MWCNT Concentration Research Articles

Characterization of alkali activated geopolymer mortar doped with MWCNT

This paper aimed to investigate the effect of MWCNTs on properties of slag geopolymeric mortar. Geopolymeric matrices containing different MWCNTs additions (0.0, 0.1, 0.2, 0.3 and 0.4% by weight of the used binder) were synthesized. The materials were prepared at water/binder ratios in the range of 0.34–0.39% depending on the amount of MWCNT; using of 6% NaOH as alkaline activation, whereas the Gelenium Ace-30 superplasticizer was used in the ratio of 1.4–2.2% from the total dry weight. Curing was performed under temperature of 40°C and 100% R.H. Results showed that the addition of MWCNTs enhanced the resulting amorphous geopolymer structure with a marked decrease in the drying shrinkage as well as water absorption specially by using 0.1% MWCNT; further increase in WCNTs addition resulted in the agglomeration of MWCNT within the matrix and, therefore, hinder the propagation of geopolymerization reaction and negatively affect the formed geopolymer structure. XRD, FTIR, and SEM of mortar nanocomposites with MWCNT concentrations of 0.1 and 0.4-wt.% confirmed an increase in amorphous geopolymer as well as CSH up to 0.1% where the individual MWCNTs spread throughout the geopolymer matrix with uniform density.

Effect of CNT as a Nucleating Agent on Cell Morphology and Thermal Insulation Property of the Rigid Polyurethane Foams.

The effects of MWCNT on the cell sizes, cell uniformities, thermal conductivities, bulk densities, foaming kinetics, and compressive mechanical properties of the rigid PUFs were investigated. To obtain the better uniform dispersed state of MWCNT, grease-type master batch of MWCNT/surfactant was prepared by three-roll mill. Average cell size of the PUF samples decreased from 185.1 for the neat PUF to 162.9 μm for the sample of 0.01 phr of MWCNT concentration. Cell uniformity was also enhanced showing the standard cell-size deviation of 61.7 and 35.2, respectively. While the thermal conductivity of the neat PUF was 0.0222 W/m(o)K, that of the sample with 0.01 phr of MWCNT showed 0.0204 W/m(o)K, resulting 8.2% reduction of the thermal conductivity. Bulk density of the PUF samples was observed as nearly the same values as 30.0 ± 1.0 g/cm3 regardless of MWCNT. Temperature profiles during foaming process showed that an indirect indication of the nucleation effect of MWCNT for the PUF foaming system, showing faster and higher temperature rising with time. The compressive yield stress is nearly the same as 0.030 x 10(5) Pa regardless of MWCNT.

VRH investigation of polyaniline–multiwalled carbon nanotube nanocomposite network

Polyaniline and polyaniline/multi-walled carbon nanotube (PAni/MWCNT) nanocomposites were synthesized by in-situ chemical oxidative polymerization of aniline. Ammonium peroxydisulphate and p-toluenesulphonic acid were used as an initiator and surfactant dopant, respectively. The molar ratio of monomer unit to initiator and dopant was 1:1:1 and the percentage of MWCNT in PAni varied from 1 to 10 wt%. The structure of the resulting nanocomposite was characterized by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The effects of MWCNT concentration on the electrical properties of the resulting nanocomposites were studied at temperatures between 90 and 300 K. Conductivity increases with the combination of MWCNT in the PAni environment. The strong coupling between the MWCNT and the PAni chains enhances the average localization length and hence conductivity increases for the nanocomposites.

Temperature Dependent Heat Transfer Performance of Multi-walled Carbon Nanotube-based Aqueous Nanofluids at Very Low Particle Loadings

Aqueous suspensions of multi-walled carbon nanotubes (MWCNTs + deionised water) have been synthesised. Carbon nanotubes (CNTs) were derived by chemical vapour deposition (CVD). Transmission electron microscopy (TEM) measurements show the formation of MWCNTs. Three samples of CNT-based aqueous nanofluids having MWCNT concentrations of 0.01 vol%, 0.03 vol% and 0.05 vol% were prepared with the help of ultrasonic irradiation. A very small amount of sodium dodecyl sulfate (SDS) was used as a surfactant to minimise the agglomeration of the MWCNTs. An effective enhancement in thermal conductivity was observed at different temperatures. The obtained results are explained with percolation theory.

Detailed study on interfacial interactions in epoxy composites cured with 1-buthylimidazole containing functionalized carbon nanotubes

This work provides a detailed information on the preparation process and characterization of functionalized multiwalled carbon nanotubes/Epidian 6 nanocomposites using ARES rheometer, TGA, and DSC measurements, with the imidazole derivative as a curing agent. Scanning electron microscopy of the fracture surfaces of the composites with a total nanofiller concentration below 0.5 wt.% reveals a uniform dispersion of MWCNT with only some minor agglomerates. At the same time, the TEM analysis of the composite with a total concentration of MWCNT–COOH higher than 0.5 wt.% confirmed the presence of carbon nanotube aggregates along with a large number of places without any presence of nanoparticles in the whole volume of the epoxy matrix. Mechanical tests (bending as well as dynamic mechanical analysis) show that compared with the neat epoxy resin, the bending strength of the composite was improved by about 30 and 21% after incorporating as little as only 0.1 and 0.2 wt.% MWCNT–COOH, respectively. The work presented hereby is a continuation of a previous study on epoxy-based nanocomposites with different types of multiwalled carbon nanotubes and it is a part of a wider project on precise charting of the influence of carbon nanotubes (particularly multiwalled carbon nanotubes) in the system of epoxy resin with 1-buthylimidazole, as a curing agent.

Schottky Diodes Based on Polyaniline/Multi-Walled Carbon Nanotube Composites

Polyaniline/multi-walled carbon nanotube composites (PANI/MWCNT), with various concentration of multi-walled carbon nanotube, were synthesized. Several Schottky diodes were fabricated, where PANI or PANI/MWCNT composites, aluminum, and gold were used as semiconductor, Schottky contact, and ohmic contact, respectively. Then current–voltage characteristics of the fabricated diodes were measured at room temperature and within the bias range of −5 to +5 V. The measurements were repeated three times for each sample to verify repeatability of experiment. The obtained results show that by increasing the MWCNT concentration, the current intensity increases. Furthermore, I-V characteristics of pure polyaniline Schottky diode follows the thermionic emission mechanism while the I-V characteristics of Schottky diodes based on PANI/MWCNT composites show two distinct power law regions. At lower voltages, the mechanism follows Ohm’s Law, whereas at higher voltages, the mechanism is compatible with space charge limited conduction emission mechanism. The parameters of Schottky diodes were determined, and it was observed that critical voltage decreased when the concentration of MWCNT in the composite increased.

Functionalized MWCNT and PVA Nanocomposite Membranes for Dielectric and Pervaporation Applications

Novel PVA nanocomposite membranes were prepared with acid functionalized multiwalled carbon nanotubes (a-MWCNT) as the reinforcing material. The presence of functional groups on MWCNT is revealed by FTIR techniques. The excess swelling of poly (vinyl alcohol) (PVA) membranes were reduced by the crosslinking of glutraldehyde (GA). The functionalized MWCNT induces hydrophilicity to the PVA nanocomposites and the hydrophilic nature of the nanocomposites was revealed by the contact angle analysis. The effect of a-MWCNT concentration on the dielectric and DC conductivities of the PVA nanocomposites was studied very well. The electrical conductivity of the nanocomposites is increased with the concentration of MWCNT, and PVA with 1.5 wt% nanotube loaded membranes showed better dielectric properties. As the concentration of MWCNT increased to 1.5 wt%, the PVA nanocomposites got transformed from a region of insulator to semiconductor. DC conductivity also showed the same trend. The Voet model showed good agreement with the experimental results of the conductivity. We also found that the developed PVA/a-MWCNT nanocomposite membranes can be used to separate the azeotropic composition of water-ethanol mixtures. The pervaporation (PV) performance of the membranes is studied in terms of permeance and intrinsic selectivity. PVA with 0.5 wt% nanotube loaded nanocomposite membranes achieved 340% increment in intrinsic selectivity. The pervaporation performance of the membranes were in good agreement with the permeation ratio model, and the separation efficiency is influenced by the morphology of the membranes and the interaction of the filler and the permeates. It is also observed that the dielectric properties of the membranes were correlated with the concentration of the conductive nanofillers. Thus the present study provides good information on dielectric and the pervaporation performance of PVA/a-MWCNT nanocomposite membranes.

Influence of preparation methods on the electrical and nanomechanical properties of poly(methyl methacrylate)/multiwalled carbon nanotubes composites

ABSTRACTPoly(methyl methacrylate)/multiwalled carbon nanotubes (PMMA/MWCNT) composites were prepared by two different methods: melt mixing and solution casting. For solution casting, two different solvents, toluene and chloroform, were used to prepare PMMA solutions with different concentrations of MWCNT. The dispersion of the CNT in the composite samples was verified by scanning electron microscopy. For the nanocomposites prepared by both methods, the electrical conductivity increased with increasing filler content, showing typical percolation behavior. In addition, an increase of 11 orders of magnitude in the electrical conductivity relative to the matrix conductivity was determined by broadband dielectric spectroscopy and four probe conductivity measurements. A maximum value of σDC ∼ 1.6 S/cm was found for the highest filler loaded sample (3.67 vol %), which was prepared by solution casting from toluene. Nanoindentation analysis was used to characterize the surface mechanical properties of the composite samples prepared by the different methods. Indentation tests were performed at various penetration depths, and it was revealed that the melt mixing process resulted in stiffer neat PMMA samples compared to the solution casted PMMA samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41721.

Wet deposition of carbon nanotube black coatings for stray light reduction in optical systems

Stray light, also known as optical noise, affects the performance of many optical devices. It can be reduced to a tolerable level by well-designed and well-baffled system or/and by using functional black coatings that are fabricated in a complex and costly process. Carbon nanotubes (CNTs) absorb light strongly, making them an ideal candidate for realizing a super black coating. CNT coatings were formed by spraying formulations composed of a silicon binder and low cost multiwalled CNTs on a pre-heated aluminum plate. The diffuse reflectance of the coatings in the VIS range (350–800nm) was in the range of 2.6–5.11%, depending on the MWCNT concentration in the coating. In the NIR range (850–2400nm), the reflectance values were in the range of 4–6.5%, however the dependence on MWCNT concentration was not very significant. Excellent adhesion to the aluminum substrates was achieved, for coatings with CNT concentration below 15%, while still having very low reflectance, even at temperature cycling between 200°C and −196°C. The proposed coating formulations enable simple and low cost approach for producing high light-absorbing coating of complex 3D structures within a very short time by wet deposition of CNTs.

Electrical properties of polyvinylidene fluoride (PVDF)/multi-walled carbon nanotube (MWCNT) semi-transparent composites: Modelling of DC conductivity

Transparent conductive composites can be achieved from PVDF–MWCNT at very low concentration of MWCNT. These composites show different degree of UV–Visible radiation absorption depending on MWCNT concentration in composites. The composition dependent dielectric properties and AC conductivity were also measured for these composites. Properties like AC conductivity, dielectric constant and loss are increasing with filler concentration. The variations of DC conductivity against composition and temperature are also reported. The electrical hysteresis and electrical set are observed for PVDF–MWCNT composites when subjected to heating–cooling cycle. The validity of different theoretical models depicting percolation threshold with respect to DC conductivity was tested for these composites.

Dielectric properties of multiwalled carbon nanotube/clay/polyvinylidene fluoride nanocomposites: Effect of clay incorporation

This study investigates the effect of clay addition on the broadband dielectric properties of multi‐walled carbon nanotube/polyvinylidene fluoride (MWCNT/PVDF) composites, that is, frequency range of 101−106 Hz. Different loadings of MWCNT and clay were used for the preparation of three‐phase (MWCNT/Clay/PVDF) nanocomposites via melt‐mixing method. The crystalline structure and morphology of nanocomposites were examined by employing characterization techniques such as X‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The dielectric spectroscopy showed that introducing clay into the MWCNT/PVDF nanocomposites at a critical MWCNT concentration improved dielectric properties tremendously. It was interestingly observed that the incorporation of a specific amount of clay, that is, 1.0 wt%, into the (MWCNT/PVDF) nanocomposite at a critical MWCNT loading, that is, 0.5 wt% MWCNT, resulted in a huge increase in the dielectric permittivity (670% at 100 Hz) and a considerable reduction in the dissipation factor (68% at 100 Hz). POLYM. COMPOS., 161–167, 2016. © 2014 Society of Plastics Engineers

Optimizing P3HT/PCBM/MWCNT films for increased stability in polymer bulk heterojunction solar cells

The effect of multi-walled carbon nanotubes on the properties of P3HT:PCBM based solar cells has been studied. The concentration of MWCNT was optimized at 0.2% and the concentration of P3HT:PCBM was increased from 20mg/ml to 30mg/ml to obtain highest efficiency. An increase in charge carrier mobility was also observed, which is attributed to high charge transport properties of MWCNT. The active layer was optically stable with respect to absorption, whereas the emission spectra revealed an increase in charge recombination with time. The solar cells doped with MWCNT exhibited increased stability as compared to undoped cells.

Inhaled Multiwalled Carbon Nanotubes Modulate the Immune Response of Trimellitic Anhydride–induced Chemical Respiratory Allergy in Brown Norway Rats

The interaction between exposure to nanomaterials and existing inflammatory conditions has not been fully established. Multiwalled carbon nanotubes (MWCNT; Nanocyl NC 7000 CAS no. 7782-42-5; count median diameter in atmosphere 61 ± 5 nm) were tested by inhalation in high Immunoglobulin E (IgE)-responding Brown Norway (BN) rats with trimellitic anhydride (TMA)-induced respiratory allergy. The rats were exposed 2 days/week over a 3.5-week period to a low (11 mg/m(3)) or a high (22 mg/m(3)) concentration of MWCNT. Nonallergic animals exposed to MWCNT and unexposed allergic and nonallergic rats served as controls. At the end of the exposure period, the allergic animals were rechallenged with TMA. Histopathological examination of the respiratory tract showed agglomerated/aggregated MWCNT in the lungs and in the lung-draining lymph nodes. Frustrated phagocytosis was observed as incomplete uptake of MWCNT by the alveolar macrophages and clustering of cells around MWCNT. Large MWCNT agglomerates/aggregates were found in granulomas in the allergic rats, suggesting decreased macrophage clearance in allergic rats. In allergic rats, MWCNT exposure decreased serum IgE levels and the number of lymphocytes in bronchoalveolar lavage. In conclusion, MWCNT did not aggravate the acute allergic reaction but modulated the allergy-associated immune response.

Giant Permittivity and Low Dielectric Loss in Three Phases BaTiO<SUB>3</SUB>/Carbon Nanotube/Polyvinylidene Fluoride Composites

Carbon nanotubes have been intensively studied because of their unique physical properties and many potential applications. One important application is when carbon nanotubes are used in polymer composites as novel conductive fillers to improve the dielectric properties of polymer blended with barium titanate (BaTiO3) ceramics. The three-phase composite with carbone nanotubes and BaTiO3 particles embedded into polyvinylidene fluoride (PVDF) were prepared by using a Haake blending mixer and pressed by hot-molding technique. The dielectric analysis show that the relative dielectric constant of the composite is slightly dependent on the frequency below 0.1 MHz and increases rapidly with MWCNT concentration. It is thus possible to reach a high dielectric constant equal to 7000. These films show interesting properties for an application in storage energy.

Morphology, mechanical, bound rubber, swelling, and dynamic mechanical studies of chlorobutyl elastomer nanocomposites: effect of multiwalled carbon nanotube and solvent

Abstract Multiwalled carbon nanotube (MWCNT) reinforced chlorobutyl elastomer nanocomposites were prepared. The morphology of nanocomposite samples has been studied from scanning electron microscopy (SEM). The effect of MWCNT loadings on mechanical properties shows increase in tensile strength, hardness, and modulus and decrease in elongation at break with MWCNT loadings, which can be attributed toward better chlorobutyl-MWCNT interaction. At higher filler loading, the rate of increase slowly decreases. The above explanation was also verified from bound rubber (BdR) measurements, showing increase in BdR contents with MWCNT loading. Swelling of the nanocomposites in chloroform, benzene, and trichloroethylene was measured and found to be dependent on both MWCNT concentration and the type of solvent used. The degree of swelling, diffusion coefficient, and penetration rate was calculated. The effect of solvent on swelling properties at different periods of time shows that the degree of swelling increases with time and decreases with concentration of MWCNT loading. Dynamic mechanical properties of nanocomposites have been studied as a function of temperature (from -100°C to 100°C) at a constant frequency of 1 Hz and 1% strain. The effect of MWCNT loading on storage modulus, loss modulus, and loss tangent has been studied. The nonlinearity in tan δ and storage modulus and loss modulus was explained on the basis of MWCNT-elastomer interaction. The smooth Cole-Cole plots explain the nonlinearity in the nanocomposites as well as good distribution of MWCNT in the elastomer matrix.

Manipulation of MWCNT Concentration in MWCNT/TiO2Nanocomposite Thin Films for Dye-Sensitized Solar Cell

Dye-sensitized solar cell (DSSC) using multiwalled carbon nanotube/titanium dioxide (MWCNT/TiO2) was successfully synthesized using sol-gel method. In this method, it has been performed under various acid treatments MWCNT concentration level at (a) 0.00 g, (b) 0.01 g, (c) 0.02 g, and (d) 0.03 g. Atomic force microscopy (AFM) was used to study surface roughness of the MWCNT/TiO2thin films. The average roughness results for 0.00 g, 0.01 g, 0.02 g, and 0.03 g were 10.995, 18.308, 24.322, and 25.723 nm, respectively. High resolution transmission electron microscopy (HR-TEM) analysis showned the inner structural design of the MWCNT/TiO2particles. The TiO2nanoparticles covered almost all the area of MWCNT particles. Field emission scanning electron microscopy (FESEM) gave the morphological surface structure of the thin films. The thin films formed in good distribution with homogenous design. The DSSC with MWCNT/TiO2electrode containing 0.03 g MWCNT were resulted in the highest efficiency of 2.80% with short-circuit current densityJscof 9.42 mA/cm2and open-circuit voltageVocof 0.65 V.

Bioinformatic Analysis of Differential Protein Expression in Calu-3 Cells Exposed to Carbon Nanotubes.

Carbon nanomaterials are widely produced and used in industry, medicine and scientific research. To examine the impact of exposure to nanoparticles on human health, the human airway epithelial cell line, Calu-3, was used to evaluate changes in the cellular proteome that could account for alterations in cellular function of airway epithelia after 24 hexposure to 10 μg/mL and 100 ng/mLof two common carbon nanoparticles, single- and multi-wall carbon nanotubes (SWCNT, MWCNT). After exposure to the nanoparticles, label-free quantitative mass spectrometry (LFQMS) was used to study the differential protein expression. Ingenuity Pathway Analysis (IPA) was used to conduct a bioinformaticanalysis of proteins identified in LFQMS. Interestingly, after exposure to ahigh concentration (10 μg/mL; 0.4 μg/cm2) of MWCNT or SWCNT, only 8 and 13 proteins, respectively, exhibited changes in abundance. In contrast, the abundance of hundreds of proteins was altered in response to a low concentration (100 ng/mL; 4 ng/cm2) of either CNT. Of the 281 and 282 proteins that were significantly altered in response to MWCNT or SWCNT respectively, 231 proteins were the same. Bioinformatic analyses found that the proteins in common to both nanotubes occurred within the cellular functions of cell death and survival, cell-to-cell signaling and interaction, cellular assembly and organization, cellular growth and proliferation, infectious disease, molecular transport and protein synthesis. The majority of the protein changes represent a decrease in amount suggesting a general stress response to protect cells. The STRING database was used to analyze the various functional protein networks. Interestingly, some proteins like cadherin 1 (CDH1), signal transducer and activator of transcription 1 (STAT1), junction plakoglobin (JUP), and apoptosis-associated speck-like protein containing a CARD (PYCARD), appear in several functional categories and tend to be in the center of the networks. This central positioning suggests they may play important roles in multiple cellular functions and activities that are altered in response to carbon nanotube exposure.

Fabrication of mixed matrix heterogeneous ion exchange membrane by multiwalled carbon nanotubes: Electrochemical characterization and transport properties of mono and bivalent cations

In this research, polyvinylchloride/multiwalled carbon nanotubes (MWCNTs) mixed matrix heterogeneous cation exchange membranes were prepared by solution casting technique. The effect of MWCNT concentration on membrane electrochemical characteristics was studied. Membrane water content was increased initially by increase of additive concentration up to 4wt.% and then showed decreasing trend by more additive content. Increase of MWCNTs' loading ratio in casting solution also caused to decrease in ion exchange capacity. Membrane permselectivity and transport number were declined initially for monovalent ionic solution by increase of additive loading up to 4wt.% and then increased by more additive concentration. Results revealed that membrane selectivity and transport number were improved slightly in bivalent ionic solution by increase of MWCNT concentration up to 8wt.% and then decreased sharply by more additive concentration. The monovalent ionic flux was enhanced by increase of additive content. Also ionic flux was improved initially for bivalent ions by increase of additive concentration up to 2wt.% and then decreased by more additive concentration from 2 to 8wt.%. The bivalent ionic flux showed increasing trend with further increase in additive concentration. Membrane areal electrical resistance was decreased by increase of additive concentration.

Coupled electro-mechanical properties of multiwall carbon nanotube/polypropylene composites for strain sensing applications

The electrical, mechanical, and coupled electro-mechanical (piezoresistive) properties of multiwall carbon nanotube/polypropylene (MWCNT/PP) composites at four MWCNT concentrations above electrical percolation (4–10 wt %) were investigated. The electrical conductivity of the composite increased monotonically from 0.77 to 15.0 S/m with the increase of MWCNT concentration. The elastic modulus also increased monotonically with increased MWCNT concentration with the concomitant reduction of ultimate strain. The coupled signal between electrical resistance and applied strain during tensile loading displayed a marked change toward higher sensitivity at the elastic-to-plastic transition zone of the polymer composite, which allowed the identification of polymer yielding by the sole monitoring of electrical resistance. Large ratios (of the order of 15–29) of normalized changes in electrical resistance over applied strain (“gage factor”) were found in the plastic zone, and such electro-mechanical sensitivity was higher for composites with lower MWCNT content.

Polymer Chain Conformations in CNT/PS Nanocomposites from Small Angle Neutron Scattering

Chain conformations dictate many of the important physical properties of polymers including their dynamics. Using small angle neutron scattering, we probed chain conformations, specifically the radius of gyration (Rg), in both SWCNT/polystyrene (rSWCNT/Rg ∼ 0.4) and MWCNT/polystyrene (rMWCNT/Rg ∼ 1) nanocomposites. We fit the scattering data using a model that includes an ideal Gaussian chain to describe the polymer conformation and a rod network to describe the carbon nanotube (CNT) network. The scattering contribution from the rod network increases with the CNT concentration in both SWCNT and MWCNT nanocomposites, and the contribution is higher for SWCNT nanocomposites due to the smaller mesh size and higher mesh density. When the SWCNT and MWCNT concentrations are below 2 wt %, there is no significant change in Rg. Above 2 wt %, Rg in the MWCNT nanocomposites decreases slightly, while Rg in the SWCNT nanocomposites increases monotonically as a function of CNT concentration, showing a ∼30% increase at 1...