MWCNTs Content Research Articles

Effect of pre-axial tensile tension, temperature, and hysteresis loss of natural rubber doped MWCNTs on the electrical properties for sensors applications

In view of its large application, one used natural rubber (NR). The effects of MWCNTs contents on electrical properties as well as the effect of both pre extension and mechanical hysteresis on the electrical properties of these composites were discussed. At low MWCNTs contents (≤6 phr), έ, σac, and σdc showed to have slight changes. Meanwhile, contents (≥9 phr) have significant increase as a result of its interfacial polarization. That is, the composite became conductive. Higher positive electrical conductivity coefficient (PTCC) intensity was detected for the 3phr sample. The effect of the electric field on the mechanical creep characteristics and its corresponding parameters were investigated. Conventional elastic modulus was found to increase with both MWCNTs concentration and the applied stress in all samples about six times its original value. Current creep curves were constructed and maximum piezoresistivity was found for sample 3phr with a negative effect on piezoresistivity, which can be employed as a pressure or force sensor. The parameters deduced from hysteresis loop such as the strain coefficient of conductivity, damage parameter, strain energy density, inelastic strain, elastic strain, and mismatch parameter are strongly dependent on both the MWCNTs concentration and the applied mechanical stress. The damage parameter increased to about 20 times with increasing the concentration, while the decreases with increasing number of hysteresis cycles. The activation energy decreased with the pre-axial tension, while no effect of electrical conductivity.

Broadband electromagnetic wave absorbing performance by designing the foam structure and double-layer for cement-based composites containing MWCNTs

This work fabricated foamed cement-based composites with different densities, MWCNTs content, and double-layer design with different layer combinations. Not only were the EMW-absorbing performance and mechanism of these composites investigated, but the mechanical properties were also examined. Single-layer composites' optimum EMW absorption performance showed an effective absorption bandwidth (EAB) of 9.76 GHz and RLmin of −13.6 dB. Compared to the single-layer samples, the double-layer samples showed the wider EAB of 12.7 GHz, RLmin of −32.9 dB at the same thickness, furthermore EAB of 14 GHz, and lower RLmin of −47.3 dB at 30 mm thickness. Attributing to the specific porous system and the internal micro conductive network, a synergistic effect of improved impedance matching characteristic and superior EMW attenuation of the double-layer composite was achieved.

Effect of MWCNTs on microstructure and properties of WC-9Co gradient cemented carbides

WC-9Co-xMWCNTs (Multiwalled carbon nanotubes) gradient cemented carbides with cubic carbides free layer (CCFL) were prepared by powder metallurgy method. The effect of different MWCNTs content on the microstructure and mechanical properties of WC-9Co gradient cemented carbides have been studied. The microstructure and phase composition of WC-9Co-xMWCNTs composites were characterized by means of optical microscope, scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, the hardness, fracture toughness, bending strength and friction coefficients were tested by Vickers indenter, universal testing machine and tribometer. The results showed that the MWCNTs could promote the growth of CCFL. The minimum grain size of WC was obtained in the WC-9Co-0.08 wt% MWCNTs composites and the sample possessed the highest hardness and bending strength, the lowest friction coefficient and the best wear resistance at the same time. The fracture toughness and relative density increased steadily together with the addition of MWCNTs. Besides, the mechanism of MWCNTs enhancing the alloys include bridge connection, crack deflection, pull-out and strengthening effect of the network structure.

Evaluation for the performance of heat transfer process in a double pipe heat exchanger using nanofluids

This research investigates the effects of employing nanofluids in a tubular heat exchanger on the heat transfer process. The performance of employing water as a base fluid and multi-wall carbon nanotubes (MWCNTs) with a varying concentration nanofluid as operational fluids was investigated in an experimental investigation. The current study makes use of an Armfield Heat Exchanger (HT31) and an Armfield heat exchange service unit (HT30X). Five volumetric concentrations of nanomaterials were used to make nanofluids (0.22%, 0.33%, 0.66%, 1.1%, 1.53%). The Reynolds number of the flow inside the tube ranged from 1598 to 8000. By measuring the variables, the overall heat transfer coefficient, pressure drop, friction factor, and mean Nusselt number are computed. The overall heat transfer coefficient increases as the concentration of MWCNTS and the mass of flow increase, according to the experimental data. In comparison to distilled water, the Nusselt number value has increased by 68%, this increase is due to the nanoparticles’ volume concentration. Pressure drop values increase significantly when nanofluids are used. The friction factor increases as the volume concentration of nanoparticles increases. A relationship between Reynolds number and MWCNT volume concentration is proposed for computing the Nusselt number. An acceptable agreement may be found by comparing the results of the current investigation to the literature.

Tunable negative permittivity behavior in percolated MWCNTs/PVDF composites

Composites with negative permittivity behavior have brought about widespread attention for their broad application prospects in electromagnetic field or being used for novel capacitance. In this work, multiwall carbon nanotubes/polyvinylidene fluoride (MWCNTs/PVDF) composites with gradually increasing MWCNT filling content were prepared by hot-pressing in order to acquire negative permittivity. The microstructure, ac conductivity, and real permittivity of the samples were elaborated. As MWCNTs content increases, the percolation phenomenon occurs accompanied by the conversion of conductive mechanism from hopping conduction to free electron conduction. It’s found that negative permittivity property was obtained at a lower filler content and can be regulated by controlling MWCNTs content, which is related to the plasma oscillation state of free electrons in MWCNTs.

Multiwalled-carbon nanotubes reinforced hydroxyapatite- tantalum pentoxide nanocomposite coating on Nitinol alloy: Antibacterial activity and Electrochemical properties

In this work to establish the antibacterial implants, the different amounts of multi-walled carbon nanotubes (MWCNTs, 0.5, 1, 1.5, and 2 wt.%) were incorporated with hydroxyapatite-tantalum pentoxide (HA-Ta2O5) and exerted on the NiTi by electrophoretic deposition (EPD) method. The increased HA-Ta2O5 coating density by adding and enhancing the MWCNTs content was shown by field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). It was affirmed that MWCNTs have still been stable in HA-Ta2O5−MWCNTs coatings after sintering at 700 °C for 1 h. The increase of MWCNTs from 0.5 to 2 wt.% caused an increment of adhesion strength of HA-Ta2O5 coating to NiTi from 10 to 27% due to providing the more contact surface area of the coating with substrate and consequently the higher chemical bonding. It was found that the antibacterial property of the HA-Ta2O5 coating was induced by MWCNTs. Such behavior originated from the antibacterial characteristic of MWCNTs and has successively improved due to the rise in MWCNTs content and concurrent diminish in HA-Ta2O5−MWCNTs surface wettability. The positive effect of MWCNTs on the electrochemical behavior of HA-Ta2O5-coated NiTi was confirmed by polarization test and electrochemical impedance spectroscopy (EIS). According to the parameters resulted from the fitting of EIS spectra with the electrical circuits (EC), the resistances of the coating and the double-layer on NiTi surface have increased due to an enhancement in the MWCNTs content. This improvement was attributed to the increased density and reduced wettability of HA-Ta2O5 coating.

Investigation on thermal properties enhancement of lauryl alcohol with multi-walled carbon nanotubes as phase change material for thermal energy storage

This paper investigates the thermal properties enhancement of lauryl alcohol, which falls in the category of organic fatty alcohol as an energy storage material for latent heat thermal energy storage using multi-walled carbon nanotubes (MWNCTs) nanoparticle additive. Nano-enhanced PCMs of lauryl alcohol with different concentrations of MWCNTs ranging from 1 wt% to 5 wt% were prepared, and the thermophysical properties were studied using various characterization techniques. From the result, it was found that the thermal conductivity of the lauryl alcohol can be significantly increased with the addition of MWCNT. The maximum increment in thermal conductivity was observed for 5 wt% MWCNT. The chemical structure was not altered by the addition of MWCNT and Gum Arabic. However, the concentration of nanoparticles affects several other important properties such as latent heat and degree of supercooling. Therefore, the optimum concentration of the nanoparticle has to be carefully determined for better thermal properties. The detailed investigation on the nano-enhanced lauryl showed that the lauryl alcohol with MWCNT could be a potential PCM for cold thermal storage applications.

Carbon nanotubes in the holding solution stimulate flower opening and prolong vase life in carnation

BackgroundCut flower longevity is often limited by adverse water relations or oxidative stress. The potential of single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) on prolonging vase life was addressed. Dose–response curves were obtained by applying five concentrations (0–80 mg L−1) of SWCNTs or MWCNTs either once as a foliar spray or continuously in the holding solution of three carnation cultivars. Next, the optimal concentration of either SWCNTs or MWCNTs was employed to evaluate several parameters critical for vase life.ResultsFoliar spray application exerted minor effects on water relations, flower opening and keeping quality. By contrast, including CNTs in the holding solution sustained a positive water balance for a longer period, improved flower opening and prolonged vase life. These effects were similar between SWCNTs and MWCNTs, and were concentration-dependent. The optimal concentration for vase life was higher for MWCNTs as compared to SWCNTs, and for two cultivars as compared to the third one. At optimal concentration, SWCNTs or MWCNTs in the holding solution generally maintained turgidity, and alleviated chlorophyll degradation, electrolyte leakage and lipid peroxidation. These effects were related to increased activation of enzymatic (ascorbate peroxidase, catalase, peroxidase and superoxide dismutase) and non-enzymatic (carotenoids, polyphenols, and flavonoids) antioxidants.ConclusionCNTs in the holding solution were very effective in stimulating vase life through improved water relations and enhanced antioxidant machinery stimulation.Graphical

MgH2-based hydrogen storage tank: Kinetics, reversibility, and MWCNTs content

The de/rehydrogenation performance, mechanism, and reversibility of a MgH2-based hydrogen storage tank with enhanced packing volume of up to 337.40 mL have been investigated. Due to significant upscaling, the MWCNTs loading content significantly affects the thermal conductivity and hydrogen diffusion in the tank. By increasing the MWCNTs content from 5 to 10 wt%, the hydrogen sorption kinetics is significantly improved. This has led to an enhancement in the reversible hydrogen capacity from 38.9 to 52.5% of the theoretical value upon 10–15 hydrogen release and uptake cycles. In addition, the de/rehydrogenation behavior at different positions in the radial and axial directions of the tank have been studied by tracking temperature and pressure changes observed during the hydrogen exchange reaction and studying the chemical compositions of the sample after cycling.

Investigation of the synergistic effect of melt-extension and nanofiller on the crystal-crystal phase transition from form II to I of isotactic polybutene-1.

New questions and conjectures are raised on the crystal-crystal phase transition of isotactic polybutene-1 (iPB-1) containing nanofiller in the flow field. In this work, we investigate the phase transition from flow-induced oriented form II to I in iPB-1 blends with multi-walled carbon nanotubes (MWCNTs) with a homemade two-drum extensional rheometer combined with in situ wide-angle X-ray diffraction (WAXD) measurements. The MWCNTs show a limited promoting effect on the phase transition kinetics under quiescent conditions, while the phase transition kinetic is highly accelerated with the impose of melt-extension. When the loading extension strain is 0.5 or 2.0, the half time of phase transition (t1/2) is shortened from tens of hours to a few hours, depending on the melt-extension strain and the MWCNTs content in iPB-1. When the extension strain increases to 3.5, t1/2 decreases to about 30 min, which is independent of the MWCNTs content in all iPB-1 blends except in blends with MWCNTs content of 1%, where the phase transition rate in the middle and late stages is restrained. It's speculated that flow-induced molecular orientation or shish-kebab morphology affects the internal stress or stress transfer. The addition of a nanofiller enlarged the effect of melt-extension through strengthening the localized intensity of flow field. In general, the combination of nanofiller and melt-extension can obviously promote the phase transition kinetics.

Fabrication and Characterization of Polypyrrole/Multi-Walled Carbon Nanotubes Thin Films Using Thermal Evaporation.

Polypyrrole/multiwalled carbon nanotubes composites (PPy/MWCNTs) were produced in an acidic solution utilizing an in situ oxidative polymerization method using ferric chloride as an oxidizing agent and sodium dodecyl sulfate as a soft template. Thermal evaporation was used to fabricate thin films from polypyrrole/multiwalled carbon nanotube composites. The resulting composites were examined by different techniques to explore their morphology, structural and electrical characteristics. The surface morphology analysis revealed that polypyrrole structure is a two-dimensional film with impeded nanoparticles and the thickness of coated PPy around the MWCNTs decreases when increasing the amount of MWCNTs. XRD analysis revealed that the average crystallite size of the prepared composites is 62.26 nm. The direct energy gap for PPy is affected by a factor ranging from 2.41 eV to 1.47 eV depending on the contents of MWCNTs. The thin film’s optical properties were examined using experimental and TDDFT-DFT/DMOl3 simulation techniques. The optical constants and optical conductivity of the composites were calculated and correlated. The structural and optical characteristics of the simulated nanocomposites as single isolated molecules accord well with the experimental results. The nanocomposite thin films demonstrated promising results, making them a viable candidate for polymer solar cell demands. Under optimal circumstances, the constructed planar heterojunction solar cells with a 75 ± 3 nm layer of PPy/MWCNTs had a power conversion efficiency (PCE) of 6.86%.

Preparation of carbon nanotube-vitrimer composites based on double dynamic covalent bonds: Electrical conductivity, reprocessability, degradability and photo-welding

Emerging as an innovative class of polymeric material, vitrimers possess the advantages of thermoplastics as well as thermosets and of great interest due to its ability to reduce environmental pollution and waste of resources caused by plastic abuse. In the present work, we prepared a series of carbon nanotube-vitrimer composites (EPCNTx) containing double dynamic covalent bonds (carboxylate and disulfide bonds), of which EPCNT5 (the MWCNTs content is 5 wt%) displayed the best electrical conductivity (1.63 S/m) and good mechanical properties (tensile stress = 16.3 MPa, fracture strain = 81.8%). Additionally, EPCNT5 has the advantages of vitrimer, i.e., reprocessability, degradability, and photo-welding performance, fully combining the advantages of vitrimer and epoxy composites. Furthermore, the EPCNT5 is fabricated as a skin sensor, demonstrating its potential application in the field of skin sensing.

Segregated polylactide/poly(butylene adipate‐co‐terephthalate)/MWCNTsnanocomposites with excellent electrical conductivity and electromagnetic interference shielding

AbstractAs plastic pollution becomes more serious, we need to find out eco‐friendly materials to alleviate the pollution. Polylactide (PLA) and poly (butylene adipate‐co‐terephthalate) (PBAT) will be one of the most attractive materials to replace those undegradable materials. However, few studies research the segregated conductive PLA/PBAT/MWCNTs nanocomposites. Herein, PLA/PBAT/MWCNTs nanocomposites with the segregated structure were successfully fabricated firstly. The MWCNTs are selectively dispersed in the continuous PBAT phase. The nanocomposite with segregated structure owns excellent electric conductivity. When the content of MWCNTs is 0.41 vol%, the electrical conductivity of composites with segregated structure is 9.43 × 10−4 S/m, which is about 5 orders higher than the nanocomposites without the segregated structure (1.75 × 10−10 S/m). The segregated nanocomposite with 2 wt% (1.18 vol%) MWCNTs owns excellent electromagnetic interference (EMI) of 24 dB, while the ordinary structure of composite is only 17 dB.

Extremely high reinforcement of high‐density polyethylene by low loading of unzipped multi‐wall carbon nanotubes

AbstractMulti‐wall carbon nanotubes (MWCNTs) are excellent potential reinforcements for composites due to their high‐mechanical properties. However, a high concentration of MWCNTs is required to reach a good reinforcement. The present study is aimed to show that using unzipped MWCNTs (uMWCNTs) results in an extraordinary enhancement of the mechanical properties of high‐density polyethylene (HDPE). Using 0.2% wt/wt of uMWCNTs as a filler increases the tensile strength and Young's modulus of HDPE by more than 100%. Transmission electron microscopy (TEM), X‐ray diffraction, Raman, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy (XPS), and differential scanning calorimeter (DSC) studies show that the structure and functionality of uMWCNTs and HDPE matrix preserve for their composites. The enhancement in the mechanical properties is mainly associated with an interfacial interaction between separate uMWCNTs sheets and HDPE matrix resulting in increasing the degree of crystallinity and decreasing the crystallite size. Our study provides a new way to fabricate high‐performance composite materials with a low concentration of carbon nanostructures.

Performance evaluation of convective heat transfer and laminar flow of non-Newtonian MWCNTs in a circular tube

Nanofluids are often designed to improve their heat transfer characteristics. However, there are some challenges regarding the increase in their viscosity and the change of the rheology. Therefore, this study investigates the laminar flow of non-Newtonian MWCNTs nanofluids in a circular tube under a constant wall heat flux condition. The rheological behavior and thermal conductivity of the nanofluids are modelled using suitable correlations derived from an experimental database. A numerical approach by finite volume method (FVM) is used for modelling the heat transfer and the laminar flow conditions in this study. The thermal behavior and the non-Newtonian characteristics of the MWCNTs nanofluids are evaluated concerning heat transfer, pressure drop and the overall energy efficiency of the system. The obtained results show that the heat transfer performance is enhanced by adding nanoparticles to the base fluid, reporting an average heat transfer enhancement of about 8.7% and 12.4% for 0.25% and 0.5% concentrations of MWCNTs, respectively. Also, it was found an average increase in pressure drop of about 9.1% and 15.3% for 0.25% and 0.5% concentrations of MWCNTs, respectively. Moreover, the overall energy efficiency of the system is enhanced by using MWCNTs nanofluids for high Reynolds number (1000 ≤ Re ≤ 2000), reaching a maximum enhancement at Re = 1000. The methodology here developed and validated, establishes an important breakthrough concerning modelling and prediction of MWCNTs nanofluids towards its tailoring for subsequent heat transfer studies and applications.

Increasing electrical conductivity of PMMA-MWCNT composites by gas phase iodination

A highly electrical conductive multi-walled carbon nanotubes based polymer composite is fabricated by iodine doping. Selective localization of carbon nanotubes in polymethyl methacrylate was obtained by intensive dry mixing of polymer and nanotubes powders followed by hot pressing. The electrical conductivity of the materials was significantly increased (10–100%) when the composites were treated with iodine by the gas phase. The electrical conductivity of the materials was significantly increased because of MWCNTs addition from the value not higher than about 10−15 to about 10−2 S/cm. The addition of iodine leads to an additional increase in electrical conductivity by 10–100%, depending on the content of MWCNTs. It is interesting to note that a more effective increase in electrical conductivity is observed at low MWCNTs concentrations. An interesting result of the work is the presentation of the fact that iodine is uniformly absorbed in the bulk of the composite filled with nanotubes; in the case of an unfilled polymer, iodine is deposited only on the sample surface. The percolation nature of the conductivity of the investigated composites was found and the percolation threshold was calculated. It was shown that the percolation threshold does not significantly change after iodination. Thus, in this work, we have shown the possibility of simple technology for producing composites with a spatial localized distribution of carbon nanotubes, providing high conductivity (2.86 × 10−2 S/cm) and a low percolation threshold (about 0.37% vol.) at the MWCNTs content of 1.55% vol.

Mechanical and thermal properties of spark plasma sintered Alumina-MWCNTs nanocomposites prepared via improvised colloidal route

This paper concentrates on the fabrication of Al2O3-MWCNTs composites by spark plasma sintering at temperature of 1400 °C by varying the percentage of MWCNTs and alumina through colloidal route. The effect of incorporating MWCNTs into Al2O3 were examined for physical, mechanical, and thermal properties and characterised using techniques like scanning electron microscopy, X-ray diffraction and elemental analysis. The characterized composites corresponded towards the phases of α-Al2O3 and carbon which were further confirmed through SEM and EDS. Densification behaviour of the nanocomposites revealed reduction in relative density with increase in MWCNTs content. Mechanical properties like Vickers hardness, fracture toughness and flexural strength of composites were analysed along with its thermal and wear behaviour under varying load and sliding distance. Composites with MWCNTs incorporation led to enhanced mechanical properties with 1 wt% reinforced Al2O3 demonstrating superior hardness (17.26 ± 0.4 GPa), fracture toughness (KIC = 5.6 ± 0.3 MPa m1/2) and flexural strength (515 ± 33 MPa) compared to the monolithic Al2O3.

Rheological, Dynamic and Tensile Mechanical Properties of Recycled Styrofoam Loaded with Carbon Nanotubes

Styrofoam was recycled and then loaded with different volume fractions of multiwalled carbon nanotubes (MWC-NTs). The frequency dependence of complex viscosity η*, storage modulus E/ and loss modulus E// were studied. All of them were increased with increasing MWCNTs concentration. The dependence of the complex viscosity on CNTs concentration was found to obey the rheological percolation behavior with low percolation threshold and depends on frequency. The addition of MWCNTs to recycled Styrofoam did not change the glass transition temperature. The tensile properties of all composites were studied at different temperatures. Stress-strain curves at temperatures 30, 50, 70 and 90 °C showed brittle behavior. The elastic modulus, ultimate strength, strain at break, and energy density to break were increased with increasing both CNTs concentration and temperature up to 90 °C. The elastic modulus had a tensile percolation behavior with a threshold value close to that obtained for η*. Plastic deformation of all composites took place at 105 °C and sharp decrease in both E and σb was observed. Conversely, sharp increase in both strain at break and energy density to break was observed at temperature 105 °C. The material at this temperature was converted from polydomain to monodomain configuration.

Tailoring nano-copolymer/CNTs composite and its application in drug delivery

This work aimed to overcome the main drawbacks of some essential anticancer drugs as 5-Fluorouracil (5-FU) by controlled loading with novel drug carriers. By a differential microemulsion technique, nanosized particles derived from a copolymer of poly(methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA)) with different monomer ratios have been synthesized and used as a drug carrier. Poly(MMA-co-HEMA)/MWCNT nanocomposite was also synthesized using an in-situ microemulsion polymerization technique and used as a 5-FU carrier. Different techniques have characterized these ground-breaking drug delivery systems such as FT-IR, XRD, TEM, TGA, zeta potential, and a particle size analyzer. The effects of monomer feed composition, 5-FU content, and MWCNTs content on morphological and structural properties, in-vitro 5-FU release, and entrapment efficiency (EE%) have been studied. It was noted that the inclusion of MWCNTs in the 5-FU-loaded polymer increases the thermal stability and raises the entrapment efficiency (EE%) to hit 99% at CNTs:5-FU ratio of 2:1. The anticancer drug release from the co-polymeric nanospheres depends on the HEMA ratio, 5-FU/copolymer ratio, CNT/5-FU ratio, and the pH of the medium. The optimized nanocomposite demonstrated higher anti-tumor activity against the cell lines CaCo-2, MCF-7, and HepG-2 and higher cytotoxicity against HepG-2 relative to CaCo-2 and MCF-7.

Electro-codeposition and properties of Cu–Ni-MWCNTs composite coatings

ABSTRACT In this work, multi-walled carbon nanotubes reinforced Cu–Ni matrix (Cu–Ni-MWCNTs) composite coatings were produced using the electro-codeposition method by adding different concentrations of MWCNTs (0.05, 0.1 and 0.15 g L−1) to the Cu–Ni plating bath. To achieve effective dispersion of the MWCNTs, the plating solution was stirred using an ultrasonicator (20 kHz and 500 W) for 120 min. Cu–Ni-MWCNTs composite coatings were characterised by scanning electron microscopy and X-ray diffraction to study the surface morphology and microstructure of the coatings. In addition, the effects of MWCNTs on the microhardness, wear resistance and electrical conductivity of the coating were investigated by microhardness tester, pin on disk wear tester and four-point probe system respectively. All Cu–Ni-MWCNTs composite coatings showed enhanced microhardness and wear performance as compared to the Cu–Ni coating. The Cu–Ni-MWCNT (0.15 g L−1) composite coating exhibited maximum microhardness of 438 HV and minimum wear loss of 0.9 mg among all the coatings, in the same pin-on-disk test conditions, which is attributed to the combined effect of microstructural refinement, higher content of MWCNTs and superior properties of MWCNTs. Electrical studies reveal that MWCNTs play a vital role in increasing electrical conductivity by 1.21 times of magnitude.