Single-walled Carbon Nanotubes Axis Research Articles

Mapping the Morphology of DNA on Carbon Nanotubes in Solution Using X-ray Scattering Interferometry.

Single-walled carbon nanotubes (SWCNTs) with adsorbed single-stranded DNA (ssDNA) are applied as sensors to investigate biological systems, with potential applications ranging from clinical diagnostics to agricultural biotechnology. Unique ssDNA sequences render SWCNTs selectively responsive to target analytes such as (GT)n-SWCNTs recognizing the neuromodulator, dopamine. It remains unclear how the ssDNA conformation on the SWCNT surface contributes to functionality, as observations have been limited to computational models or experiments under dehydrated conditions that differ substantially from the aqueous biological environments in which the nanosensors are applied. We demonstrate a direct mode of measuring in-solution ssDNA geometries on SWCNTs via X-ray scattering interferometry (XSI), which leverages the interference pattern produced by AuNP tags conjugated to ssDNA on the SWCNT surface. We employ XSI to quantify distinct surface-adsorbed morphologies for two (GT)n ssDNA oligomer lengths (n = 6, 15) that are used on SWCNTs in the context of dopamine sensing and measure the ssDNA conformational changes as a function of ionic strength and during dopamine interaction. We show that the shorter oligomer, (GT)6, adopts a more periodically ordered ring structure along the SWCNT axis (inter-ssDNA distance of 8.6 ± 0.3 nm), compared to the longer (GT)15 oligomer (most probable 5'-to-5' distance of 14.3 ± 1.1 nm). During molecular recognition, XSI reveals that dopamine elicits simultaneous axial elongation and radial constriction of adsorbed ssDNA on the SWCNT surface. Our approach using XSI to probe solution-phase morphologies of polymer-functionalized SWCNTs can be applied to yield insights into sensing mechanisms and inform future design strategies for nanoparticle-based sensors.

A dispersion-corrected density functional theory study of the noncovalent interactions between nucleobases and carbon nanotube models containing stone-wales defects.

The noncovalent bonding between nucleobases (NBs) and Stone-Wales (SW) defect-containing closed-end single-walled carbon nanotubes (SWNTs) was theoretically studied in the framework of density function theory using a dispersion-corrected functional PBE-G06/DNP. The models employed in this study were armchair nanotube (ANT) (5,5) and zigzag nanotube (ZNT) (10,0), which incorporated SW defects in different orientations. In one of them, the (7,7) junction is tilted with respect to SWNT axis (ANT-t and ZNT-t), whereas in ANT-p and ZNT-p models the (7,7) junction is parallel and perpendicular to the axis, respectively. The binding energies for uracil, thymine, cytosine, 5-methylcytosine, adenine, and guanine interacting with the defect-containing nanotube models were compared to the values previously obtained with the same calculation technique for the case of defect-free SWNTs, both in the gas phase (vacuum) and in aqueous medium. For most models, the interaction strength tends to be higher for purine than for pyrimidine complexes, with a clear exception of the systems including ZNT-p, both in vacuum and in aqueous medium. As it could be expected, the binding strength in the latter case is lower as compared to that in vacuum, roughly by 2-4 kcal/mol, due to the implicit inclusion of a medium (i.e., water) via the conductor-like screening model model. The closest contacts between NBs and SWNT models, frontier orbital distribution, and highest-occupied molecular orbital-lowest-unoccupied molecular orbital gap energies are analyzed as well. © 2019 Wiley Periodicals, Inc.

Modeling the Field Emission Enhancement Factor for Capped Carbon Nanotubes Using the Induced Electron Density.

In many field electron emission experiments on single-walled carbon nanotubes (SWCNTs), the SWCNT stands on one of two well-separated parallel plane plates, with a macroscopic field FMapplied between them. For any given location"L" on the SWCNT surface, a field enhancement factor (FEF) is defined as FL/FM, where FL is a local field defined at "L". The best emission measurements from small-radii capped SWCNTs exhibit characteristic FEFs that are constant (i.e., independent of FM). This paper discusses how to retrieve this result in quantum-mechanical (as opposed to classical electrostatic) calculations. Density functional theory (DFT) is used to analyze the properties of two short, floating SWCNTs, capped at both ends, namely, a (6,6) and a (10,0) structure. Both have effectively the same height (∼5.46 nm) and radius (∼0.42 nm). It is found that apex values of local induced FEF are similar for the two SWCNTs, are independent of FM, and are similar to FEF values found from classical conductor models. It is suggested that these induced-FEF values are related to the SWCNT longitudinal system polarizabilities, which are presumed similar. The DFT calculations also generate "real", as opposed to "induced", potential-energy (PE) barriers for the two SWCNTs, forFM values from 3 V/μm to 2 V/nm. PE profiles along the SWCNT axis and along a parallel "observation line" through one of the topmost atoms are similar. At low macroscopic fields, the details of barrier shape differ for the two SWCNT types. Even for FM = 0, there are distinct PE structures present at the emitter apex (different for the two SWCNTs); this suggests the presence of structure-specific chemically induced charge transfers and related patch-field distributions.

Influence of electrostatic field on the adsorption of phenol on single-walled carbon nanotubes: A study by molecular dynamics simulation

Molecular dynamics simulations were carried out to study the influence of electrostatic field with different strengths and directions on the adsorption of phenol on single-walled carbon nanotubes (SWNT). It is examined in term of the structural parameters, the self-diffusion coefficients and the interaction energy. The results show that with the increase of electrostatic field strength, the number of phenol around SWNT increases, the hydration between phenol and coordinated water molecules decreases, the phenol-phenol’s interaction increases, the SWNT-phenol’s interaction energy increases, the water-phenol’s interaction energy decreases and the self-diffusion coefficient of phenol and water decreases. Furthermore, comparing with the electrostatic field perpendicular to the central axis of SWNT, the electrostatic field along the central axis of SWNT can make more obvious effect to the parameters of system. The simulations results provide useful guidance for understanding the influence of electrostatic field on the adsorption of phenol on SWNT.

Nonlinear vibrations and energy exchange of single-walled carbon nanotubes. Radial breathing modes

In this paper, the nonlinear vibrations and energy exchange of single-walled carbon nanotubes (SWNTs) are analysed. The Sanders-Koiter shell theory is used to model the nonlinear dynamics of the system in the case of finite amplitude of vibration. The SWNT deformation is described in terms of longitudinal, circumferential and radial displacement fields. Simply supported, clamped and free boundary conditions are applied. The resonant interaction between radial breathing (axisymmetric) modes (RBMs) is analysed. An energy method, based on the Lagrange equations, is considered in order to reduce the nonlinear partial differential equations of motion to a set of nonlinear ordinary differential equations, which is then solved applying the implicit Runge-Kutta numerical method. The present model is validated in linear field comparing the RBM natural frequencies numerically predicted with data reported in the literature from experiments and molecular dynamics simulations. The nonlinear energy exchange between the two halves along the SWNT axis in the time is studied for different amplitudes of initial excitation applied to the two lowest frequency resonant RBMs. The influence of the SWNT aspect ratio on the numerical value of the nonlinear energy beating period under different boundary conditions is analysed.

Enhancement of catalytic activity of a programmed gold nanoparticle superstructure modulated by supramolecular protein assembly

Improving the efficiency of the oxygen reduction reaction (ORR) for use in commercial fuel cells has been the subject of diverse synthetic research activities. However, due to their inferior catalytic performance and dispensability, there are still limitations to achieving breakthroughs regarding ORR catalytic activity using carbon nanomaterials, despite their high electron-transfer and mass-transport properties. In this study, we mimicked nature by using a biomineralization approach for controlling the growth of inorganic materials and demonstrated improved ORR values. The designed peptide, Hexcoil-Ala, is able to supramolecular assembly on single-walled carbon nanotubes (SWNTs), leading to SWNTs that are well dispersed in aqueous solution. In order to direct gold nanoparticle (AuNP) nucleation sites, we substitute two residues in Hexcoil-Ala with cysteine to provide the mutated peptide, HexCoil-Ala-2Cys. This peptide affords a sophisticated, size-controlled, and well-dispersed arrangement of AuNPs. High-resolution transmission electron microscopy studies confirmed the homogeneously well-aligned distribution of nanosized AuNPs on the HexCoil-Ala-2Cys structure, along the direction of SWNT axis. The (AuNPs/P-SWNT) composite in water provides dispersed and stable metallic nanoparticles of electrostatically modified Au through synergistic effects involving the peptide. Consequently, this catalyst exhibits improved ORR performance compared to bulk gold and even, in case of number of electrons (n) transferred, higher than the number of Pt/C. X-ray photoelectron and Raman spectroscopies reveal the details of the electronic interactions among the components of the AuNP/P-SWNT composite, and how they facilitate the four-electron reaction pathway. This study provides valuable information for the optimization of catalyst synthesis and precise particle-size control, leading to stable, water-dispersive composites, with improved electronic properties for enhanced ORR performance in fuel cells.

Measurement of optical anisotropy in ultrathin films using surface plasmon resonance

The optical phenomenon, surface plasmon resonance (SPR) is employed for the measurement of optical anisotropy in the ultrathin films fabricated through Langmuir–Blodgett (LB) and self-assembled monolayer (SAM) techniques onto 50 nm gold film supported on BK7 glass substrates. The resonance angle (RA) is measured using a home built setup in Kretschmann configuration. The LB films and SAM can provide a single layer of highly ordered and organized molecules on the two dimensional surface. If the film forming molecules are anisotropic, their organization in the LB films and SAM can yield an anisotropic film due to tilt of the molecules with respect to the surface normal. The SPR spectra are recorded for the two orthogonal directions of the film with respect to the plane of incidence. The spectra are simulated by modeling the Fresnel's reflection from 4-layers viz., prism, gold, ultrathin films and air; and the real and imaginary parts of refractive index are estimated. Our study shows the metallic and dielectric nature of the LB films of bundles of single walled carbon nanotubes (SWCNTs) when the long axis of SWCNTs are aligned parallel and perpendicular to plane of incidence, respectively. The optical anisotropy was estimated from the change in real part of refractive index (Δnr) of the ultrathin films measured in the orthogonal directions. In addition, we have also studied such optical anisotropy in the LB film of cadmium-stearate and self-assembled monolayer of octadecanethiol.

Sensitization of Rare Earth Ions with Carbon Nanotube Plasmonic Antennas

Complexes containing rare earth ions (REI) and single-walled carbon nanotubes (SWNT) functionalized with single stranded DNA show promise to be utilized for the optical sensing of bio-molecules [1]. However, the electromagnetic interactions between the SWNT and the REI have not been sufficiently studied. In this work, we focus on the plasmonic interaction between the SWNT and a REI such as Terbium or Europium for their use as a biosensing complex. The SWNT may act as a plasmonic antenna and generate a local field in the vicinity of the REI. We use the transmission line model [2] to model the plasmonic properties of the SWNT antenna. The incoming light induces a surface current distribution: I(z)=(V0/Zc)sinh[γp(l/2-|z|)] where V0 is the input voltage into the transmission line model determined by the applied electric field, Zc is the characteristic impedance of the SWNT which is approximately 12 kΩ, γp is the plasmon propogation constant, and l is the length of the tube which we take to be 1 μm. We estimate a field enhancement factor of approximately 106in the near field given by: F=ωl(LC/2)1/2/(k2r2) where L is the kinetic inductance of the SWNT, C is the total capacitance including both electrostatic and quantum capacitances, r is the radial distance between the SWNT axis and the REI, and k and ω are the wavevector and frequency of the incoming light, respectively. The electromagnetic fields will be calculated using the electric Hertz potential satisfying the Helmholtz equation with proper boundary conditions. The conductivity of the SWNT antenna in the transmission line model is given by: σ=iωL-1/(ω2+iωL-1R-C-1L-1 γp 2) where R is the resistance of the SWNT. The interaction of these calculated plasmonic fields with the REI will modulate the lifetimes of the REI. The modulated lifetimes of an electric dipole emitter will be calculated to model the allowed optical transitions of the particular REI. To include the modulations of the optically dark REI transitions, a magnetic dipole emitter will be used. To conclude, these results will give a better understanding of the near field electromagnetic interactions that take place in complexes containing SWNTs and REIs and allow for more efficient sensors. Acknowledgement: This work was supported by: NSF ECCS-1202398

Structural characteristics of liquid nitromethane at the nanoscale confinement in carbon nanotubes.

The stability of energetic materials confined in the carbon nanotubes can be improved at ambient pressure and room temperature, leading to potential energy storage and controlled energy release. However, the microscopic structure of confined energetic materials and the role played by the confinement size are still fragmentary. In this study, molecular dynamics simulations have been performed to explore the structural characteristics of liquid nitromethane (NM), one of the simplest energetic materials, confined in a series of armchair single-walled carbon nanotubes (SWNTs) changing from (5,5) to (16,16) at ambient conditions. The simulation results show that the size-dependent ordered structures of NM with preferred orientations are formed inside the tubular cavities driven by the van der Waals attractions between NM and SWNT together with the dipole-dipole interactions of NM, giving rise to a higher local mass density than that of bulk NM. The NM dipoles prefer to align parallel along the SWNT axis in an end-to-end fashion inside all the nanotubes except the (7,7) SWNT where a unique staggered orientation of NM dipoles perpendicular to the SWNT axis is observed. As the SWNT radius increases, the structural arrangements and dipole orientations of NM become disordered as a result of the weakening of van der Waals interactions between NM and SWNT.

Dynamic interactions between poly(3-hexylthiophene) and single-walled carbon nanotubes in marginal solvent.

Interfacial interactions between conjugated polymers and carbon nanotubes are pivotal in determining the device performance of nanotube-based polymer electronic devices. Here, we report on interfacial structures and crystallization kinetics of poly(3-hexylthiophene) (P3HT) in the presence of single-walled carbon nanotubes (SWNTs) in anisole by means of transmission electron microscope (TEM) and ultraviolet-visible (UV-vis) absorption spectroscopy. Confined on SWNT surfaces, the P3HT forms nanofibril crystals perpendicular to the long axis of SWNTs. The equilibrium dissolution temperature of the P3HT crystals in anisole is determined to be 381 ± 10 K according to the Hoffman-Weeks extrapolation approach. Upon cooling, the polymer solution spontaneously undergoes a time-dependent chromism. Various kinetics factors such as crystallization temperature, concentration, and SWNT loading have been investigated. It is found that the growth rate (G) of the crystals scales with concentration (C) as G ∝ C(1.70±0.16). The Avrami model is utilized to analyze the nucleation mechanism and the Avrami exponents vary between 1.0 and 1.3. The Lauritzen-Hoffman theory is applied to study the chain-folding process. The fold surface free energy is calculated to be (5.28-11.9) × 10(-2) J m(-2). It is evident that the addition of 0.30 wt % SWNTs reduces the fold surface free energy by 55.6%.

Stretching induced interfacial crystallization and property enhancement of poly(l-lactide)/single-walled carbon nanotubes fibers

In this work, poly(l-lactide) (PLLA)/single-walled carbon nanotubes (SWNTs) fibers were first prepared at high drown ratio and low drown ratio, respectively. Then they subjected to tensile testing. It was found that the composite fibers obtained at low drown ratio showed no obvious enhancement of tensile strength and elongation at break, compared with the pure PLLA fibers obtained at the same low drown ratio. However, a significant property enhancement was observed for the composites fibers obtained at high drown ratio. Structure analysis of the as spun fibers before and after tensile testing suggests a possible stretching induced formation of brush-like hybrid structure in which the PLLA lamellae growing perpendicular to the SWNTs axis for fibers obtained at high drown ratio. This unique brush-like hybrid structure could largely enhance the interfacial interaction between PLLA and SWNTs, thus results in greatly improved tensile strength and elongation at break.

Carbon Nanotube‐Directed Polytetrafluoroethylene Crystal Growth via Initiated Chemical Vapor Deposition

Initiated chemical vapor deposition (iCVD) has been shown to be suitable for blanketing surfaces with thin polymer coatings of ≈1-2 nm and greater. In this work, iCVD coatings of polytetrafluoroethylene (PTFE) deposited on carbon nanotube (CNT)-based surfaces show CNT-templated PTFE single crystal growth. While the coating forms disoriented agglomerates when deposited on an amorphous carbon background, "shish-kebab" structures are observed when grown on single-walled carbon nanotubes (SWCNT) as well as CNT buckypaper. It is shown that the shish-kebab structure is composed of PTFE lamellae arranged with the chain backbones running parallel to the SWCNT axis. This result allows one to control not only the surface chemistry using PTFE but also the coating surface topology.

Resolving strain in carbon nanotubes at the atomic level

Details of how atomic structure responds to strain are essential for building a deeper picture of mechanics in nanomaterials. Here, we provide the first experimental evidence of atomic displacements associated with shear strain in single-walled carbon nanotubes (SWNTs) by direct imaging using aberration-corrected transmission electron microscopy. The atomic structure of a zig-zag SWNT is resolved with unprecedented accuracy and the strain induced by bending is mapped in two dimensions. We show the existence of a dominant non-uniform shear strain that varies along the SWNT axis. The direction of shear is opposite to what would be expected from a simple force applied perpendicular to the axis to produce the bending. This highlights the complex atomistic strain behaviour of beam-bending mechanics in highly anisotropic SWNTs.

Dielectric Properties of Water inside Single-Walled Carbon Nanotubes

In this paper, we report novel ferroelectric properties of a new form of ice inside single-walled carbon nanotubes (SWCNTs). These are called "ice nanotubes" (ice NTs) and they consist of polygonal water rings stacked one-dimensionally along the SWCNT axis. We performed molecular dynamics (MD) calculations for the ice NTs under an external electric field and in a temperature range between 100 and 350 K. It is revealed that ice NTs show stepwise polarization with a significant hysteresis loop as a function of the external field strength. In particular, pentagonal and heptagonal ice NTs are found to be the world's smallest ferroelectrics with spontaneous polarization of around 1 microC/cm(2). The n-gonal ice NT, where n = 5, 6, or 7, has (n + 1)-polarized structures with different polarizations. These findings suggest potential applications of SWCNTs encapsulating dielectric materials for the fabrication of the smallest ferroelectric devices. Experimental evidence for the presence of ice NTs inside SWCNTs is also discussed in great detail.

Magnetism of Single-Walled Carbon Nanotube with Pd Nanowire

Magnetism of single-walled carbon nanotubes (SWNTs) filled with Pd in pseudo one-dimension is investigated based on the electronic structure obtained using the first-principle calculation. In addition, the stability of Pd nanowire inside SWNT is evaluated through the calculation of binding energy. The Pd monostrand nanowire with the inter-atomic distance of 2.49 A, which shows ferromagnetism in the free-standing state, has the ferromagnetic moment also in the armchair type SWNTs with the diameter lager than 6.9 A although the magnetic moment is smaller than that of the corresponding free-standing Pd nanowire. The pseudo one-dimensional fcc Pd nanowire with the cross section of the (111) plane in the (14, 0) SWNT has ferromagnetic moment, where the inter-atomic distance is elongated by 28% along the longitudinal axis of SWNT compared with the equilibrium distance, so as to adjust the unit cell size of SWNT. However, the Pd(100) nanowire in (8, 8) SWNT does not show ferromagnetism although it has almost the...

Determining the Diameter of Functionalized Single-Walled Carbon Nanotubes with 13C NMR: A Theoretical Study

NMR chemical shifts of N-R-functionalized (n, 0) single-walled carbon nanotubes (SWNTs) with n = 11, 13-17 were computed from first principles. The chemical shifts of functionalized carbons at a bond diagonal to the SWNT axis are strongly dependent upon the C-C distance in the C-NR-C moiety. This distance, in turn, is sensitive to the SWNT radius. Monitoring these shifts could therefore help to determine the diameter distribution within a sample. Proton shifts are also reported.