Anisotropic Nanotube Research Articles

Facile synthesis methodology and characterization studies of silica‐decorated hybridized anisotropic nanotubes and nanosheets

Carbonaceous nanomaterials and their derivatives have been inspired tremendous enthusiasm in the scientific community. They have been excogitated as the encouraging attributes and the qualified dispersed phase to develop multi‐functional composites. Particularly, graphene and carbon nanotube (anisotropic fillers) have gained substantial research interest owing to their promising characteristics. This highlights an innovative technique to synthesize hybridized nanotube and nanosheet. Initially, parent materials have been synthesized: The pristine CNT has been modified by acid mixture solution, and reduced graphene oxide has been prepared by chemical reduction method. Henceforth, the self‐assembly in situ sol–gel technique has been endorsed here. The synthesized nanohybrids have been characterized by different spectroscopic techniques: FTIR, Raman, UV, and XPS to confirm the attachment of multifunctionalities; meanwhile, the composition and stability have been investigated from XRD and TGA plots. The magnitude of surface charge and particle size distribution have been evaluated for the parent and hybridized products; further, morphology of all the samples has been authenticated from FESEM and TEM.

Isotropic Seebeck coefficient of aligned single-wall carbon nanotube films

How the morphology of a macroscopic assembly of nanoobjects affects its properties is a long-standing question in nanomaterials science and engineering. Here, we examine how the thermoelectric properties of a flexible thin film of carbon nanotubes depend on macroscopic nanotube alignment. Specifically, we have investigated the anisotropy of the Seebeck coefficient of aligned and gated single-wall carbon nanotube thin films. We varied the Fermi level in a wide range, covering both the p-type and n-type regimes, using electrolyte gating. While we found the electrical conductivity along the nanotube alignment direction to be several times larger than that in the perpendicular direction, the Seebeck coefficient was found to be fully isotropic, irrespective of the Fermi level position. We provide an explanation for this striking difference in anisotropy between the conductivity and the Seebeck coefficient using Mott's theory of hopping conduction. Our experimental evidence for an isotropic Seebeck coefficient in an anisotropic nanotube assembly suggests a route toward controlling the thermoelectric performance of carbon nanotube thin films through morphology control.

The Effect of Orientational Distribution of Nanotubes on Buckypaper Nanocomposite Mechanical Properties

This study is concerned with the effects of single-wall carbon nanotubes’ orientational distribution in the buckypaper on the overall mechanical properties of a buckypaper nanocomposite. A micromechanical model that includes prescribed orientational dependence and anisotropy of nanotubes is considered. The model is based on the Mori-Tanaka approach. The validity of the model is discussed in the context of rigorous classical bounds. The results show that all five transversely isotropic effective moduli of buckypaper nanocomposites show strong dependence on the degree of nanotubes’ alignment.

Rheology of polymer carbon nanotubes composites.

In this review paper the rheology of polymer nanocomposites with dispersed carbon nanotubes is presented. The major factors controlling the rheology of these nanocomposites are the overall concentration of the nanotubes and their state of dispersion. Percolation of anisotropic nanotubes and the transition from isotropic to nematic structures bound the range of concentrations over which the rheological properties of these nanocomposites is dominated by the meso-scale structure and dispersion and are of significance to the processing of nanotube based polymer nanocomposites. The percolation threshold and the concentration for the isotropic to nematic transition are strong functions of the inverse of the effective aspect ratio of the dispersed nanotubes and therefore restrict the range of concentrations over which such nanocomposites can be deployed. In this review we briefly describe the rheology in the dilute regime, where especially for the case of polymer nanocomposites the rheology is dominated by that of the polymer. Subsequently, the percolation phenomenon and rheological significances are presented. Finally, both linear and non-linear rheologies of semi-dilute dispersions with random orientation of nanotubes are discussed in detail. Where possible, the rheological responses are contextualized through the underlying structure of the nanocomposites and interplay of different forces.

Orthogonal Growth of Horizontally Aligned Single-Walled Carbon Nanotube Arrays

Direction-controlled growth of horizontally aligned single-walled carbon nanotubes (SWNTs) on r-plane sapphire substrates and their alignment mechanisms are demonstrated. On a flat r-plane substrate, anisotropic nanotube−substrate interaction is known to align SWNTs parallel to the [1101] direction of the sapphire. We find that the introduction of a slight miscut (−1° inclined to the [1101] direction) on the substrate changed the SWNT growth direction by 90°, aligning perpendicular to the [1101] direction. This dramatic change of the growth direction is explained by the contribution of newly proposed one-dimensional surface atomic rows and/or atomic steps appeared on the r-plane. Annealing the substrate in hydrogen atmosphere prior to SWNT growth recovers the original nanotube growth direction, while annealing in air deteriorates the alignment. The direct growth of an orthogonally aligned SWNT array is achieved through optimized surface treatment. Site-selective directional control of aligned SWNTs ...

Centerline Placement and Alignment of Anisotropic Nanotubes in High Aspect Ratio Cylindrical Droplets of Nanometer Diameter

Centerline Placement and Alignment of Anisotropic Nanotubes in High Aspect Ratio Cylindrical Droplets of Nanometer Diameter

Gold Nanoparticle Mediated Formation of Aligned Nanotube Composite Films

We report on the formation of highly anisotropic nanotube composite materials, made by the attachment of gold nanoparticles to the surface of the single-walled carbon nanotubes, followed by preparation of an aligned composite film by compression in a Langmuir-Blodgett trough. The gold is attached in a one-step sonication procedure. The gold-modified nanotube material forms a stable suspension in toluene and has been characterized by atomic force and scanning force microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. The aligned films have highly anisotropic electrical properties, with a factor of approximately 3000 difference in the conductivity between the aligned and perpendicular directions.

Optical anisotropy of nanotube suspensions.

A semimacroscopic model of an optically anisotropic nanotube suspension is derived perturbatively from Maxwell's equations in a dielectric medium. We calculate leading-order expressions, valid in the dilute and semidilute limits, for the intrinsic and form contributions to the complex dielectric tensor in terms of the volume fraction, mean orientation, aspect ratio, optical anisotropy, and optical contrast of the nanotubes. The birefringence and dichroism are derived explicitly to leading order in fluctuations, and the connection with depolarized light scattering is established. The results are generalized to include tube deformation.

Remotely actuated polymer nanocomposites--stress-recovery of carbon-nanotube-filled thermoplastic elastomers.

Stimuli-responsive (active) materials undergo large-scale shape or property changes in response to an external stimulus such as stress, temperature, light or pH. Technological uses range from durable, shape-recovery eye-glass frames, to temperature-sensitive switches, to the generation of stress to induce mechanical motion. Here, we demonstrate that the uniform dispersion of 1-5 vol.% of carbon nanotubes in a thermoplastic elastomer yields nanocomposites that can store and subsequently release, through remote means, up to 50% more recovery stress than the pristine resin. The anisotropic nanotubes increase the rubbery modulus by a factor of 2 to 5 (for 1-5 vol.%) and improve shape fixity by enhancing strain-induced crystallization. Non-radiative decay of infrared photons absorbed by the nanotubes raises the internal temperature, melting strain-induced polymer crystallites (which act as physical crosslinks that secure the deformed shape) and remotely trigger the release of the stored strain energy. Comparable effects occur for electrically induced actuation associated with Joule heating of the matrix when a current is passed through the conductive percolative network of the nanotubes within the resin. This unique combination of properties, directly arising from the nanocomposite morphology, demonstrates new opportunities for the design and fabrication of stimuli-responsive polymers, which are otherwise not available in one material system.

Simulations of electron energy-loss spectra of an electron passing near a locally anisotropic nanotube

Electron Energy-Loss Spectroscopy (EELS) is a very well adapted tool to study the dielectric response of nanotubes. Due to the ‘curved anisotropy’ of such nano-objects, the interpretation of the EEL spectra is far from being straightforward and an adapted theoretical framework is then required. In this contribution, we extend the continuum dielectric approach to hollow anisotropic cylindrical nanoparticles, showing that the energy-loss probability can be handled both analytically and numerically.

Electron energy-loss spectrum of an electron passing near a locally anisotropic nanotube

a ´´ ˆ Laboratoire de Physique des Solides , Associe au CNRS ,( UMR 8502) Universite Paris-Sud, Batiment 510, Orsay 91405, France b ´ Laboratoire de Physique du Solide , Facultes Universitaires Notre-Dame de la Paix ,6 1rue de Bruxelles, 5000 Namur, Belgium Abstract Electron Energy-Loss Spectroscopy (EELS) is a very well adapted tool to study the dielectric response of nanotubes. Due to the 'curved anisotropy' of such nano-objects, the interpretation of the EEL spectra is far from being straightforward and an adapted theoretical framework is then required. In this contribution, we extend the continuum dielectric approach to hollow anisotropic cylindrical nanoparticles, showing that the energy-loss probability can be handled both analytically and numerically.