Types Of CNTs Research Articles

Growth inhibitions of four types of CNTs on Scenedesmus obliquus

Growth inhibitions of four types of CNTs on Scenedesmus obliquus

도로 융설체 개발을 위한 탄소나노튜브-시멘트 복합체 특성에 관한 실험적 연구

PURPOSES : This study aims to review the possibility of developing a road snow-melting system that can prevent slip accidents by maintaining a constant temperature of the winter roads and enhance performance of structures, including improvement of compressive strength by mixing carbon nanotube (hereafter referred to as CNT) with cement paste, the basic material. METHODS : To achieve the above purpose, an experiment was conducted by mixing power-type CNT and wrap-type CNT up to cement paste formulation by weight of 0.0wt%~4.1wt% in accordance with KS L ISO 679(of cement strength test method), and compressive strength was measured at 28 days of curing. In addition, the volume resistivity of the specimen was measured to test thermal and electrical characteristics, and the rate of temperature changes in specimen surface by power consumption was measured by passing electricity through the cross-sections of the specimen. Meanwhile, the criteria for checking the performance as a road snow-melting system was determined as volume resistivity of or less. RESULTS : A comparative analysis between specimen with 0wt% CNT content in plain status and specimen containing various types of CNTs was carried out. From its results, it was found that compressive strength increased approximately 19%, showing the highest rate when 0.2wt% of wrap-type CNT was contained, but volume resistivity of or less appeared only in specimens containing more than 0.2wt% CNT. In addition, it was observed that the surface temperature increased by per minute on average in specimens containing 3.2wt% CNT. CONCLUSIONS : In this study, CNT was examined as an underlying material for a road snow-melting system, and the possibility of developing the road now-melting system was reviewed by conducting various experiments using CNT-Cement composites. From the experimental results, the specimens were found to have a superior performance when compared to the existing road snow-melting systems that place the heat transfer medium such as copper on the road. However, satisfactory strength performance were not obtained from the specimen containing CNT(2.0% or more) that functions as a heating element, which leads to the need for reviewing methods to increase the strength by using plasticizer or admixture.

Floating Catalyst Method for Preparation of Carbon Nanotubes Using Fe/Co/Al Catalyst by Thermal-CVD

Carbon nanotubes (Cnts) produced using single furnace thermal CVD method by the floating catalyst method, at low temperature condition; 650oC. Carbon nanotubes were produced from natural source of camphor oil, using Fe/Co/Al as catalyst source, yielding a thickened submicron vapor grown of multi-wall Cnts. Carbon nanotubes are observed to form by different weight composition of catalyst. For the production of carbon nanotubes, natural precursor was used as the carbon feedstock, and the catalysts were added in a precursor compound. FESEM analysis confirms that this type of stacked-cup Cnts is produced by vaporize catalyst and mixing with the hydrocarbon source. In fact, few Cnts have either a particle tip at the end or trapped metal particle inside the wide hollow core of this type of produced carbon material. Chemical properties carried out by FTIR and Raman spectroscopy.

Comparative study of membranotropic action of single- and multi-walled carbon nanotubes

The aim of the present work is the investigation of the interactions of single-walled and multi-walled carbon nanotubes (further referred as SWCNTs and MWCNTs, respectively) with bimolecular lipid model membrane (BLM) and cellular plasma membrane (PM). The findings demonstrate that both SWCNTs and MWCNTs (in concentration range of 10⁻⁴ to 10⁻¹ mg ml⁻¹) are capable to penetrate through the region of hydrophobic fatty acid residues of phospholipids and to form molecular associates in the bilayer that have conductive properties of molecular pores type. The formed pores were shown to enable phosphatidylserine externalization from inner to outer PM leaflet. Both types of CNTs increase the specific conductivity and decrease the specific capacity of BLM.

Preparation and characterization of carboxylated styrene butadiene rubber (XSBR)/multiwall carbon nanotubes (MWCNTs) nanocomposites

This study deals with the preparation of carboxylated styrene butadiene rubber (XSBR)/multiwall carbon nanotubes (MWCNTs) nanocomposites prepared in the latex form by means of a ball mill. Two types of CNTs, i.e., non-functionalized and OH-functionalized (CNT–OH) were used. The rheological properties, FTIR spectrums, SEM micrographs and stress relaxation experiments were exploited to evaluate the resulting nanocomposites. For a given frequency, both the viscosity and storage modulus increased as the concentration of CNT was augmented with the greatest value for the nanocomposites loaded with CNT–OH. The viscosity of nanocomposites exhibited a shear thinning behavior throughout applied frequency and indicated a power law index of about n = 0.22. Nanocomposite ATR analyses revealed the presence of physical interaction of H-bonding type between hydroxyl group of CNT–OH and carboxyl group of XSBR for XSBR–CNTOH nanocomposites. A mechanism based on the chemistry of medium was proposed to explain the development of H-bonding. SEM micrographs confirmed the uniformity of carbon nanotubes dispersion in the resulting microstructure. A two-step innovative stress relaxation experiment was performed on the prepared nanocomposites through which the resulting microstructure of nanocomposites was further explored. The relaxation behavior of nanocomposites (both in first and second steps) were modeled and well predicted using Prony series and the parameters of generalized Maxwell equation for stress relaxation, \( \tau_{i} \) and \( g_{i} \) were computed, as well.

Characterization of CNT Enhanced Conductive Adhesives in Terms of Thermal Conductivity

CNTs have excellent thermal, electrical and mechanical properties. They can be used in various ways. One researched field of application is CNT-polymer composites which combine common technologies with advanced materials. This paper will focus on the thermal property of CNT-Ag-filled adhesives and compares the new materials with conventional, electrical Ag-filled conductive adhesives. Several analytical methods, FTIR, Raman analysis, SEM and TEM have been carried out to examine the different surface conditions after physicval and chemical modification of CNTs. The thermal conductivities of composites containing different types of CNTs were investigated. The incorporation of CNTs into polymers resulted in enhancement of the thermal conductivity compared to Ag-filler. The increase of thermal conductivity with addition of CNT filler is obvious, especially for the purified CNT. The value of thermal conductivity is about two times higher than the Ag-filled conductive adhesive. However, improvement on thermal conductivity of the surface modified CNT-filled conductive adhesives is not so obvious. Since the thermal conduction in CNT is by phonon transfer, the nanometric size and the huge interface lead to strong phonon-scattering at the interface. Thus, a relatively low interfacial area, weak interfacial adhesion promotes the conduction of phonons and minimizes coupling losses. According to this, the non-treated MWCNTs seem to have the highest potential to improve the thermal conductivity of epoxies.

The ohmic resistance effect for characterisation of carbon nanotube paste electrodes (CNTPEs)

In this study, carbon nanotube paste electrodes (CNTPEs) have been characterised using their ohmic resistance, RCNTPE, when examining a set of six different electrodes prepared from three types of CNTs and two altered pasting liquids (binders); the latter represented by traditional mineral or silicone oils. It is shown that simple measurements of the ohmic resistance can alternate to the standard electrochemical characterisation by cyclic voltammetry with model systems. During the proper experimentation, particular attention has been paid to the changes of the consistency and of the resultant RCNTPE in dependence of both main constituents used and upon the carbon-to-pasting liquid ratio chosen. The results obtained were compared to those of “classical” carbon paste electrodes (CPEs) prepared from common graphite powder. The most evident and surprising difference ascertained is associated with the optimal carbon-to-pasting liquid: whereas the ordinary CPEs could contain up to 20% (w/w) oily phase, the CNTPEs reached the optimum at about 60% (w/w) binder, while retaining still satisfactory physical as well as electrochemical properties. The explanation of this finding is given and the problems connected with homogeneity and stability of various carbon pastes are discussed.

Dependence of mechanical characteristics and the fracture and buckling behavior of single-walled carbon nanotubes on their geometry

The dependence of the mechanical characteristics of single-walled carbon nanotubes on their length, radius, and chirality is investigated by molecular dynamics simulation. The observed changes in the mechanical properties with radii are compared with the results reported by other authors under both tensile and compressive loading. The tensile properties of zigzag and armchair CNTs are not dependent on their lengths. Slight changes in the mechanical properties with chirality are also reported. However, their compressive properties, primarily their stiffness and critical compressive stress, vary with length for all types of CNTs. The fracture patterns show different modes in each case. Buckling produces kinks, wavy structures, shell-wall buckling, columnar buckling, bending, and twisting.

OH and COOH functionalized single walled carbon nanotubes-reinforced alumina ceramic nanocomposites

Alumina ceramics reinforced with 1 wt.% single-walled carbon nanotube (SWCNT) were fabricated via spark plasma sintering (SPS) of composite powders containing carboxyl (COOH) or hydroxyl (OH) group functionalized single-walled carbon nanotubes. The samples were SPS’ed at 1600 °C under 50 MPa pressure for holding time of 5 min and at a heating rate of 4 °C/s. The effects of CNT addition having different surface functional groups on microstructure, conductivity, density and hardness were reported. It was shown that nanotube addition decreased the grain sizeof alumina from 3.17 μm to 2.11 μm for COOH-SWCNT reinforcement and to 2.28 μm for COOH-SWCNT reinforcement. The hardness values of the composites are similar for all samples but there is 4.5 and 7.5 times increase in electrical conductivity with respect to monolithic alumina for COOH-SWCNT and OH-SWCNT, respectively. It was also shown by TEM and FEG SEM observations that transgranular fracture behaviour of alumina was changed to mostly intergranular fracture mode by the addition of both types of CNTs which may be due to location of CNTs along the grain boundaries. A significant grain size reduction in alumina is considered toresult fromthe suppressing effect of CNTs during sintering.

AN INVESTIGATION INTO THE TORSIONAL BUCKLING OF CARBON NANOTUBES USING MOLECULAR AND STRUCTURAL MECHANICS

In this work, the critical twist angles of two types of CNTs, zigzag and armchair of different lengths are determined using molecular and structural mechanics. The results show that the torsional buckling modes predicted by the two methods are the same. It is also shown that critical twist angle decreases as CNTs length increases. Structural mechanics underpredicts the critical angle for both armchair and zigzag nonotubes. It is also shown that the critical angle for armchair nanotubes is higher than that for zigzag nanotubes.

Noise Mitigation Techniques for Carbon Nanotube-Based Piezoresistive Sensor Systems

ABSTRACTCarbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper we will demonstrate several noise mitigation techniques that can be used to decrease noise in the CNT-based sensor system without reducing the sensor’s strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental variations. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost two orders of magnitude and increase the dynamic range of the sensors by 29 dB.

Advancement in carbon nanotubes: basics, biomedical applications and toxicity

Carbon nanotubes (CNTs) have attracted much attention by researchers worldwide in recent years for their small dimensions and unique architecture, and for having immense potential in nanomedicine as biocompatible and supportive substrates, as a novel tool for the delivery of therapeutic molecules including peptides, RNA and DNA, and also as sensors, actuators and composites. CNTs have been employed in the development of molecular electronic, composite materials and others due to their unique atomic structure, high surface area-to-volume ratio and excellent electronic, mechanical and thermal properties. Recently they have been exploited as novel nanocarriers in drug delivery systems and biomedical applications. Their larger inner volume as compared with the dimensions of the tube and easy immobilization of their outer surface with biocompatible materials make CNTs a superior nanomaterial for drug delivery. Literature reveals that CNTs are versatile carriers for controlled and targeted drug delivery, especially for cancer cells, because of their cell membrane penetrability. This review enlightens the biomedical application of CNTs with special emphasis on utilization in controlled and targeted drug delivery, as a diagnostics tool and other possible uses in therapeutic systems. The review also focuses on the toxicity aspects of CNTs, and revealed that genotoxic potential, mutagenic and carcinogenic effects of different types of CNTs must be explored and overcome by formulating safe biomaterial for drug delivery. The review also describes the regulatory aspects and clinical and market status of CNTs.

Processing of Poly(propylene)/Carbon Nanotube Composites using scCO2‐Assisted Mixing

AbstractscCO2 was used to assist in the preparation of PP/CNT composites. Two types of CNTs were used: MWNTs with and without HDPE coating (cMWNTs). The morphology of the nanocomposites and their mechanical and thermal properties were investigated and compared with samples made by traditional melt compounding. The use of cMWNT leads to better dispersion and properties in melt‐compounded nanocomposites. For systems prepared using scCO2‐assisted mixing, however, better properties were obtained using pristine MWNTs, avoiding the additional costs of nanotube modification. It was also shown that observed improvements in the mechanical properties for these materials were due to a combination of matrix modification and nanotube reinforcement, rather than a reinforcement effect caused solely by MWNTs.magnified image

Multifunctional poly(2,5‐benzimidazole)/carbon nanotube composite films

AbstractThe AB‐monomer, 3,4‐diaminobenzoic acid dihydrochloride, was recrystallized from an aqueous hydrochloric acid solution and used to synthesize high‐molecular‐weight poly(2,5‐benzimidazole) (ABPBI). ABPBI/carbon nanotube (CNT) composites were prepared via in situ polymerization of the AB‐monomer in the presence of single‐walled carbon nanotube (SWCNT) or multiwalled carbon nanotube (MWCNT) in a mildly acidic polyphosphoric acid. The ABPBI/SWCNT and ABPBI/MWCNT composites displayed good solubility in methanesulfonic acid and thus, uniform films could be cast. The morphology of these composite films was studied by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The results showed that both types of CNTs were uniformly dispersed into the ABPBI matrix. Tensile properties of the composite films were significantly improved when compared with ABPBI, and their toughness (∼200 MPa) was close to the nature's toughest spider silk (∼215 MPa). The electrical conductivities of ABPBI/SWCNT and ABPBI/MWCNT composite films were 9.10 × 10−5 and 2.53 × 10−1 S/cm, respectively, whereas that of ABPBI film was 4.81 × 10−6 S/cm. These values are ∼19 and 52,700 times enhanced by the presence of SWCNT and MWCNT, respectively. Finally, without acid impregnation, the ABPBI film was nonconducting while the SWCNT‐ and MWCNT‐based composites were proton conducting with maximum conductivities of 0.018 and 0.017 S/cm, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1067–1078, 2010

Electrocatalytic oxygen reduction on single-walled carbon nanotubes supported Pt alloys nanoparticles in acidic and alkaline conditions

The objective of this study is to improve the catalytic activity of platinum by alloying with transition metal (Pd) in gas diffusion electrodes (GDEs) by oxygen reduction reaction (ORR) at cathode site and comparison of the acidic and alkaline electrolytes. The high porosity of single-walled carbon nanotubes (SWCNTs) facilitates diffusion of the reactant and facilitates interaction with the Pt surface. It is also evident that SWCNTs enhance the stability of the electrocatalyst. Functionalized SWCNTs are used as a means to facilitate the uniform deposition of Pt on the SWCNT surface. The structure of SWCNTs is nearly perfect, even after functionalization, while other types of CNTs contain a significant concentration of structural defects in their walls. So catalysts supported on SWCNTs are studied in this research. The electrocatalytic properties of ORR were evaluated by cyclic voltammetry, polarization experiments, and chronoamperometry. The morphology and elemental composition of Pt alloys were characterized by X-ray diffraction (XRD) analysis and inductively coupled plasma atomic emission spectroscopy (ICP-AES) system. The catalytic activities of the bimetallic catalysts in GDEs have been shown to be not only dependent on the composition, but also on the nature of the electrolytes. The GDEs have shown a transition from the slow ORR kinetics in alkaline electrolyte to the fast ORR kinetics in the acidic electrolyte. The results also show that introduction of Pd as transition metal in the Pt alloys provides fast ORR kinetics in both acidic and alkaline electrolytes. The performance of GDEs with Pt–Pd alloy surfaces towards the ORR as a function of the alloy’s overall composition and their behavior in acidic electrolyte was also studied. These results show that the alloy’s overall composition and also the nature of the electrolytes have a large effect on the performance of GDEs for ORR.

Kinetically Controlled Side-Wall Functionalization of Carbon Nanotubes by Nitric Acid Oxidation

The nitric acid oxidation followed by sodium hydroxide washing was applied for functionalization of single-walled carbon nanotubes (SWCNTs), few-walled CNTs (FWCNTs), and multiwalled CNTs (MWCNTs). The surface functionalization of CNTs via acidic oxidation was studied by transmission electron microscopy, Raman scattering spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The oxidation of CNTs involves the exfoliation of functionalized carbon layers into smaller carbonaceous fragments (CF), which might influence the performance of composite materials based on modified CNTs. Optimizing oxidation time increased the selectivity to thermodynamically unstable functionalized CNTs. Thicker CNTs, including FWCNTs and MWCNTs, are better for high-density surface functionalization, due to higher structure stability. It was proposed that a rational selection of the oxidation process and type of CNTs is important for the applications involving CNT-related composite materials.

A Study on Gas Sensor Based on Carbon Nanotubes on Anodized Aluminum Oxide

A new type of CNTs based ammonia gas sensor was investigated. The array of carbon nanotubes was synthesized into the pore of anodized aluminum oxide (AAO) by thermal chemical vapor deposition method without metal catalyst. The anodized aluminum oxide was synthesized on the p–type Si(100) substrates by two step anodization process. After removing the carbon top layer, a thin Ag electrode was deposited on the surface of sample to get the opened end of the CNTs for gas sensor. The electrical and gas sensing properties of carbon nanotubes based sensor were characterized by I-V test after metal deposition on the top of carbon nanotubes. The device shows high sensitivity for detecting the NH3 gas at room temperature.

Morphology-controlled SWCNT/polymeric microsphere arrays by a wet chemicalself-assembly technique and their application for sensors

Large-scale morphology-controlled SWCNT/polymeric microsphere arrays can be obtainedby a wet chemical self-assembly technique. The loading of SWCNTs, the length ofSWCNTs, and the size and nature of polymeric microspheres can easily be controlled.Similar results can also be reached using this method for MWCNTs. In both types ofCNTs, they form an interesting interactive ‘net’ structure on spheres and sphere joints. TheSWCNT/PS-modified Au electrode was used for detection of uric acid by cyclicvoltammetry and single-potential time-based techniques. The preliminary results showthat the modified electrode presents good sensitivity and stability to uric acid.

Hydrogen adsorption in single-walled and multi-walled carbon nanotubes grown in a hot-wire CVD (Cat-CVD) reactor

We have employed hot-wire chemical vapor deposition (HWCVD) for the growth of single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs). The reactor consisted of a quartz tube and two tungsten filaments. Often additional molybdenum wires were incorporated into the system serving as additional heat sources and possibly providing via evaporation an additional gas-phase catalyst. Transmission electron microscopy indicated the presence of both types of CNTs with diameters ranging from ∼ 1–30 nm. Thermal desorption experiments showed the presence of the both physisorbed and chemisorbed hydrogen.

Correlation between Field Electron Emission and Structural Properties in Randomly and Vertically Oriented Carbon Nanotube Films

We investigated the influence of the structural properties of randomly oriented carbon nanotube (R-CNT) and vertically oriented carbon nanotube (V-CNT) films on their field electron emission properties. The R-CNT and V-CNT films were synthesized using FeNi catalysts by means of thermal and dual-RF plasma-enhanced chemical vapor depositions, respectively. The structural properties of the R-CNT and V-CNT films were dependent on the initial thickness of the FeNi catalyst. As the FeNi film thickness decreased, the diameters of both types of CNTs decreased. Although the field electron emission property of the V-CNT film was improved with increasing the aspect ratio of V-CNT, the field enhancement factor, β, obtained from the Fowler–Nordheim plot was found to be 100 times larger than that obtained from the geometric properties. R-CNTs exhibited a lower threshold field than V-CNTs. These results suggest that the field emission property is markedly influenced by the surface state rather than by the geometric factors of CNTs.