High Aspect Ratio Nanoparticles Research Articles

Synthesis of novel micro- and mesoporous zeolite nanostructures using electrospinning techniques

Micro- and mesoporous nanostructured zeolites are fabricated for rapidly responding, selective detection of individual gases in a multigas environment. These nanostructures are synthesized by an electrospinning technique wherein the process parameters are varied through a design of experiment (DoE) methodology. Various morphologies, namely, high aspect ratio nanofibers, nanoparticles, and mixed microstructures, were obtained at different DoE variable settings. The zeolites of interest in this paper are silica and silicalite, wherein the aluminum content is zero. In the case of mesoporous silica, the sol-gel solution consisting of the silica source and the structure-directing agent is directly electrospun to obtain the nanostructured material on a device substrate. The structure-directing agent is later removed by calcination to obtain the porous nanostructures. In the case of microporous silica, the nanostructured silica is first synthesized and then co-electrospun with a polymer to obtain the desired nanostructure. The structure-directing agent and polymer are later removed by calcination.

Infrared extinction performance of high aspect ratio carbon nanoparticles

Infrared volume extinction coefficients have been theoretically calculated for high aspect ratio carbon microparticles and nanoparticles. Two principal types of carbon material were modelled: layered crystalline graphite and microcrystalline graphite. The infrared extinction performance of each material was assessed and compared for two high aspect ratio particle geometries, thin lamellar flakes and acicular fibres. Optimum dimensions for both geometries of each material for maximum volume efficient extinction performance have been identified. The volume extinction coefficient calculations were performed using the finite difference time domain method (FDTD), the T-matrix method (TMM) and the infinite cylinder solution (ICS). Phase functions were calculated for all particle geometries and morphologies modelled. Transmission calculations were also performed using the six-flux method of radiative transfer. Finally, an attempt was made to compare the theoretical calculations to an experimental measurement.

Controlling Dimensions of Polymerized Micelles: Micelle Template versus Reaction Conditions

The polymerization of elongated micellar structures offers a novel approach to the production of high aspect ratio, water-soluble amphiphilic nanoparticles. Three different surfactants were synthesized consisting of a cationic surfactant of the form (C(X)H(2X+1))trimethylammonium (where X = 14, 16, or 18) and a vinyl-containing counterion, 4-vinylbenzoate. The resulting polymer-surfactant aggregates have been polymerized to produce high aspect ratio nanoparticles which are insensitive to changes in solution conditions. The radius of the initial template is maintained on polymerization, whereas the template length is not. The aggregate radius is varied by changing the length of the surfactant tail, in this case producing aggregates with radii of 1.7, 2.0, or 2.4 nm. Variation of the initiator decomposition half-life, by means of using different initiators and varying temperature, is used to control the aggregate length between 80 and 500 nm. Through the process discussed here, both the radius and length of the aggregates are controlled independently.

Effects of carbon nanotubes on flame spread rate over 1-propanol

This paper discusses the potential for thermally conductive nanoparticles to reduce flame spread velocities over fuel dispersion mixtures. Multi-walled carbon nanotubes (MWNTs) were dispersed in 1-propanol at levels above the mixture's percolation limit, 0.5, 1.0, 2.0, 4, 8, and 12 wt%, and tested in a rectangular fuel tray and a shallow pan flame spread system. The MWNTs/1-propanol mixtures had much lower flame spread rates than the original fuel itself at temperatures below 1-propanol's flash point. A 2 wt% MWNT loading reduced the flame spread rate to 9–15% of the neat fuel rate (the corresponding increase in the average flame spreading time over a 16 cm horizontal test length is approximately 6–11 times) and significantly inhibited the pulsating flame spread behavior. Flame spread rate was calculated for both the pure fuel and MWNT mixtures with a surface-tension-driven spread rate equation. The calculations favorably compare with corresponding measured values despite several assumptions made. Thermally conductive high aspect ratio nanoparticles could be effective flame spread suppressants for liquid fuels.

Biological applications of high aspect ratio nanoparticles

This review describes recent advances in nanomaterials fabrication that have led to the synthesis of high aspect ratio particles on nanometer length scales. The elongated structure of these materials often result in inherent chemical, electrical, magnetic, and optical anisotropy that can be exploited for interactions with cells and biomolecules in fundamentally new ways. We briefly describe the synthetic procedures that have been developed to fabricate nanorods, nanowires, and nanotubes. We summarize literature reports that describe the use of high aspect ratio nanoparticles for biological sensing, separations, and gene delivery. We emphasize the recent discovery of single nanowire field-effect transistors that may revolutionize biological sensing and yield extremely low detection limits. Separations technology with chemically modifiable nanotube membranes and with magnetic nanowires that can be tailored to selectively interact with molecules of interest is also described. Other areas of biotechnology that have been improved by the integration of high aspect ratio nanoparticles are also described.