Fabrication and mechanical/conductive properties of multi-walled carbon nanotube (MWNT) reinforced carbon matrix composites

Multi-walled carbon nanotube (MWNT) reinforced carbon matrix (MWNT/C) composites have been explored using mesophase pitch as carbon matrix precursor in the present work. Results show that carbon nanotubes (CNTs)can enhance the mechanical properties of carbon matrix significantly. The maximal increment of the bending strength and stiffness of the composites, compared with the carbon matrix, are 147% and 400%, respectively. Whereas the highest in-plane thermal conductivity of the composites is 86 W m^− 1 K^− 1 which much lower than that of carbon matrix (253 W m^− 1 K^− 1).At the same time the electrical resistivity of the composites is much higher than that of matrix. It is implicated that CNTs seem to play the role of thermal/electrical barrier in the composites. FSEM micrograph of the fracture surface for the composites shows that the presence of CNTs restrains the crystallite growth of carbon matrix, which is one of factors that improve mechanical properties and decrease the conductive properties of the composites. The defects and curved shape of CNTs are also the affecting factors on the conductive properties of the composites.     

Effect of dispersion condition of multi-walled carbon nanotube (MWNT) on bonding properties of solderable isotropic conductive adhesives (ICAs)

Carbon nanotubes have been considered as reinforcements in composite materials because of their exceptional mechanical, electrical, and thermal properties. In this paper, the effect of dispersion conditions of multi-walled carbon nanotubes (MWNTs) on bonding properties of solderable isotropic conductive adhesives (ICA) was investigated. Two types of ICAs, untreated pristine MWNT-filled ICAs and acid-treated MWNT (a-MWNT)-filled ICAs were formulated with 1 wt% MWNTs and 83 wt% low-melting-point alloy (LMPA) fillers. X-ray photoelectron spectroscopy analysis was conducted to characterize the surface chemical states of pristine and a-MWNTs and verify the effectiveness of a-MWNTs. The fracture surface of the polymer matrix and solderable ICAs with a-MWNTs showed good dispersion conditions through field-emission scanning electron microscope. After the interconnection process, the a-MWNT-filled solderable ICA showed uniform dispersion of MWNTs in the polymer matrix and formed a stable metallurgical conduction path because of the good rheology-coalescence-wetting behavior of LMPA. Alternatively, pristine MWNT-filled ICA showed poor dispersion and an unstable conduction path formed by aggregated MWNTs.     

Preparation,characterization and micromolding of multi-walled carbon nanotube polydimethylsiloxane conducting nanocomposite polymer

We present the preparation, characterization and micromolding of a flexible electrically conducting nanocomposite polymer which has been prepared by ultrasonic agitation with multi-walled carbon nanotubes (MWCNT) in polydimethylsiloxane (PDMS). We demonstrate microfabrication of the conducting nanocomposite through soft lithography micromolding of hole and post structures (minimum feature size of 200 ± 10 μm, with a height of approximately 200 μm) against a polymer master. We characterize and compare the current–voltage characteristics of films 1 mm × 1 mm × 200 µm in size as a function of different weight percentages of MWCNT (ranging from 0.8 to 2.5 wt.%) with the result that the conductivity remains low until approximately 1.5 wt.%.     

Synthesis of MnO2/short multi-walled carbon nanotube nanocomposite for supercapacitors

Multi-walled carbon nanotubes (MWNTs) were selectively etched in molten nitrate to produce short MWNTs (s-MWNTs). MnO₂/s-MWNT nanocomposite was synthesized by a reduction of potassium permanganate under microwave irradiation. For comparative purpose, MnO₂/MWNT nanocomposite was also synthesized and investigated for its physical and electrochemical performance. Uniform and conformal MnO₂ coatings were more easily formed on the surfaces of individual s-MWNTs. MnO₂/s-MWNT nanocomposite estimated by cyclic voltammetry (CV) in 0.5 M Na₂SO₄ aqueous solution had the specific capacitance as high as 392.1 F g⁻¹ at 2 mV s⁻¹. This value was more than 48.9% larger than MnO₂/s-MWNT nanocomposite. In addition, MnO₂/s-MWNT nanocomposite was also examined by repeating the CV test at a scan rate of 50 mV s⁻¹, exhibiting an excellent cycling stability along with 99.2% specific capacitance retained after 1000 cycles. Therefore, MnO₂/s-MWNT nanocomposite is a promising electrode material in the supercapacitors.     

Poly(adipic acid-hexamethylene diamine)-functionalized multi-walled carbon nanotube nanocomposites

Poly(adipic acid-hexamethylene diamine) (PA66)-functionalized multi-walled carbon nanotubes (PACNT) were fabricated using amino multi-walled carbon nanotubes (AMWNT), adipic acid-hexamethylene diamine salt as reactants at 260–270 °C. The solubility of AMWNT in formic acid is improved after PA66 functionalization. PA66 was successfully grafted onto the surface of AMWNT to form a core–shell nanostructure. AMWNT are surrounded by PA66 chains with an average thickness of 3 nm. The length of PA66 chains on the surface of AMWNT decreases, with the content of AMWNT increasing. The thermal decomposition temperature of the composite is lower than that of PA66 functionalized carboxylic multi-walled carbon nanotubes. The storage modulus of PACNT containing 5 wt% AMWNT is 2.8-fold that of PA66; and it increases as the content of AMWNT increases.     

Microwave-irradiated novel mesoporous nickel oxide carbon nanocomposite electrodes for supercapacitor application

Journal of Materials Science: Materials in Electronics - The present work accentuates the aspects of electrochemical analysis determined by cyclic voltammeter (CV), especially enhancement in...     

Direct electrochemistry and electrocatalysis of myoglobin immobilized on zirconia/multi-walled carbon nanotube nanocomposite

Zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) nanocomposite was prepared by hydrothermal treatment of MWCNTs in ZrOCl₂·8H₂O aqueous solution. The morphology and structure of the synthesized ZrO₂/MWCNT nanocomposite were characterized by transmission electron microscopy and X-ray diffraction analysis. It was found that ZrO₂ nanoparticles homogeneously distributed on the sidewall of MWCNTs. Myoglobin (Mb), as a model protein to investigate the nanocomposite, was immobilized on ZrO₂/MWCNT nanocomposite. Ultraviolet–visible spectroscopy and electrochemical measurements showed that the nanocomposite could retain the bioactivity of the immobilized Mb to a large extent. The Mb immobilized in the composite showed excellent direct electrochemistry and electrocatalytic activity to the reduction of hydrogen peroxide (H₂O₂). The linear response range of the biosensor to H₂O₂ concentration was from 1.0 to 116.0 μM with the limit of detection of 0.53 μM (S/N = 3). The ZrO₂/MWCNT nanocomposite provided a good biocompatible matrix for protein immobilization and biosensors preparation.     

Ultralong aligned multi-walled carbon nanotube for electrochemical sensing

We have investigated electrochemical sensing properties of electrodes fabricated with ultralong aligned multi-walled carbon nanotube (MWNT) bundles synthesized using water-assisted chemical vapor deposition on aluminum (Al) and iron (Fe) coated silicon wafer with ethylene and argon/hydrogen gas as carbon source and buffer gas respectively. Cyclic voltammograms performed on these electrodes show diffusion-controlled-reversible reaction. The dominance of radial diffusion mass transport at these electrodes was also indicated by sigmoidal-shaped voltammograms obtained at various scan rates. These electrodes were able to sense very low concentration of ascorbic acid (approximately 0.7 microM) and dopamine (approximately 1.87 microM), two model species often used in electro-analysis. The excellent electrochemical properties along with good single species detection ability suggest that these MWNTs are promising electrode materials for developing very sensitive chemical and/or biological sensors.     

Planar silver nanowire,carbon nanotube and PEDOT:PSS nanocomposite transparent electrodes

Abstract

Highly conductive, transparent and flexible planar electrodes were fabricated using interwoven silver nanowires and single-walled carbon nanotubes (AgNW:SWCNT) in a PEDOT:PSS matrix via an epoxy transfer method from a silicon template. The planar electrodes achieved a sheet resistance of 6.6 ± 0.0 Ω/□ and an average transmission of 86% between 400 and 800 nm. A high figure of merit of 367 Ω^?1 is reported for the electrodes, which is much higher than that measured for indium tin oxide and reported for other AgNW composites. The AgNW:SWCNT:PEDOT:PSS electrode was used to fabricate low temperature (annealing free) devices demonstrating their potential to function with a range of organic semiconducting polymer:fullerene bulk heterojunction blend systems.     

Planar silver nanowire,carbon nanotube and PEDOT:PSS nanocomposite transparent electrodes

Highly conductive, transparent and flexible planar electrodes were fabricated using interwoven silver nanowires and single-walled carbon nanotubes (AgNW:SWCNT) in a PEDOT:PSS matrix via an epoxy transfer method from a silicon template. The planar electrodes achieved a sheet resistance of 6.6 ± 0.0 Ω/□ and an average transmission of 86% between 400 and 800 nm. A high figure of merit of 367 Ω⁻¹ is reported for the electrodes, which is much higher than that measured for indium tin oxide and reported for other AgNW composites. The AgNW:SWCNT:PEDOT:PSS electrode was used to fabricate low temperature (annealing free) devices demonstrating their potential to function with a range of organic semiconducting polymer:fullerene bulk heterojunction blend systems.     

Synthesis of multi-walled carbon nanotube/silver nanocomposite powders by chemical reduction in aqueous solution

Carbon nanotube (CNT)/silver nanocomposite powders with different volume fractions of CNTs 2.5, 5 and 10?vol.% were prepared by chemical reduction in solution. Multi-walled CNTs underwent surface modifications for functionalisations by acid treatments. The acid-treated CNTs were investigated by FT-IR and X-ray photoelectron spectroscopy. The spectroscopic investigations of the acid-functionalised CNTs detected that several kinds of functional groups attached with the graphene structure as well as produced short and de-caped CNTs. Acidic stannous chloride solution was used to sensitise the surface of the functionalised CNTs. Silver was deposited on the surface of sensitised CNTs with chemical reduction reaction of alkaline silver nitrate solution by formaldehyde at room temperature and pH?～?9. The morphology of the produced CNT/silver nanocomposite powder was investigated by high-resolution SEM and TEM. It was observed that the produced CNT/silver nanocomposite powders have decorated type of spherical silver particle size 2–5?nm deposited on the surface of CNTs as well as the CNTs were implanted in large spherical silver nanoparticles of particle size ～200?nm. The chemical analysis of the produced powder indicates that some oxygen content is included in the prepared powders which can be reduced by heat treatment at temperatures between 300°C and 400°C under hydrogen atmosphere.     

多壁碳纳米管(MWNT)/聚丙烯腈(PAN)共混复合膜的制备及性能研究

为了提高PAN膜的性能,首先用超声分散将MWNT溶解在N,N-二甲基甲酰胺(DMF)中,之后加入PAN,通过相转化法制备MWNT/PAN共混复合膜.研究表明,随着MWNT添加量的增加,共混膜的拉伸强度呈先增加后减少的趋势,从2.2 MPa上升到2.4MPa后拉伸强度开始下降.这是由于适量的MWNT起到物理交联的作用,而添加过多,导致MWNT团聚,降低共混膜的拉伸强度.断裂伸长率随着添加量的增加缓慢下降,从20%下降到18.6%;水通量随着MWNT添加量的增加呈先增加后减少的趋势,在添加量为质量分数1%时较纯PAN膜增加了近60%,后水通量呈下降趋势,但是仍然高于PAN膜.这一变化趋势是由膜孔结构的变化和MWNT堵孔共同作用的结果.共混膜的截留率也呈先增加后减少的趋势.当MWNT添加量为4%时,截留率达到最大值96%.抗污染性能测试结果显示膜的水通量恢复率随着添加量的增加呈先增后减少的趋势,在添加量为7%时,达到70%.抗污染性能提高的原因是膜的润湿性得到改善.     

Preparation and properties of multi-walled carbon nanotube/poly(organophosphazene) composites

Carbon nanotubes (CNTs) are promising materials because of their unique properties. However, the poor solubility in solvents limits the function of CNTs and hinders their applications in many fields. Surface modification of CNTs with polymers is an efficient method to solve this problem. Several polymers were tested for the preparation of CNT dispersions. In comparison with organic polymers, poly(organophosphazenes) are highly stable macromolecules with adjustable properties which depend on the side groups. This article is to describe the synthesis of thermally stable and soluble multi-walled CNT/poly(organophosphazene) composites. The poly(organophosphazene)s substituted with (a) 100 % quaternary protonated pyridinoxy (PPY), (b) 50 % quaternary protonated pyridinoxy and 50 % a long aliphatic chain alcohol (1-dodecanol) (PDK), and (c) 50 % quaternary protonated pyridinoxy and 50 % a glycol ether [(2-(2-methoxyethoxy)ethanol] (PET) have been synthesized. f-MWCNT/poly(organophosphazene) composites have been prepared by the treatment of the functionalized multi-walled carbon nanotubes (f-MWCNT) with the protonated polyphosphazenes (PPY, PDK, and PET) using different feed ratios [R _feed = 1:1, 1:3, 1:5, 1:10 (w:w)]. The thermal stability of prepared composites (f-MWCNT/PPY, f-MWCNT/PDK, and f-MWCNT/PET) have been investigated by TGA. By considering thermal stabilities and solubility of all prepared composites, f-MWCNT/PPY_1:5, f-MWCNT/PDK_1:5, and f-MWCNT/PET_1:5 have been chosen as optimum composite composition and characterized by ³¹P NMR, ¹H NMR, XRD, Raman spectroscopy, and EDX analysis. The morphologic characterizations of the f-MWCNT/PPY_1:5, f-MWCNT/PDK_1:5, f-MWCNT/PET_1:5 nanocomposites have been carried out by HRTEM. Excellent dispersions of the nanocomposites in water and common organic solvents have been achieved. The solubility and thermal stability of nanocomposites depend on the side groups on poly(organophosphazene).     

A comparative study of enzyme immobilization strategies for multi-walled carbon nanotube glucose biosensors

This work addresses the comparison of different strategies for improving biosensor performance using nanomaterials. Glucose biosensors based on commonly applied enzyme immobilization approaches, including sol-gel encapsulation approaches and glutaraldehyde cross-linking strategies, were studied in the presence and absence of multi-walled carbon nanotubes (MWNTs). Although direct comparison of design parameters such as linear range and sensitivity is intuitive, this comparison alone is not an accurate indicator of biosensor efficacy, due to the wide range of electrodes and nanomaterials available for use in current biosensor designs. We proposed a comparative protocol which considers both the active area available for transduction following nanomaterial deposition and the sensitivity. Based on the protocol, when no nanomaterials were involved, TEOS/GOx biosensors exhibited the highest efficacy, followed by BSA/GA/GOx and TMOS/GOx biosensors. A novel biosensor containing carboxylated MWNTs modified with glucose oxidase and an overlying TMOS layer demonstrated optimum efficacy in terms of enhanced current density (18.3 ± 0.5 μA mM(-1) cm(-2)), linear range (0.0037-12 mM), detection limit (3.7 μM), coefficient of variation (2%), response time (less than 8 s), and stability/selectivity/reproducibility. H(2)O(2) response tests demonstrated that the most possible reason for the performance enhancement was an increased enzyme loading. This design is an excellent platform for versatile biosensing applications.     

Turning refuse plastic into multi-walled carbon nanotube forest

Abstract

A novel and effective method was devised for synthesizing a vertically aligned carbon nanotube (CNT) forest on a substrate using waste plastic obtained from commercially available water bottles. The advantages of the proposed method are the speed of processing and the use of waste as a raw material. A mechanism for the CNT growth was also proposed. The growth rate of the CNT forest was ～2.5 μm min^?1. Transmission electron microscopy images indicated that the outer diameters of the CNTs were 20–30 nm on average. The intensity ratio of the G and D Raman bands was 1.27 for the vertically aligned CNT forest. The Raman spectrum showed that the wall graphitization of the CNTs, synthesized via the proposed method was slightly higher than that of commercially available multi-walled carbon nanotubes (MWCNTs). We expect that the proposed method can be easily adapted to the disposal of other refuse materials and applied to MWCNT production industries.     

Ultrasonically prepared polystyrene/multi-walled carbon nanotube nanocomposites

Polystyrene (PS) and multi-walled carbon nanotube (MWNT) nanocomposites were synthesized via an in situ bulk polymerization by employing an ultrasonicator without adding an initiator, in which the ultrasonication was found to do a favor in producing well-dispersed MWNT in the PS matrix. Morphology of the as-synthesized PS/MWNT nanocomposite was investigated by both scanning electron microscopy and transmission electron microscopy. Electrical conductivity of the PS/MWNT nanocomposite film fabricated by a solvent casting method was also examined to be enhanced with MWNT content, while average molecular weights of the synthesized PS in the PS/MWNT nanocomposites analyzed by a gel permeation chromatography increased and then saturated at 2 wt% MWNT. Rheological properties of MWNT containing PS were enhanced because of improved dispersion of the MWNT through an interaction between MWNT and PS.     

Near-superhydrophobic behavior of multi-walled carbon nanotube thin films

Thin films of multi-walled carbon nanotubes created by standard drop and dry methodology are reported here to give water contact angles of ~ 138° accessing an intermediate region between smooth, apolar materials and superhydrophobic surfaces. Their near-superhydrophobic nature is attributed to hierarchical nanoscale roughness leading to the formation of Cassie-Baxter interfaces. While complete quantitative determination of surface energy parameters was prevented due to the porous nature of the films, the dispersive component of nanotube surface energy was found to be in the range of 39.1-47.8 mJ/m².