Pristine Multi-walled Carbon Nanotubes Research Articles

Adsorption of Triclocarban on Pristine and Irradiated MWCNTs in Aqueous Solutions

The adsorption of triclocarban was investigated on pristine and irradiated MWCNTs, at different temperatures, in aqueous synthetic samples at different pH values and for different concentrations of humic acid (HA) from natural organic matter. Commonly used models of the adsorption isotherms, Freundlich and Langmuir were selected to fit the experimental data. The effects of TCC concentration, of the temperature and of the concentration of humic acid from natural organic matter were tested to study the impact of the environmental conditions over the sorption process.

High Efficiency Crumpled Carbon Nanotube Heaters for Low Drift Hydrogen Sensing.

This work presents the fabrication of crumpled carbon nanotubes (C-CNTs) thin film heaters and their application towards high sensitivity and low drift hydrogen gas sensing. Utilizing a spray coating of pristine multi-walled carbon nanotubes (MWCNTs) and thermal shrinkage of polystyrene (PS) substrate, we have fabricated C-CNTs with closely packed junctions. Joule heating of C-CNTs gives higher temperature at a given input voltage compared to as-deposited CNTs. In addition, temperature coefficient of resistance (TCR) is analyzed for accurate temperature control and measurement of the heater. The C-CNT heaters are capable of hydrogen gas sensing while demonstrating higher measurement sensitivities along with lower drift compared to as-deposited CNT devices. In addition, the self-heating of C-CNT heaters help rapid desorption of hydrogen, and thus allowing repetitive and stable sensor operation. Our findings reveal that both CNT morphologies and heating temperatures affect the hydrogen sensing performances.

Insight to aspirin sorption behavior on carbon nanotubes from aqueous solution: Thermodynamics, kinetics, influence of functionalization and solution parameters

The chronic exposure to the pharmaceuticals and personal care products contaminants in water represent a serious public health problem to man and animal. We studied the removal of aspirin (Asp) as an example to these hazardous materials from an aqueous solution using functionalized (FMCNT) and pristine multiwall carbon nanotubes (PMCNT). The characterization of synthetic sorbents was examined with scanning electron energy-dispersive microscopy and transmission electron microscopy. The effects of adsorption time, sorbent mass, solution pH, ionic strength, and temperature were optimized. The functionalization increased the surface area from 151 to 181 m2 g−1. Consequently, the adsorption capacity increased from 41 mg g−1 to 58 mg g−1 for PMCNT and FMCNT, respectively. The results showed that the adsorption kinetic follows the pseudo-second-order model with very good agreement. Whereas, the adsorption mechanism study showed a partial agreement with the liquid-film diffusion model on PMCNT and FMCNT at 25 °C and 35 °C, respectively, with acceptable linear regression coefficients. The adsorption isotherm results revealed that the adsorption fits the Freundlich model. The thermodynamic study revealed that, Asp adsorption on both sorbents is exothermic, spontaneous and favorable. FMCNT showed relatively high removal efficiency when compared with the PMCNT when used for most of the conditions investigated.

Activity and Durability Study of Carbon Nanotube-Based Anode Electrocatalyst for Water Electrolyzer

Water electrolysis is a promising hydrogen production system because of its high efficiency and cleanness in a carbon-neutral energy cycles, which is followed by the hydrogen production and power generation by fuel cells. Especially, proton exchange membrane water electrolyzers (PEMWEs) are currently the most promising candidate due to their compactness, superior efficiency, better load flexibility, and higher purity of hydrogen than alkaline electrolysis. In the PEMWE anode, iridium oxide (IrOx) is regarded as the most suitable anode electrocatalyst for the four-electron oxygen evolution reaction (OER) compared to the other catalysts such as ruthenium oxide (RuOx) due to its higher chemical stability even under a high anodic polarization in a strong acidic environment. Since Ir is a very expensive metal and scarce resource, it is highly desired to decrease the amount of Ir in the catalysts. Especially, maximizing the surface area of IrOx by minimizing the size of IrOx is the promising strategy to increase the utilization efficiency of the IrOx. However, it has been considered that a carbonbased conductive support such as carbon blacks (CBs) is difficult to use since the operating conditions of the PEMWE anode (> 1.23 V vs. RHE @ 25 °C) are much more positive than the oxidation potential of carbon (C + 2H2O→CO2 + 4H+ + 4e-, 0.207 V vs. RHE) and, therefore, the carbon can be easily oxidized under PEMWE condition. Therefore, large quantities of bulk IrOx powder without any support material are currently used for the anode catalyst, which increases the cost of the PEMWEs. Recently, non-carbon-based electrocatalyst using semiconducting metal oxides with a high surface area and stability in acid, such as SnO2, Ta2O5, SiO2, etc., were investigated. However, since the electrical conductivities of these oxides are not as good as carbon materials, further improvement of the conductivity is strongly required. In this study, we chose multi-walled carbon nanotubes (MWNTs) as a conductive supporting material for the IrOx because of the following reasons; i) MWNTs are composed of sp2 carbon and it was pointed out the oxidation potential of the sp2 carbon is much higher than those of the sp3 carbons, which agreed well with the experimental facts that the MWNTs have a superior electrochemical stability compared to other conductive carbons, ii) we have developed a unique and promising technique to immobilize metal nanoparticles without introducing sp3 carbons into MWNTs; that is, the polymer-wrapping method using polybenzimidazole (PBI) as an anchoring layer on the surfaces of the MWNTs,and iii) PBI-wrapped MWNTs decollated by Pt nanoparticles exhibited an extremely high durability even when they are polarized in the high potential region of 1.0-1.5 V vs. RHE in an acidic electrolyte fuel cell tests. Based on such advantages, we newly developed an electrocatalyst based on IrOx nanoparticles loaded on the PBI-wrapped pristine MWNTs (MWNT/PBI/IrOx).As the result, Very high OER mass activity and durability of the MWNT-based electrocatalyst were found in half-cell and single-cell tests.

Surface modification of MWCNT and its influence on properties of paraffin/MWCNT nanocomposites as phase change material

ABSTRACTMultiwalled carbon nanotubes (MWCNTs) were modified by an organo‐silane in order to improve their dispersion state and stability in paraffin wax. A family of paraffin‐based phase change material (PCM) composites filled with MWCNTs was prepared with different loadings (0, 0.1, 0.5, and 1 wt%) of pristine MWCNTs and organo‐silane modified MWCNTs (Si‐MWCNT). Structural analyses were performed by means of Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and rheological studies using temperature sweeps. Moreover, phase change transition temperatures and heat of fusion as well as thermal and electrical conductivities of the developed PCM nanocomposites were determined. The SEM micrographs and FTIR absorption bands appearing at approximately 1038 and 1112 cm−1 confirmed the silane modification. Differential scanning calorimetery (DSC) results indicate that the presence of Si‐MWCNTs leads to slightly favorable enhancement in the energy storage capacity at the maximum loading. It was also shown that the thermal conductivity of the PCM nanocomposites, in both solid and liquid phases, increased with increasing the MWCNT content independent of the kind of MWCNTs by up to about 30% at the maximum loading of MWCNTs. In addition, the modification of MWCNTs made the samples completely electrically nonconductive, and the electrical surface resistivity of the PCMs containing pristine MWCNTs decreased with increasing MWCNTs loading. Furthermore, the rheological assessment under consecutive cyclic phase change demonstrated that the samples containing modified MWCNTs are more stable compared to the PCM containing pristine MWCNTs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48428.

Characterization of short-length multi-walled carbon nanotubes and cytotoxicity on MDA-MB-231 and HUVEC cell lines

Multi-walled carbon nanotubes (MWNTs) are suitable for delivering large biomolecules with lower cytotoxicity values and low prime cost. Surface modifications of MWNTs affect interaction with cells and proteins. Oxidation with strong acids decreases cytotoxicity of CNTs and increases protein-loading capacity. Here, after oxidation, TEM images revealed more aligned structure and carboxylated groups at the surface which decreases toxicity. Functionalized MWNTs showed more gradual degradation than the pristine MWNTs and mass loss increased by 2% in the same temperature range. Raman spectroscopy corrected graphitic structure with characteristic D and G bands at 1330 and 1579 cm−1 and increased intensity after oxidation. FTIR spectroscopy peaks at 1443 cm−1, 1560, 1640 cm−1, 2100–2200 cm−1 and 3426 cm−1 are ascribed to C–O–C vibrational stretch, C=C bonds, vibration of C≡C bonds and stretch of hydroxyl groups, respectively. The sonication-driven dispersion of in phosphate-buffered saline, distilled water and cell culture medium were detected by UV–vis–NIR spectroscopy, water-dispersed functionalized MWNTs revealed the highest absorbance value. Cytotoxicity of MWNTs was investigated before and after functionalization in breast cancer (MDA-MB-231) and human vein endothelial (HUVEC) cells. Relatively low-toxicity results were obtained in functionalized MWNTs and cellular uptake of MWNTs were corrected with fluorescent imaging of cells and cell lysates. Protein-loading capacity of fsMWNTs (functionalized short-length multi-walled carbon nanotubes) was evaluated by using bovine serum albumin (BSA) and with an equal amount of fsMWNTs and BSA; 36% binding yield was obtained. Protein corona after covalent functionalization potentially lowered cytotoxicity up to 6%.

Influence of multi-walled carbon nanotubes on the toxicity and removal of carbamazepine in diatom Navicula sp.

Information on nanomaterial interactions with co-contaminants, including their influence on toxicity and environment fate in aquatic environment is rather limited. In this study, the effect of multiwall carbon nanotubes (MWCNTs) co-exposure on the toxicity, biodegradation and bioaccumulation of carbamazepine (CAB) in diatom Navicula sp. was evaluated. Results showed that the three tested MWCNTs showed high sorption capability of CAB, especially for hydroxyl-functionalized MWCNT (OH-MWCNT) with a Q0 of 24 and 0.7 times higher than that of two pristine MWCNTs (pMWCNT-1 and pMWCNT-2), respectively. The pMWCNT-1 posed no significant effects on growth of Navicula sp., whereas the algal growth was inhibited by 10 mg L−1 pMWCNT-2 (P < 0.05). The toxicity of pristine MWCNTs to algae increased with the diameters. OH-MWCNT stimulated the growth of Navicula sp. within 72 h, indicating that surface functionality of MWCNTs played a role in toxicity to Navicula sp. The presence of pMWCNT-1 and pMWCNT-2 could significantly aggravate the toxicity of CAB to Navicula sp., while OH-MWCNT exhibited insignificant effect on CAB toxicity. MWCNTs with a concentration of <10 mg L−1 played a protective role in the photosynthetic function of Navicula sp. Both pMWCNT-1 and pMWCNT-2 had no significant effect on the removal of CAB by Navicula sp., but OH-MWCNT could inhibit the degradation of CAB at the end. MWCNT co-exposure suppressed the bioavailability of CAB in Navicula sp. The results from the present study clearly demonstrated that CAB could be sorbed onto the surface of MWCNTs and sorption of CAB on MWCNTs had a key effect on the toxicity, biodegradation and bioaccumulation of CAB. The physicochemical properties and surface functionality of MWNCTs played an important role in toxicity and fate of CAB to Navicula sp.

Silane Modification of Carbon Nanotubes and Preparation of Silane Cross‐Linked LLDPE/MWCNT Nanocomposites

The objective of this study is to investigate the effects of carbon nanotube (CNT) content, surface modification, and silane cross‐linking on mechanical and electrical properties of linear low‐density polyethylene/multiwall CNT nanocomposites. CNTs were functionalized by vinyltriethoxysilane to incorporate the ─O─C2H5 functional groups and were melt‐blended with polyethylene. Silane‐grafted polyethylene was then moisture cross‐linked. Silanization of CNT was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), and EDX analysis. Hot‐set test results showed that silane cross‐linking of polyethylene and incorporation of modified CNTs into polyethylene led to an increase in cross‐linking density and the number of entanglements resulting in a decrease in elongation. It was found that the addition of pristine multiwall carbon nanotubes (MWCNTs) and functionalized MWCNTs does not affect silane cross‐linking density. Silane modification resulted in a stronger adhesion of the silane cross‐linked LLDPE to silanized MWCNTs according to scanning electron microscopy micrographs. Additionally, the electrical tests revealed that the silane modification of CNTs results in an improvement in electrical properties of nanocomposites, while silane cross‐linking will not have an effect on electrical properties. Rheological properties of MWCNT/LLDPE nanocomposites have been studied thoroughly and have been discussed in this study. Moreover, according to TGA test results, modification of the MWCNTs led to a better dispersion of them in the LLDPE matrix and consequently resulted in an improvement in thermal properties of the nanocomposites. Crystallinity and melting properties of the nanocomposites have been evaluated in detail using DSC analysis. J. VINYL ADDIT. TECHNOL., 26:113–126, 2020. © 2019 Society of Plastics Engineers

Enhancement in mechanical properties of multiwalled carbon nanotube‐reinforced epoxy composites: Crosslinking of the reinforcement with the matrix via diamines

In this study, the effect of diamine molecular structure, attached to the multiwalled carbon nanotubes (MWCNTs), on the interfacial interactions of the MWCNTs and the epoxy matrix was studied. Pristine MWCNTs were successfully functionalized with multiple aliphatic and aromatic diamines. It has been found that, compared to aliphatic molecules, aromatic diamines can yield higher functionalization degree, due to higher activity and longer half‐life of aromatic intermediates. However, at the same functionalization degree, the aliphatic ligands were more successful in reacting with epoxy chains and forming covalent bonds between the MWCNTs and the matrix. Considerable improvements were achieved in the mechanical properties of functionalized MWCNT‐reinforced epoxy composites in comparison with the pristine MWCNT‐reinforced composites. Fractography observations revealed distinct differences in the failure modes of reinforced composites after functionalization of the MWCNTs with diamines. POLYM. ENG. SCI., 59:1905–1910, 2019. © 2019 Society of Plastics Engineers

Integration of PDA Chemistry and Surface‐Initiated ATRP to Prepare Poly(methyl methacrylate)‐Grafted Carbon Nanotubes and Its Effect on Poly(vinylidene fluoride)–Carbon Nanotube Composite Properties

AbstractPoly(methyl methacrylate)‐grafted carbon nanotubes (PMMA@MWCNTs) are nondestructively prepared via the integration of mussel‐inspired polydopamine (PDA) chemistry and the surface‐initiated atom transfer radical polymerization (ATRP) method. The structures and properties of the poly(vinylidene fluoride)‐based (PVDF‐based) nanocomposites filled with pristine MWCNTs and PMMA@MWCNTs are investigated. The results show that the encapsulation of PMMA on the MWCNTs surface not only improves the dispersibility of MWCNTs in the PVDF matrix but also enhances the interfacial interaction between MWCNTs and PVDF. The addition of PMMA@MWCNTs nanofillers to PVDF can effectively induce the crystal structure of PVDF to transform from the α‐phase to the β/γ ‐phase, and nearly 100% β/γ ‐phase PVDF formed when the nanofiller loading is higher than 5 wt%. Compared with the MWCNTs/PVDF composites, the PMMA@MWCNTs/PVDF composites exhibit obvious improvement in the percolation threshold because the PMMA shells hinder the direct contact of the MWCNTs. Moreover, the loss tangent of the PMMA@MWCNTs/PVDF composites is effectively suppressed due to the reduced leakage current in the composites and the enhanced interfacial strength between the nanofiller and the matrix.

Microwave dielectric properties and Targeted heating of polypropylene nano-composites containing carbon nanotubes and carbon black

The complex dielectric constants of three polypropylene (PP) composite samples were measured at microwave frequency ranges of X (8.2–12.4 GHz) and Ka band (26.5–40 GHz), and as a function of filler content. Three types of carbon filler materials – pristine multiwall carbon nanotubes (p-CNTs), functionalized multiwall carbon nanotubes (f-CNTs), and carbon black (p-CB) were investigated. Attenuation constant for each composite was calculated, based on its measured complex dielectric constant, to highlight the importance of studying frequency dependent performance of composite materials for microwave heating. Most of the reported works for polymer composite heating using microwave power, have been conducted using commercial microwave ovens operating at 2.45 GHz. The results of this investigation for the CNT-composite samples indicate the importance of frequency optimization for creating maximum heat generation. The composite samples were also irradiated using low-power microwave energy at 2.6, 10 and 28 GHz and using a thermographic camera their relative capabilities for producing heat was investigated. The heating results corroborated those of the dielectric property measurements.

Epoxy functionalization of multiwalled carbon nanotubes for their waterborne polyurethane composite with crosslinked structure

In order to achieve covalent bond between multiwalled carbon nanotubes (MWCNTs) and waterborne polyurethane (WPU), pristine MWCNTs were first oxidized by strong acids and then underwent ring-opening reaction with epoxy resin to chemically attach epoxy moiety onto their surface. For fabrication of the MWCNTs/WPU composite, the epoxy moiety facilitates the dispersion of MWCNTs in the polymer matrix and could react with carboxylic acid or amine groups in the WPU macromolecules to form a crosslinked structure in their composite, resulting in a great improvement in their mechanical property, thermal stability, water resistance, and electrical conductivity. As the content of MWCNTs reached 1.5 wt%, the tensile strength of functionalized MWCNTs composite was improved by about 108% and the electrical conductivity was increased by six orders of magnitude compared to that of the pristine MWCNTs composite.

Removal of a non-steroidal anti-inflammatory by adsorption on polypyrrole/multiwalled carbon nanotube composite—Study of kinetics and equilibrium in aqueous medium

The purpose of this study was to evaluate the effect of the adsorption of the potassium diclofenac (PD) on a pristine multiwalled carbon nanotube (pristine MWCNT) and on the composite formed by the addition of polypyrrole (PPy) to pristine MWCNT, named PPy/MWCNT. They were characterized by scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller, surface wettability and point of zero charge. The adsorption procedure of the PD in the adsorbent materials was analysed by varying some parameters. After optimization, the materials exhibited adsorption of 93.48% and 94.98%, for pristine MWCNT and PPy/MWCNT, respectively. The kinetic data were adequately adjusted to the pseudo-second-order model for the two materials. The results of the isotherm studies showed that the models that best fit the data were the dual-site Langmuir–Freundlich and Fritz-Schlunder models, presenting Q = 59.67 mg g–1 for the pristine MWCNT and Q = 229.93 mg g–1 for the PPy/MWCNT. The thermodynamic study showed that from the values of ΔH and ΔG it was possible to conclude that an endothermic and favourable adsorption process occurred during the study. It can be observed that the addition of PPy in MWCNT causes a significant improvement in the maximum adsorption capacity of pristine MWCNT.

Enhancement of CO2 Desorption from Reinforced 2-(2-Aminoethylamine) Ethanol Aqueous Solution by Multi-walled Carbon Nanotubes

CO2 desorption in 2-(2-aminoethylamine) ethanol (AEE) aqueous solution promoted by different types of multi-walled carbon nanotubes (pristine MWCNT, MWCNT-OH, and MWCNT-COOH) was investigated in a ...

Polydopamine functionalized multi-walled carbon nanotubes supported PdAu nanoparticles as advanced catalysts for ethylene glycol oxidation

Design of high performance and low cost electrocatalysts for the oxidation of small organic molecules remains a great challenge for the practical application of direct fuel cells. Herein, a novel composite catalyst composed of PdAu nanoparticles (NPs) uniformly dispersed on the polydopamine functionalized MWCNTs (PDA-MWCNTs) has been synthesized. TEM images indicate that MWCNTs are successfully coated by PDA, and the as-prepared PdAu NPs are homogeneously dispersed on the PDA functional MWCNTs with smaller sizes than those on pristine MWCNTs. Electrochemical tests reveal that PDA-MWCNTs is a promising catalyst carrier for direct ethylene glycol fuel cell (DEGFC), and the PdAu(1:1)/PDA-MWCNTs catalyst displays the highest peak current density among all catalysts towards ethylene glycol oxidation reaction (EGOR) in alkaline medium, with mass activity of 1540.3 mA mgPd−1, which is 1.5, 2.6, 9.8, 13.4 and 2.0 times greater than those of PdAu(1:3)/PDA-MWCNTs, PdAu(3:1)/PDA-MWCNTs, Pd/PDA-MWCNTs, Pd/MWCNTs and commercial Pd/C catalysts, respectively. In addition, PdAu(1:1)/PDA-MWCNTs catalyst also exhibits the best stability. These findings are valuable for the development of advanced Pd-based catalysts, which will help promote the industrialization of direct fuel cell.

Histological study of the effect of pristine versus functionalized polyethylene glycol-multiwalled carbon nanotubes on the lung alveoli of the adult male albino rats

Background: Carbon nanotubes are used in a variety of applications. However, their toxicity on different body tissues has an impact on human health. Therefore, functionalization emerged as a tool to reduce CNTs toxicity and hence expand their applications.Aim: The goal of this study was to clarify the impact of pristine MW CNTs on lung alveoli of the adult male albino rat and the possibility of amelioration of this effect by functionalized PEG-MWCNTs.Materials and Methods:60 adult male rats were categorized among 3 groups. Group I: control group, group II: 20 rats received an intratracheal instillation of a single dose of 1 mg/kg of pristine MWCNTs, then subdivided into two equal subgroups (each 10 rats) and were sacrificed after 3 days and 45 days respectively, group III: 20 rats were received an intratracheal instillation of a single dose of 1 mg/kg of PEG-MWCNTs and then subdivided and sacrificed as in group II. At the end of the experiment, the lungs were harvested for histological examination. The thickness of the interalveolar septum and the collagen area were morphometrically evaluated and statistically analyzed.Results: Pristine MWCNTs caused variable degree of histological changes that were more evident after 45 days. These changes manifested by collapsed alveoli alternating with wide ones, thickening of the interalveolar septa, deposition of collagen, cellular and nuclear changes suggestive of pulmonary toxicity and accumulation of particulate laden macrophages. Morphometric and statistical studies demonstrated significant increase in the thickness of the interalveolar septa as compared to control group. Ultrastructurally, type II pneumocytes showed degenerative changes and formed the predominant cell lining. The changes were less evident by instillation of functionalized PEG-MWCNTs with more or less preservation of the normal alveolar architecture.Conclusion: Pristine MWCNTs have a toxic effect on the lung tissue which could be reduced by functionalized PEG-MWCNTs.

Effect of the oxidation process on the molecular interaction of polyaromatic hydrocarbons (PAH) with carbon nanotubes: Adsorption kinetic and isotherm study

Agglomeration is a major setback in the use of pristine multiwall carbon nanotube for many applications. Therefore, application of hydroxyl functionalized multiwall carbon nanotubes (MWCNT-OH) for the removal of naphthalene and fluorine was investigated and compared with pristine MWCNT for the first time. FTIR, BET, TGA, SEM, and TEM were used to investigate the functional group, microstructure and morphology of MWCNT and MWCNT-OH. The BET results showed more mesoporosity for MWCNT-OH than MWCNT. Batch equilibrium adsorption data were fitted to the Langmuir, Freundlich and Temkin models, of which the Langmuir model exhibited the best fit. The correlation of Langmuir model for naphthalene adsorption on MWCNT-OH was observed to be higher (i.e. R2 = 0.9703 for MWCNT-OH and R2 = 0.5082 for MWCNT) while the correlation for adsorption of flourene is higher for MWCNT (i.e. R2 = 0.998 for MWCNT and R2 = 0.9517 for MWCNT-OH). The maximum adsorption capacity (qe) for MWCNT-OH (57.401 ng/g-356.121 ng/g for naph and 61.235 ng/g - 367.361 ng/g for fluorene) was generally higher and more stable for lower concentration ranges while it is comparable with MWCNT (48.177 ng/g - 354.00 ng/g for naph and 59.635 ng/g- 366.709 ng/g for fluorene) at higher concentration. The qe calculated (344.828 ng/g for naph and 357.143 ng/g for fluorene) using PSO was observed to be much closer to experimental qe (356.121 ng/g for naph and 367.361 ng/g for fluorine) for MWCNT-OH adsorbent than MWCNT (cal qe are 384.615 ng/g for naph and 400.000 ng/g for fluorene; exp qe 354.00 ng/g for naph and 366.709 ng/g for fluorene). The value of boundary layer thickness, is >0, this indicates the reaction process is quite complex and is not solely controlled by the intra-particle diffusion. The results of this study indicate the high potential of the developed MWCNT-OH adsorbent as an efficient and successful material for the removal of carcinogenic PAHs from the water body.

The influence of multi-walled carbon nanotube doping on liquid crystalline phase transitions of a smectogen octylcyanobiphenyl: A high-resolution birefringence study

High-resolution optical birefringence measurements are reported on the weakly first order nematic-isotropic (N–I) and the continuous nematic-smectic A (N–Sm A) phase transitions in smectic liquid crystal 8CB (octylcyanobiphenyl) doped with both pristine multi-walled carbon nanotubes (p-MWCNTs) and carboxyl group (-COOH) functionalized MWCNTs (f-MWCNTs). It has been observed that the inclusion of MWCNTs substantially decreases both the N–I and the N–Sm A transition temperatures compared to 8CB host while the order of the transitions remains the same being the I–N weakly first-order and the N-SmA continuous for all 8CB-MWCNT composites regardless of the surface functionalization. The optical birefringence data have been used to probe the temperature behavior of the nematic order parameter S(T) in the vicinity of both the N–I and the N–Sm A transitions. Sufficiently far away from the Sm A phase, the average value of the critical exponent β characterizing the limiting behavior of S(T) near the N–I transition was found to be 0.245±0.002 This value of β seems to be in accord with the tricritical nature (TCH) of the N–I transition. Thus, concluded is the fact that the nature of the N–I transition of nanomaterial-based composites dispersed in liquid crystals remains tricritical up to at least the reported dopant contents and within the experimental resolution. The pre-transitional smectic behavior has also been noted to continue up to 4.3K on average above TNA for all 8CB-MWCNT composites. From the detailed inspection of S(T) data in the immediate vicintiy of the N–Sm A transition TNA, we have then obtained the upper limits for a possible latent heat ΔHNA across TNA for all 8CB-MWCNT composites. A slight change in ΔHNA has been observed due to the inclusion of MWCNTs as compared to 8CB host. By exploiting the fact that the temperature derivative of the order parameter S(T) near TNA exhibits the same power law divergence as the specific heat capacity, we have also extracted the effective critical exponent α values characterizing the critical fluctuations near the N-SmA transition for all 8CB-MWCNT composites. From both α and ΔHNA values, we have concluded that the nematic and smectic fluctuations remain essentially bulk-like for both 8CB-p-MWCNT and 8CB-f-MWCNT composites and thus the fact that the coupling between the N and the Sm A order parameters for all composites are comparable to that of 8CB host has been documented.

Fabrication of carbon fiber grafted with acyl chloride functionalized multi-walled carbon nanotubes for mechanical reinforcement of nylon 6,6

Carbon fiber (CF) grafted with acyl chloride functionalized multi-walled carbon nanotube (MWCNT), or (MWCNT-CF), was prepared by the reaction of aminopyrene (AP) adsorbed on CF (CF-AP) and 1-pyrenebutyric chloride (PBC) adsorbed on MWCNT (MWCNT-PBC). It is introduced that four kinds of PA66 composites, containing single incorporation of pristine CF, two-component incorporation of pristine CF and pristine MWCNT, two-component incorporation of PBC adsorbed CF (PBC-CF) and MWCNT-PBC, and single incorporation of MWCNT-CF were fabricated by melt extrusion, and their fatigue life and tensile and interfacial properties were explored. The residual PBC on the MWCNT of MWCNT-CF was reacted with the amine end group of PA66 during the melt extrusion process to produce PA66 grafted MWCNT-CF. When the content of total carbon fillers was fixed, PA66/MWCNT-CF and PA66/CF-PBC/MWCNT-PBC composites exhibited better fatigue life and tensile strength than PA66/pristine CF/pristine MWCNT composites owing to improved interfacial adhesion between PA66 and carbon fillers. Among the composites examined, the highest fatigue life and tensile strength of the PA66/MWCNT-CF composite were owing to the hierarchical structure of MWCNT-CF and optimal interfacial adhesion caused by chain entanglement between the PA66 grafted to MWCNT-CF and matrix PA66.

Pulmonary toxicity of two different multi-walled carbon nanotubes in rat: Comparison between intratracheal instillation and inhalation exposure

Multi-walled carbon nanotubes (MWCNTs), which vary in length, diameter, functionalization and specific surface area, are used in diverse industrial processes. Since these nanomaterials have a high aspect ratio and are biopersistant in the lung, there is a need for a rapid identification of their potential health hazard. We assessed in Sprague-Dawley rats the pulmonary toxicity of two pristine MWCNTs (the “long and thick” NM-401 and the “short and thin” NM-403) following either intratracheal instillation or 4-week inhalation in order to gain insights into the predictability and intercomparability of the two methods. The deposited doses following inhalation were lower than the instilled doses. Both types of carbon nanotube induced pulmonary neutrophil influx using both exposure methods. This influx correlated with deposited surface area across MWCNT types and means of exposure at two different time points, 1–3 days and 28–30 days post-exposure. Increased levels of DNA damage were observed across doses and time points for both exposure methods, but no dose-response relationship was observed. Intratracheal instillation of NM-401 induced fibrosis at the highest dose while lower lung deposited doses obtained by inhalation did not induce such lung pathology. No fibrosis was observed following NM-403 exposure.When the deposited dose was taken into account, sub-acute inhalation and a single instillation of NM-401 and NM-403 produced very similar inflammation and DNA damage responses.Our data suggest that the dose-dependent inflammatory responses observed after intratracheal instillation and inhalation of MWCNTs are similar and were predicted by the deposited surface area.