Individual Multiwalled Carbon Nanotubes Research Articles

An investigation of the impact of functionalized MWCNT reinforcement on interlaminar strength of glass/epoxy composites: a comparative view

ABSTRACT In the present investigation, diverse functionalized states of multi-walled carbon nanotubes (MWCNT) were employed in fabricating glass/epoxy composites, with the MWCNT consistently incorporated at a 0.5 wt.% concentration. These functionalization states included pristine, hydroxyl, amine, and carboxylic conditions, systematically compared against neat glass/epoxy composites. The findings elucidated that all three functionalizations positively influenced the enhancement of interlaminar shear strength, mode-I interlaminar fracture toughness, and mode-II interlaminar fracture toughness properties. Notably, the amine-functionalized MWCNT exhibited superior performance relative to other formulations. The composite reinforced with amine MWCNT demonstrated significant improvements in ILSS, mode-I ILFT, and mode-II ILFT by 41.82%, 37.75%, and 40.93%, respectively. These enhancements are attributed to factors such as the presence of a more functional group, the quantity of individual MWCNT, and the introduction of additional damage mechanisms, including MWCNT pullout and bridging.

Locally controlled MOF growth on functionalized carbon nanotubes

Metal-organic frameworks (MOFs) are highly versatile materials because of their tunable properties. However, the typically poor electrical conductivity of MOFs presents challenges for their integration into electrical devices. By adding carbon nanotubes to MOF synthesis, a highly intergrown material with increased conductivity and chemiresistive sensing properties can be obtained. Here, we present a patterning technique to control MOF growth on predefined areas of one particular carbon nanotube. We found that electron beam pretreatment of -COOH functionalized multi-walled carbon nanotubes inhibits the growth of UiO-66 MOF on these multi-walled carbon nanotubes. By irradiating individual multi-walled carbon nanotubes, we show that MOF growth can be inhibited in predefined tube areas, creating MOF-free spaces on the nanotube. In this way, our method shows a possibility to pattern MOF growth on individual nanotubes.

Selectivity enhancement by the presence of HOF + CNT composite membranes investigated by non-equilibrium molecular dynamics

Hydrogen purification through membrane separation offers convenience and suitability for on-site operation, especially in automotive fuel cells that utilize reformed methanol as a hydrogen source. In this study, the molecular dynamics simulation method was employed to investigate the micro-separation mechanism of hydrogen purification using multi-walled carbon nanotubes (MWNTs) and hydrogen-bonded organic frameworks (HOFs) as membrane materials. Novel composite membranes combining different HOF and MWNT materials were designed to enhance the interaction energy with CO2. The results demonstrated that these composite membranes exhibited higher selectivity in the separation of H2/CO2 gas mixtures, achieving higher hydrogen permeability compared with individual HOF and MWNT membranes. Notably, the PhTCz1 + CNT, UPC-H4a + CNT, and TCPP-1,3-DPP + CNT-3 composite membranes demonstrated 100 % CO2 retention and reached a maximum flux hydrogen of 4.782 × 105 GPU, which was higher than traditional membranes by 6 orders of magnitude. Furthermore, the PhTCz1 + CNT-3 composite membrane had a significant ability to simultaneously intercept CO2 and CO. The MD calculation results show that this newly synthesized HOF + CNT composite membrane material can provide high permeability as well as ultrahigh selectivity simultaneously, making it a prospective H2 separation membrane with superior performance.

Differential multi-probe thermal transport measurements of multi-walled carbon nanotubes grown by chemical vapor deposition

Carbon nanotubes (CNTs) are quasi-one dimensional nanostructures that display both high thermal conductivity for potential thermal management applications and intriguing low-dimensional phonon transport phenomena. In comparison to the advances made in the theoretical calculation of the lattice thermal conductivity of CNTs, thermal transport measurements of CNTs have been limited by either the poor temperature sensitivity of Raman thermometry technique or the presence of contact thermal resistance errors in sensitive two-probe resistance thermometry measurements. Here we report advances in a multi-probe measurement of the intrinsic thermal conductivity of individual multi-walled CNT samples that are transferred from the growth substrate onto the measurement device. The sample-thermometer thermal interface resistance is directly measured by this multi-probe method and used to model the temperature distribution along the contacted sample segment. The detailed temperature profile helps to eliminate the contact thermal resistance error in the obtained thermal conductivity of the suspended sample segment. A differential electro-thermal bridge measurement method is established to enhance the signal-to-noise ratio and reduce the measurement uncertainty by over 40%. The obtained thermal resistances of multiple suspended segments of the same MWCNT samples increase nearly linearly with increasing length, revealing diffusive phonon transport as a result of phonon-defect scattering in these MWCNT samples. The measured thermal conductivity increases with temperature and reaches up to 390 ± 20 W m−1 K−1 at room temperature for a 9-walled MWCNT. Theoretical analysis of the measurement results suggests submicron phonon mean free paths due to extrinsic phonon scattering by extended defects such as grain boundaries. The obtained thermal conductivity is decreased by a factor of 3 upon electron beam damage and surface contamination of the CNT sample.

Highly Efficient Dispersion of Individual Multiwalled Carbon Nanotubes by Polylactide in High Elastic State

Highly Efficient Dispersion of Individual Multiwalled Carbon Nanotubes by Polylactide in High Elastic State

Surface Diffusion of C1–C3 Alcohols on Multiwall Carbon Nanotubes

The diffusion of methanol, ethanol, and 2-propanol using individual multiwall carbon nanotubes (MWCNT) and MWCNT bundles was investigated for the first time via application of the quartz crystal microbalance. At small times, the release of alcohol obeys the advective mechanism. In contrast, no deviations from Fick’s law were justified at large times. This situation holds for either individual MWCNTs or MWCNT bundles. The utilized MWCNTs are mainly closed from both ends. Therefore, the alcohol release is controlled by surface diffusion. The measured surface diffusivity is in the order of 10-13 m2/s. The obtained diffusivities are in close proximity with the known surface diffusion coefficients on carbon materials.

Sonochemical fabrication of a hybrid electrode material based on pristine carbon nanotubes and bentonite clay for fast and highly sensitive determination of dopamine in the presence of ascorbic and uric acid

This work focuses on the attachment of bentonite clay to external surface of individual pristine multiwalled carbon nanotubes (MWCNTs) and the use of the resulting hybrid material for the fast and highly sensitive electrochemical determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). XRD, FE-SEM and EDX highlighted the pristine state of MWCNTs and bentonite clay. HR-TEM confirmed the adsorption of clay on the external surfaces of individual pristine MWCNTs. Electrochemical characterization showed that the fabricated sensor possesses a large electrochemical surface area with excellent electron transfer properties. The influence of parameters likely to affect sensor performance was studied; 40 s, 10 μL suspension, and pH 7.4 were found to be the optimal accumulation time, optimal suspension volume, and optimal electrolyte pH, respectively. Under these optimal conditions, DPV peak currents were linearly related to DA concentrations in the range of 0.4–14 μM, and the detection limit was found to be 6 nM (S/N = 3). The Interference study revealed that the sensor eliminates AA and UA interference up to concentrations above their blood levels. Furthermore, the developed sensor exhibited good repeatability, satisfactory long-term stability, and was successfully applied to the detection and quantification of DA in human serum sample with satisfactory recoveries.

Evidence of in-depth incorporation of carbon nanotubes in alumina layers grown by plasma electrolytic oxidation

Incorporation of carbon nanotubes (CNTs) into ceramic layers during plasma electrolytic oxidation (PEO) is promising for direct synthesis of composite protective coating on lightweight metallic alloys. In the present study, complementary characterization techniques were used in order to definitively assess the presence of CNTs through the thickness of a PEO alumina coating formed in a silicate-based electrolyte containing dispersed multi-walled carbon nanotubes (MWCNTs). Cross-checked results helped in evidencing that MWCNTs are partially incorporated in the thickness of the PEO alumina coating, and more precisely through the porous outer sublayer. They were mainly found in the form of scaffolds that line the interior walls of pores. To a lesser extent, some individual MWCNTs were found interlocked in the fine grain structure of alumina. The analysis of the specific Raman bands of MWCNTs also highlighted that incorporation is associated with an alteration of the structural integrity of the MWCNTs. It was also established that the increase in the amount of dispersed MWCNTs results in a thicker but more porous CNTs-enriched PEO coating. Based on the collected results, some precisions regarding the incorporation mechanisms were proposed.

Dry Synthesis of Binder-Free Ruthenium Nitride-Coated Carbon Nanotubes as a Flexible Supercapacitor Electrode.

Ruthenium nitride was successfully deposited on a multiwalled carbon nanotube (MWCNT) forest grown on a stainless-steel mesh substrate by radiofrequency plasma-assisted pulsed laser deposition. This novel dry fabrication method for flexible supercapacitor electrodes eliminates toxic byproducts and the need for any binder component. Experimental results show a successful thin film coating of the individual MWCNTs with RuNx under various synthesis conditions. The electrochemical characterization demonstrates a significant improvement in capacitance of the synthesized RuNx-MWCNT electrode compared to the bare MWCNT forest, with a large potential window of 1.2 V. Capacitance values as high as 818.2 F g-1 (37.9 mF cm-2) have been achieved.

The Role of Phase Migration of Carbon Nanotubes in Melt-Mixed PVDF/PE Polymer Blends for High Conductivity and EMI Shielding Applications.

In this work, the effects of blend ratio and mixing time on the migration of multi-walled carbon nanotubes (MWCNTs) within poly(vinylidene fluoride) (PVDF)/polyethylene (PE) blends are studied. A novel two-step mixing approach was used to pre-localize MWCNTs within the PE phase, and subsequently allow them to migrate into the thermodynamically favored PVDF phase. Light microscopy images confirm that MWCNTs migrate from PE to PVDF, and transmission electron microscopy (TEM) images show individual MWCNTs migrating fully into PVDF, while agglomerates remained trapped at the PVDF/PE interface. PVDF:PE 50:50 and 20:80 polymer blend nanocomposites with 2 vol% MWCNTs exhibit exceptional electromagnetic interference shielding effectiveness (EMI SE) at 10 min of mixing (13 and 16 dB, respectively-at a thickness of 0.45 mm), when compared to 30 s of mixing (11 and 12 dB, respectively), suggesting the formation of more interconnected MWCNT networks over time. TEM images show that these improved microstructures are concentrated on the PE side of the PVDF/PE interface. A modified version of the “Slim-Fast-Mechanism” is proposed to explain the migration behavior of MWCNTs within the PVDF/PE blend. In this theory, MWCNTs approaching perpendicular to the interface penetrate the PVDF/PE interface, while those approaching in parallel or as MWCNT agglomerates remain trapped. Trapped MWCNTs act as barriers to additional MWCNTs, regardless of geometry. This mechanism is verified via TEM and scanning electron microscopy and suggests the feasibility of localizing MWCNTs at the interface of PVDF/PE blends.

Influence of crystallinity on the electrical conductivity of individual carbon nanotubes

The material properties of graphene and carbon nanotubes are highly sensitive to defects. Future exploitation of these materials will thereby rely on both a detailed understanding and classification schemes for material quality. Here we have used electron diffraction to measure the mean effective crystallite size of individual multiwalled carbon nanotubes, while also probing their electrical resistance. At room temperature we find a drastic shift in linear resistance of two orders of magnitude at a critical grain size of about 11 nm, which we interpret as an effect from quantum confinement and edge effects in the individual crystallites. For the regions above and below the critical grain size value we suggest a scaling model for the electrical conductivity within a single layer of a multiwalled carbon nanotube which connects its electrical conductivity with the effective crystallite size and tube diameter.

Electrical Conductivity and Wettability of Nanofluids Prepared by Nanocomposite of MWCNTs and Dialkyl Pentasulfide

Background: Multi-walled carbon nanotubes (MWCNTs) were filled with dialkyl pentasulfide (DPS) to prepare MWCNTs-DPS composite (nanocomposite) additives for use in nanofluid- based machining. Methods: The nanocomposite was prepared by employing a liquid phase wet chemistry method, and was then added in pure water with a surfactant to form the nanofluids. The present study comprehensively reveals the effects of additive concentration, acid treatment time, testing temperature and electrowetting conditions on the electrical conductivity and wettability of nanofluids. Results: The nanocomposite was successfully produced with a maximum filling rate of 27.4%. Its additives displayed an optimal performance at a concentration of about 0.1%. Consequently, the electrical conductivity and wettability of the nanofluids were increased by over 13.7% and 6.35%, respectively in comparison with individual MWCNTs additives. Under the electro-wettability conditions, the wetting performance of the nanofluids produced by the nanocomposite increased with the increase in charging voltage. Moreover, due to higher conductivity and greater charge capacity, the nanofluids with a higher additive concentration displayed better wetting performance. Conclusion: The modification and filling enhanced properties such as the surface activity, electrical conductivity and capacitance of the MWCNTs, thereby improving the performance.

Slippage-inhibiting effect of interfacial cross-linking of nanotubes by defluorination on the mechanical properties of free-standing multi-walled carbon nanotube yarns: Comparison with individual multi-walled carbon nanotubes

Carbon nanotube yarns (CNTYs) spun only by twisting have a low mechanical strength due to the slippage of individual CNTs. This hinders the practical applications of CNTYs. Here, we studied the slippage-inhibiting effect of the interfacial cross-linking of the nanotubes by defluorination on the mechanical properties of free-standing MWCNTYs and compared with the fracture tensile strength of the individual defluorinated MWCNTs. The mechanical properties of defluorinated MWCNTYs increased with increasing annealing temperature, and MWCNTYs defluorinated at 800 °C under a pressure of 76 Pa (p-deF800-MWCNTYs) exhibited an average specific fracture strength of 0.69 N/tex and an average specific fracture stiffness of 103.2 N/tex, with high flexibility. As the fracture tensile strength of individual defluorinated MWCNTs was low, the high strength of the p-deF800-MWCNTYs was attributed to the cross-linking of the active carbon atoms in the outer nanotubes with those of the adjacent nanotubes through sp2C and sp3C bonds, which led to the transfer of load to the yarns. Thus, the results of our study highlight the importance of good balance between the defects of CNTs and cross-linking between CNTs.

Ultra-long carbon nanotube-paraffin composites of record thermal conductivity and high phase change enthalpy among paraffin-based heat storage materials

Phase change materials (PCMs) are capable of storage considerably more energy than the conventional systems based on sensible heat. Despite immense and global research, there is a continuous pursuit for high-performance PCMs among which carbon nanocomposites emerge as the most prospective ones. In this paper, by comprehensive analysis of carbon nanotubes (CNTs) of three various morphologies (crystallinity, number of walls, and aspect ratio), we report record-breaking characteristics of CNT-paraffin nanocomposites based on ultra-long (770 μm) in-house multi-wall CNTs (MWCNTs) as fully functional PCMs prepared by a melting technique. By systematic investigations covering scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and analysis of thermophysical properties, we have constructed the most promising MWCNT(0.5% wt.)-paraffin nanocomposite of 37%-enhanced thermal conductivity and 6.3%-higher enthalpy of phase change (∆Hm), in reference to the base paraffin, as well as excellent cycling stability (>50 heating/cooling cycles), and as low supercooling temperature (∆T=Tm–Tc) as 2.4 °C. The superior characteristics derive from rapider nucleation of larger crystallites by MWCNTs proceeding via short- and long-range templating as well as intrinsic characteristics of individual and fibrous ultra-long MWCNTs. Additionally, even a 161%-enhancement in thermal conductivity is available for the long MWCNT-paraffin composite, but at the cost of preserving the remaining thermophysical characteristics of neat paraffin. The results clearly point out the potential of the elaborated PCMs toward thermal energy storage.

Study on the mechanical and electrical properties of twisted CNT yarns fabricated from CNTs with various diameters

The mechanical and electrical properties of multiwalled carbon nanotube (MWCNT) yarns with a wide variety of MWCNT diameters were studied to understand the relationship between the microscopic structures of MWCNTs and the load/charge transport properties of macroscopic MWCNT assemblies. The MWCNT diameters were varied from 14.6 nm to 41.6 nm by varying the amount of catalyst loaded in the synthesis by the chloride-mediated chemical vapor deposition method. We found a drastic change in the tensile behavior of twisted yarns from nonlinear deformation to elastic manner associated with the increases in the tensile strength, Young’s modulus, and electrical conductivity of the twisted MWCNT yarns for smaller-diameter MWCNTs. These improvements are due to the increase in the surface area of MWCNTs in the yarn structure. We also carried out microscopic direct tensile tests on the MWCNTs in a scanning electron microscope to investigate the tensile properties of the individual MWCNTs. The in situ experiments revealed that the obtained high value of the Young’s modulus of the yarn originated from that of the individual MWCNTs.

Pressure dependent conduction of individual multi-walled carbon nanotubes: the effect of mechanical distortions.

Multi-walled carbon nanotubes (MWCNTs) show an oscillation in electrical resistance (from I–V measurements) during mechanical distortion in which peak separation is inversely correlated with the diameter of the MWCNTs. These results provide the first experimental support of the theoretical prediction that distortion causes Van Hove singularities and Dirac cones in MWCNTs to misalign and cause the opening of the band gap, and suggest that when fabricating contacts for CNTs for device applications, the pressure caused by the contact deposition method must be taken into account for manufacturing devices with consistent properties.

Direct Electron Transfer Between Single-Walled Carbon Nanotube and Fructose Dehydrogenase

In this paper, we report the direct electron transfer (DET) reaction between debundled single-walled carbon nanotubes (SWCNTs) and the enzyme flavin adenine dinucleotide (FAD)-dependent fructose dehydrogenase (FDH). An anionic surfactant, sodium cholate (SC), was used to debundle the SWCNTs and disperse them in an aqueous solution, and the experimental conditions were optimized. The DET electrode, FDH/SWCNT-SC, was fabricated by the layer-by-layer drop-casting technique. Cyclic voltammetry experiments were conducted, and the experimental results revealed the presence of a high level of fructose concentration-dependent current (FDC). In the control experiment, FDC was not observed with either multi-walled carbon nanotubes (MWCNTs) or graphene flakes. The reported dimension of the FDH molecule is ~7 nm, which is larger than the diameter of an individual SWCNT (1 nm) but smaller than the diameter of an individual MWCNT (10 nm) and the dimensions of a graphene flake (~100 nm square). Only individual SWCNTs can reside in close proximity (within the distance for DET) of the cofactors FAD and heme c, both of which remain deeply embedded within the protein shell. The FDH/SWCNT-SC electrode had a sensitivity of 27 μA mM <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , a linear dynamic range of 1.4-18.5 mM, and a detection limit of 2.1 μM. The electrode, combined with the enzyme invertase (IVT), can detect the total concentration of fructose and sucrose in samples (using the IVT/FDH/SWCNT-SC electrode). Therefore, fructose and sucrose can be separately quantified when both FDH/SWCNT-SC and IVT/FDH/SWCNT-SC electrodes are used. The amounts of fructose and sucrose in real food samples (100% fruit juice in the present case) determined using these electrodes agreed well with the amounts obtained from high-performance liquid chromatography (HPLC) experiments.

Functionalization of Individual Multi-Wall Carbon Nanotubes during Irradiation and Annealing

The structure of individual multi-wall carbon nanotubes exposed to irradiation by a argon ions and electron flux, as well as subsequent heat processing in an inert medium has been studied using transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that irradiation with argon ions and electrons leads to the formation of defects in the structure of carbon nanotubes, changes in the interlayer distance in the walls of nanotubes, and the fixing of functional oxygen-containing groups on their surface. Annealing of pre-irradiated nanotubes in an inert atmosphere causes a partial restoration of the multi-wall carbon nanotube structure. At the same time, in the case of irradiation with argon ions, the nanotube structure is being recovered and the oxygen concentration decreases. In the case of electron irradiation after annealing, extended multi-vacancy defects occur, on which functional groups containing a double chemical bond of carbon and oxygen (C=O) are formed. Using calculations carried out within the framework of density functional theory, the coupling energy values and optimized geometry for various configurations of vacancy clusters in the graphene plane have been obtained.

Probing electrical properties of individual carbon nanotubes filled with Fe3C nanowires

The electrical properties of individual multiwall carbon nanotubes (CNTs) filled with Fe3C nanowires (Fe-CNTs) grown by chemical vapor deposition were investigated. The individual Fe-CNTs were measured by two-probe configuration in a scanning electron microscope, in which one probe was used to contact one end of the nanotubes and the other varied its contact position to measure the resistance along the Fe-CNTs. The data suggest that the ferromagnetic nanowires and the CNTs were well connected into a conduction network, and the resistance of the individual Fe-CNTs decreased as the filling rate increased. Analysis shows that the encapsulated ferromagnetic nanowires played a profound part in determining the electrical behavior of individual Fe-CNTs. The results may be useful for understanding of electronic transport of individual Fe-CNTs and applications based on individual Fe-CNTs.

Mechanically activated ionic transport across single-digit carbon nanotubes.

Fluid and ionic transport at the nanoscale has recently demonstrated a wealth of exotic behaviours1-14. However, artificial nanofluidic devices15-18 are still far from demonstrating the advanced functionalities existing in biological systems, such as electrically and mechanically activated transport19,20. Here, we focus on ionic transport through 2-nm-radius individual multiwalled carbon nanotubes under the combination of mechanical and electrical forcings. Our findings evidence mechanically activated ionic transport in the form of an ionic conductance that depends quadratically on the applied pressure. Our theoretical study relates this behaviour to the complex interplay between electrical and mechanical drivings, and shows that the superlubricity of the carbon nanotubes4-8,21 is a prerequisite to attaining mechanically activated transport. The pressure sensitivity shares similarities with the response of biological mechanosensitive ion channels19,20, but observed here in an artificial system. This paves the way to build new active nanofluidic functionalities inspired by complex biological machinery.