Pumping of confined water in carbon nanotubes by rotation-translation coupling

Bidirectional single file water transport in a carbon nanotube is known to occur in "bursts" in short nanotubes. Here we show that in long carbon nanotubes, when the orientation of the water molecules is maintained along one direction, a net water transport along that direction can be attained due to coupling between rotational and translational motions. The rotations of the water molecules are correlated more with the translation of the neighboring water molecule with the acceptor oxygen than the neighbor with the donor hydrogen. This mechanism can be used to pump water through nanotubes.     

Dynamical behavior of the kink motion in carbon nanotubes

By performing molecular dynamics calculations, we studied the motion of the kink between two carbon nanotubes. Based on the sequential evaporation of the most energetic carbon atom, our calculations show that the kink has complex longitudinal and spiral motions, in good agreement with the experiments. The kink moves towards the nanotube of larger diameter, resulting in an overall diameter shrinking of the nanotubes without inducing any disorder or damage. The kink motions are found to be dependent on the chirality of the nanotubes. The kink connecting two zigzag nanotubes can have either a pseudoclimb or a spiral motion, while the kink between the armchair nanotubes has an interesting spiral motion with periodic split and recombination of the topological defects.     

Anomalous conductance quantization in carbon nanotubes

Conductance measurements of carbon nanotubes containing gated local depletion regions exhibit plateaus as a function of gate voltage, spaced by approximately 1e(2)/h, the quantum of conductance for a single (nondegenerate) mode. Plateau structure is investigated as a function of bias voltage, temperature, and magnetic field. We speculate on the origin of this surprising quantization, which appears to lack band and spin degeneracy.     

Collective properties of water confined in carbon nanotubes: A computer simulation study

The collective properties of water confined in the (10,10), (8,8) and (6,6) carbon nanotubes are studied by analysing the longitudinal-current autocorrelation function, calculated from computer-simulated trajectories. The corresponding spectra clearly show the presence of two excitations, but their behaviour is quite different from that observed in the case of bulk water. Instead of the strong positive dispersion of the hydrodynamic sound mode characteristic of bulk water (the fast-sound phenomenon), the sound dispersion relation of confined water is observed to flatten into a non-propagating mode, while a second excitation appears at a higher frequency. This behaviour is analysed in terms of the localized oscillation modes of the hydrogen-bond network.     

Anomalous magnetotransport in chemically doped carbon nanotubes

We report on anomalous magnetotransport features in chemically doped, weakly disordered carbon nanotubes. Under the application of a magnetic field parallel to the tube axis, hole conduction is shown to be strongly affected by impurity scattering with short mean free path and negative magnetoresistance, strongly different from electron conduction with much longer mean free path and positive magnetoresistance behavior.     

Quasi-one-dimensional liquid hydrogen confined in single-walled carbon nanotubes

H₂ molecules confined in single-walled carbon nanotubes were studied using molecular dynamics simulations and ab initio calculations. It was found that at zero-temperature, H₂ molecules with low density tended to condense. Increasing the linear density of the H₂ molecules confined in the tube, various quasi-one-dimensional solid lattices were observed at low temperature. Heating the lattices above room temperature, molecular H₂ liquids with varying densities were observed. The quenching behavior of the H₂ fluids was examined. PACS 61.46.+w; 78.67.Bf     

Liquid dimethyl sulphoxide confined by carbon nanotubes

Here, we report the molecular dynamics simulation on liquid dimethyl sulphoxide (DMSO) confined by single-walled carbon nanotubes (SWCNTs) in comparison with DMSO in the bulk phase at 298 K. The local order of DMSO, analysed in terms of radial distribution functions is similar to that in the bulk except the case with the SWCNT (8, 8) where the anomalous structure pattern is realized. Meanwhile, the translational self-diffusion coefficients of DMSO in confinements are much lower then in the bulk phase (by a factor of 2–3) and correlate with a value of the SWCNT internal diameter. Using cylindrical distribution functions of DMSO atoms we elucidate that the slowdown of self-diffusion coefficient of DMSO confined in the SWCNTs is reduced by the first layer of DMSO molecules close to the SWCNT wall.     

Magnetic side bands induced by zero point motion

In this letter we show that zero point motion can cause magnetic side bands on optical transitions in insulating magnetic crystals. This mechanism should be dominant when the optical excited state is non-magnetic.     

Water alignment and proton conduction inside carbon nanotubes

First-principles molecular dynamics simulations have been carried out to investigate the structure, electronic properties, and proton conductivity of water confined inside single-walled carbon nanotubes. The simulations predict the formation of a strongly connected one-dimensional hydrogen-bonded water wire resulting in a net electric dipole moment directed along the nanotube axis. An excess proton injected into the water wire is found to be significantly stabilized, relative to the gas phase, due to the high polarizability of the carbon nanotube.     

Axisymmetric vibration of single-walled carbon nanotubes in water

A double shell-Stokes flow model is developed to study the axisymmetric vibration of single-walled carbon nanotubes (SWCNTs) immerged in water. In contrast to macroscopic solid-liquid system, a submerged SWCNT is coupled with surrounding water via the van der Waals interaction. It is shown that this unique feature substantially reduces viscous damping of the axisymmetric radial, longitudinal and torsional vibrations and significantly up-shifts the frequency of the radial vibration of an SWCNT. The study offers a theoretical explanation for the experimental observation and molecular dynamics simulations available in particular cases, and provides an efficient modelling tool and useful guidance for the study of the general dynamic behaviour of SWCNTs in a fluid.     

Fabrication of completely filled carbon nanotubes with copper nanowires in a confined space

Carbon nanotubes (CNTs) filled completely with polycrystalline Cu nanowires were synthesized by laser vaporization of Cu and graphite under high-pressure Ar gas atmosphere. Depending on the Ar gas pressure (0.1–0.9 MPa) and the Cu content (1–40 at.%) in graphite targets for laser vaporization, various products with different morphologies were observed by scanning and transmission electron microscopy. The ratios of the Cu-filled CNTs and carbon nanocapsules particularly increased as Ar gas pressure was increased. The maximum ∼60% fraction of Cu-filled CNTs with outer diameter of 10–50 nm and length of 0.3–3 μm was achieved at 0.9 MPa from graphite containing 20 at.% Cu. Most of the encapsulated Cu-nanowires were surrounded by single, double, or triple graphitic layers. Although the yield of the Cu-filled CNTs was also dependent on the Cu content in the graphite targets, no unfilled CNTs were produced even for low Cu content. The growth of Cu-filled CNTs is explained by the formation of molten Cu–C composite particles with an unusually C-rich composition in a space confined by high-pressure Ar gas, followed by precipitating Cu and C from the particles and subjecting them to phase separation.     

Kink formation and motion in carbon nanotubes at high temperatures

We report that kink motion is a universal plastic deformation mode in all carbon nanotubes when being tensile loaded at high temperatures. The kink motion, observed inside a high-resolution transmission electron microscope, is reminiscent of dislocation motion in crystalline materials: namely, it dissociates and multiplies. The kinks are nucleated from vacancy creation and aggregation, and propagate in either a longitudinal or a spiral path along the nanotube walls. The kink motion is related to dislocation glide and climb influenced by external stress and high temperatures in carbon nanotubes.     

Curvature-induced condensation of lithium confined inside single-walled carbon nanotubes: First-principles calculations

We carry out first-principles calculations to explore the potential energy profiles of Li confined inside single-walled carbon nanotubes (SWNTs) and the subsequent condensation processes. We found that Li has high mobility around tube axis with the energy barrier less than 47 meV, whereas the diffusion barrier along radial direction is as higher as 380 meV. This characterizes the condensation of Li atoms when placed randomly into SWNTs, resulting in nanowires with single or multi-shelled morphologies depending on the diameter of SWNTs. The charge transfer from Li nanowires to SWNTs is significant, indicating stronger couplings between them.     

Observation of fluid layering and reverse motion in double-walled carbon nanotubes

Most modelling-based research in the field of carbon nanotube-related nano-fluidics has been concerned with the fluid flow in single-walled carbon nanotubes (SWCNTs), showing that the dynamics of the channel affect the structure and behaviour of the fluid. We have extended this work by modelling the flow of Ar in a double-walled carbon nanotube, and have modelled the flow in both the inner shell and the outer annular region of such a nanotube. We have found that the flows in these channels are strongly correlated, such that the fluid moves in opposite directions in these two regions. This phenomenon can give rise to a circulatory motion which can be exploited in nano-fluidic devices. Fluid layering phenomenon, that is usually associated with the flow of fluids in nano-scale channels, is also observed. Furthermore, we have also found that the fluid velocity in dynamic channels is smaller than in static channels, in line with the findings reported for single-walled carbon nanotubes.     

Dynamic behavior of triple-walled carbon nanotubes conveying fluid

In this study, the instability of triple-walled carbon nanotubes (TWCNTs) conveying fluid is studied based on an Euler–Bernoulli beam model. The van der Waals (vdW) interactions between different carbon nanotubes (CNTs) are taken into account in the analysis, and the Galerkin discretization approach is used to solve the coupled equations of the motions. Numerical simulations show that the interlayer vdW interactions play a significant role in the natural frequencies and the stability of TWCNTs. The critical flow velocities—associated with divergence, restabilization and flutter—are determined. The effects of different inner radius and the value of mode N used in Galerkin discretization on the dynamical behaviors of the fluid-conveyed TWCNTs are also examined in detail. Results reveal that the internal moving fluid plays an important role in the instability of TWCNTs.     

Correlated transport and non-Fermi-liquid behavior in single-wall carbon nanotubes

We derive the effective low-energy theory for single-wall carbon nanotubes including the Coulomb interactions among electrons. The generic model found here consists of two spin-fermion chains which are coupled by the interaction. We analyze the theory using bosonization, renormalization-group techniques, and Majorana refermionization. Several experimentally relevant consequences of the breakdown of Fermi liquid theory observed here are discussed in detail, e.g., magnetic instabilities, anomalous conductance laws, and impurity screening profiles. Received: 12 December 1997 / Revised: 9 March 1998 / Accepted: 12 March 1998     

Anomalous aggregation of squaraine dyes in confined solutions

Enhanced aggregation of squaraine (SQ) dyes in solution capillary layers in contrast to the monomer behavior of the bulk solutions has been observed through differences in electronic absorption spectra of the capillary and bulk SQ solutions of the same concentration. The spectra of the capillary solutions were also different from spectra of SQ condensed films. The spectral differences were dependent on both chemical structure of the dye used and the solvent. It was found that aggregation was stronger in dimethylformamide (DMFA) capillary solutions when compared to the chloroform capillary solutions where aggregation was negligible. It is proposed that the driven force of the observed phenomena is enhanced adsorption of SQ molecules and formation of a liquid crystalline state of the solution near the liquid/solid interface.     

Universal behavior of nearly free electron states in carbon nanotubes

The nearly free electron state of a carbon nanotube drops rapidly in energy relative to the other conduction bands under alkali doping. A natural (and previously proposed) explanation for this rapid downshift is hybridization with the potassium states. However, we show that the downshift occurs even when the extra electrons are compensated by a uniform positive background, wherein there can be no hybridization, since there are no alkali atoms. Instead, the motion of the nearly free band arises from a universal electrostatic mechanism, which applies for any type of positive countercharge independent of tube diaf/meter and helicity. The nearly free electron state, being weakly bound to the tube wall, is extraordinarily labile and deforms onto the countercharge, whereas the remaining pi* conduction band states are held to the surface of the carbon sheet by the strong carbon potential.     

Electronic behavior in mats of single-walled carbon nanotubes under pressure

Single-walled carbon nanotubes (SWNTs) have many interesting properties; they may be metallic or semiconducting depending on their diameter and helicity of the graphene sheet. Hydrostatic or quasi-hydrostatic high pressures can probe many electronic features. Resistance-temperature measurements in SWNTs from normal condition and under 0.4 GPa of quasi-hydrostatic pressures reveal a semiconducting-like behavior. From 0.5 to about 2.0 GPa, the resistance changes to a Kondo-like feature due to magnetic impurities used to catalyse the nanotube formation. Above 2.0 GPa, they become metallic and at about 2.4 GPa, the resistance decreases dramatically around 3 K suggesting a superconducting transition.