Carbon Nanotube Interface Research Articles

SiC/SiC composite fabricated with carbon nanotube interface layer and a novel precursor LPVCS

Continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) have been studied as promising candidate materials for nuclear applications. Three-dimensional SiC/SiC composite was fabricated via polymer impregnation and pyrolysis (PIP) process using carbon nanotubes (CNTs) as the interface layer and LPVCS as the polymer precursor. The microstructural evolution of the fiber/matrix interface was studied. The porosity, mechanical properties, thermal and electrical conductivities of the SiC/SiC composite were investigated. The results indicated that the high densification efficiency of the liquid precursor LPVCS resulted in a low porosity of the SiC/SiC composite. The SiC/SiC composite exhibited non-brittle fracture behavior, however, bending strength and fracture toughness of the composite were relatively low because of the absence of CNTs as the interface layer. The thermal and electrical conductivities of the SiC/SiC composite were low enough to meet the requirements desired for flow channel insert (FCI) applications.

Modeling the tensile stress–strain response of carbon nanotube/polypropylene nanocomposites using nonlinear representative volume element

This paper presents a finite element model for predicting the mechanical behavior of polypropylene (PP) composites reinforced with carbon nanotubes (CNTs) at large deformation scale. Existing numerical models cannot predict composite behavior at large strains due to using simplified material properties and inefficient interfaces between CNT and polymer. In this work, nonlinear representative volume elements (RVE) of composite are prepared. These RVEs consist of CNT, PP matrix and non-bonded interface. The nonlinear material properties for CNT and polymer are adopted to solid elements. For the first time, the interface between CNT and matrix is simulated using contact elements. This interfacial model is capable enough to simulate wide range of interactions between CNT and polymer in large strains. The influence of adding CNT with different aspect ratio into PP is studied. The mechanical behavior of composites with different interfacial shear strength (ISS) is discussed. The success of this new model was verified by comparing the simulation results for RVEs with conducted experimental results. The results shows that the length of CNT and ISS values significantly affect the reinforcement phenomenon.

SurfaceModification of Carbon Nanotubes Using Acid Treatment to Enhance Gas Separation Performance of Hybrid Nanocomposite Mixed Matrix Membrane

Recently, many researchers have explored the idea of hybrid mixed matrix membranes. Membrane separation processes based on hybrid mixed matrix membrane comprising inorganic material such as zeolite and carbon nanotubes (CNTs) embedded in polymer matrix have become one of the emerging technologies and extensively discussed in membrane separation literature. The present study is performed primarily to investigate the effect of chemical modification on carbon nanotubes surface towards gas separation performance of mixed matrix membrane. Polyethersulfone (PES)-carbon nanotubes mixed matrix membrane for modified and unmodified carbon nanotubes were casted using dry/wet phase inversion technique. The modified carbon nanotubes were prepared by treating the carbon nanotubes with acid treatment to allow PES chains to be attached to carbon nanotubes surface. The results of FESEM, DSC and FTIR analysis confirmed that chemical modification on carbon nanotubes surface had taken place. Meanwhile, the nanogaps in the interface of polymer and carbon nanotubes were appeared in the PES mixed matrix membrane with unmodified of carbon nanotubes. The modified carbon nanotubes mixed matrix membrane increases the mechanical properties, the productivity and purity of gas mixture compare to neat PES and unmodified carbon nanotubes mixed matrix membrane. For PES-modified carbon nanotubes mixed matrix membrane the maximum selectivity achieved for CO /CH are 24 32.59.

Mechanical properties and in situ crack growth observation of SiC/SiC composites

Continuous SiC fibre reinforced SiC matrix composites (SiC/SiC) have been studied as materials for high temperature and nuclear applications. In this work, 3D SiC/SiC composites with pyrolytic carbon (PyC) interface or carbon nanotubes (CNTs) interface were fabricated by polymer infiltration and pyrolysis (PIP) process, mechanical properties of the SiC/SiC composites were characterized and crack growth processes were observed in situ by SEM. The results indicated that the flexural strengths of both composites are similar but the fracture toughness of the SiC/SiC composite with PyC interface is twice as much as that of the SiC/SiC composite with CNTs interface. The crack propagated along the fibre–matrix interface in the SiC/SiC composite with PyC interface, while the crack propagated rapidly through the fibres in the SiC/SiC composite with CNTs interface.

Modeling transport properties of single-wall carbon nanotube between metal and graphene electrodes

In this article, transport properties of a single-wall carbon nanotube having chirality (4, 0), connected to copper, gold and graphene electrodes, have been investigated. Electronic structures have been analyzed using the density functional theory calculator. Transport properties of the devices formed by interfacing of single-wall carbon nanotube and electrodes are computed using the nonequilibrium Green’s functional method coupled with density functional theory approach. Contact effects due to metal–carbon nanotube interface have significant impact on transport properties of charge carriers. Therefore, transport properties have been critically analyzed with the help of transmission spectra, differential conductance and conductance plots and I–V characteristics. From these results, it has been concluded that formulation of the electrode material is not the single-factor responsible for creating conduction problems. Along with the electrode material, interface position of metal–carbon nanotube configuration and heterostructure contacts are also responsible in influencing transport phenomenon. In this way, varying the contact geometry is found to play an important role in integrated circuit interconnect technologies for exploring the transport properties. Gold is best among all three simulated contact electrodes, and for low-power applications, graphene can be next choice over an applied bias range of −1 to +1 V. Atomistix software tool has been used to analyze transport properties of interconnect models.

Analysis of carbon nanotube-reinforced alumina matrix nanocomposites with a broken fiber

Multi-scale finite element analysis has been performed for determination of longitudinal and transverse Young’s moduli of carbon nanotube (CNT)-reinforced alumina matrix nanocomposites considering a square representative volume element (RVE). The square RVE has been used to simulate the stress redistribution around a broken CNT at the interface of CNT and matrix, and ineffective length of the broken CNT has been determined. It has been observed that ineffective length of the broken CNT does not show sufficient dependence on the volume fraction. It is also been observed that high magnitude of interfacial shear stress around the broken CNT exists indicating the chances of fiber debonding.

Efficiency Increasing of Thermoelectric Micro Generator Using Carbon Nanotube Interface

Thermoelectric (TE) devices are an interested family of energy harvesters which could convert the thermal energy into electricity. However, the temperature drops at interface between thermoelectric materials and heat source, heat sink and electrodes reduce efficiency of thermoelectric devices. As a solution, thermal interface materials (TIM) which have high thermal conductance and low thermal interface resistance with adjacent materials are added to the device. In this paper, the organic material is considered as the base material for a TE energy harvester device. Also, carbon nanotube (CNT) is applied as TIM, because of its high one dimentional electrical and thermal conductance. A finite element analysis is carried out in order to investigate the role of thermal contact resistance on heat transfer at TE device. To do this, a thermoelectric leg is simulated with two structure consist of (a) TE material and electrodes in direct contact (b) TE material and electrodes with CNT interface and the results are compared. It is shown that CNT layer reduces heat dissipation at the interface and so the temperature difference at the both sides of polymer is increased, which finally results the enhancement of device output voltage.

Role of interface on electrical conductivity of carbon nanotube/alumina nanocomposite

Interface of multiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites have been studied using TEM. At low sintering temperature (Tsin=1500°C), a 3–5nm thick amorphous interface region was noticed. Nanocomposite sintered at 1700°C possessed a well-defined graphene layer coating on matrix grains as the interface between CNT and Al2O3. A mechanism of such layered interface formation has been proposed. No traceable chemical reaction product was observed at the interface even after sintering at 1700°C. It was noticed that while DC electrical conductivity (σDC) of 1500°C sintered 2.4vol% MWCNT/Al2O3 nanocomposite was only~0.02S/m, it raised to ~21S/m when sintering was done at 1700°C. Such 103 times increase in σDC of present nanocomposite at a constant CNT loading was not only resulted from the exceptionally high electron mobility of CNT but the well-crystallized graphene interface on insulating type Al2O3 grains also significantly contributed in the overall increase of electrical performance of the nanocomposite, especially, when sintering was done at 1700°C.

Enhanced biogas separation performance of nanocomposite polyethersulfone membranes using carbon nanotubes

This study is performed primarily to investigate the effect of chemical modification on carbon nanotubes surface towards biogas purification performance of mixed matrix membrane. In this study, polyethersulfone (PES)-carbon nanotubes mixed matrix hollow fiber membrane for modified and unmodified carbon nanotubese were spun using dry/wet spinning technique. The modified carbon nanotubes were prepared by treating the carbon nanotubes with acid treatment to allow PES chains to be attached on carbon nanotubes surface. The results from the FESEM, DSC and FTIR analysis confirmed that chemical modification on carbon nanotubes surface had taken place. Meanwhile, the nanogaps in the interface of polymer and carbon nanotubes were appeared in the PES mixed matrix membrane with unmodified of carbon nanotubes. The modified carbon nanotubes mixed matrix membrane increases the mechanical properties, the productivity and purity of biogas compare to neat PES and unmodified carbon nanotubes mixed matrix membrane. For PES-modified carbon nanotubes mixed matrix membrane the maximum selectivity achieved for CO 2 /CH 4 is 32.59.

Microwave sintering carbon nanotube/Ni0.5Zn0.5Fe2O4 composites and their electromagnetic performance

Carbon nanotube (CNT)–Ni0.5Zn0.5Fe2O4 powders were prepared by in situ chemical precipitation and hydrothermal processing, and further sintered by microwave sintering technology. The results show that CNTs acted as ‘heating source’ and promoted the consolidation of composites during the microwave sintering process. However, too much CNTs (such as 5 wt%) led to phase decomposition and reduction of ferrite materials because of the ultra-high localized temperature building up in the interface of CNTs and ferrite grains. The electrical conductivity of composites increased by more than seven orders of magnitude when compared to that of pure Ni0.5Zn0.5Fe2O4, and remained a high value at the temperature of 70 K (for example, 1 wt% CNT/Ni0.5Zn0.5Fe2O4 sample kept conductivity of 0.1 S/m). The saturation magnetization was strongly dependent on the mass percentage of CNTs. With the increase in CNT content, both the real and the imaginary permittivity were increased in the frequency region 0.6–5 GHz (L and S bands). According to the measured results of ϵr and μr, the frequency-dependent reflectance loss (RL) of CNT/Ni0.5Zn0.5Fe2O4 composite ceramics with different CNT content was evaluated. The CNT-doped ferrite ceramics discussed herein is very promising to be used in an on-beam-line high-order mode (HOM) load in particle accelerators based on superconducting RF due to their excellent low-temperature characteristics.

Joint properties between carbon nanotube and gold at different energy levels from molecular dynamics

We report on the interfacial structure and the load–displacement characteristics of joints between gold and carbon nanotube (CNT) based on molecular dynamics study. We find that all energy levels lead to similar bonding strength but different displacement bearing ability, which correlates well with the predicted cohesive strength of the electrode–CNT interface, though the high energy level distorts the CNT structure. 1000K leads to stable load–displacement curve up to 5nm, suggesting an increased bonding status. This nanostructure shows significantly improved bonding status that allows for utility and transportation in severe environments.

Carbon nanotube thermal interfaces enhanced with sprayed on nanoscale polymer coatings

Vertical carbon nanotube (CNT) forests bonded at room temperature with sprayed on nanoscale polymer coatings are found by measurement to produce thermal resistances that are on a par with those of conventional metallic solders. These results are achieved by reducing the high contact resistance at CNT tips, which has hindered the development of high performance thermal interface materials based on CNTs. A spray coating process is developed for depositing nanoscale coatings of polystyrene and poly-3-hexylthiophene onto CNT forests, as a bonding agent that mitigates thermal resistance by enhancing the area available for heat transfer at CNT contacts. Resistances as low as 4.9 ± 0.3 mm2 K W−1 are achieved for the entire polymer coated CNT interface structure. The suitability of the spray coating process for large-scale implementation and the role of polymer and CNT forest thickness in determining the thermal resistance are also examined.

Investigation of the interfacial phases formed between carbon nanotubes and aluminum in a bulk material

This research describes an investigation of the interfacial phases formed between aluminum (Al) and carbon nanotubes (CNT) which properties depend on the processing temperature (below, slightly above and over the melting point of Al). Al–CNT compacts were prepared by spark plasma sintering followed by heat treatment in order to observe the interface phases. The microstructures of both the as-sintered and heat-treated materials have been observed by optical, scanning and transmission electron microscopies. The amorphous Al oxide observed at the boundaries in the as-sintered material is transformed to crystalline Al oxide after the heat treatment. In addition, some of the CNTs decomposed and reacted with the Al, resulting in the formation of Al carbide which shows different size distributions depending on the heat treatment temperature. According to the results, it is possible to control the phase formed at the Al–CNT interface by controlling the process temperature and those controlled interfaces will be playing important role to the properties in a bulk materials.

A Microcalorimeter Integrated With Carbon Nanotube Interface Layers for Fast Detection of Trace Energetic Chemicals

Detection of trace explosives is still a challenging task because of the extremely low vapor concentrations. This paper reports a new microcalorimeter for detection of trace explosives with low detection limit and fast detection rate. The microcalorimeter consists of a suspended micromembrane with integrated heaters and thermistors and a carbon nanotube (CNT) interface layer in-situ synthesized on the membrane surface. Due to the large surface areas, the CNT interface layer improves adsorption to target chemical molecules. By operating the microcalorimeter in differential scanning calorimetry mode and differential thermal analysis mode, trace chemical detection is achieved through heating the adsorbed chemicals to deflagration and measuring the induced thermal response features and the total heat. The microcalorimeter is verified by explosive detection, and an equivalent limit of detection of 2.6 pg has been achieved by extrapolating the measurement results. Theoretically, detection is distinguishable upon 10-s fast exposure to saturated explosive vapors. These preliminary results demonstrate the ability of the microcalorimeter in detection of trace energetic chemicals.

Effects of CNT waviness on the effective elastic responses of CNT-reinforced polymer composites

In this study, the effects of fiber waviness on the effective elastic responses of CNT–polymer composites are investigated based on the framework of micromechanics and homogenization. By taking advantage of an ad hoc Eshelby tensor, the load-transfer capability of wavy carbon nanotube (CNT) embedded in the polymer matrix is accounted for. Further, the effective elastic responses of composites are simulated by using the multi-phase Mori–Tanaka method to study the influence of randomly oriented wavy CNT. It is demonstrated that the proposed micromechanics-based closed form solution is effective to tackle the underlying problem. The present predictions and the comparisons with the available experimental data indicate that the CNT waviness leads to the degradation of effective responses of composites. Finally, in addition to the effect of CNT waviness, the significance of CNT interface is briefly discussed based on the experimental observations.

NADH Oxidation Catalyzed by Electropolymerized Azines on Carbon Nanotube Modified Electrodes

AbstractElectropolymerizing azines on a carbon nanotube (CNT) modified electrode yields a high‐surface area interface with excellent electrocatalytic activity towards NADH oxidation. Electrodeposition of poly(methylene green) (PMG) and poly(toluidine blue) (PTBO) on the carboxylated CNT‐modified electrodes was achieved by cyclic voltammetry. The PMG‐CNT interface demonstrates 5.0 mA cm−2 current density for NADH oxidation at 50 mV vs. Ag|AgCl in 20 mM NADH solution. The kinetics of NADH electrocatalysis were analyzed using a quantitative mass‐transport‐corrected model with NADH bulk concentration and applied potential as independent variables. This high‐rate poly(azine)‐CNT interface is potentially applicable to high‐performance bioconversion, bioenergy and biosensors involving NADH‐dependent dehydrogenases.

Tuning the functional interface of carbon nanotubes by electrochemistry: Toward nanoscale chemical sensors and biosensors

Abstract

Increasing the Performance of PES-CNTs Mixed Matrix Membrane using Carbon Nanotubes (CNTs) Functionalization

A new type of mixed matrix membrane consisting of functionalized carbon nanotubes (CNTs) and polyethersulfone (PES) is prepared for biogas purification. PES mixed matrix membrane with and without modification of carbon nanotubes were prepared by a dry/wet phase inversion technique using a pneumatically flat sheet membrane casting machine system. The modified carbon nanotubes were prepared by treating the carbon nanotubes with chemical modification using Dynasylan Ameo (DA) silane agent to allow PES chains to be grafted on carbon nanotubes surface. The results from the FESEM, DSC and FTIR analysis confirmed that chemical modification on carbon nanotubes surface had taken place. Meanwhile, the nanogaps in the interface of polymer and carbon nanotubes were appeared in the PES mixed matrix membrane with unmodified of carbon nanotubes. The modified carbon nanotubes mixed matrix membrane increases the mechanical properties, the productivity and purity of biogas. For PES-modified carbon nanotubes mixed matrix membrane the maximum selectivity achieved for CO2/CH4 is 36.78

The Uses of Carbon Nanotubes Mixed Matrix Membranes (MMM) for Biogas Purification

A new type of mixed matrix membrane consisting of polyethersulfone (PES) and carbon nanotubes (CNTs) is prepared for biogas purification application. PES mixed matrix membrane with and without modification of carbon nanotubes were prepared by a dry/wet phase inversion technique using a pneumatically membrane casting machine system. The modified carbon nanotubes were prepared by treating the carbon nanotubes with chemical modification using acid treatment to allow PES chains to be grafted on carbon nanotubes surface. The results from the FESEM, DSC and FTIR analysis confirmed that chemical modification on carbon nanotubes surface had taken place. Meanwhile, the nanogaps in the interface of polymer and carbon nanotubes were appeared in the PES mixed matrix membrane with unmodified of carbon nanotubes. The modified carbon nanotubes mixed matrix membrane increases the mechanical properties and the permeability of all gases. For PES-modified carbon nanotubes mixed matrix membrane the maximum selectivity achieved for CO2/CH4 is 23.54.

A biopolymer-based carbon nanotube interface integrated with a redox shuttle and a D-sorbitol dehydrogenase for robust monitoring of D-sorbitol

We describe the preparation and characterization of a glassy carbon electrode modified with a bionanocom- posite consisting of a hyaluronic acid, dispersed carbon nanotubes, and electrostatically bound toluidine blue. The electrode was used to detect NADH in the batch and flow-injection mode of operation. The electrode was further modified by immobilizing sorbitol dehydrogenase to result in biosensor for D-sorbitol that displays good operational stability, a sensitivity of 10.6 μ Am M −1 cm −2 , a response time of 16 s, and detection limit in the low micromolar range. The biosensor was successfully applied to off-line monitoring of D-sorbitol during its bioconversion into L-sorbose (a precursor in the synthesis of vitamin C) by Gluconobacter oxydans. The sample assay precision is 2.5% (an average RSD) and the throughput is 65 h −1 if operated in the flow-injection mode. The validation of this biosensor against a reference HPLC method resulted in a slope of correlation of 1.021±0.001 (R 2 =0.99997).