Joseph A. Libera

In situ multiphase fluid experiments in hydrothermal carbon nanotubes

Hydrothermal multiwall closed carbon nanotubes are shown to contain an encapsulated multiphase aqueous fluid, thus offering an attractive test platform for unique in situ nanofluidic experiments in the vacuum of a transmission electron microscope. The excellent wettability of the graphitic inner tube walls by the aqueous liquid and the mobility of this liquid in the nanotube channels are observed. Complex interface dynamic behavior is induced by means of electron irradiation. Strong atomic-scale interactions between the entrapped liquid phase and the wetted terminated graphite layers are revealed by means of high-resolution electron microscopy. The documented phenomena in this study demonstrate the potential of implementing such tubes in future nanofluidic devices.

Hydrothermal synthesis of multiwall carbon nanotubes

Multiwall open-end and closed carbon nanotubes with the wall thickness from several to more than 100 carbon layers were produced by a principally new method— hydrothermal synthesis—using polyethylene/water mixtures in the presence of nickel at 700–800 °C under 60–100 MPa pressure. An important feature of hydrothermal nanotubes is a small wall thickness, which is about 10% of the large inner diameter of 20–800 nm. Closed nanotubes were leak-tight by virtue of holding encapsulated water at high vacuum and can be used as test tubes for in situ experiments in transmission electron microscope (TEM). Raman microspectroscopy analysis of single nanotubes shows a well-ordered graphitic structure, in agreement with high-resolution TEM. The hydrothermal synthesis has the potential for producing multiwall nanotubes for a variety of applications. The fabrication of nanotubes under hydrothermal conditions may explain their presence in coals and carbonaceous rocks and suggests that they should be present in natural graphite deposits formed under hydrothermal conditions.

Hydrothermal synthesis of graphite tubes using Ni catalyst

Abstract While many forms of carbon nanotubes and filamentous carbon have been reported, both a large inside diameter and highly graphitic wall structure have not been created. This paper describes such tubes from 70 to 1300 nm in diameter which were synthesized hydrothermally in the C–H–O–Ni system at 100 MPa and 730–800°C by first establishing a post-pyrolysis C–H–O equilibrium followed by an increase in pressure during which time growth of graphitic carbon occurred. Depending on the size of the Ni catalyst particles, flake-like graphite or carbon tubules were formed. Tubes were also synthesized without water, i.e., in the C–H–Ni system, but these tubes had multiple internal caps while those produced with water present had very few internal obstructions and a large inside diameter. The exceptional quality of the tube walls is demonstrated by straight and perfect lattice fringing in the tube walls and electron diffraction spot patterns free of diffuse amorphous rings. Raman spectral evidence shows high similarity to the spectra obtained from high purity natural graphite. The high integrity of hydrothermal nanotubes is demonstrated by the existence of liquid inclusions trapped inside the tubes during synthesis. The properties of hydrothermal graphite tubes suggest their use in nano-fluidic devices and as lightweight reinforcement for composites.

In situ chemical experiments in carbon nanotubes

Abstract Understanding the interaction of water-based liquids with carbon at the nanoscale is very important for exploring the potential of carbon nanotubes in nanofluidic chips, probes, and capsules for drug delivery. By using hydrothermal synthesis, we produced closed hydrophilic multiwall carbon nanotubes filled with aqueous fluid. They allow for the first time high-resolution in situ studies of an interface between fluid and carbon in TEM. Strong interaction between the liquid and walls, intercalation of nanotubes with O–H species and dissolution of walls upon heating have been demonstrated. Thermodynamics simulation was used to explain the interaction of nanotubes with fluid.

Attoliter fluid experiments in individual closed-end carbon nanotubes: Liquid film and fluid interface dynamics

A hydrothermal method of catalytic nanotube synthesis has been shown to produce high-aspect-ratio, multiwall, capped carbon nanotubes, which are hollow and contain a high-pressure encapsulated aqueous multicomponent fluid displaying clearly segregated liquid and gas by means of well-defined curved menisci. Thermal experiments are performed using electron irradiation as a means of heating the contents of individual nanotubes in the high vacuum of a transmission electron microscope (TEM). The experiments clearly demonstrate that TEM can be used to resolve fluid interface motion in nanochannels. Good wettability of the inner carbon walls by the water-based fluid is shown. Fully reversible interface dynamic phenomena are visualized, and an attempt is made to explain the origin of this fine-scale motion. Experimental evidence is presented of nanometer-scale liquid films rapidly moving fluid along the nanochannel walls with velocities 0.5 μm/s or higher.

In-situ Fluid Experiments in Carbon Nanotubes

Closed-end multi-wall carbon nanotubes, which contain an encapsulated aqueous multi-phase fluidunder high pressure, have been produced by hydrothermal synthesis. These nanotubes are leak-tight by virtue of holding the fluid at the high vacuum of a transmission electron microscope (TEM) and can be used as a testplatform for unique in-situ nanofluidic experiments in TEM. They form an experimental apparatus, which is at least two orders of magnitude smaller than the smallest capillaries used in fluidic experiments so far. Excellent wettability of the carbon tube walls by the liquid and a dynamic behavior similar to that in micro-capillaries demonstrates the possibility of use of nanoscale (