Multi-walled Carbon Nanotubes In Solution Research Articles

Hydroxyapitite-multiwalled carbon nanotubes nanocomposite for adhesion and electrochemical study of human osteoblast-like cells (MG-63)

A new biocompatible interface made up of hydroxyapitite-multiwalled carbon nanotubes (HA-MWCNTs) nanocomposite was developed for adhesion and electrochemical detection of human osteoblast-like cells (MG-63). The HA-MWCNTs nanocomposite was synthesized by self-assembling nano-hydroxyapitite onto multiwalled carbon nanotubes in solution, which was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The adhesion of the MG-63 on the nanocomposite film was studied by quartz crystal microbalance and cyclic voltammetry. The nanocomposites interface showed improved immobilization capacity for cells and good biocompatibility for preserving the activity of immobilized living cells. The living cells immobilized on an HA-MWCNTs modified glassy carbon electrode exhibited an irreversible anodic peak response being positively associated with the density and viability of cells, which was used to describe the cells growth and evaluate the effectiveness of antitumor drug 5-fluorouracil (5-FU) on the cells. The obtained 5-FU cytotoxicity results agreed well with those from conventional MTT assays. The highly biocompatible HA-MWCNTs nanocomposite is also expected to be an appropriate matrix for the electrochemical investigation of adhesion, proliferation, and apoptosis of many other relevant mammalian cells.

Functionalization of Multi‐Walled Carbon Nanotubes by Thermo‐Grafting with α‐Methylstyrene‐Containing Copolymers

AbstractThe present article reports on a strategy for the functionalization of multi‐walled carbon nanotubes (MWCNTs) by grafting with various polymer chains. Copolymers consisting of α‐methylstyrene (AMS) and a second monomer, that is glycidyl methacrylate (GMA) or styrene (St), were synthesized in advance. The copolymers were heated in the presence of MWCNTs in solution, decomposition of the AMS sequences occurred, providing macroradicals, which further attacked the double bonds on the MWCNT surfaces. Grafting of the copolymer chains onto the surface of the MWCNTs was thus achieved, as demonstrated by FT‐IR, XPS and Raman technologies. The resulting poly(AMS‐co‐GMA)‐g‐MWCNTs could be uniformly dispersed in N,N‐dimethylformamide (DMF) and acetone, and the poly(AMS‐co‐St)‐g‐MWCNTs also could be uniformly dispersed in DMF.magnified image

Dispersion and noncovalent modification of multiwalled carbon nanotubes by various polystyrene‐based polymers

AbstractThis article investigated the dispersion and modification of multiwalled carbon nanotubes (MWCNTs) through solution mixing based on the noncovalent interactions between polystyrene (PS) and MWCNTs. It was found that the interactions were robust enough to stabilize the debundled MWCNTs in solution after vigorous sonication. The PS attached, which altered the surface properties of MWCNTs and made them easily soluble in organic solvents, can remain even after careful washing with solvents. Besides, many other PS‐based polymers were proved to retain the ability to disperse MWCNTs to form stable solutions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The third-order optical nonlinearities of carbon nanotube modified conjugated polymer in the femtosecond and nanosecond regimes

Multiwalled carbon nanotubes (MWCNTs) have been noncovalently modified with poly[2-methoxy 5-octyoxy]-p-phenylene vinylene (MO-PPV) to form a series of solution of MWCNTs and the conjugated polymers. The third-order nonlinearities of the solutions were investigated by the optical Kerr effect technique with femtosecond pulses, and degenerate four-wave mixing, open aperture, and closed aperture Z-scan techniques with nanosecond pulses. We attempted to quantify the contributions from various channels including the real and imaginary parts, the dynamic carriers, two-photon absorption, and thermal effect. The MO-PPV/MWCNTs composites showed much larger third-order nonlinearities than the pristine polymers. The enhanced optical nonlinearities were attributed to the strong interaction between the π-π electrons of MO-PPV and MWCNTs in their photoexcited state.

Surfactant effects on carbon nanotube interactions with human keratinocytes

Interactions of multiwalled carbon nanotubes (MWCNTs) with human epidermal keratinocytes (HEKs) were studied with respect to the effect of surfactant on dispersion of MWCNT aggregates and cytotoxicity. Our earlier studies had shown that the unmodified MWCNTs were localized within the cytoplasmic vacuoles of HEKs and elicited an inflammatory response. However, MWCNTs in solution tend to aggregate and, therefore, cells are exposed to large MWCNT aggregates. The purpose of this study was to find a surfactant that prevents the formation of large aggregates of MWCNTs without being toxic to the HEKs. HEKs were exposed to serial dilutions (10% to 0.1%) of L61, L92, and F127 Pluronic and 20 or 60 Tween for 24 hours. HEK viability, proportional to surfactant concentration, ranged from 27.1% to 98.5% with Pluronic F127; viability with the other surfactants was less than 10%. Surfactants dispersed and reduced MWCNT aggregation in medium. MWCNTs at 0.4 mg/mL in 5% or 1% Pluronic F127 were incubated with HEKs and assayed for interleukin 8 (IL-8). MWCNTs were cytotoxic to HEKs independent of surfactant exposure. In contrast, MWCNT-induced IL-8 release was reduced when exposed to 1% or 5% Pluronic F127 ( P < .05). However, both MWCNTs and surfactant, alone or in combination, increased IL-8 release compared with control exposures at 12 and 24 hours. These results suggest that the surfactant-MWCNT interaction is more complex than simple dispersion alone and should be investigated to determine the mode of interaction.

Controllable Pt Nanoparticle Deposition on Carbon Nanotubes as an Anode Catalyst for Direct Methanol Fuel Cells

We report a novel process to prepare well-dispersed Pt nanoparticles on CNTs. Pt nanoparticles, which were modified by the organic molecule triphenylphosphine, were deposited on multiwalled carbon nanotubes by the organic molecule, which acts as a cross linker. By manipulating the relative ratio of Pt nanoparticles and multiwalled carbon nanotubes in solution, Pt/CNT composites with different Pt content were achieved. The so-prepared Pt/CNT composite materials show higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation than the commercial E-TEK catalyst, which can be ascribed to the high dispersion of Pt nanoparticles on the multiwalled carbon nanotube surface.

The effect of the shape of a tip's apex on the fabrication of an AFM tip with an attached single carbon nanotube

We show how the shape of the apex on the tip of an atomic force microscope (AFM) affects the fabrication of a tip with an attached single multi-walled carbon nanotube (MWNT). To make an MWNT-attached AFM tip, we dropped a drop of MWNT solution onto the electrode surface on which we applied an ac electric field. The MWNTs that had been dispersed into a dielectric solution were directly assembled onto the apex of the AFM tip with the aid of the alignment and attraction of the dielectrophoretic force. To verify the effect of the shape of the tip's apex in the fabrication of a tip attached a single carbon nanotube, we used three types of tips: sharp, blunt and cylindrical. We found from the simulation results and repeated experiments that blunt tips with a 150–250 nm radius are more effective than sharp or cylindrical tips. When we applied an electric field of 0.6–0.7 V pp/μm, we obtained an AFM tip with a single MWNT attached, and, by using this tip to scan the surface of the reference, we were able to evaluate the performance of the tip. In summary, we have demonstrated that under various experimental conditions the shape of the apex of an AFM's tip deeply affects the fabrication of tips attached a single MWNT.

Use of Dielectrophoresis in a High-Yield Fabrication of a Carbon Nanotube Tip

This paper reports on the development of an atomic force microscope (AFM) tip with single multiwalled carbon nanotube (MWNT). We used an ac electric field, which causes dielectrophoresis (DEP), to align and deposit single MWNT on a metal-coated AFM tip. By dropping an MWNT solution and applying an electric field between the AFM tip and the electrode, we were able to directly assemble one of MWNTs that were dispersed in the diluted solution on the apex of the AFM tip. We investigated the experimental conditions under which the aligning angle of the CNT to the tip's axis varied according to changes in the angle of alignment between the tip and the electrode. We found the experimental condition of 75% success rate to fabricate CNT tips, and we show how the CNT tip compares with a conventional silicon tip with respect to the imaging of 15 nm gold particles.

The morphology and thermal properties of multi‐walled carbon nanotube and poly(hydroxybutyrate‐co‐hydroxyvalerate) composite

AbstractNanocomposites based on poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) and multi‐walled carbon nanotubes (MWNTs) were prepared by solution processing. Ultrasonic energy was used to uniformly disperse MWNTs in solutions and to incorporate them into composites. Microscopic observation reveals that polymer‐coated MWNTs dispersed homogenously in the PHBV matrix. The thermal properties and the crystallization behavior of the composites were characterized by thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction, the nucleant effect of MWNTs on the crystallization of PHBV was confirmed, and carbon nanotubes were found to enhanced the thermal stability of PHBV in nitrogen. Copyright © 2004 Society of Chemical Industry

Carbon Nanotubes‐Modified Screen‐Printed Electrodes for Chemical Sensors and Biosensors

Multiwalled carbon nanotubes (MWCNT) have been used for modification of working graphite ink electrode of the three‐electrode screen‐printed sensing stripe. Modification has been made by evaporating on the graphite surface a solution of MWCNT in dimethylformamide. The effect of modification on reversibility of the electrode process of the system hexacyanoferrate(II)/(III) has been shown, along with improvement of the sensitivity of detection of pesticide paraoxon with biosensors containing organophosphorus hydrolase immobilized by adsorption on the nanotubes‐modified graphite ink electrode. The catalytic sensing of methanol was also demonstrated with the use of a screen‐printed sensor modified with MWCNT and Co(II) salt present in the measuring solution.

Optical Absorption and Fluorescence of a Multi-walled Nanotube-Polymer Composite

We report on the optical studies of an organic composite containing an unusual phenylene vinylene copolymer and multi-walled carbon nanotubes in solution. The nanotubes appear to be held in the polymer matrix through a weak interaction between the backbone of the polymer and the lattice of the nanotube. This incorporation greatly effects the absorption and emission properties of the composite. We have also shown that it is possible to control the quantum efficiency of the system by varying the mass fraction of the nanotubes present.