Vicinity Of Carbon Nanotube Research Articles

Hybrid multiwalled‐carbon nanotube/nanosilica/polypropylene nanocomposites: Morphology, rheology, and mechanical properties

AbstractPolymer composite are very interesting materials in automotive industry. Nanocomposites play a crucial role in the automotive parts and cars weight reduction fields. Hybridization of polymer nanocomposites is appeared as a process of choice in obtaining the required property/weight ration. Simple and hybrid nanocomposites of polypropylene (PP) blend with carbon nanotubes (CNTs) having different aspect ratios and nanosilica at different nanosilica contents were prepared in molten state in an internal mixer. Scanning electron microscopic images along with rheological and tensile properties revealed that only 0.2 wt% CNT is high enough to finely disperse nanosilica particles in PP matrix in the absence of any chemical compatibilizer. Differential scanning calorimetric thermograms showed that none of nanoparticles has any effect on crystallinity of PP. Mechanical characterizations showed that hybrid composites are superior to PP‐S3 composite. Due to its more intensive hydrodynamic motions it was also observed that the longer CNT showed a higher ability to disintegrate nanosilica particles aggregates. Transmission electron microscopic images well portrayed the nanosilica particles in the vicinity of CNTs' surfaces which accounts for electrostatic adsorption of fine nanosilica particles. At such a low CNT content (say 0.2 wt%) in the absence of any chemical compatibilizer, elongation at break of the tensiled nanocomposites raised from 13.23% to 35.41% and fracture energy was mounted from 1253 to 2750 J. This divulges the effectiveness of CNTs to disperse nanosilica in PP matrix but a poor adhesion between the particles and PP matrix is an overwhelming drawback yet. Under these conditions a maleic anhydride grafted PP (PP‐g‐MA) was added to the composite in molten state. The tensile strength of these chemically compatibilized nanocomposites increased with respect of that of their counterpart physically mixed nanocomposites. For example, in the presence of this chemical compatibilizer, the tensile strength of PP‐S3 nanocomposite raised from 21 to 28 MPa.

Micromechanical simulations and experimental characteristics of randomly distributed carbon nanotubes reinforced Mg matrix composites

In this study, finite element analysis was performed using representative volume elements (RVE). The cohesive zone model was implemented to govern the failure behavior of the CNTs/matrix interface. The RVE to understand the micromechanical response and damage behavior of randomly distributed carbon nanotubes (CNTs)/Mg matrix composites (MMCs). The cohesive zone model was implemented to govern the failure behavior of the CNTs/Mg interface. The RVE for macroscopic structural analysis was strained under assumed boundary conditions, where it provided a stress-strain curve for the composite. The simulation data can achieve excellent agreement with the experimental results. The simulations and experimental results indicate that the initial damage in the composite occurs in the vicinity of CNTs. The stress concentration at the CNT end increases with the increasing tensile load, resulting in interfacial debonding, the main form of crack growth of the CNTs/Mg composite. The CNTs can passivate the crack tip and change the propagation direction of the main crack, causing a delay in fracture. CNTs played an important role in governing the fracture pattern of composite. The pullout and bridging of CNTs were the main strengthening mechanisms of the composites, which was beneficial for improving strength and toughness.

Quantum chemical analysis of 5-aminolevulinic acid anticancer drug delivery systems: Carbon nanotube, –COOH functionalized carbon nanotube and iron oxide nanoparticle

Drug delivery systems including the 5-aminolevulinic acid anticancer drug (ALA) and carbon nanotube (CN), COOH functionalized carbon nanotube (FCN) and iron oxide nanoparticle (ION) were examined. For each of the CN, FCN and ION nanocarriers, four (CN/ALA1-4), three (FCN/ALA1-3) and three (ION/ALA1-3) configurations were considered, respectively. All structures were optimized at B3LYP/6-31G(d,p) in aqueous solution. Dispersion corrections were considered using M06-2X density functional. Binding energies, solvation energies and the contribution of each configuration in the drug delivery system were calculated. The binding energies of FCN/ALA1-3 and ION/ALA1-3 are about the same and much larger than those of CN/ALA1-4. On the other hand, the solvation energies of ION/ALA1-3 are more negative than those of CN/ALA1-4 and FCN/ALA1-3, which is an important advantage for iron oxide nanoparticles. Quantum molecular descriptors indicate that the reactivity of ALA increases in the vicinity of CN, FCN and ION. The AIM analysis showed that the hydrogen bonds play important roles in FCN/ALA1-3 and ION/ALA1-3 configurations.

Molecular Dynamics Study of an Atactic Poly(methyl methacrylate)-Carbon Nanotube Nanocomposite.

Molecular dynamics (MD) is used to simulate a model atactic poly(methyl methacrylate) (PMMA) system in which carbon nanotubes (CNTs) have been randomly dispersed. Our purpose is to elucidate the equilibrium structure and dynamic behavior of PMMA chains at the interface with a CNT. CNTs with different diameters and at different concentrations in the host PMMA matrix are studied, and their effect on the equilibrium squared radius-of-gyration and squared end-to-end distance of PMMA chains is examined. We have analyzed PMMA density, structure, and conformation both axially and normal to the CNT surface. Our MD simulations indicate that the presence of CNTs causes a small decrease in the size of the polymer chains, which becomes more pronounced as the concentration (volume fraction) and diameter of CNTs in the nanocomposite increases. We also provide a detailed analysis of adsorbed PMMA chain conformations in terms of trains, loops, and tails, and their statistical properties. An important finding of our work is that PMMA chains tend to penetrate significantly into the CNTs through their faces; as a result of CNT filling by PMMA chains, the area near the CNT mouths is characterized by significantly higher polymer mass density (almost by 45%) than the bulk of the nanocomposite. Additional simulation results for local and terminal relaxation in the PMMA-CNT nanocomposites reveal that due to strong PMMA-CNT attractive forces, all relaxation times in the interfacial region are significantly prolonged in comparison to the bulk, and the same happens with the diffusive (translational) motion of the chains. The density profile that develops (both axially and radially) in the vicinity of CNTs appears to significantly delay PMMA dynamics at all length scales. How this affects the glass-transition temperature of the nanocomposite is also analyzed.

Experimental and theoretical investigation of spontaneous and surface-enhanced Raman scattering (SERS) spectroscopy of pure and boron-doped carbon nanotubes

In this paper, due to the importance and abundant applications of carbon nanotubes doped with boron (CNT/B2O3) in various industries with changes in the electrical, mechanical and chemical properties, mode identification and intensity of the Raman spectra of pure and boron oxide molecule-doped spectra have been performed. The main task in this paper is to monitor the alteration of the relevant vibrational mode intensities of the pure and B-doped samples. In experimental approach, by utilizing a simple method we synthesized CNT doped with B2O3 using laser ablation in liquid environment technique. The silver nanoparticles were made by the Lee–Meisel method, and then the spontaneous and surface-enhanced Raman scattering (SERS) spectra of pure and B-doped carbon nanotubes were collected. In simulation approach, using the Gauss View and Gaussian software [basis set 6-31G, computational method DFT (B3LYP)], the spontaneous and SERS spectroscopy of pure and B-doped carbon nanotubes was calculated. Due to the presence of silver nanoparticles in the vicinity of carbon nanotube and boron element, SERS intensity to spontaneous Raman (NR) intensity ratio left( {{raise0.7exhbox{{I_{text{SERS}} }} !mathord{left/ {vphantom {{I_{text{SERS}} } {I_{text{NR}} }}}right.kern-0pt} !lower0.7exhbox{{I_{text{NR}} }}}} right) increases in the D, G and boron oxide modes of up to 12-fold were observed. A good agreement is found between the computational and the experimental SERS results for the vibrational spectra of the synthesized composite materials.

Morphology correlated free volume studies of multi-walled carbon nanotube plasticized poly (vinyl chloride) nanocomposites: Positronium probes and electrical properties

Herein we present a new approach to develop nanocomposites based on plasticized poly (vinyl chloride)/multi-walled carbon nanotubes. The free volume is found to increase with increase in MWCNT content up to 1% CNT, but exceptional decrease was observed at higher loading. The increase in free volume is as a result of intercalation of carbon nanotubes between polymer chains, there by introducing slight disorder to nanocomposites. The decrease in free volume is as a result of bridging of polymer chains by carbon nanotubes, resulting in the decrease in free volume at the vicinity of carbon nanotubes. Structural studies via Raman spectra and Doppler Broadening reveals disorder and interfacial interactions in nanocomposites. A frequency up shift of G band is due to π electron transfer from MWCNT to chlorine in PPVC. Using Tao-Eldrup model, radius of free volume (R) and volume of free volume (Vf) are calculated for nanocomposites. Morphological studies via FESEM and TEM reveal uniform dispersion of MWCNT throughout the polymer matrix. Hence, nanocomposite with maximum MWCNT loading showed electrical conductivity of 4.2E-10 S/cm. Thus this is a new composite material for antistatic application.

A Theoretical Study of the Size Effect of Carbon Nanotubes on the Removal of Water Chemical Contaminants

The issue of contamination is considered one of the most important and acute issues of human civilization in today's world. In the new decade, humans are facing the problem of clearing natural resources and the environment, including climate. Among the sources of water contaminants are chemical compounds that enter the water naturally through various methods and as a result of human activity. A group of water chemical contaminants is pesticides and herbicides which are widely used in agricultural consumptions. Carbon nanotubes are one of the ways to clean contaminated water, given that carbon nanotubes are in a wide level, they can be very effective in dealing with contaminants, on the other hand, carbon nanotubes can be used as clearing at the site of contamination. In this paper, six chemical contaminants of water including atrazine, simazine, benzoate, ethylbenzene, chloronaphthalene, xylene, have been placed in the vicinity of carbon nanotubes. Adsorption effect has been investigated through parameters such as composition stability, system volume, molecule level and toxicity criterion, polarity level using simulation methods in specialized software, by resizing the carbon nanotubes and finally the most important factor in resizing carbon nanotubes has been introduced.

Reinforced local heterogeneities in interfacial tension distribution in polymer blends by incorporating carbon nanotubes

The modification of interface using nanoparticles in emulsions and immiscible polymer blends introduces elaborate methods to develop functional materials. In this study, we perform dissipative particle dynamics simulations to evaluate the distribution of interfacial tension over a polymer-polymer interface in the presence of carbon nanotubes (CNTs). The localization and interfacial self-assembly of CNTs is discussed in connection with their aspect ratio (AR) and entropic contributions. The distribution of interfacial tension is demonstrated in terms of the distribution of pressure differences across the interface. The results show large variations in the local pressure differences in the vicinity of CNTs. These variations are more pronounced when low AR CNTs are incorporated into the blends. It is argued that the self-assembly of large AR CNTs at the interface severely restricts their domain of influence while random dispersions of low AR CNTs can effectively dominate the entire interface of the dispersed phase. These new findings can help explain the shape irregularities observed in the particle-covered droplets.

Tailoring selectivity of sprayed carbon nanotube sensors (CNT) towards volatile organic compounds (VOC) with surfactants

The vapour sensing performances of various surfactant–carbon nanotube (CNT) sensors fabricated by spray layer by layer (sLbL) towards various VOC including eleven lung cancer biomarkers have been investigated. It is found that changing the surfactants’ nature allows to efficiently tailor both the selectivity and the sensitivity of CNT vapour sensors to detect specifically some VOC biomarkers of lung cancer. An original boosting effect of chemo-resistive responses has also been evidenced and assumed to result from the combined expansion of surfactant molecules directly sheathing CNT at junctions and of those organised in micelles in the vicinity of CNT, upon analytes’ diffusion. The performances of surfactant–CNT sensors, hierarchically structured by sLbL with sodium deoxycholate (DOC), sodium dodecylbenzenesulfonate (SDBS), 1-hexadecyl trimethyl ammonium bromide (CTAB), benzalkonium chloride (BnzlkCl), and triton® x-405 (TX405) were found to depend on the interactions of the surfactants with the analytes, on their supramolecular assembly with CNT but also on the initial resistance R0 that can be adjusted by CNT content, surfactant:CNT ratio or the surfactant concentration over its CMC. CNT-DOC sensors were found sensitive to methanol and other alcohols but also water. TX405-CNT sensors were found sensitive to benzene, n-pentane and chloroform. SDBS-CNT sensors could detect ethanol, acetone, chloroform and water but not much biomarkers, excepted isopropanol. BnzlkCl-CNT sensors were sensitive to n-pentane, isoprene, acetone and ethanol. CTAB-CNT sensors were slightly sensitive to most VOC but did not show any strong selectivity, whereas pristine CNT sensors were found to be good to detect most aromatic VOC of the set. Moreover it is remarkable that the technique of fabrication used here is almost exclusively based on eco-friendly aqueous solutions of CNT.

Analysis of random telegraph noise observed in semiconducting carbon nanotube quantum dots

We have investigated random telegraph noise (RTN) observed in individual semiconducting carbon nanotubes (CNTs) in Coulomb-blockade regime. RTN characteristics are studied as a function of gate-voltage and drain–source voltage. Our results are explained by the capture and emission of carriers by charge traps in the vicinity of CNTs. Because of the large RTN amplitude, often greater than ∼50% of the total current, RTN measurements can be developed into an effective tool to estimate the trap energy and the location of the trap in CNT quantum dot devices.

Hydrogen storage in MgH 2 coated single walled carbon nanotubes

We present a density functional theory (DFT) study on the hydrogen storage capacity of (5,5) arm-chair single walled carbon nanotubes (SWCNTs) functionalized with magnesium hydride (MgH 2). Being lightweight and rich in hydrogen, MgH 2 adsorbs H 2 molecules in the vicinity of carbon nanotubes. The H 2 molecules are adsorbed dissociatively on SWCNT + MgH 2 complex. The H–H distance gets increased by more than ten times of the initial bond length 0.74 Å of the H 2 molecule. The hydrogen storage capacity of three configurations namely C1MgH 2, C5MgH 2 and C10MgH 2 is reported. The density of states is computed for all the systems. The average binding energies of C5MgH 2 and C10MgH 2 when H 2 molecule is adsorbed are 1.86 eV/H 2 and 1.96 eV/H 2, which are approximately equal. Thus, increasing the number of MgH 2 molecule does not vary the binding energy of H 2 adsorption. The corresponding temperature, in which desorption will take place, is 2285 K and 2457 K for C5MgH 2 and C10MgH 2 systems respectively, which are much above the room temperature.

Simultaneous global and local strain sensing in SWCNT–epoxy composites by Raman and impedance spectroscopy

Polymer composites can be benefited in many ways through the addition of carbon nanotubes (CNT). For instance, CNT can build up a percolated network within the polymer matrix, which results in a composite material with electrical conductivity and piezoresistive characteristics. This has very important implications for the realization of self-stress sensing structural composites. Moreover, the remarkable optical and transport properties of CNT permit to obtain information about the stress state of the composite at different scales. In the present work, the local and global stress response of SWCNT–epoxy composites is characterised by simultaneous Raman spectroscopic and electrical measurements on nanocomposite specimens submitted to different levels of surface strain. Both the Raman G′-band resonance frequency and the electrical resistance of the composite are found to change monotonically with strain until an inflection point is reached at ∼1.5% strain. Increased sensitivity of the piezoresistive network and lower load transfer efficiency occur beyond this strain level, and are considered to be the result of CNT slippage from the polymer. The reversibility of the stress sensitivity of the composites is verified by performing cyclic loading tests. Hysteresis loop are found to develop earlier on the Raman curves as in the resistance curves, which indicates that even at low strain levels, permanent damage is induced in the vicinity of carbon nanotubes. The use of Raman spectroscopy in combination with electrical methods provides a further insight on the stress sensing capabilities of CNT and the factors which affect the sensitivity and reproducibility of this behaviour.

Functionalization of single-walled carbon nanotube with borane for hydrogen storage

In this first principles study, we report the high storage capacity exhibited by (5,5) single-walled carbon nanotube functionalized with BH 3 for two different coverages. Being light weight and hydrogen rich, BH 3 is able to adsorb H 2 molecules in the vicinity of carbon nanotube. While BH 3 is chemisorbed on the carbon nanotube, H 2 are physisorbed on the (CNT+BH 3) complex. On half coverage of BH 3 molecules, single-walled carbon nanotube can adsorb 6.8 wt% of hydrogen and the wt% is increased to 11.5 for full coverage. In both cases each BH 3 can bind up to 4H 2 molecules with the binding energy in the range recommended for efficient hydrogen storage medium.

Speaking from experience

We present a density functional theory (DFT) study on the hydrogen storage capacity of (5,5) arm-chair single walled carbon nanotubes (SWCNTs) functionalized with magnesium hydride (MgH2). Being lightweight and rich in hydrogen, MgH2 adsorbs H2 molecules in the vicinity of carbon nanotubes. The H2 molecules are adsorbed dissociatively on SWCNT + MgH2 complex. The H–H distance gets increased by more than ten times of the initial bond length 0.74 Å of the H2 molecule. The hydrogen storage capacity of three configurations namely C1MgH2, C5MgH2 and C10MgH2 is reported. The density of states is computed for all the systems. The average binding energies of C5MgH2 and C10MgH2 when H2 molecule is adsorbed are 1.86 eV/H2 and 1.96 eV/H2, which are approximately equal. Thus, increasing the number of MgH2 molecule does not vary the binding energy of H2 adsorption. The corresponding temperature, in which desorption will take place, is 2285 K and 2457 K for C5MgH2 and C10MgH2 systems respectively, which are much above the room temperature.