Aligned Multi-walled Carbon Nanotubes Research Articles

Evaluating the osteogenic properties of polyhydroxybutyrate-zein/multiwalled carbon nanotubes (MWCNTs) electrospun composite scaffold for bone tissue engineering applications

In this investigation, the electrospun nanocomposite scaffolds were developed utilizing poly-3-hydroxybutyrate (PHB), zein, and multiwalled carbon nanotubes (MWCNTs) at varying concentrations of MWCNTs including 0.5 and 1 wt%. Based on the SEM evaluations, the scaffold containing 1 wt% MWCNTs (PZ-1C) exhibited the lowest fiber diameter (384 ± 99 nm) alongside a suitable porosity percentage. The presence of zein and MWCNT in the chemical structure of the scaffold was evaluated by FTIR. Furthermore, TEM images revealed the alignment of MWCNTs with the fibers. Adding 1 % MWCNTs to the PHB-zein scaffold significantly enhanced tensile strength by about 69 % and reduced elongation by about 31 %. Hydrophilicity, surface roughness, crystallinity, and biomineralization were increased by incorporating 1 wt% MWCNTs, while weight loss after in vitro degradation was decreased. The MG-63 cells exhibited enhanced attachment, viability, ALP secretion, calcium deposition, and gene expression (COLI, RUNX2, and OCN) when cultivated on the scaffold containing MWCNTs compared to the scaffolds lacking MWCNTs. Moreover, the study found that MWCNTs significantly reduced platelet adhesion and hemolysis rates below 4 %, indicating their favorable anti-hemolysis properties. Regarding the aforementioned results, the PZ-1C electrospun composite scaffold is a promising scaffold with osteogenic properties for bone tissue engineering applications.

Potassium doping of vertically aligned multi-walled carbon nanotubes.

Alkali metal doping of multi-walled carbon nanotubes is of great interest, both fundamentally to explore the effect of dopants on quasi-one-dimensional electrical systems and for energy applications such as alkali metal storage. We present an investigation with complementary photoemission and Raman spectroscopies, fully carried out in an ultra-high vacuum, to unveil the electronic and vibrational response of a forest of highly aligned multi-walled carbon nanotubes by in situ potassium doping. The charge donation by the alkali adatoms induces a plasmon mode, and the density of states undergoes an energy shift consistent with electron donation and band filling of the multi-walled carbon nanotube band structure. The π-states in the valence band and the Raman peaks unveil an evolution that can be ascribed to charge donation and partially to a tensile strain exerted by the K adatoms on the carbon lattice. All these effects are thermally reversible, fostering these materials as a potential system for electronic charge harvesting.

Anisotropic Piezoresistive Sensors Made with Magnetically Induced Vertically Aligned Carbon Nanotubes/Polydimethylsiloxane.

A piezoresistive material consisting of internal vertically aligned carbon nanotubes acting in concert with an external microdome structure is prepared to obtain a flexible piezoresistive sensor with high anisotropy. Here, we first obtained flexible piezoresistive composites (VCP) with anisotropic properties by inducing the vertical alignment of multiwalled carbon nanotubes in the pressure direction under a weak magnetic field of 0.6 T. Then, the composite with a microdome structure on the surface (m-VCP) was fabricated by a mold with a microstructure to further increase the anisotropy of the composite. The m-VCP microstructure was docked with VCP and placed between two layers of copper foil. With the synergistic effect of vertically aligned carbon nanotubes and the microdome structure, the sensitivity of the flexible sensor in the pressure direction was dramatically increased. In the low-strain range (0-6%), the sensitivity of m-VCP (GF = 9.208) is improved by 49% compared to m-CP and by 86% compared to VCP. The sensor has high anisotropy in the piezoresistive direction and retains good fatigue resistance under fatigue testing for 2000 cycles. This means that the sensor can be used in emerging fields such as human health monitoring, wearable electronics, and intelligent human-computer interaction.

Open-hole fatigue testing of UD-GFRP composite laminates containing aligned CNTs using infrared thermography

The present study aims to characterize the open-hole fatigue (OHF) behavior of unidirectional glass fiber-reinforced polymer matrix (UD-GFRP) epoxy composites containing aligned multi-walled carbon nanotubes (MW-CNTs) locally reinforcing the composite in the vicinity of the hole. The performance of these multi-scale composites has been compared with that of composites containing randomly oriented MW-CNTs around the hole. UD-GFRP containing neat epoxy (without MW-CNTs) as a matrix were the control samples in the study. Infrared thermography has been used to investigate the damage evolution in composites during the OHF tests. MW-CNTs, aligned perpendicular to the loading direction, improved the fatigue strength of the UD-GFRP composites by over 12% compared to the control samples. Fractography results are also presented in support of the findings from fatigue testing. Infrared thermography is presented as a method to rapidly determine the high cycle fatigue strength of the OHF specimens.

Multi-Walled Carbon Nanotube Array Modified Electrode with 3D Sensing Interface as Electrochemical DNA Biosensor for Multidrug-Resistant Gene Detection.

Drug resistance in cancer is associated with overexpression of the multidrug resistance (MDR1) gene, leading to the failure of cancer chemotherapy treatment. Therefore, the establishment of an effective method for the detection of the MDR1 gene is extremely crucial in cancer clinical therapy. Here, we report a novel DNA biosensor based on an aligned multi-walled carbon nanotube (MWCNT) array modified electrode with 3D nanostructure for the determination of the MDR1 gene. The microstructure of the modified electrode was observed by an atomic force microscope (AFM), which demonstrated that the electrode interface was arranged in orderly needle-shaped protrusion arrays. The electrochemical properties of the biosensor were characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Chronocoulometry (CC) was used for the quantitative detection of the MDR1 gene. Taking advantage of the good conductivity and large electrode area of the MWCNT arrays, this electrochemical DNA sensor achieved a dynamic range from 1.0 × 10-12 M to 1.0 × 10-8 M with a minimal detection limit of 6.4 × 10-13 M. In addition, this proposed DNA biosensor exhibited high sensitivity, selectivity, and stability, which may be useful for the trace analysis of the MDR1 gene in complex samples.

Alignment of multiwalled carbon nanotubes‐reinforced epoxy by a novel shear assisted method in the presence of the electric field

AbstractThe application of multiwall carbon nanotubes (MWCNTs) alignment associated with external field techniques is fairly limited in the industry due to the cost implications of scaling such external fields. To address this problem, a new shear‐assisted method is introduced to increase the effectiveness of MWCNTs alignment techniques using electric field. In addition, the effect of curing temperature of polymer in CNT‐reinforced nanocomposites, is studied on the alignment of MWCNTs using our novel shear‐assisted technique. The results show that increasing the temperature during the curing process of the polymer can help with the alignment of MWCNTs using our shear‐assisted technique. This may be attributed to lower gel‐time of polymer matrix at high temperatures that can prevent agglomeration of the MWCNTs in the matrix. Moreover, fractography of reinforced composites has been studied by scanning electron microscopy to investigate the effects of curing temperature on the alignment of MWCNTs in the epoxy matrix.

Raman spectroscopy used for estimating the effective elastic modulus of carbon nanotubes in aligned multi-walled carbon nanotubes/ epoxy composites under tensile loading

Raman spectroscopy used for estimating the effective elastic modulus of carbon nanotubes in aligned multi-walled carbon nanotubes/ epoxy composites under tensile loading

Reversible, voluminous and tunable patterning of multiwalled carbon nanotubes in ferrofluid: Partial or complete?

A new kind of hybrid fluids showing multiwalled carbon nanotubes (MWCNTs) coupled with magnetic nanoparticles have been synthesized and investigated for their structural, magnetic, and magneto-viscoelastic properties. The experimental results confirmed the cooperative coupling between MWCNTs and Fe3O4 nanoparticles forming the basis of magnetorheological mechanism which narrates the rheological properties. The molecular dynamics (MD) simulation and interaction calculations for particle-particle, particle-tube and tube-tube have been described and explained comprehensively in view of the interface properties of nanoparticles and nanotubes. The whole of the experimental and theoretical investigations confirms the bulk alignment of bent MWCNTs in ferrofluidic system which can be tuned with an applied magnetic field. The MD simulation predicts a weak and short-range molecular ordering mediated via free oleic acid molecules between MWCNTs and coated nanoparticles of ferrofluid. The interparticle interaction calculations (van der Waals, steric and magnetic energies) showed that the surface coated magnetic nanoparticles are kinetically stable in the fluid while the MWCNTs form chain-like aggregates. Moreover, by application of classical beam theory, a thermodynamic energy barrier comparison was made for the unbending of particle impregnated MWCNTs. Thus, considering the dimensional compatibility of nanotubes and nanoparticles, a field-induced partial alignment of MWNCTs by virtue of their bent form in ferrofluidic system is proposed. A partial or complete accomplishment of the reversibility and tunability of the patterning of MWCNTs on a large scale in ferrofluid has been investigated in detail.

Effect of aspect ratio on piezo-resistance properties of aligned multi-walled carbon nanotube polymer composites

Multi-walled carbon nanotubes (MWNTs) are actively used as reinforcing and electrical filler materials in composites owing to their superior electrical and mechanical performances. The electrical, mechanical, and piezoresistive performances of MWNT/polymer composites vary depending on the filler direction and aspect ratio (A/R). In this study, we fabricated MWNT/polymer composites with fillers aligned at different A/R. To prepare the aligned MWNT polymer composite with three different A/R, well dispersed MWNTs in the polymer matrix were applied continuous shear force in one direction by two-roll mill. Also, randomly oriented composites using same fillers were compared their mechanical, electrical, and piezoresistive properties to aligned composites. The aligned composite with the high A/R showed 6.03 times higher in elastic modulus and 17.4 times higher in electrical conductivity compared to the randomly oriented composite with the low A/R. The piezo-resistance, expressed as the maximum resistance change in tension, of the aligned composite with the low A/R had 84% higher than that of the randomly arrayed composite with the high A/R. In contrast to the enhancement of mechanical and electrical properties as the A/R rises and alignment occurs, the resistance in tension increases as the A/R decreases and the fillers are aligned. Thus, the influence of the filler alignment on the piezo-resistance properties of the composite is significant.

Carbon Nanotube Based Robust and Flexible Solid-State Supercapacitor.

All solid-state flexible electrochemical double-layer capacitors (EDLCs) are crucial for providing energy options in a variety of applications, ranging from wearable electronics to bendable micro/nanotechnology. Here, we report on the development of robust EDLCs using aligned multiwalled carbon nanotubes (MWCNTs) grown directly on thin metal foils embedded in a poly(vinyl alcohol)/phosphoric acid (PVA/H3PO4) polymer gel. The thin metal substrate holding the aligned MWCNT assembly provides mechanical robustness and the PVA/H3PO4 polymer gel, functioning both as the electrolyte as well as the separator, provides sufficient structural flexibility, without any loss of charge storage capacity under flexed conditions. The performance stability of these devices was verified by testing them under straight and bent formations. A high value of the areal specific capacitance (CSP) of ∼14.5 mF cm-2 with an energy density of ∼1 μW h cm-2 can be obtained in these devices. These values are significantly higher (in some cases, orders of magnitude) than several graphene as well as single-walled nanotube-based EDLC's utilizing similar electrolytes. We further show that these devices can withstand multiple (∼2500) mechanical bending cycles, without losing their energy storage capacities and are functional within the temperature range of 20 to 70 °C. Several strategies for enhancing the capacitive charge storage, such as physically stacking (in parallel) individual devices, or postproduction thermal annealing of electrodes, are also demonstrated. These findings demonstrated in this article provide tremendous impetus toward the realization of robust, stackable, and flexible all solid-state supercapacitors.

Study of Mechanical and Optical Properties of Aligned Multiwall Carbon Nanotubes in Poly(methyl methacrylate) Matrix in Electric and Magnetic Fields

Study of Mechanical and Optical Properties of Aligned Multiwall Carbon Nanotubes in Poly(methyl methacrylate) Matrix in Electric and Magnetic Fields

Analysis of the Piezoelectric Properties of Aligned Multi-Walled Carbon Nanotubes

Recent studies reveal that carbon nanostructures show anomalous piezoelectric properties when the central symmetry of their structure is violated. Particular focus is given to carbon nanotubes (CNTs) with initial significant curvature of the graphene sheet surface, which leads to an asymmetric redistribution of the electron density. This paper presents the results of studies on the piezoelectric properties of aligned multi-walled CNTs. An original technique for evaluating the effective piezoelectric coefficient of CNTs is presented. For the first time, in this study, we investigate the influence of the growth temperature and thickness of the catalytic Ni layer on the value of the piezoelectric coefficient of CNTs. We establish the relationship between the effective piezoelectric coefficient of CNTs and their defectiveness and diameter, which determines the curvature of the graphene sheet surface. The calculated values of the effective piezoelectric coefficient of CNTs are shown to be between 0.019 and 0.413 C/m2, depending on the degree of their defectiveness and diameter.

Ni2+ enriched carbon nanotubes nanohybrids based non-platinum counter electrodes for dye sensitized solar cells

The development of competent substitutes for Pt counter electrode (CE), possessing excellent electrocatalytic activity, stability, and ready availability, is a key issue to materialize the long-term stability and economical large-scale industrial production of future generation dye sensitized solar cells (DSSCs). In the present work, a cost effective and solution processable hydrothermal technique has been utilized to synthesize Ni2+ enriched nanohybrids of nickel oxide (NiO) and nickel sulfide (Ni3S2) nanoparticles with multi-walled carbon nanotubes (MWCNTs) as CE in DSSCs. NiO/MWCNTs nanohybrids showed superior electrocatalytic behaviour among MWCNTs, NiO, Ni3S2, nanohybrids, and Pt. The nanohybrids containing aligned network MWCNTs exhibited good electrical conductivity, high specific surface area and better stability. These nanohybrids have been further employed as CE in DSSCs and observed higher Power Conversion Efficiency (PCE) for NiO/MWCNTs nanohybrids CE (3.80%) among others and is almost comparable to that of Pt based DSSC (3.90%). It has been explained on the basis of Ni2+content present in the nanohybrids. The higher content of Ni2+species provides a greater number of active sites representing higher electrocatalytic activity that would further productively catalyze the reactions occurring at CE/electrolyte interface in DSSCs.

Laser Patterning of Aligned Carbon Nanotubes Arrays: Morphology, Surface Structure, and Interaction with Terahertz Radiation.

The patterning of arrays of aligned multi-walled carbon nanotubes (MWCNTs) allows creating metastructures for terahertz (THz) applications. Here, the strips and columns from MWCNTs vertically grown on silicon substrates are prepared using CO2 laser treatment. The tops of the patterned arrays are flat when the laser power is between 15 and 22 W, and craters appear there with increasing power. Laser treatment does not destroy the alignment of MWCNTs while removing their poorly ordered external layers. The products of oxidative destruction of these layers deposit on the surfaces of newly produced arrays. The oxygen groups resulting from the CO2 laser treatment improve the wettability of nanotube arrays with an epoxy resin. We show that the patterned MWCNT arrays absorb the THz radiation more strongly than the as-synthesized arrays. Moreover, the pattern influences the frequency behavior of the absorbance.

Nanoplates forced alignment of multi-walled carbon nanotubes in alumina composite with high strength and toughness

Although the strengthening and toughening effects on ceramic composites are expected to be maximized by alignment of multi-walled carbon nanotubes (MWCNTs) in matrices, this concept has been rarely realized in practice due to the lack of convenient processing strategy. Here, the alignment of MWCNTs in alumina composite can be readily obtained by using α-Al2O3 nanoplates as raw powder. With the assistance of vacuum filtration and pressure in sintering, the highly aligned MWCNTs in alumina matrix are formed in in-plane direction. Accordingly, the strength and toughness in 1.5 wt% MWCNTs/alumina composite are improved by 58 % and 66 % with respect to monolithic alumina, respectively. Transmission electron microscopy observation reveals that the MWCNTs under great compressive residual stress are mainly embedded inside the grains, leading to much stronger grain boundaries. Meanwhile, the toughening effect is mainly attributed to the highly energy dissipating bridging and pullout, owing to the very effective load transfer.

Reorientation and Flow of Liquid Crystal for a Pressure Sensor Using Carbon Nanotube Sheets

AbstractThe network formation of carbon nanotubes (CNTs) and the viscoelasticity of liquid crystals (LCs) are synergetic properties that enable the formation of composites very sensitive to external pressure. Using a layered structure with nematic LCs and anisotropic networks formed by highly aligned multiwall CNT sheets, the pressure sensor capability of such structure and its piezoresistive response are demonstrated. The application of pressure on the upper substrate is transmitted via LC elastic deformation and flow onto the underlying CNT sheets, improving the electrical conductance. The fabrication process here is relatively facile and versatile as stretched CNT sheets can be easily transferred to any chosen substrate. The sensor response is linear with decrease of 2.42 Ω kPa−1 as the pressure value increases and it is reversible. The sensitivity depends on the thickness of the overlying LC layer and by its relative change, affected by the spacers during force application, but also on the electrical characteristics of the CNTs. The highest sensitivity is obtained with one single CNT sheet and the responsiveness decreases with the increase of number of layers due to the smaller influence of the LC on the contact resistance of the CNT sheets.

Electrical and Optical Properties of Silicone Oil/Carbon Nanotube Nanocomposites.

The present work describes the preparation and the investigation of the room temperature electrical and optical properties of a series of liquid nanocomposites (lnC) prepared with different concentrations of multiwalled carbon nanotubes (MWCNT) in a variety of liquid matrices: glycerin, Vaseline, glucose, propylene glycol and silicone oil (SIO). Special attention is deserved to the SIO matrix, owing to its convenient electrical properties for our purposes. We verified that a small percent fraction of MWCNT dispersed along the SIO matrix is capable of improving the electrical conductivity of the matrix by orders of magnitude, indicating that the MWCNT strongly participates in the electrical conduction mechanism. Also, the application of an external electric field to this lnC resulted in large changes in the optical transmittance, that were interpreted as a consequence of the fieldinduced MWCNT alignment into the liquid matrix. The characteristics of such a new category of nanocomposite in the liquid state suggest further studies.

Analysis of neural cell behaviour on anisotropic electrically conductive polymeric biodegradable scaffolds reinforced with carbon nanotubes

AbstractThe advent of biocompatible and biodegradable scaffolds has opened up a plethora of possibilities in neural tissue engineering. An emerging approach to overcome some existing drawbacks of neural scaffold design and functioning is a natural conductive polymeric scaffold. It is analogous to the extracellular matrix and provides an environment conducive to neural growth. This study focuses on the fabrication of soft polymeric neural scaffold, reinforced with multi‐walled carbon nanotubes (MWCNTs) in a chitosan matrix, for directional neuronal growth. The scaffolds were fabricated by varying the nanofiller content as 0.5, 1.0 and 2.0. wt%, which were aligned in the chitosan matrix by an alternating bias electric field and compared with their random counterpart. The uniform distribution of the nanofillers in the matrix, good combinatorial bonding, and the directional alignment of the MWCNTs resulted in enhancement of mechanical properties and electrical conductivity in comparison to scaffolds with randomly arranged reinforcements. Additionally, the degradation kinetics of the fabricated scaffolds was tuned to the regeneration regime of peripheral nerves. After physical characterization, the biocompatibility of the designed scaffolds was evaluated by culturing HT‐22 neuronal cells on the scaffolds. Along with biocompatibility, the suitability of anisotropic conductivity of the scaffolds was evaluated by the directional growth of cells cultured on aligned MWCNT–chitosan scaffold. The preferential direction of neurite growth achieved on chitosan‐aligned MWCNT films and the improved mechanical and electrical properties in the MWCNT alignment direction are very encouraging for their potential use in neural tissue engineering.

Electrically activated chemical bath deposition of CdS on carbon nanotube arrays

Electrically stimulated depositions of CdS nanoparticles on the surface of aligned multi-walled carbon nanotube (CNT) arrays were investigated by applying a voltage of 3 V to the electrodes placed into a chemical bath with an aqueous ammonium solution of CdCl2 and thiourea. The CNT arrays were fixed on positive, negative, and neutral electrodes. Morphology, composition and structure of CdS-CNT hybrids were studied using scanning electron microscopy, Raman scattering and X-ray photoelectron spectroscopy. CdS nanocrystallites in the hybrids were found to exhibit synthesis-dependent luminescence properties. S-vacancy enriched CdS grown on the positively charged CNT array possessed red photoluminescence (PL). Purple emission was attributed to small-size CdS nanocrystals synthesized on the negatively charged CNTs. The CNT array located on a neutral electrode was uniformly covered by CdS nanoparticles with a highly intense blue PL. Our results indicate a promising effect of the electrical field for enhancement of the growth rate of CdS nanocrystals.

Enhancement of open hole tensile strength via alignment of carbon nanotubes infused in glass fiber - epoxy - CNT multi-scale composites

Cut-out or holes are unavoidable features in composites for structural assembly and functionality. To enhance the strength of the unidirectional glass fiber reinforced plastic (UD-GFRP) laminates around the cut-outs, multi-walled carbon nanotubes (MW-CNTs) were locally aligned at the periphery of the cut-outs via non-uniform electric field. These multi-scale UD-GFRP composites were fabricated in two configurations based on CNT alignment in parallel and perpendicular directions to the glass fiber orientation. The performance was compared with composites containing randomly oriented MW-CNTs in epoxy matrix and composites without MW-CNTs. The damage evolution was investigated using digital image correlation (DIC) techniques during open hole tensile (OHT) tests. The presence of aligned MW-CNTs around the hole perpendicular to the fiber orientation was able to arrest the pertinent damage modes leading to an increase of the tensile strength by 27% as compared to the control samples fabricated using neat epoxy resin.