiCN matrix. With the same CNT content in the feed, the SSP‐derived CNTs‐SiCN nanocomposites possess significant improvements of electromagnetic (EM) absorbing properties compared to those from physically‐blended‐precursors, due to the quality of the dispersion of CNTs in the ceramic matrices.

Synthesis and characterization of UHMWPE nanocomposite fibers containing carbon nanotubes coated with a PVP surfactant layer

Ultra‐high‐molecular‐weight polyethylene (UHMWPE) nanocomposite fibers were fabricated using solution spinning, consisting of surface modified single‐walled carbon nanotubes (SWCNTs) embedded into the fiber matrix. The SWCNTs were modified using polyvinylpyrrolidone (PVP) noncovalent functionalization process, which acts as a surfactant and has the ability to enhance the dispersion of CNTs in the base polymer matrix by reducing aggregation and promoting interfacial adhesion with the fiber polymer matrix. Tensile testing of fibers containing PVP‐coated SWCNTs showed substantial improvements in the tensile strength and fracture strain by 125% and 137%, respectively, compared to fibers containing pristine CNTs. The amount of PVP coated onto the surfaces of CNTs was determined to be about 32.5% using thermogravimetric analysis (TGA). Differential scanning calorimetry (DSC) analysis of the nanocomposite fibers showed significant increase in crystallinity and upshift in the melting point compared to that of neat UHMWPE fibers. Fourier transform infrared spectroscopy (FTIR) analysis showed the presence of characteristic absorbance bands of PVP functional groups (CN @ 1289 cm−1 and CO @ 1651 cm−1) on the modified CNTs. Scanning electron microscopy (SEM) imaging of modified CNTs and nanocomposite fibers showed an increase in average tube diameter and reduced aggregate formation compared to pristine CNTs, indicating the successful coating of the nanotubes with PVP. Preferential alignment of the modified CNTs along the direction of fiber extrusion and crack bridging of the fiber by nanotubes were also observed. POLYM. COMPOS., 39:E1025–E1033, 2018. © 2017 Society of Plastics Engineers

An electroless plating and planetary ball milling process for mechanical properties enhancement of bulk CNTs/Cu composites

CNTs/Cu composite powders were prepared by an electroless plating and planetary ball milling process. The structure of composite powders was investigated. Results showed that Cu particles are homogeneously deposited on CNTs surface, and CNTs are deeply embedded into Cu matrix after milling, which play an important role in the dispersion and the wettability of CNTs within matrix and subsequently in the mechanical properties of composites. And the bulk CNTs/Cu was fabricated by vacuum sintering, re-pressing and re-sintering, and cold drawing process. It revealed that comparing pure Cu and composite without electroless plating, the tensile strength of composite with electroless plating increases obviously, up to 207 MPa. SEM images revealed that agglomeration is the main reason of deteriorating mechanical properties of composites. Finally, higher strength composites were successfully obtained by cold drawing. Results demonstrated that it can significantly improve the mechanical properties of the composites. Also, the tensile strength and the yield strength are up to 311 MPa and 185 MPa, respectively. SEM images clearly revealed that it is the dispersion and directional distribution of CNTs in matrix that further improve the strength of composites in drawing orientation. The load transfer theory was also employed to testify the results, effectively.

Multi-scale bending, buckling and vibration analyses of carbon fiber/carbon nanotube-reinforced polymer nanocomposite plates with various shapes

Using a finite element-based multi-scale modeling approach, the bending, buckling and free vibration of hybrid polymer matrix composites reinforced by carbon fibers and carbon nanotubes (CF/CNT-RP) are analyzed herein. Thick composite plates with rectangular, circular, annular and elliptical shapes are considered. First, the equivalent material properties of CF/CNT-RP are calculated for different volume fractions of CF and CNT. To accomplish this aim, a two-step procedure is presented through which the coupled effects of nano- and micro-scale are taken into account. In the first step, modeling of dispersion of CNTs into the polymer matrix is done with considering interphase formed by their chemical interaction with the matrix, and the equivalent properties of resulting composite material are determined accordingly. CFs are then dispersed into CNT-RP which is considered a homogenous material in this step. Both distributions of CNTs and CFs are assumed to be random. After computing the equivalent properties of CF/CNT-RP for different volume fractions of its constituents, the bending, buckling and free vibration analyses of plates with different shapes are performed. It is shown that the reinforcement of the polymer matrix with both CF and CNT significantly affects the bending, buckling and free vibration characteristics of plates.

Temperature dependent structural evolution in nickel/carbon nanotube composites processed by high-pressure torsion

Nickel/Carbon nanotube (CNT) composites with varying amounts of CNTs were processed at different temperatures by high-pressure torsion (HPT) with the aim to optimize the process parameters to obtain a homogenous dispersion of CNTs in the metallic matrix. As the CNT distribution has an enormous influence on the composite properties, the structural evolution with increasing strain and the final microstucture of the composites are investigated by scanning and transmission electron microscopy. Microhardness measurements were additionally performed. Microhardness increases up to 800 Vickers (HV) and the mean grain size decreases to an equivalent radius smaller than 40 nm for HPT at room temperature (RT), while the CNTs form rather large agglomerates. HPT deformation at 200 °C shows no significant change in hardness, grain size and CNT agglomerate size. For HPT deformation at 300°C and 400°C grain sizes increase to 60 nm respectively 90 nm, microhardness decreases to 500 HV respectively 400 HV and the size of the CNT agglomerates decreases from more than 5 times the grain size at RT to smaller than the grain size. It could be shown that the optimal HPT processing route to improve the CNT distribution is a combination of deformation at 400°C with subsequent deformation at RT.

Influence of chemical admixtures on the dispersion of carbon nanotubes in water and cement pastes

The influence of ultrasonic and three types of chemical surfactants (including cationic surfactants: CTAB, anionic surfactants: SDS, and nonionic surfactants: TX-405) on the dispersion of CNTs was investigated. The techniques include UV-Vis-NIR spectrophotometer, laser particle size analyser and scanning electrical microscope (SEM). The results show that: 1) Ultrasonic leads to a dispersive effect on CNTs in water, and the optimal ultrasonic time is 120 s; 2) Three types of surfactants have positive effects on the dispersion of CNTs in water, among which cationic surfactant (CATB) leads to the best dispersibility; 3) CNTs with more carboxyl groups show better dispersion in water indicated from UV-vis-NIR spectra and particle size measurement; 4) The optimum concentration of surfactants is 5:1 (the mass ratio of dispersant to CNTs); 5) Three types of surfactants can improve the dispersion of CNTs in cement pastes indicated from SEM images at the optimum dosage.

Microstructure and mechanical properties of Mg-4.0Zn alloy reinforced by NiO-coated CNTs

Mg-4.0Zn alloy composite reinforced by NiO-coated CNTs (NiO@CNTs) was synthesized by combining ball-milling and a casting process. The yield strength (YS) and elongation to failure of the composite were dramatically increased by 44.9% and 38.6%, respectively, compared to its alloy counterpart. The significantly enhanced mechanical properties of the as-synthesized composite are mainly ascribed to an improved interfacial bond, grain refinement and good dispersion of CNTs in the matrix via. coating NiO on CNTs. It is shown that the NiO-nanolayer on the CNTs significantly enhances the interfacial bonding strength and effectively prevents the agglomeration of CNTs. NiO@CNTs are, therefore, expected to be a highly sustainable and dispersible reinforcement for magnesium matrix composites with superior performance.

Development of CNTs-filled photopolymer for projection stereolithography

PurposePolymeric parts produced by 3D stereolithography (SL) process have poorer mechanical properties as compared to their counterparts fabricated via conventional methods, such as injection or compression molding. Adding nanofillers in the photopolymer resin for SL could help improve mechanical properties. This study aims to achieve enhancement in mechanical properties of parts fabricated by SL, for functional applications, by using well-dispersed nanofillers in the photopolymers, together with suitable post-processing.Design/methodology/approachCarbon nanotubes (CNTs) have high strength and Young’s modulus, making them attractive nanofillers. However, dispersion of CNTs in photopolymer is a critical challenge, as they tend to agglomerate easily. Achieving good dispersion is crucial to improve the mechanical properties; thus, suitable dispersion mechanisms and processes are examined. Solvent exchange process was found to improve the dispersion of multiwalled carbon nanotubes in the photopolymer. The UV-absorbing nature of CNTs was also discovered to affect the curing properties. With suitable post processing, coupled with thermal curing, the mechanical properties of SL parts made from CNTs-filled resin improved significantly.FindingsWith the addition of 0.25 wt.% CNTs into the photopolymer, tensile stress and elongation of the 3D printed parts increased by 70 and 46 per cent, respectively. With the significant improvement, the achieved tensile strength is comparable to parts manufactured by conventional methods.Practical implicationsThis allows functional parts to be manufactured using SL.Originality/valueIn this paper, an improved procedure to incorporate CNTs into the photopolymer was developed. Furthermore, because of strong UV-absorption nature of CNTs, curing properties of photopolymer and SL parts with and without CNT fillers were studied. Optimized curing parameters were determined and additional post-processing step for thermal curing was discovered as an essential step in order to further enhance the mechanical properties of SL composite parts.

The effect of heat treatment on microstructure evolution in artificially aged carbon nanotube/Al2024 composites synthesized by mechanical alloying

Although carbon nanotubes/aluminum (CNT/Al) composites are promising materials in the production of structural components, their mechanical behavior under overaging conditions has not been considered. In this paper the effect of CNTs on the microstructural and mechanical behavior of a 2024 aluminum alloy (Al2024) synthesized by mechanical alloying (MA) and powder metallurgy routes is discussed, as well as the effect of aging heat treatments at different temperatures and aging times. The mechanical behavior of composites was screened by hardness measurements as function of aging time. After 96h of aging time, composites showed mechanical stability in their hardness performance. Images from transmission electron microscopy showed that the mechanical stability of composites was due to a homogeneous dispersion of CNTs in the aluminum matrix and a subsequent alteration in the kinetics of precipitation is due to their presence in the aluminum matrix. Even though strengthening precipitation took place during aging, this was not the main strengthening mechanism observed in composites.

In situ Preparation of Aramid-MWCNT Nano-composites: Morphology, Thermal Mechanical and Dielectric Properties

In situ polymerization technique was used to link chemically the amine-terminated high molecular weight aramid chains with acid-functionalized MWCNTs. The The X-ray photoelectron spectroscopy (XPS) was used to study the chemical linkage between aramid chains and MWCNTs and the composite morphology was investigated by scanning electron microscopy. Dynamic mechanical analysis (DMA) showed a higher increase in the storage modulus. The temperature involving α-relaxations on MWCNTs loading was found higher in comparison to the system where pristine MWCNTs were used. Iinterfacial interactions between the matrix and MWCNTs including hydrogen bonding, π–π stacking and chemical bonding are considered the key parameters responsible and the chemical bonding of the MWCNTs with the matrix resulted in better dispersion of CNTs and the higher visco-elastic properties. The maximum glass transition and the thermal decomposition temperature of these composites respectively were observed around 346°C and 533°C. The inclusion of pristine CNTs increased the electric conductivity of the aramid films with a minimum threshold value at the loading of 1.67 vol.%. Such mechanically strong and thermally stable aramid composites are suitable for many applications including high performance materials for electromagnetic shielding and radar absorption.

Bionanocomposite regenerated cellulose/single-walled carbon nanotube films prepared using ionic liquid solvent

Electrically conductive regenerated cellulose/single-walled carbon nanotube (RC/CNT) bionanocomposite films were fabricated using an environmentally benign ionic liquid, 1-ethyl-3-methylimidazolium chloride (EMIMCl). CNTs were well dispersed in EMIMCl by employing ultrasonication prior to solution casting. The films were characterized by X-ray diffraction analysis, field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Introduction of CNTs greatly improved the tensile strength and Young’s modulus of the bionanocomposite films, without compromising their elongation at break. Homogeneous dispersion of CNTs was confirmed by FESEM and TEM micrographs. The bionanocomposites exhibited a rapid insulator to conductor transition at CNT content as low as 0.75 wt%. Incorporation of CNTs also enhanced the thermal stability, oxygen barrier properties, as well as water absorption resistance.

Evaluation of concentration and dispersion of functionalized carbon nanotubes in aqueous media by means of Low Field Nuclear Magnetic Resonance

Dispersions of functionalized carbon nanotubes (fx-CNTs) have been analyzed by means of Low Field Nuclear Magnetic Resonance measurements (LF-NMR). This technique showed that the presence of the fx-CNTs strongly influences the structuring of the water molecules. Thereupon, the water transversal relaxation rate (r2) can be used to get information about the concentration of the CNTs in aqueous dispersion and their aggregation tendency. Finally, the effect of the addition of an anionic polyelectrolyte, namely alginate, on aqueous dispersion of CNTs was explored by using LF-NMR, which revealed different dependence of r2 from CNT concentration, depending on the type and charge of fx-CNTs.

HfB2-CNTs composites with enhanced mechanical properties prepared by spark plasma sintering

HfB2-x vol%CNTs (x=0, 5, 10, and 15) composites are prepared by spark plasma sintering. The influence of CNTs content and sintering temperature on densification, microstructure and mechanical properties is studied. Compared with pure HfB2 ceramic, the sinterability of HfB2-CNTs composites is remarkably improved by the addition of CNTs. Appropriate addition of CNTs (10vol%) and sintering temperature (1800°C) can achieve the highest mechanical properties: the hardness, flexural strength and fracture toughness are measured to be 21.8±0.5GPa, 894±60MPa, and 7.8±0.2MPam1/2, respectively. This is contributed to the optimal combination of the relative density, grain size and the dispersion of CNTs. The crack deflection, CNTs debonding and pull-out are observed and supposed to exhaust more fracture energy during the fracture process.

Effects of CNTs content on the microstructure and mechanical properties of spark plasma sintered TiB2-SiC ceramics

Monolithic TiB2 ceramics and TiB2−20vol%SiC-x vol%CNTs (x=0, 5, 10, 15, 20, 25 and 30) composites were prepared by spark plasma sintering. The influence of CNTs content and sintering temperature on sintering behavior, microstructure and mechanical properties were investigated. It was indicated that the fine grains, increased densification and homogenous dispersion of CNTs were the main dominate factors for the improved mechanical properties. The highest flexural strength (925±45MPa) and fracture toughness (10.4±0.3MPam1/2) were achieved in composite with 15vol% CNTs sintered at 1750°C. The toughness mechanism was ascribed to be crack deflection, crack bridging, CNTs debonding and pull-out. However, porous rope-like structure of agglomerated CNTs was observed by more than 20vol% CNTs addition, resulting in the reduction of relative density and mechanical properties.