Showing papers by "Yury Gogotsi published in 2007"

Monitoring oxidation of multiwalled carbon nanotubes by Raman spectroscopy

Abstract: Multiwalled carbon nanotubes (MWCNTs) were oxidized in air and acids while varying the treatment time and/or temperature. The goal of this approach was to create the highest density of carboxyl groups with moderate sample loss, which is necessary for nanocomposite applications. In situ Raman experiments allowed real-time observation of the structural changes in MWCNTs upon oxidation. The ratio of the Raman intensities of the D and G bands was used to estimate the concentration of defects. It was found that while an oxidation for 6 h in H2SO4/HNO3 provided the strongest effect, a ‘flash oxidation’ in air (15 min at 550 °C) also leads to an efficient functionalization in a cost-effective and environmentally friendly way. Transmission electron microscopy, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis and electrophoretic mobility analysis were used to study the oxidized nanotubes. Copyright © 2007 John Wiley & Sons, Ltd.

Magnetically assembled carbon nanotube tipped pipettes

Abstract: The authors have developed a biological probe at the nanoscale with a magnetic carbon nanotube (mCNT) tip that has the ability to transfer fluids. Fabrication is performed by injection of mCNTs into micropipettes, which are then positioned as probe tips via magnetophoresis, and affixed with polymeric adhesive. In this letter the authors discuss the magnetic fabrication process and demonstrate the versatility of this probe.

Arbitrarily Shaped Fiber Assemblies from Spun Carbon Nanotube Gel Fibers

Abstract: Experimental methods, apparatus, and practically useful theoretical analysis are provided for the coagulation-based spinning of effectively unlimited lengths of carbon nanotube fibers having exceptional toughness and reasonably high strength. This spinning process fundamentally depends on the mechanical properties of intermediate gel state fibers, which we find are surprising elastic up to about 20 % strain and sufficiently strong for diverse processing methods. More specifically, we show that assemblies of these gel fibers can be used as intermediates for making nanotube sheets, large diameter fibers, and conformal coatings. When suitably processed, these composites (comprising many parallel solution-spun nanotube fibers) have useful strength and extraordinary toughness.

Induction and measurement of minute flow rates through nanopipes

Abstract: A simple technique to simultaneously induce fluid flow through an individual nanopipe and measure the flow rate and the pressure difference across the pipe is described. Two liquid drops of different sizes are positioned at the two ends of the nanopipe. Due to the higher capillary pressure of the smaller drop, flow is driven from the smaller drop to the bigger drop. The instantaneous pressures of the two drops are estimated from the drops’ shapes and sizes. The flow rate is estimated by monitoring the sizes of the drops as functions of time with a microscope and a video camera. A theory that correlates the drops’ sizes and the flow rate is derived. Measurements are carried out with an ionic salt and glycerin to estimate the effective tube radius of the nanopipes with diameters ranging from 200 to 300nm. The tubes’ diameters are independently measured with a scanning electron microscope. The method is also verified by tracking the motion of fluorescent particles through the nanopipe. The paper provides a s...

Multifunctional carbon nanotubes with nanoparticles embedded in their walls

Abstract: Controlled amounts of nanoparticles ranging in size and composition were embedded in the walls of carbon nanotubes during a template-assisted chemical vapour deposition (CVD) process. The encapsulation of gold nanoparticles enabled surface enhanced Raman spectroscopy (SERS) detection of glycine inside the cavity of the nanotubes. Iron oxide particles are partially reduced to metallic iron during the CVD process giving the nanotubes ferromagnetic behaviour. At high nanoparticle concentrations, particle agglomerates can form. These agglomerates or larger particles, which are only partially embedded in the walls of the nanotubes, are covered by additional carbon layers inside the hollow cavity of the tube producing hillocks inside the nanotubes, with sizes comparable to the bore of the tube.

Micro- and nanoscale graphite cones and tubes from hackman valley, kola peninsula, russia

Abstract: We describe several unusual forms of natural graphite from an alkaline pegmatite that cross-cuts rischorrite in the Hackman Valley, Khibiny Massif, Kola Peninsula, Russia. The graphite occurs macroscopically in two forms: as spherical aggregates up to 2 cm in diameter of friable, radially aligned fibers ~20 μm in cross section, and as fine-grained surface coatings in cavities covering aegirine, strontian fluorapatite and K-feldspar. Optical microscopy and field emission scanning electron microscopy (FESEM) show that the fibers are actually hollow channels whose walls are composed of tabular crystals of graphite greatly elongate in the direction of the fiber axis and with their basal planes oriented parallel to the channel walls. Inside and among the channels occur rolled graphitic structures (RGS): scrolls, tubes, and cones up to 2 μm in diameter and up to 15 μm in length. The fine-grained graphite coatings on the surfaces of cavities, on the other hand, consist almost solely of micro- and nanoscale RGS. The largest of the RGS are hollow scrolls, with the c axis predominantly perpendicular to the scroll axis. These are usually cigar-shaped but can also be more tubular. Conical RGS occur at the micro- and nanoscales. The nanoscale cones tend not to be hollow and may have a cone–helix structure. Transmission electron microscopy (TEM), Raman spectroscopy, and FESEM indicate that the RGS are composed of well-ordered graphitic layers but are commonly coated by amorphous carbon. The morphologies and paragenesis of these unusual graphite forms suggest a possible hydrothermal origin.

Process of purifying nanodiamond compositions and applications thereof

Abstract: The presence of large amounts of non-diamond carbon in detonation synthesized nanodiamond (ND) severely limits applications of this exciting nanomaterial. An environmentally-friendly process is disclosed to selectively remove sp2- bonded carbon from ND. The content of up to 96% of sp3 -bonded carbon in the oxidized samples is comparable to that found in microcrystalline diamond and is unprecedented for ND powders. Transmission electron microscopy and Fourier transform infrared spectroscopy studies show high purity 5-nm ND particles covered by oxygen-containing surface functional groups. The surface functionalization can be controlled by subsequent treatments. In contrast to current purification techniques, the disclosed process does not require the use of toxic or aggressive chemicals, catalysts or inhibitors and opens avenues for numerous new applications of nanodiamond.

Carbothermal Synthesis of α‐SiC Micro‐Ribbons

Abstract: We report the synthesis of microscopic α-SiC ribbons (belts) on the surface of a graphite rod at 1800°–1900°C by a carbothermal process. The width of the ribbons produced ranged from 500 nm to 5 μm and the aspect ratio was up to 400. The ribbon thickness ranged from 50 to 800 nm. Their growth mechanism was explained by accelerated growth along the twin boundary. SiC whiskers grew on the rod along with the ribbons. Frequently, ribbons were growing from the tip of a whisker or whiskers were growing from the edge of a ribbon. SiC ribbons may find applications in high-temperature sensors, photo-electronic devices, or robust cantilevers in micro (or nano) electro mechanical systems. Alternatively, they can be used as reinforcements in composite materials, conferring anisotropic mechanical properties, such as unidirectional flexibility, to the composite.

High Temperature Functionalization and Surface Modification of Nanodiamond Powders

Abstract: High temperature annealing in vacuum, air, hydrogen, chlorine, and ammonia are described as a means to change surface chemistry and phase composition of nanodiamond powders of three different grades, which have different sp2/sp3 carbon ratios. The changes in surface chemistry and phase composition of the powders are analyzed using Raman spectroscopy and Fourier Transform Infra Red (FTIR) spectroscopy. Advantages and limitation of high-temperature treatment techniques as well as potential applications of the gas-treated nanodiamond powders are discussed.

In situ Fluid Studies in Carbon Nanotubes with Diameters Ranging from 1 to 500 nm

Abstract: The processes that govern fluid transport in pipes are well understood for diameters in the range of micrometers and above. As the diameters diminish (e.g., in the range of a few nanometers), the roles of surface tension and capillarity seem to vary. Thus, the expected promise of carbon nanotubes (CNT, 1-50 nm inner diameter) and nanopipes (CNP, 50-300 nm inner diameter) in technological applications is in urgent need of a well-documented, basic understanding of such forces, especially since no consistent experimental data have been collected until recently. We have investigated the liquid/vapor distribution in nanotubes, the interaction of fluids with the tube walls, and the effect of surface chemistry on liquid behavior in carbon nanotubes. On this basis, we are developing a research program that will thoroughly explore the various aspects of phase interfacing in a number of different nanotube situations. Hydrothermal and CVD-grown CNP and CNT have been examined. Fluid behavior and chemical modification of the tubes have been investigated. This paper will give an overview of experimental studies of behavior of aqueous fluids in carbon nanotubes.

Nanoporous carbonaceous membranes and related methods

Abstract: Disclosed are nanoporous carbonaceous membranes and related devices, along with associated methods.

Nanowires and coatings of self-assembled nanoparticles

Abstract: Disclosed are composite materials comprising a nanofiber having a cross-sectional dimension in the range of from 1 nm to about 10,000 nm, and an outer surface, and a plurality of nanoparticles grafted to the outer surface of the fiber via a polyelectrolyte. Also disclosed are methods for manufacturing such composite materials. Further disclosed are methods and apparatuses for forming patterns of nanoparticle-coated nano fibers on substrates.

Self-assembled Multi-walled Carbon Nanotube Coatings

Abstract: Multi-walled carbon nanotube (MWCNTs) grafting onto electrospun poly(acrylonitrile) (PAN) nanofibers and silicon carbide (SiC) microfibers yields a layer by layer deposition of self assembled nanotube filaments or nanowires. PAN fibers were first functionalized with carboxylic groups through a sodium hydroxide treatment. Then, poly(diallyldimethylammonium chloride) (PDDAC), a positively charged polyelectrolyte was adsorbed onto the fibers via electrostatic interaction. When placed in contact with the modified fibers, acid treated MWCNTs (ac-MWCNTs) self-assemble onto the polymer nanofibers. The electrical conductivity of nanofibers improves due to the formation of a continuous MWCNTs monolayer on the surface, as opposed to traditional incorporation of large amounts of nanotubes into the bulk of the polymer. The use of polymers capable of forming hydrogen bonding with ac-MWCNTs, e.g. polyamides, further offers a perfect scenario in which no binding agent (PDDAC) or polymer modification is required. Polyamide 11 (PA 11) has been electrospun to provide a dense network of 100 nm and greater fibers for deposition of ac-MWCNTs. The resulting mats yielded an electrical conductivity of about 0.1 S/cm.

The Effect of Deformation on Room Temperature Coulomb Blockade using Conductive Carbon Nanotubes

Abstract: We report fluctuations in resistivity and the manifestation of Coulomb blockade phenomena of conductive multiwalled carbon nanotubes under buckling loads. Individual nanotubes were suspended and soldered between two indium-dipped tungsten probe tips. Using the electrical connection between the probes and the nanotube, electrical measurements were taken with the tube straight (unstrained) and bent (strained). Typical resistances were in the 10 GOmega range with resistivities in the 15 to 30 Omega-m range within the Coulomb blockade region of -1.0 to -0.4 V. Coulomb blockade, or electron tunneling events, appeared to occur at one of the contact points. This effect was diminished or lost once the carbon weld was broken.

Supercapacitors and methods for producing same

Abstract: Disclosed are microporous carbon compositions suitable for use in supercapacitor devices, which compositions comprise pores having an average characteristic cross -sectional dimension of less than about lnm. Also described are electrodes and electrochemical cells that utilize the disclosed compositions and methods of making the disclosed compositions.