Length Of Multi-walled Carbon Nanotubes Research Articles

Effect of surface-active substances on the macrodispersion behavior of thermal stress-modified multi-wall carbon nanotubes in cryogenic environments

In the preparation of nanocomposites, the agglomeration of multi-walled carbon nanotubes (MWCNTs) in the composite due to their low colloidal stability limits their use in industrial areas. To overcome these problems, it is important to develop simpler, economical, high-yield and non-hazardous techniques to replace existing techniques with low yields, expensive additional equipment or hazardous liquids. This study explores how surfactants affect the macrodispersion of thermal stress-modified MWCNTs in cryogenic environments, focusing on their application in polymer film preparation. Firstly, optimal conditions for modifying MWCNTs through thermal stress were identified using liquid nitrogen. Parameters assessed included the number of cycles (2, 4, and 6), duration in liquid nitrogen (10, 20, and 30 min), and subsequent waiting time at room temperature (5, 12, and 20 min). Results showed that the highest surface area was obtained with 2 cycles, 20 min in liquid nitrogen, and 5 min at room temperature. Analytical techniques such as Brunauer-Emmett-Teller (BET), X-Ray Diffraction (XRD), High Contrast Transmission Electron Microscopy (CTEM) and Raman spectroscopy were used to evaluate the functionalization process's effects on MWCNTs' internal graphitic structure and physicochemical properties. CTEM micrographs indicated that thermal stress reduced the length of MWCNTs, while Raman analysis showed improved graphite quality. The modification process, carried out with 100 % efficiency and no sample loss, increased the BET surface area from 297.551 m2/g to 397.295 m2/g. The study also investigated the impact of surfactants (polyethylene glycol sorbitan monooleate-Tween 80, sodium dodecyl sulfate-SDS, and hexadecyltrimethylammonium bromide-CTAB) on MWCNTs' macrodispersion degrees (DM%) and energy band gaps via UV–visible (UV–Vis) absorption spectroscopy. CTAB provided the highest and most stable macrodispersion, reducing the energy band gaps of MWCNTs from 5.65 to 5.75 eV to 3.53–3.60 eV. CTAB showed excellent colloidal stability with a zeta potential of 44.2 mV, while SDS had −49.9 mV. Polyvinyl alcohol (PVA) polymer films, created using MWCNT solutions with optimal macrodispersion, were confirmed by Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimeters (DSC), and BET surface area analyses to have successfully and homogeneously incorporated MWCNTs. In addition to the superior properties of MWCNTs modified with the functionalization technique developed within the scope of this study by increasing their specific surface area and porosity, the excellent colloidal stability provided may have various effects in many industrial areas. These advantages enable MWCNTs functionalized with the developed technique to have a wider range of applications in industrial applications and provide more efficient and sustainable solutions.

Influence of Twin Screw Extrusion Conditions on MWCNT Length and Dispersion and Resulting Electrical and Mechanical Properties of Polycarbonate Composites

The processing conditions were varied during the production of polycarbonate-based composites with the multiwalled carbon nanotubes (MWCNTs) Baytubes® C150 P (Bayer MaterialScience AG, Leverkusen, Germany), by melt mixing with an extruder on a laboratory scale. These included the screw design, rotation speed, throughput, feeding position and MWCNT content. Particular attention was paid to the shortening of the MWCNT length as a function of the conditions mentioned. It was found that there is a correlation between the applied specific mechanical energy (SME) during the melt mixing process and MWCNT dispersion, which was quantified by the agglomerate area ratio of the non-dispersed nanotubes based on optical microscopic analysis. The higher the SME value, the lower this ratio, which indicates better dispersion. Above an SME value of about 0.4 kWh/kg, no further improvement in dispersion was achieved. The MWCNT length, as measured by the quantitative analysis of TEM images of the MWCNTs dissolved from the composites, decreased with the SME value down to values of 44% of the original MWCNT length. At a constant loading of 3 wt.%, the tensile strength and tensile modulus were almost independent of the SME, while the elongation at break and notched impact strength showed an increasing trend. The variation in the feeding position showed that feeding the MWCNTs into a side feeder led to slightly better electrical and mechanical properties for both types of MWCNTs studied (Baytubes® C150 P and Nanocyl™ NC7000 (Nanocyl S.A., Sambreville, Belgium)). However, feeding into the hopper led to better CNT dispersion with Baytubes® C150 P, while this was the case with Nanocyl™ NC7000 when feeding into the side feeder. The screw profile had an influence on the dispersion, the MWCNT length and the electrical resistance, but only to a small extent. Distributive screws led to a greater shortening of the MWCNT length than dispersive screws. By varying the MWCNT content, it was shown that a greater MWCNT shortening occurred at higher loadings. Two-stage masterbatch dilution leads to stronger shortening than composite production with direct MWCNT incorporation.

Mechanical improvement of carbon fiber/epoxy composites by sizing functionalized carbon nanotubes on fibers

AbstractA sizing agent mainly consisting of polyethersulfone and acidified multi‐walled carbon nanotubes (MWCNT) was developed for surface modification of carbon fibers (CF) to enhance the interfacial bond and to form carbon fiber‐carbon nanotube (CF‐MWCNT) multiscale reinforcements. To prepare the modified carbon fiber/epoxy resin composites (CFRP), a vacuum molding technique was used in this study. The effects of the MWCNT‐containing sizing agent on the morphology and chemical structure of the CF surface were observed by scanning electron microscopy and Fourier transform infrared spectroscopy. The influence of MWCNT length and content on the mechanical properties of CFRP were also studied. The experimental results showed that the strength of the CFRP decreased with the increase of MWCNT length, and the MWCNT with a content of 0.05 wt% had a good reinforced effect on the CFRP. After the sizing treatment, the interlaminar shear strength (ILSS) of the CFRP is increased. These enhancements are attributed to the improved mechanical bonding and chemical bonding between CF and resin matrix. The MWCNT provides nanosized rough surface to CF and these acidified MWCNTs attached to the surface of CF with polar oxygen‐containing functional groups improve the compatibility with reinforcement and resin matrix.Highlights Carbon fiber was modified by a sizing agent mainly consisting of polyethersulfone and acidified carbon nanotube (CNT). CNTs enhance the interfacial chemical bonding and mechanical bonding. The CNT length affects the mechanical properties of the carbon fiber/epoxy resin composites (CFRP). The modified carbon fiber has enhanced the mechanical properties of the CFRP.

Effect of size of multiwalled carbon nanotubes on thermal conductivity and viscosity of ethylene glycol-based nanofluids for solar thermal applications

The paper investigates the influence of the length of multi-walled carbon nanotubes (MWCNTs) dispersed as an additive in solar thermic fluids to enhance thermal conductivity. Here, pure ethylene glycol was chosen as solar thermic fluid due to its low viscosity, high boiling point, excellent chemical stability, and compatibility with the materials used in solar thermal systems. Pristine multi-walled carbon nanotubes are ball milled for 5, 10, and 20 h to reduce the length due to attrition. The effect of ball milling duration on the defect formation and damage to the tubular structure is assessed using Raman spectroscopy. Furthermore, the ball-milled MWCNTs were oxidized to separate amorphous carbon produced during ball milling, increasing their purity. The pristine long nanotubes and ball-milled nanotubes are mixed in pure ethylene glycol in 0.25 wt. %, and the stability of liquids is estimated using Ultraviolet–Visual (UV-Vis) spectroscopy for two months. The stability of the fluids and thermal conductivity have considerably enhanced with the dispersion of shortened MWCNTs. The dispersion of short MWCNTs in ethylene glycol resulted in a 20%–30% increase in thermal conductivity compared to pure ethylene glycol. It was also found that higher ball milling times resulted in ultra-high stability but the properties deteriorated due to the destruction of the MWCNTs' tubular structure, making them useless.

Effect of multiwalled carbon nanotube size on electrical properties of cement mortar composites

Cement mortars (CM) containing different contents and sizes of multiwalled carbon nanotubes (MWCNTs) were prepared using surfactants in combination with ultrasonic dispersion. The effects of the content, diameter and length of MWCNTs on the electrical conductivity of cement mortar and the self-inductive piezoresistive rate under single and cyclic loading were studied using the four-electrode method. The results show that the conductive percolation thresholds of CMs containing MWCNTs with different length–diameter ratios occur at an approximate MWCNT content of 0.1 wt%. The electrical conductivity of cement mortars with MWCNT diameters of 10–20 nm was the largest for a content of 0.1 wt%, and the values were 112% and 128.3% of the conductivity of the MWCNTs/CM with diameters of 20–40 nm and 40–60 nm, respectively. In addition, the fractional change in resistivity of the cement mortar specimens varied most significantly at a content of 0.75 wt% of MWCNTs; the fractional change in resistivity reached 14.27%. Adding small-diameter MWCNTs to cement mortar can maximise the sensitivity of electrical resistance of cement mortar to compressive stress.

Microwave absorption performance of MWCNTS derived from plant based oil

The carbon nano structure (CNS) have excellent dielectric properties and hence shows better microwaveabsorbingperformance. The economically obtained CNS are efficient microwave absorbing materials (MAMs) demonstrate a big potential in industrial and defense application. The synthesis of CNS from Plant based precursors has become one of the newest approach in the field ofmicrowaveabsorption due to its economical, immense availability and sustainability. Chemical Vapour deposition (CVD) is most utilized method to synthesize Multiwall Carbon Nano Tubes (MWCNTs) using plant based oil due to its easy to control experiment condition, economical, controllable diameters and better yield compare to others methods.Plant-based precursors i.e., Olive oil was used as source of carbon to obtained MWCNTs over Ni-Co catalyst in inert atmosphere of Hydrogen gas. Acid treated MWCNTs were characterized using XRD, FEG-SEM, EDAX, HR-TEM. The average diameter and length of MWCNTs are 48 nm and 736 nm, respectively. MWCNTs/Acrylic composite with 9 wt% and 3.8 mm thickness, shows an optimal Reflection loss (RL) value of −44.0 dB at 10.9 GHz. The effective absorption (RL ≤ -20 dB) has a bandwidth of 10.14–11.59 GHz.

Influence of CNT Length on Dispersion, Localization, and Electrical Percolation in a Styrene-Butadiene-Based Star Block Copolymer.

This study followed the approach of dispersing and localizing carbon nanotubes (CNTs) in nanostructured domains of block copolymers (BCPs) by shortening the CNTs via ball milling. The aim was to selectively tune the electrical and mechanical properties of the resulting nanocomposites, e.g., for use as sensor materials. Multiwalled carbon nanotubes (MWCNTs) were ground into different size fractions. The MWCNT length distribution was evaluated via transmission electron microscopy and dynamic light scattering. The nanostructure of the BCPs and the glass transition temperatures of the PB-rich and PS phases were not strongly affected by the addition of CNTs up to 2 wt%. However, AFM and TEM investigations indicated a partial localization of the shortened CNTs in the soft PB-rich phase or at the interface of the PB-rich and PS phase, respectively. The stress-strain behavior of the solution-mixed composites differed little from the mechanical property profile of the neat BCP and was largely independent of CNT amount and CNT size fraction. Significant changes could only be observed for Young’s modulus and strain at break and may be attributed to CNT localization and small changes in morphology. For nanocomposites with unmilled CNTs, the electrical percolation threshold was less than 0.1 wt%. As the CNTs were shortened, the resistivity increased and the percolation threshold shifted to higher CNT contents. Composites with CNTs ground for 7.5 h and 13.5 h showed no bulk conductivity but significantly decreased surface resistivity on the bottom side of the films, which could be attributed to a sedimentation process of the grind and thereby highly compressed CNT agglomerates during evaporation.

Evaluation and modeling of electrical conductivity in conductive polymer nanocomposite foams with multiwalled carbon nanotube networks

Conductive filler/polymer composite foams (CPC) with micro-/nano-scale bubbles have attracted much attention due to their various advantages. Understanding the evolution of electrical behavior in CPC foams is important for their functional application. There have been many experimental investigations of the electrical behavior of CPC foams, but how the electrical conductivity varies with bubble growth is not fully understood. Here, a novel resistive network model based on Monte Carlo simulation to directly predict the electrical conductivity of CPC foams is reported. The model uses multiwalled carbon nanotubes (MWCNTs) as a conductive filler and considers both the intrinsic electrical conductivity of the nanotubes and the electron tunneling effect. The model predictions agreed very well with the experimental data for both the solid and foamed composites. The results showed that the percolation threshold and the conductivity are strongly affected by the relative sizes of MWCNT length and bubble diameter. At relatively low void fractions (up to ~20%), the growth of bubbles with size comparable to the MWCNT length increased the conductivity. Further growth of cells (>30%) resulted in a gradual decrease in the conductivity. This model can be used in the design and optimization of conductive foams.

Synthesis and characterization of multi-walled carbon nanotubes decorated with hydroxyapatite

In this paper, multi-walled carbon nanotubes have been prepared at low synthesis temperatures and without high pressure by a simple chemical route. Fourier transformed infrared spectroscopy, Raman spectroscopy and X-ray diffraction analysis was used to determine the purity of the synthetized compound. Also, by transmission electron microscopy and atomic force microscopy, a diameter between 9 nm and 43 nm and approximately 500–600 nm in length of multi-walled carbon nanotubes, was confirmed. Further, the multi-walled carbon nanotubes functionalized with negative charged functional groups (anionic groups) were decorated with hydroxyapatite by co-precipitation method. The decoration of multi-walled carbon nanotubes with hydroxyapatite was confirmed by transmission electron microscopy, Fourier transformed infrared spectroscopy and X-ray diffraction analysis. Also, energy-dispersive X-ray analysis proved the successfully obtaining of the nanocomposites. The simple method presented here may be extended to synthesize other composites based on coated multi-walled carbon nanotubes.

A systematic investigation of dispersion concentration and particle size distribution of multi-wall carbon nanotubes in aqueous solutions of various dispersants

Surfactant-assisted exfoliation of multi-walled carbon nanotubes (MWNTs) in aqueous solution have become a common procedure to generate high fraction of individualized nanotubes. Since well-controlled experimental methodologies and reliable comparative metrics are scarce, a systematic research was conducted in order to analyze the dispersibility and the dispersing mechanisms of MWNTs in aqueous solutions of various surfactants. The concentration of dispersed MWNTs was accurately measured for a wide range of surfactant concentration, using combined UV–vis spectroscopy and thermogravimetric analysis (TGA). The obtained dispersibility results indicated that the highest dispersion concentration and efficiency is achieved in the SDBS-assisted MWNTs dispersion. Furthermore, the nanotube morphology and surfactant properties can be evaluated and rationalized by analyzing the dispersed nanotube mass and the surfactant amount per nanotube surface area. The amount of dispersed MWNTs remaining after varying levels of sonication and centrifugation was investigated, and a controllable sonication-centrifugation method for the preparation of well-dispersed MWNTs was established. The experimental data of the concentration of MWNTs dispersions versus centrifugation speed (ω) are fitted reasonably well by a Boltzmann function. The SDBS-assisted MWNTs dispersion will be more susceptible to the high centrifugal speed,while PVP-assisted MWNTs dispersion will be sediment fast at the mild centrifugation. The distributions of diameter and length of MWNTs at maximum dispersibility show that the sizes for the MWNTs dispersed by SDBS are much more polydisperse. The results further suggest that preparation of controllable carbon nanotubes morphology and design of rational configuration of surfactants are the key factors for increasing the dispersion stability and maximum concentration of well-dispersed MWNT.

Graphene oxide-assisted multi-walled carbon nanotube reinforcement of the transport properties in cementitious composites

The superior mechanical properties of multi-walled carbon nanotubes (MWCNTs) and prominent dispersibility of graphene oxide (GO) make their hybrid materials have the potential capability for modifying the transport properties of cementitious composites. GO sheets will produce π–π stacking interactions between MWCNTs which not only assist the dispersion but also inhibit the re-agglomeration of the materials. However, as one type of tough two-dimensional materials, GO sheets would cut down the tube length of MWCNTs at the same time, particularly during the ultrasonication process. Thereby, this study characterizes the influence of GO on the dispersion and hydrodynamic size of the hybrid particles using an ultraviolet–visible spectrophotometer and laser particle-size analyzer, respectively. The transport properties of GO/MWCNTs-OPC pastes containing different ratios of hybrid materials were measured, and their microstructure was investigated by mercury intrusion porosimetry and scanning electron microscopy (SEM). The results of this study confirm that 0.02 wt% GO mixed into 0.04 wt% MWCNTs would balance the dispersion-assisted and nanoparticle cutdown effects well and obtain the optimal decrease in resisting water permeability of the materials, about 55.3%, while excessive GO mixing may deteriorate particle-size and influence reinforcing efficiency. Two analytical models and SEM images reveal the mechanism of transport properties reinforcement; GO/MWCNTs not only play a significant role as nucleating sites in assisting the hydration reaction but also form a net-like distribution in the microstructure of cementitious composites. The findings of this study can guide GO/MWCNTs hybrid composite implementation in the future.

Electromagnetic interference shielding behavior of hybrid carbon nanotube/exfoliated graphite nanoplatelet coated glass fiber composites

We investigated the tailored electromagnetic interference shielding effectiveness (EMI SE) of polyester-matrix composites consisting of glass fiber textiles coated with multiwalled carbon nanotubes (MWCNTs) and exfoliated graphite nanoplatelets (xGnPs). The effects of various combinations of material parameters, including MWCNT length, xGnP size, MWCNT:xGnP weight ratio, host-substrate surface configuration of carbon nanomaterials (CNMs), and their amount coated per unit area, on the EMI SE were studied. The shielding mechanisms, namely, absorption, reflection, and multiple reflections, are discussed based on the underlying governing physics. EMI SE measurements showed that coating glass fibers with hybrid MWCNTs/xGnPs at 8/2 ratio yields EMI SEs higher than those of composites containing the same content of a single-type of CNM, ranging from 56.8 dB at 30 MHz to 35.3 dB at 1.5 GHz. Morphological studies showed that, upon placement on glass fiber surfaces, 1D fiber-like MWCNTs serve as interconnects that bridge the randomly oriented 2D platelet-like xGnPs to form an efficient plane shield of electromagnetic waves.

Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating

The concerns regarding potential environmental release and ecological risks of multi-walled carbon nanotubes (MWCNTs) rise with their increased production and use. As a result, there is the need for an analytical method to determine the environmental concentration of MWCNTs. Although several methods have been demonstrated for the quantification of well-characterized MWCNTs, applying these methods to field samples is still a challenge due to interferences from unknown characteristics of MWCNTs and environmental media. To bridge this gap, a recently developed microwave-induced heating method was investigated for the quantification of MWCNTs in field samples. Our results indicated that the microwave response of MWCNTs was independent of the sources, length, and diameter of MWCNTs; however, the aggregated MWCNTs were not able to convert the microwave energy to heat, making the method inapplicable. Thus, a pre-treatment process for dispersing bundled MWCNTs in field samples was crucial for the use of the microwave method. In the present paper, a two-step pre-treatment procedure was proposed: the aggregated MWCNTs loaded environmental samples were first exposed to high temperature (500°C) and then dispersed by using an acetone-surfactant solution. A validation study was performed to evaluate the effectiveness of the pre-treatment process, showing that an 80-120% recovery range of true MWCNT loading successfully covered the microwave-measured MWCNT mass.

Effect of carbon nanotube length on the piezoresistive response of poly (methyl methacrylate) nanocomposites

Multiwall carbon nanotubes (MWCNTs) were systematically fragmented using high density ultrasonic energy and used as fillers of a poly (methyl methacrylate) matrix (PMMA). MWCNT fragmentation was confirmed by scanning electron microscopy and atomic force microscopy. Dedicated MWCNT length measurements yielded a log-normal statistical distribution, with mean value of 1.33 μm for the as-received MWCNTs and 0.66 μm for the fragmented MWCNTs. Higher electrical percolation threshold and lower electrical conductivity were obtained for MWCNT/PMMA composites (0.01–1 wt.% MWCNT concentration) using the fragmented MWCNTs. Higher electro-mechanical (piezoresistive) sensitivity under tensile tests was measured for PMMA nanocomposites with fragmented MWCNTs, which was explained by a competition of mechanisms related to the MWCNT length.

Immunological impact of graphene oxide sheets in the abdominal cavity is governed by surface reactivity

Graphene oxide (GO) is an oxidised form of graphene that has attracted commercial interest in multiple applications, including inks, printed electronics and spray coatings, which all raise health concerns due to potential creation of inhalable aerosols. Although a number of studies have discussed the toxicity of GO sheets, the in vivo impact of their lateral dimensions is still not clear. Here, we compared the effects of large GO sheets (l-GO, 1–20 µm) with those of small GO sheets (s-GO, < 1 µm) in terms of mesothelial damage and peritoneal inflammation, after intraperitoneal (i.p.) injection in mice. To benchmark the outcomes, long and rigid multi-walled carbon nanotubes (MWCNTs) that were shown to be associated with asbestos-like pathogenicity on the mesothelium were also tested. Our aim was to assess whether lateral dimensions can be a predictor of inflammogenicity for GO sheets in a similar fashion as length is for MWCNTs. While long MWCNTs dispersed in 0.5% BSA induced a granulomatous response on the diaphragmatic mesothelium and immune cell recruitment to the peritoneal cavity, GO sheets dispersed under similar conditions did not cause any response, regardless of their lateral dimensions. We further interrogated whether tuning the surface reactivity of GO by testing different dispersions (5% dextrose instead of 0.5% BSA) may change the biological outcome. Although the change of dispersion did not alter the impact of GO on the mesothelium (i.e. no granuloma), we observed that, when dispersed in protein-free 5% dextrose solution, s-GO elicited a greater recruitment of monocytic cells to the peritoneal cavity than l-GO, or when dispersed in protein-containing solution. Such recruitment coincided with the greater ability of s-GO to interact in vivo with peritoneal macrophages and was associated with a greater surface reactivity in comparison to l-GO. In conclusion, large dimension was not a determining factor of the immunological impact of GO sheets after i.p. administration. For an equal dose, GO sheets with lateral dimensions similar to the length of long MWCNTs were less pathogenic than the MWCNTs. On the other hand, surface reactivity and the ability of some smaller GO sheets to interact more readily with immune cells seem to be key parameters that can be tuned to improve the safety profile of GO. In particular, the choice of dispersion modality, which affected these two parameters, was found to be of crucial importance in the assessment of GO impact in this model. Overall, these findings are essential for a better understanding of the parameters governing GO toxicity and inflammation, and the rational design of safe GO-based formulations for various applications, including biomedicine.

Influence of different hydrocarbons on the height of MWCNT carpets: Role of catalyst and hybridization state of the carbon precursor

The length of multi-walled carbon nanotubes (MWCNT) has a particular relevance for a wide range of application. To that end, in an aerosol assisted chemical vapour deposition process MWCNT carpets with different heights were synthesized on an oxidized silicon substrate by using ferrocene as Fe-catalyst precursor and some hydrocarbons with different hybridization state. By variation of the synthesis temperature from 600 °C up to 900 °C, for every used hydrocarbon different carpet heights were measured depending on the temperature. Cyclohexane generated the highest MWCNT carpets and for all carbon precursor the maximum carpet height was measured at 850 °C. To elucidate this, the thermal decomposition of the used hydrocarbons was discussed and the corresponding main decomposition products methane, ethene and benzene were identified. Subsequently, these substances were directly used in a second chemical vapour deposition equipment to simulate the growth mechanism by the intermediate carbon precursors. It was found, that with comparable content of carbon in the gas phase, ethene is much higher efficient for growing high MWCNT carpets than methane. Moreover, benzene was figured out to be also an adequate carbon precursor under specific gas phase conditions, explaining the carpet heights when using toluene and xylene.

Carbon nanotubes reinforced reactive powder concrete

In this paper, four types of multi-walled carbon nanotubes (MWCNTs) were incorporated into reactive powder concrete (RPC) with water or heat curing. The enhancing effects of MWCNT types and curing methods on mechanical properties of RPC were investigated. Experimental results indicate that adding proper type and content of MWCNTs can effectively improve mechanical properties of RPC including flexural strength, fracture energy, compressive strength/toughness and flexural strength to compressive strength ratio. In general, these mechanical properties of MWCNTs filled RPC with heat curing are superior to that with water curing, which indicates that heat curing is more beneficial for reinforcing impact of MWCNTs to RPC than water curing. In most cases, the critical length of MWCNTs in RPC is smaller than actual length, which indicates MWCNTs will be snapped when damage occurs in RPC. In addition, the reinforcement of MWCNTs to RPC results from crack bridging and pull out effects.

Size-dependent thermal properties of multi-walled carbon nanotubes embedded in phase change materials

This study has focused on the systematical investigation of effect of mass fraction and size of multi-walled carbon nanotubes (MWCNTs) doped in phase change material (PCM) on thermal properties such as thermal conductivity, melting/solidification temperatures and latent heats. Thermal conductivity, melting/solidification temperatures and latent heats of MWCNTs/PCM composites with three different diameters and two different lengths, obtained by doping MWCNTs into PCM at the mass fraction of 1–5%, were evaluated according to the criteria such as particle size and mass fraction. The results demonstrated that not only mass fractions but also size of MWCNTs are effective on the thermal properties of the composites. It was concluded that increase in diameter and length of MWCNTs positively affects enhancement of thermal conductivity; on the other hand, it does not cause a significant change at melting/solidification temperatures. In addition to these, a decline was observed at melting/solidification latent heats of MWCNTs/PCM composites, depending on doped mass fractions of MWCNTs.

Preparation of PEEK/MWCNTs composites with excellent mechanical and tribological properties

The high strength of multiwalled carbon nanotubes (MWCNTs) indicates promising properties for industry applications to reduce frictional coefficient and improve mechanical properties, yet few researches have referred to its structural morphology on the thermal, mechanical, and tribological properties of composites. In this work, three different lengths of MWCNTs were used to prepare polyether ether ketone (PEEK) composites and investigate the effect of structural morphology of MWCNTs on the thermal, mechanical, and tribological properties of composites. Different lengths of MWCNTs endowed PEEK composites with different thermal, mechanical, and tribological properties. On thermal and mechanical properties, the incorporation of 10–30 μm length of MWCNTs increased more the effectiveness on the crystallization rate, showing a higher crystallization temperature and the best mechanical properties of the PEEK composites. On tribological properties, approximately 50 μm MWCNTs can effectively decrease adhesive wear, which is a benefit of forming a thin transfer film, thereby effectively decreasing the coefficient of friction and improving the wear resistance.

The adverse vascular effects of multi-walled carbon nanotubes (MWCNTs) to human vein endothelial cells (HUVECs) in vitro: role of length of MWCNTs

BackgroundIncreasing evidences indicate that exposure to multi-walled carbon nanotubes (MWCNTs) could induce adverse vascular effects, but the role of length of MWCNTs in determining the toxic effects is less studied. This study investigated the adverse effects of two well-characterized MWCNTs to human umbilical vein endothelial cells (HUVECs).MethodsThe internalization and localization of MWCNTs in HUVECs were examined by using transmission electron microscopy (TEM). The cytotoxicity of MWCNTs to HUVECs was assessed by water soluble tetrazolium-8 (WST-8), lactate dehydrogenase (LDH) and neutral red uptake assays. Oxidative stress was indicated by the measurement of intracellular glutathione (GSH) and reactive oxygen species (ROS). ELISA was used to determine the release of inflammatory cytokines. THP-1 monocyte adhesion to HUVECs was also measured. To indicate the activation of endoplasmic reticulum (ER) stress, the expression of ddit3 and xbp-1s was measured by RT-PCR, and BiP protein level was measured by Western blot.ResultsTransmission electron microscopy observation indicates the internalization of MWCNTs into HUVECs, with a localization in nuclei and mitochondria. The longer MWCNTs induced a higher level of cytotoxicity to HUVECs compared with the shorter ones. Neither of MWCNTs significantly promoted intracellular ROS, but the longer MWCNTs caused a higher depletion of GSH. Exposure to both types of MWCNTs significantly promoted THP-1 adhesion to HUVECs, accompanying with a significant increase of release of interleukin-6 (IL-6) but not tumor necrosis factor α (TNFα), soluble ICAM-1 (sICAM-1) or soluble VCAM-1 (sVCAM-1). Moreover, THP-1 adhesion and release of IL-6 and sVCAM-1 induced by the longer MWCNTs were significantly higher compared with the responses induced by the shorter ones. The biomarker of ER stress, ddit3 expression, but not xbp-1s expression or BiP protein level, was significantly induced by the exposure of longer MWCNTs.ConclusionsCombined, these results indicated length dependent toxic effects of MWCNTs to HUVECs in vitro, which might be associated with oxidative stress and activation of ER stress.