Length Of Multi-walled Carbon Nanotubes Research Articles

Effects of carbon nanotubes aspect ratio on the qualitative and quantitative aspects of frequency response of electrical conductivity and dielectric permittivity in the carbon nanotube/polymer composites

To study the effect of carbon nanotube aspect ratio (AR) on the frequency response of the electrical properties, the alternating current (AC) electrical conductivity and dielectric permittivity of different AR multi-wall carbon nanotubes (MWCNTs)/thermoplastic elastomer (TPE) composites were studied in the AC frequency range of 100 Hz to 10 MHz. Qualitatively, the effect of frequency on the electrical properties of the composites was the same for all AR MWCNTs and shared many typical features of electrically percolative composites. Quantitatively, the frequency responses of electrical properties were found to be independent of nominal AR, concentration, percolation threshold, and the diameter of the MWCNT. Instead, frequency response of electrical properties was dependent on the MWCNT length and initial electrical conductivity of the composites. With the same initial conductivity of the MWNT composites, frequency-conductivity sensitivity varied inversely with the nominal length of the MWCNTs. Composites with MWCNTs of the same nominal length and similar electrical conductivity values, regardless of whether the MWCNT concentration was below or above the percolation threshold, exhibited quantitatively similar frequency-conductivity sensitivity. The frequency-dielectric sensitivity at the percolation threshold was a reflection of frequency-conductivity sensitivity and was also found to be dependent on the initial conductivity of the composites.

S125 Pro-Fibrotic Effects of Multi-Walled Carbon Nanotube Exposure on Primary Human Alveolar Type II Epithelial Cells and Fibroblasts

Multi-walled carbon nanotubes (MWCNTs) are hollow fibre-like nanomaterials which are being investigated for use in drug delivery and as biosensors. However, due to their structural similarity to asbestos fibres, inhaled...

Short Multiwall Carbon Nanotubes Promote Neuronal Differentiation of PC12 Cells via Up‐Regulation of the Neurotrophin Signaling Pathway

Numerous unique properties of carbon nanotubes make them attractive for applications in neurobiology such as drug delivery, tissue regeneration, and as scaffolds for neuronal growth. In this study, the critical roles of the length of multiwall carbon nanotubes (MWCNTs) on a neuronal-like model cell line PC12 cells are investiaged. Incubation of PC12 cells with carboxylated MWCNTs did not significantly affect cellular morphology and viability at lower concentrations. Short MWCNTs show higher cellular uptake and more obvious removal compared to longer ones, which can result in higher ability to promote PC12 cell differentiation. Pre-incubation of short MWCNTs can up-regulate the expression of neurotrophin signaling pathway-associated TrkA/p75 receptors and Pincher/Gap43/TH proteins, which might be the underlying mechanism for the improved differentiation in PC12 cells. The current results provide insight for future applications of MWCNTs in neuron drug delivery and neurodegenerative disease treatment.

Different cellular response mechanisms contribute to the length-dependent cytotoxicity of multi-walled carbon nanotubes

To date, there has not been an agreement on the best methods for the characterisation of multi-walled carbon nanotube (MWCNT) toxicity. The length of MWCNTs has been identified as a factor in in vitro and in vivo studies, in addition to their purity and biocompatible coating. Another unresolved issue relates to the variable toxicity of MWCNTs on different cell types. The present study addressed the effects of MWCNTs' length on mammalian immune and epithelial cancer cells RAW264.7 and MCF-7, respectively. Our data confirm that MWCNTs induce cytotoxicity in a length- and cell type-dependent manner. Whereas, longer (3 to 14 μm) MWCNTs exert high toxicity, especially to RAW264.7 cells, shorter (1.5 μm) MWCNTs are significantly less cytotoxic. These findings confirm that the degree of biocompatibility of MWCNTs is closely related to their length and that immune cells appear to be more susceptible to damage by MWCNTs. Our study also indicates that MWCNT nanotoxicity should be analysed for various components of cellular response, and cytotoxicity data should be validated by the use of more than one assay system. Results from chromogenic-based assays should be confirmed by trypan blue exclusion.

Transport behavior of functionalized multi-wall carbon nanotubes in water-saturated quartz sand as a function of tube length

A series of one-dimensional column experiments was conducted to examine the effects of tube length on the transport and deposition of 4-ethoxybenzoic acid functionalized multi-wall carbon nanotubes (MWCNTs) in water-saturated porous media. Aqueous MWCNTs suspensions were prepared to yield three distributions of tube lengths; 0.02–1.3 μm (short), 0.2–7.5 μm (medium), and 0.2–21.4 μm (long). Results of the column studies showed that MWCNT retention increased with increasing tube length. Nevertheless, more than 76% of the MWCNT mass delivered to the columns was detected in effluent samples under all experimental conditions, indicating that the functionalized MWCNTs were readily transported through 40–50 mesh Ottawa sand. Examination of MWCNT length distributions in the effluent samples revealed that nanotubes with lengths greater than 8 μm were preferentially deposited. In addition, measured retention profiles exhibited the greatest MWCNT deposition near the column inlet, which was most pronounced for the long MWCNTs, and decreased sharply with travel distance. Scanning electron microscope (SEM) images showed that MWCNTs were deposited on sand surfaces over the entire column length, while larger MWCNT bundles were retained at grain intersections and near the column inlet. A mathematical model based on clean bed filtration theory (CBFT) was unable to accurately simulate the measured retention profile data, even after varying the weighting function and incorporating a nonuniform attachment rate coefficient expression. Modification of the mathematical model to account for physical straining greatly improved predictions of MWCNT retention, yielding straining rate coefficients that were four orders-of-magnitude greater than corresponding attachment rate coefficients. Taken in concert, these experimental and modeling results demonstrate the potential importance of, and need to consider, particle straining and tube length distribution when describing MWCNT transport in water-saturated porous media.

Dispersion and aspect ratio of carbon nanotubes in aqueous suspension and their relationship with electrical resistivity of carbon nanotube filled polymer composites

Multiwalled carbon nanotube (MWCNT)/acrylonitrile butadiene styrene (ABS) composites were prepared by a processing method using solvent–nonsolvent precipitation. Size distributions of MWCNT agglomerates in aqueous suspension were investigated in order to predict aspect ratio of nanotubes by evaluating the effects of sonication time, MWCNT content, and surfactant. Aspect ratios of MWCNTs were predicted on the basis of the size distribution measurements for MWCNT agglomerates. Sonication time or applied sonic energy has a strong effect on the size distribution of MWCNT agglomerates. Compared with simple shear mixing method, it was shown that this processing method is more suitable for the MWCNT/ABS composites. An electrical percolation threshold was observed for the weight fraction of MWCNTs in the range of about 0.5–1.0wt.%. Shorter MWCNTs are more suitable to induce fine dispersion, but lead to higher percolation threshold weight fraction. It was illustrated that fine dispersion can overcome the handicap of short length or low aspect ratio of MWCNTs.

Axisymmetric compressive buckling of multi-walled carbon nanotubes under different boundary conditions

The paper studies the axisymmetric compressive buckling behavior of multi-walled carbon nanotubes (MWNTs) under different boundary conditions based on continuum mechanics model. A buckling condition is derived for determining the critical buckling load and associated buckling mode of MWNTs, and numerical results are worked out for MWNTs with different aspect ratios under fixed and simply supported boundary conditions. It is shown that the critical buckling load of MWNTs is insensitive to boundary conditions, except for nanotubes with smaller radii and very small aspect ratio. The associated buckling modes for different layers ofMWNTs are in-phase, and the buckling displacement ratios for different layers are independent of the boundary conditions and the length of MWNTs. Moreover, for simply supported boundary conditions, the critical buckling load is compared with the corresponding one for axial compressive buckling, which indicates that the critical buckling load for axial compressive buckling can be well approximated by the corresponding one for axisymmetric compressive buckling. In particular, for axial compressive buckling of double-walled carbon nanotubes, an analytical expression is given for approximating the critical buckling load. The present investigation may be of some help in further understanding the mechanical properties of MWNTs.

Increasing the interfacial strength in carbon fiber/epoxy composites by controlling the orientation and length of carbon nanotubes grown on the fibers

Multi-walled carbon nanotubes (MWCNTs) were grafted onto carbon fibers (CFs) using an injection chemical vapor deposition method. The orientation and length (16.6–108.6 μm) of the MWCNTs were controlled by the surface treatment of the CFs and the growth time, respectively. The interface between the MWCNTs and the CFs indicated the grafted CNTs were immobilized by embedding catalyst on CFs. Two orders of magnitude increase in the specific surface areas of CFs was obtained by grafting the MWCNT. MWCNT–CF hybrids exhibited good wettability with the epoxy resin due to the surface roughness and capillary action. Single-fiber composite fragmentation tests revealed an remarkable improvement of interfacial shear strength (IFSS) controlled by the orientation and length of MWCNTs. MWCNTs with an perpendicular alignment and long length showed a high IFSS in epoxy composites due to better wettability and a large contact interface between the hybrids and the resin. Hybrids with an optimum length (47.2 μm) of aligned MWCNTs showed a dramatic improvement of IFSS up to 175% compared to that of pristine CFs.

Surface oxidation and effect of electric field on dispersion and colloids stability of multiwalled carbon nanotubes

Chemical functionalization is a procedure to oxidize the surface of materials. Multiwalled carbon nanotubes (MWCNTs) were purified and functionalized using oxidizing mixture acids (sulfuric and nitric acids). The effect of purification and functionalization on the decrease of MWCNTs length and solubility in polar solvents was studied. The length of MWCNTs decreased when the purification and functionalization time was increased. The functionalization of MWCNTs was confirmed by Raman spectroscopy measurements. It was found that, by functionalization the solubility and colloidal stability of MWCNTs were increased in polar media like water and methanol. We found also dispersion status of functionalized MWCNTs in water is evidently improved by applying an AC electric field of 25 V at low frequency and proper applying time.

Influence of dry grinding in a ball mill on the length of multiwalled carbon nanotubes and their dispersion and percolation behaviour in melt mixed polycarbonate composites

Ball milling of carbon nanotubes (CNTs) in the dry state is a common way to produce tailored CNT materials for composite applications, especially to adjust nanotube lengths. For Nanocyl TM NC7000 nanotube material before and after milling for 5 and 10 h the length distributions were quantified using TEM analysis, showing decreases of the mean length to 54% and 35%, respectively. With increasing ball milling time in addition a decrease of agglomerate size and an increase of packing density took place resulting in a worse dispersability in aqueous surfactant solutions. In melt mixed CNT/polycarbonate composites produced using masterbatch dilution step, the electrical properties, the nanotube length distribution after processing, and the nano- and macrodispersion of the nanotubes were studied. The slight increase in the electrical percolation threshold in the melt mixed composites with ball milling time of CNTs can be assigned to lower nanotube lengths as well as the worse dispersability of the ball milled nanotubes. After melt compounding, the mean CNT lengths were shortened to 31%, 50%, and 66% of the initial lengths of NC7000, NC7000-5 h, and NC7000-10 h, respectively.

Measurement of contact resistance of multiwall carbon nanotubes by electrical contact using a focused ion beam

Carbon nanotubes (CNTs) have found many potential applications but using CNTs as building blocks for nanoelectronics is still challenging. Various micro- and nanofabrication techniques including focused ion beam (FIB) are therefore being developed for combining CNTs into a nanodevice or to help assess the electrical properties of integrated CNTs. In this paper, multiwall carbon nanotubes (MWNTs) are assembled between a pair of gold (Au) electrodes by dielectrophoresis (DEP). Contact resistances of MWNT-Au and, in particular, MWNT-MWNT are measured with the help of making electrical connections between a MWNT and electrodes by FIB induced tungsten deposition. A method for resistance calculation is presented which considers the contact length of MWNTs. Under the conditions of this research, measured conducting resistances of MWNTs were from 1–10 kΩ/μm and the contact resistance of MWNTs with Au was around 100 kΩ μm. The contact resistance between MWNTs varied depending on contact configurations and could be as low as 50 KΩ. The effect of FIB parameters on the measurement results is discussed.

Investigation on Buckling Behavior of Short MWCNT

This paper aims to investigate the buckling behavior of short multi-walled carbon nanotubes (MWCNTs) under compression using molecular dynamics simulations. The effect of the number of walls and length of MWCNT on the buckling behaviors is investigated. The results show that the buckling behaviors of short MWCNTs are different from single wall carbon nanotubes (SWCNTs) and slender MWCNTs. Interestingly, the buckling strain of short MWCNTs has a downward trend with the number of walls increasing. In addition, the length of MWCNT has also significant effect on the buckling strain. These benchmark data may be used to examine the applicability of continuum mechanics models in predicting the buckling behavior of short MWCNTs.

Application of Carbon Nanotubes (CNT) to Photosensitive Diazo/PVA Resist (3)-Effect of CNT Length

Degradation temperature, D.T. of the para-substituted benzene diazo compound (SBD) mixed with various length of multi-walled carbon nanotubes (CNT) : 3-20, 20-40, 40-70 nm, was determined by TDA and DTA in solid. Temperature rise ratio of D.T. of SBD with electron-withdrawing substitutent (WSB) was larger than that of SBD with electron-donating substituent (DSB). It is considered that a cationic diazo group of SBD is easily coordinated by electron-rich CNT surface. The D.T. of SBD with long CNT was higher than that with short CNT. Stabilization energies of diazo compounds with CNT were calculated by WinMOPAC, to be about 37 kJ/mol per diazo molecule. Oxidation treatment of CNT led to better dispersion of CNT particles. Photodecomposition rate of Diazo/PVA resist film with CNT was increased, but effect of CNT length on the photodecomposition was not observed. Shorter ox-CNT in length showed higher transmittance. Hardness of the film with long CNT was larger than that with short CNT. It is considered that degree of packing of the polymer chain with long CNT is higher than that with short CNT.

A new solution on the buckling and stable length of multi wall carbon nanotube probes near graphite sheets

In this paper, a power series solution is used to study effect of intermolecular forces on the instability of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. A power series method basis on symbolic computation is introduced to obtain an analytical solution for the distributed parameter model. The critical values of MWCNT tip deflection and MWCNT-graphite attraction at the onset of the instability are computed. Minimum nanotube-graphite initial gap and stable length of freestanding carbon nanotube are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers. The obtained results are compared with the Adomian decomposition and Green's function as well as numerical results. The obtained results in compare with numerical results represent remarkable accuracy rather than the Adomian decomposition method and Green's function.

Effect of Surface Modification of Carbon Nanotube on the Strength Properties of Carbon Nanotube/Alumina Composites and Their Fracture Process

We report the mechanical properties and microstructures of multi-walled carbon nanotube (MWCNT)/alumina composites made with MWCNTs that absorb negatively charged functional groups at the MWCNT ends and along their length from an acid treatment. We conducted the fracture surface observations of the composites, in order to evaluate the effects of the acid treatment conditions of MWCNTs on the mechanical properties of the composites and the microstructures such as dispersibility and protrusion length of MWCNTs. According to the SEM observations, it was found that the dispersibility of MWCNTs affected the mechanical properties of the composites, and the protrusion length of MWCNTs decreased with increasing of the acid treatment time of MWCNTs. These observations revealed that the high structural homogeneity rather than pullout behavior of MWCNTs leads to an increase in the mechanical properties of the MWCNT/alumina composite. There is an optimal acid treatment time for improving the mechanical properties of the composites. The dispersibility of the MWCNTs and mechanical properties of the composites was increased by the acid treatment with treated for 2 hours compared to the pristine MWCNTs and acid treatment MWCNTs with treated for 0, 0.5, 1, 3 and 4 hours.

라텍스 기법으로 제조한 폴리스티렌/다중벽 탄소나노튜브 나노복합재료의 나노튜브 길이가 유변학적 특성에 미치는 영향

라텍스 블렌딩 기법을 이용하여 폴리스티렌(PS)/다중벽 탄소나노튜브(MWCNT) 나노복합재료를 제조하여 나노튜브 길이에 따른 나노복합재료의 유변학적 특성을 고찰하였다. 나노복합재료 제조에 사용된 단분산 PS 입자는 무유화제 유화중합으로 제조하였고 NWCNT는 불순물 제거와 분산성 향상을 위해 표면개질 과정을 거친 후 사용하였다. 최종적인 나노복합재료는 단분산 PS 입자와 개질한 MWCNT를 초음파 교반조에서 분산시킨 후 동결건조 과정을 거쳐 제조하였다. 나노복합재료의 MWCNT 함량과 나노튜브 길이에 따른 유변학적 특성은 소진폭 진동 전단유동을 부과시켜 평가하였다. 본 연구에서 고찰한 PS/MWCNT 나노복합재료는 MWCNT의 함량이 증가할수록, 나노튜브 길이가 길수록 유변물성 향상 효과가 뚜렷하였다. 이는 MWCNT 함량이 증가할수록 나노복합재료의 유변학적 특성이 액체적 특성에서 점차 고체적 특성으로 변화하기 때문이며. 나노튜브 길이가 길수록 네트워크 구조를 달성하는 임계 농도가 직아 지지 때문인 것으로 판단된다.

New approach to model the buckling and stable length of multi walled carbon nanotube probes near graphite sheets

Modeling the buckling of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite has been carried out for the first time via two analytical approximation methods as well as a numerical one. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. The critical values of MWCNT tip deflection and MWCNT-graphite attraction at the onset of the instability are computed. In addition, minimum nanotube-graphite initial gap and stable length of freestanding CNT are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers.

The effect of multiwalled carbon nanotube dimensions on the morphology, mechanical, and electrical properties of melt mixed polypropylene‐based composites

AbstractThe effect of multiwalled carbon nanotube (MWCNT) dimensions and surface modification on the morphology, mechanical reinforcement, and electrical properties of PP‐based composites, prepared by melt mixing, has been studied. The MWCNTs of small (d < 10 nm) and large (d = 40–60 nm) diameters with various intrinsic aspect ratios (L/d) have been used as filler. Transmission electron microscopy and very cold neutrons (VCN) scattering showed that both as‐received and surface modified small diameter MWCNT(1)s exhibit a strong tendency to bundle or cluster together in melt compared to both long MWCNT(3)s and short MWCNT(2)s large diameter nanotubes. The fractions of isolated nanotubes are higher and the mass‐fractal dimensions are lower for thick MWCNT‐based nanocomposites. The nanotubes of all types are heterogeneous nucleation sites for PP crystallization. The tensile and DMA testing results revealed that both long thick MWCNT(3)s with L/d ≈ 300 and thin MWCNT(1)s with highest intrinsic L/d > 1000 exhibit similar reinforcing effects, because drastically decreasing the effective aspect ratio (L/d)eff of the thin flexibly nanotubes within polymer matrix. The nanocomposites based on the long large diameter MWCNT(3)s demonstrated the lowest percolation threshold equal to 1.5 vol % loading, highest dielectric and electromagnetic waves shielding properties. It was concluded that the choice of optimal diameter and length of MWCNTs is right approach to the improvement in the dispersion state and straightness of multiwelled carbon nanotubes in polymer melt as well as to enhancement of their efficiency as reinforcing and conductive nanosized filler. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effects of grafted chain length on mechanical and electrical properties of nanocomposites containing polylactide-grafted carbon nanotubes

We herein report the effects of interfacial reinforcement on mechanical and electrical properties of nanocomposites based on polylactide (PLA) and multi-walled carbon nanotube (MWCNT). For this purpose, a series of MWCNTs grafted with PLA chains of various lengths (MWCNT- g-PLAs) were prepared by ring-opening polymerization of l-lactide with carboxylic acid-functionalized MWCNT (MWCNT-COOH). MWCNT- g-PLAs were then mixed with commercial PLA to obtain PLA/MWCNT- g-PLA nanocomposites with 1.0 wt.% MWCNT content. It was revealed that morphological, mechanical, and electrical properties of PLA/MWCNT- g-PLA nanocomposites were strongly dependent on the PLA chain length of MWCNT- g-PLAs. FE-SEM images exhibited that the nanocomposites containing MWCNT- g-PLA with longer PLA chain length exhibited better dispersion of MWCNTs in the PLA matrix. Initial moduli and tensile strengths of PLA/MWCNT- g-PLA composites increased with the increment of chain length of PLA grafted on MWCNTs, which attributes to the improved interfacial adhesion between the grafted PLA chains of MWCNT- g-PLA and the PLA matrix. As a result, the experimental initial modulus (2775 ± 193 MPa) of the nanocomposite including MWCNT- g-PLA with PLA chains of average molecular weight of 530 g/mol was quite close to the theoretical value (2911 MPa) predicted for the nanocomposite with perfect interfacial adhesion. Unexpectedly, electrical resistivities of PLA/MWCNT- g-PLA nanocomposites were found to increase from ∼10 4 to ∼10 12 Ω/sq with increasing the PLA chain length of MWCNT- g-PLA, which is due to the fact that the PLA chains grafted on MWCNTs prevent the formation of the electrical conduction path of MWCNTs in the PLA matrix.

Aspect ratio control of acid modified multiwalled carbon nanotubes

This study examined the effects of acid treatments on the length of multiwalled carbon nanotubes (MWCNTs) as well as the influence of the aspect ratio of the MWCNTs on the electrical percolation threshold. In particular, the length distribution, intensity ratio of the G and D Raman peaks, BET surface area, and maximum decomposition temperatures of the MWCNTs were investigated. The MWCNTs showed different electrical percolation thresholds depending on the aspect ratio. The higher aspect ratio MWCNTs had lower electrical percolation thresholds than those with smaller ratios due to their ease of contact with other MWCNTs. In terms of the electrical behavior of a MWCNT film, many more short MWCNTs were necessary to reach the electrical percolation threshold than long MWCNTs. These results demonstrate the need to control the aspect ratio of MWCNTs in order for them to be used efficiently in electrical applications.