Almila G. Yazicioglu

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.

MEASUREMENT OF FRACTAL PROPERTIES OF SOOT AGGLOMERATES IN LAMINAR COFLOW DIFFUSION FLAMES USING THERMOPHORETIC SAMPLING IN CONJUNCTION WITH TRANSMISSION ELECTRON MICROSCOPY AND IMAGE PROCESSING

ABSTRACT Aerosol property measurements including primary particle, radius of gyration, and number of primary particles per agglomerate have been performed for soot collected thermophoretically from the soot annulus at selected heights of laminar ethene/air, methane/air, and methane/oxygen diffusion flames and analyzed using a digital image processing technique. The fractal dimension Df and prefactor term kf calculated from these measurements were used to determine whether there exists a universality of these properties for inflame soot or any correspondence with previous measurements performed in the overfire region of large turbulent flames. The fractal dimension measured in this study ranged from 1.65 to 1.75, in agreement with previous measurements obtained for both inflame and overfire soot. Measurable variations in the prefactor values, which ranged from 6.75 for the methane/air diffusion flame, to 8.47 for the ethylene/air diffusion flame, were observed. An error analysis performed for these results indicated that there is up to 6 percent and 22 percent uncertainty in the fractal dimension and prefactor values, respectively.

Wall structure and surface chemistry of hydrothermal carbon nanofibres

A transmission electron microscopy examination of hydrothermally produced carbon nanofibres/nanotubes with outer diameter 50–200xa0nm suggests that the tube walls are inclined with respect to the tube axis. The apex angles are in the range 8°–16°. The structure of these tubes and their growth mechanism can be described by a conical-scroll model. The conical-scroll structure enables functionalization of both inner and outer tube surfaces. The outer wall of these nanofibres is shown to be covered by a hair-like layer, with a characteristic length of about 0.5xa0nm. Electron energy loss spectroscopy suggests that these hairs are functional groups containing oxygen and carbon. The presence of these groups on the tube surface can account for the reported hydrophilic character of these tubes.

Theoretical and experimental investigation of aqueous liquids contained in carbon nanotubes

The dynamic response—as caused by different means of thermal stimulation or pressurization—of aqueous liquid attoliter volumes contained inside carbon nanotubes is investigated theoretically and experimentally. The experiments indicate an energetically driven mechanism responsible for the dynamic multiphase fluid behavior visualized in real time with high spatial resolution using electron microscopy. The theoretical model is formulated using a continuum approach, which combines temperature-dependent mass diffusion with intermolecular interactions in the fluid bulk, as well as in the vicinity of the carbon walls. Intermolecular forces are modeled by Lennard-Jones potentials. Several one-dimensional and axisymmetric cases are considered. These include situations which physically represent liquid volume pinchoff, jetting, or fluid relocation due to thermal stimulation by a steady or modulated electron beam, as well as liquid precipitation (condensation) from vapor due to overcooling or pressurization. Compar...

Thermal stimulation of aqueous volumes contained in carbon nanotubes: Experiment and modeling

The dynamic response, as caused by thermal stimulation, of aqueous liquid attoliter volumes contained inside multiwall carbon nanotubes is investigated theoretically and experimentally. The experiments indicate an energetically driven mechanism responsible for the dynamic multiphase fluid behavior visualized under high resolution in the transmission electron microscope. The theoretical model is formulated using a continuum approach, which combines temperature-dependent diffusion with intermolecular interactions in the fluid bulk, as well as in the vicinity of the carbon wall. Intermolecular van der Waals forces are modeled by Lennard-Jones 12-6 potentials. Comparisons between theoretical predictions and experimental data demonstrate the ability of the model to describe the major trends observed in the experiments.

Electron Microscope Visualization of Multiphase Fluids Contained in Closed Carbon Nanotubes

Aqueous multiphase fluids trapped in closed multiwall carbon nanotubes are visualized with high resolution using transmission electron microscopy (TEM). The hydrothermally synthesized nanotubes have inner diameter of 70 nm and wall thickness 20 nm, on average. The nanotubes are hydrophilic due to oxygen groups attached on their wall surfaces. Segregated liquid inclusions contained in the nanotubes under high pressure can be mobilized by heating. A resistive heating stage is utilized to heat a thin membrane inside a nanotube, causing the membrane to evaporate slowly and eventually pinch off. Focused electron beam heating is employed as a second means of thermal stimulation, which results in localized heating. With the latter method, gas/liquid interface motion is observed inside the thin channel of a carbon nanotube. Experiments like the ones presented herein may help understand the dynamics of fluids contained in nanoscale channels.

Fluid transport and phase transition experiments in closed multiwall carbon nanotubes

Multiwall carbon nanotubes show potential for use in various micro- and nanofluidic devices, since they resemble cylindrical channels used in the macroscopic world. However, in situ experimental studies of fluid behavior in nanotubes or nanochannels have been rare. In this work, transmission electron microscopy experiments are performed on closed-end multiwall carbon nanotubes filled with an aqueous multiphase fluid. The nanotubes form an experimental apparatus that is a few orders of magnitude smaller than the smallest channels used in other fluidic experiments. These nanotubes are synthesized hydrothermally, using Ni as a catalyst, and they contain segregated aqueous liquid and gas inclusions with clearly defined interfaces. Using electron irradiation, the multiphase fluid inside individual nanotubes is excited thermally, by expanding and contracting the electron beam. The excellent wettability of the graphitic inner tube walls by the aqueous fluid and the mobility of this liquid in the nanotubes are observed in real time with nanometer-scale resolution. Interface dynamic phenomena are visualized, as driven by thermocapillary forces as well as by evaporation and condensation. The hydrothermal nanotubes examined herein offer a promising platform for studying the behavior of multicomponent, multiphase fluids in nanosize channels at high-pressure conditions. The phenomena documented in this study demonstrate the potential of implementing such tubes in future nanofluidic devices.Copyright

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 (