Different Concentrations Of Multi-walled Carbon Nanotubes Research Articles

Optical, Structural and Electrical Investigations of TiO<SUB>2</SUB>/Multi-Walled Carbon Nanotube Composites

Nanocomposites of TiO2 and multi-walled carbon nanotubes (MWNTs) were produced by the addition of different concentrations of MWNTs to a TiO2 sol matrix. Conductive coatings were prepared by spin coating the nanocomposite sols on glass substrates and sintering the samples at 300 degrees C for 15 min. No crystalline phase of TiO2 was formed at this temperature. The sheet resistance of the coatings was decreased from some hundreds of Momega/sq to just a few komega/sq by the addition of MWNTs to the TiO2 matrix. Moreover, sintering of the coatings in a reducing atmosphere has lead to a lower sheet resistance than that presented by coatings sintered in air. The lowest resistivity of 2.0 x 10(-1) omega x cm was obtained by coatings prepared with 5.0 mg/ml MWNTs in the composite sol. The optical, structural and electrical properties of the coatings were correlated and demonstrated.

Dramatic effect of multiwalled carbon nanotubes on the electrical properties of alumina based ceramic nanocomposites

We report recent work on electrical properties of multiwalled carbon nanotubes (MWNTs)/alumina composites. The composites with different contents of MWNTs were consolidated by spark plasma sintering and their temperature dependence dc conductivity was scrutinized in the temperature range from 5 to 300 K. The analysis of the temperature dependence of the conductivity suggests that for temperatures higher than 50 K, conduction can be ascribed to thermal fluctuation induced tunneling of the charge carriers through insulating barriers between MWNTs, while at temperatures below 50 K, the conduction can be attributed to three dimensional variable range hopping through MWNTs network in the alumina matrix. The frequency dependence of the conductivity was studied from 5 to 1.3 × 10 7 Hz. The universality of the ac conduction in MWNT/alumina composites was examined by construction of master curve.

Impact of Multi-Walled Carbon Nanotubes on Aquatic Species

To understand the environmental impacts of carbon nanotubes (CNTs), the toxicity study was carried out with water-soluble multi-walled carbon nanotubes (MWCNTs) using zebrafish (Danio rerio) as a model system. Zebrafish embryos were treated with different concentrations of MWCNTs. Teratogenic effects were evaluated through changes in embryonic development after 24 hours post-fertilization (hpf), 48 hpf and 72 hpf. No observable effect concentration (NOEC) was at 40 microg/mL. Lowest effect concentration (LOEC) of MWCNTs which caused significant phenotypic defects in zebrafish embryo was 60 microg/mL. At concentration above 60 microg/mL, slimy mucus like coating was observed around the embryo. At high concentrations, MWCNTs was found to be involved in the apoptosis, delayed hatching and formation of abnormal spinal chords. Thus, the toxicity of multi-walled carbon nanotubes is concentration dependent.

Enhancement of the crack growth resistance of a carbon/epoxy composite by adding multi-walled carbon nanotubes at a cryogenic temperature

Abstract The improvement of crack resistance is essential to the application of fiber reinforced composites for cryogenic use. In this study, the authors attempted to enhance the crack resistance of a carbon/epoxy composite by adding multi-walled carbon nanotubes (MWNTs) into the resin formulation. Prior to assessing the effect of MWNTs, the effect of a toughened epoxy resin on the mode I interlaminar fracture toughness was investigated at −150 °C using double cantilever beam (DCB) specimens. It was found that the degree of fracture toughness enhancement obtained from application of the toughened epoxy at cryogenic temperature was less than that at room temperature, due to embrittlement of the epoxy resin. MWNT-added carbon/epoxy unidirectional prepregs were fabricated via a filament winding method with different concentrations of MWNTs (0.0 wt% for baseline, 0.2 wt% and 0.7 wt%). Material systems blended with 0.2 wt% and 0.7 wt% of MWNTs showed enhanced fracture toughness and low crack density at the cryogenic temperature.

Modification of Performances of Various Membranes Using MWNTs as a Modifier

AbstractThe effect of multi‐walled carbon nanotubes (MWNTs) incorporated for the modification of membrane performances was studied. Two different types of membranes were prepared by using MWNTs: one was polysulfone (PSf) ultrafiltration (UF) membrane and the other was polyvinyl alcohol (PVA) pervaporation membrane. The PSf UF membranes with different contents of MWNTs were prepared by the conventional phase inversion process, and used for water‐treatment. On the other hand, the PVA membranes with different amount of MWNTs were prepared by the casting and drying method, and used for the pervaporation separation of water out of ethanol solution containing 10% of water. The two different types of membranes were then characterized with several analytical methods to figure out how the MWNTs were distributed through the membranes and affect on the properties of them: For the PSf membranes, the MWNTs mainly located on the surface of the membranes made them more hydrophilic and improved the selective permeation performances of the membranes. In the case of the PVA membranes, the MWNTs were distributed rather homogeneously through out the membranes, and affected on the micro‐morphology of the membranes, causing them to have different pervaporation performances.

Improvement of the Crack Resistance of a Carbon/Epoxy Composite at Cryogenic Temperature

The improvement of crack resistance is essential to the application of composites for cryogenic use such as structures storing liquid oxygen or liquid hydrogen. In this study, an effort to improve the crack resistance of a carbon/epoxy composite was made by adding MWNTs (Multi-Walled Carbon Nanotubes) to the resin formulation. Ahead of the investigation of MWNT effect, an epoxy matrix system was developed by mixing two kinds of epoxy resins and adding additives for high toughness at cryogenic temperature. The MWNT-added carbon/epoxy unidirectional prepregs were fabricated by way of a filament winding method with different concentrations of MWNTs (0.2wt% and 0.7wt%). The mechanical tests were performed inside an environmental chamber at room temperature and -150°C. The developed material system has little influence on interlaminar shear strength but resulted in higher fracture toughness at -150°C than those of baseline material. Microcrack densities after thermo-mechanical cycles were measured through an optical microscope.

Poly(3-hydroxybutyrate)/Bioglass® composite films containing carbon nanotubes

Poly(3hydroxybutyrate)(P(3HB))/Bioglass® composites incorporating multiwalled carbon nanotubes (MWCNTs) have been successfullyprepared by the solvent casting technique. The microstructure, electrical properties andbioactivity of the composites were characterized using scanning electron microscopy, x-raydiffraction and current–voltage measurements. Different concentrations of MWCNTs wereused to determine their effect on the electrical properties of the composites. MWCNTs andBioglass® particles were found to be homogeneously dispersed throughout the P(3HB) matrix. Theelectrical resistance of the composite samples decreased on increasing the MWCNTconcentration, as expected. An in vitro degradation study in simulated body fluid (SBF)was carried out on composite samples. The formation of hydroxyapatite on the surfaces ofP(3HB)/Bioglass®/MWCNT composite films was confirmed after two months of immersion in SBF. This hydroxyapatite layerwas not formed on the neat polymeric films and on composites containing MWCNTs only (withoutBioglass®). It was found that the presence of MWCNTs did not hinder the bioactivity of theBioglass® particles, as confirmed by SEM and XRD studies on composite samples.