Enrique V. Barrera

Nanotube film based on single-wall carbon nanotubes for strain sensing

Carbon nanotubes change their electronic properties when subjected to strains. In this study, the strain sensing characteristic of carbon nanotubes is used to develop a carbon nanotube film sensor that can be used for strain sensing on the macro scale. The carbon nanotube film is isotropic due to randomly oriented bundles of single-wall carbon nanotubes (SWCNTs). Using experimental results it is shown that there is a nearly linear change in voltage across the film when it is subjected to tensile and compressive stresses. The change in voltage is measured by a movable four-point probe in contact with the film. Multidirectional and multiple location strains can be measured by the isotropic carbon nanotube film.

Nanofiber-reinforced thermoplastic composites. I. Thermoanalytical and mechanical analyses

This article is a portion of a comprehensive study on carbon nanofiber–reinforced thermoplastic composites. The thermal behavior and dynamic and tensile mechanical properties of polypropylene–carbon nanofibers composites are discussed. Carbon nanofibers are those produced by the vapor-grown carbon method and have an average diameter of 100 nm. These hollow-core nanofibers are an ideal precursor system to working with multiwall and single-wall nanotubes for composite development. Composites were prepared by conventional Banbury-type plastic-processing methods ideal for low-cost composite development. Nanofiber agglomerates were eliminated because of shear working conditions, resulting in isotropic compression-molded composites. Incorporation of carbon nanofibers raised the working temperature range of the thermoplastic by 100°C. The nanofiber additions led to an increase in the rate of polymer crystallization with no change in the nucleation mechanism, as analyzed by the Avrami method. Although the tensile strength of the composite was unaltered with increasing nanofiber composition, the dynamic modulus increased by 350%. The thermal behavior of the composites was not significantly altered by the functionalization of the nanofibers since chemical alteration is associated with the defect structure of the chemical vapor deposition (CVD) layer on the nanofibers. Composite strength was limited by the enhanced crystallization of the polymer brought on by nanofiber interaction as additional nucleation sites.

Iodine doped carbon nanotube cables exceeding specific electrical conductivity of metals

Creating highly electrically conducting cables from macroscopic aggregates of carbon nanotubes, to replace metallic wires, is still a dream. Here we report the fabrication of iodine-doped, double-walled nanotube cables having electrical resistivity reaching ∼10−7 Ω.m. Due to the low density, their specific conductivity (conductivity/weight) is higher than copper and aluminum and is only just below that of the highest specific conductivity metal, sodium. The cables exhibit high current-carrying capacity of 104∼105 A/cm2 and can be joined together into arbitrary length and diameter, without degradation of their electrical properties. The application of such nanotube cables is demonstrated by partly replacing metal wires in a household light bulb circuit. The conductivity variation as a function of temperature for the cables is five times smaller than that for copper. The high conductivity nanotube cables could find a range of applications, from low dimensional interconnects to transmission lines.

Analysis of stress responsive genes induced by single-walled carbon nanotubes in BJ Foreskin cells.

It is known that the mechanical properties of clay-reinforced nanocomposites are significantly affected by the dispersion of clay particles in the matrix. In this study, the effect of surface-treatment of Montmorillonite (MMT) on the fracture behavior of MMT/epoxy nanocomposite was investigated. For this purpose, fracture tests were performed using samples with three different clay concentration level. After fracture tests, SEM analysis was made on the fracture surfaces to examine the fracture mechanism. It was found that the MMT treatment using 3-aminopropyltriethoxysilane enhanced the fracture toughness increased of the MMT/epoxy nanocomposite. This is due to the improved intercalation effect and interfacial strength between MMT and epoxy matrix.

Investigation of the effect of single wall carbon nanotubes on interlaminar fracture toughness of woven carbon fiber—epoxy composites:

Single wall carbon nanotubes (SWCNTs) were introduced in the interlaminar region of woven carbon fiber—epoxy composites and the mode-I delamination behavior was investigated. Pristine (P-SWCNT) and functionalized (F-SWCNT) nanotubes were sprayed in the mid-plane of these laminates and delamination was initiated using a teflon pre-crack insert. The composite laminates were produced using vacuum-assisted resin transfer molding process. The interlaminar fracture toughness (ILFT) represented by mode-I critical strain energy release rate (GIc) for the initiation of delamination was measured using double cantilever beam tests. The specimens with pristine nanotubes and functionalized nanotubes showed a small effect on the ILFT. The specimens with P-SWCNTs showed stable crack growth and the potential for enhanced crack bridging along with slightly higher GIc than F-SWCNT specimens. Scanning electron microscopy images showed enhanced fiber—matrix interfacial bonding in the specimens with F-SWCNTs. However, large unstable crack propagation was observed in these F-SWCNT specimens from load—displacement curves and crack propagation videos. This research helps in understanding the differences in mechanisms by addition of functionalized and unfunctionalized (pristine) nanotubes to the woven carbon fiber—epoxy matrix composite laminates.

Interface Toughness of Carbon Nanotube Reinforced Epoxy Composites

Traditional single-fiber pull-out type experiments were conducted on individual multiwalled carbon nanotubes (MWNT) embedded in an epoxy matrix using a novel technique. Remarkably, the results are qualitatively consistent with the predictions of continuum fracture mechanics models. Unstable interface crack propagation occurred at short MWNT embedments, which essentially exhibited a linear load-displacement response prior to peak load. Deep embedments, however, enabled stable crack extension and produced a nonlinear load-displacement response prior to peak load. The maximum pull-out forces corresponding to a wide range of embedments were used to compute the nominal interfacial shear strength and the interfacial fracture energy of the pristine MWNT-epoxy interface.

Surface functionalization of two-dimensional metal chalcogenides by Lewis acid–base chemistry

Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid-base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti(4+) to form planar p-type [Ti(4+)n(InSe)] coordination complexes. Using this strategy, we fabricate planar p-n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B(3+), Al(3+) and Sn(4+)) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid-base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

Unzipping Carbon Nanotubes at High Impact

The way nanostructures behave and mechanically respond to high impact collision is a topic of intrigue. For anisotropic nanostructures, such as carbon nanotubes, this response will be complicated based on the impact geometry. Here we report the result of hypervelocity impact of nanotubes against solid targets and show that impact produces a large number of defects in the nanotubes, as well as rapid atom evaporation, leading to their unzipping along the nanotube axis. Fully atomistic reactive molecular dynamics simulations are used to gain further insights of the pathways and deformation and fracture mechanisms of nanotubes under high energy mechanical impact. Carbon nanotubes have been unzipped into graphene nanoribbons before using chemical treatments but here the instability of nanotubes against defect formation, fracture, and unzipping is revealed purely through mechanical impact.

Flexural strain sensing using carbon nanotube film

Strain sensing characteristic of carbon nanotubes has been established in the past at nanoscale. In this study, it is shown that the carbon nanotube film sensors, made up of randomly oriented carbon nanotubes, can be used as strain sensors at macro level. A nearly linear trend between the change in voltage, measured using a movable four point probe, and strains, measured using conventional electrical strain gage, indicates the potential of such carbon nanotube films for measuring flexural strains at macro level. Isotropic strain sensing capability of the carbon nanotube film sensors, due to randomly oriented carbon nanotubes, allows multidirectional and multi‐location measurements.

DEVELOPMENT OF FULLERENE-REINFORCED ALUMINUM

Powder metallurgy and casting have been used to produce aluminum with 1.3, 4, and 8 vol. % fullerene additions. Fullerene extract was mixed with Al and heat-treated to obtain various levels of dispersion of the fullerenes. Intergranular dispersion of stable fullerenes was accomplished by both powder metallurgy and casting; however, x-ray diffraction indicated the formation of some Al 4 C 3 . Homogeneous dispersion did not occur because of limited diffusion in the solid state or limited solubility of fullerene in Al in the liquid state. Enhancements in hardness over that for Al were observed yet were not comparable to precipitation hardened Al alloys since a less homogeneous dispersion was achieved. Interest in Al having fullerene additions is for development of fullerene strengthened materials where fullerenes act as nanosize dispersoids for dispersion strengthening of metals or as a lightweight reinforcement in metal-matrix composites.