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.     

Dynamic properties of propylene glycol confined in ZSM-5 zeolite matrix—A computer simulation study

We performed all atom computer simulations of molecular dynamics of propylene glycol confined in ZSM-5 zeolite host matrix in order to study the characteristic of dipolar relaxation process in this system and compare it with recently published results for similar molecular systems confined in single walled carbon nanotubes. We focused on the influence of the geometric confinement inside ZSM-5 1D channels and interaction with the host system on the observed change in the character of deviation from exponential relaxation, as well as on thermal activation characteristic of the process.     

Dynamics of polymer chains in confined space. A computer simulation study

We studied the properties of simple models of star-branched polymer chains confined in a slit. The chains were constructed of united atoms (segments) and were restricted to vertices of a simple cubic lattice. We modeled good solvent conditions and thus the chains interacted with the excluded volume only. The macromolecules were put between two parallel and impenetrable surfaces and the surfaces were attractive for polymer segments. The properties of the model chains were determined by means of Monte Carlo simulations with a sampling algorithm based on chain's local changes of conformation. The differences and similarities in the structure for different adsorption regimes and the size of the slit were shown and discussed. The dependence of the short- and long-time scale dynamic behavior of chains on these factors was determined.     

Anomalous behavior of proton zero point motion in water confined in carbon nanotubes

The momentum distribution of the protons in ice Ih, ice VI, high density amorphous ice, and water in carbon nanotubes has been measured using deep inelastic neutron scattering. We find that at 5 K the kinetic energy of the protons is 35 meV less than that in ice Ih at the same temperature, and the high momentum tail of the distribution, characteristic of the molecular covalent bond, is not present. We observe a phase transition between 230 and 268 K to a phase that does resemble ice Ih. Although there is yet no model for water that explains the low temperature momentum distribution, our data reveal that the protons in the hydrogen bonds are coherently delocalized and that the low temperature phase is a qualitatively new phase of ice.     

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.     

Thermodynamic properties of water in confined environments: a Monte Carlo study

Monte Carlo simulations of Mercedes-Benz water in a crowded environment were performed. The simulated systems are representative of both composite, porous or sintered materials and living cells with typical matrix packings. We studied the influence of overall temperature as well as the density and size of matrix particles on water density, particle distributions, hydrogen bond formation and thermodynamic quantities. Interestingly, temperature and space occupancy of matrix exhibit a similar effect on water properties following the competition between the kinetic and the potential energy of the system, whereby temperature increases the kinetic and matrix packing decreases the potential contribution. A novel thermodynamic decomposition approach was applied to gain insight into individual contributions of different types of inter-particle interactions. This decomposition proved to be useful and in good agreement with the total thermodynamic quantities especially at higher temperatures and matrix packings, where higher-order potential-energy mixing terms lose their importance.     

Twisting carbon nanotubes: A molecular dynamics study

We simulate the twist of carbon nanotubes using atomic molecular dynamic simulations. The ultimate twist angle per unit length and the deformation energy are calculated for nanotubes of different geometries. It is found that the thick tube is harder to be twisted while the thin tube exhibits higher ultimate twisting ratio. For multi-walled nanotubes, the zigzag tube is found to be able to stand more deformation than the armchair one. We observed the surface transformation during twisting. Formation of structural defects is observed prior to fracture.     

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.     

相互作用势对模拟计算单壁碳纳米管物理吸附储氢的影响

采用巨正则Monte Carlo方法模拟氢分子在单壁碳纳米管中的储存与分布,重点研究了Lennard-Jones势、Crowell-Brown势和Silvera- Goldman势对模拟计算单壁碳纳米管物理吸附储氢的影响.计算结果显示,碳纳米管与氢分子间的相互作用宜采用Lennard-Jones势描述;氢分子与氢分子间相互作用的描述则与碳纳米管的管径有关,管径较小时选Lennard-Jones势较佳,管径偏大时取七参数Silvera-Goldman 势更为合理,而三参数Silvera-Goldman势则不宜采用;并给出了相应的理论解释.     

Electron-phonon interaction in single-wall carbon nanotubes: A time-domain study

We investigate the electron-phonon (e-ph) interaction in single-wall carbon nanotube samples at room temperature using femtosecond time-resolved photoemission. By probing electrons from the vicinity of the Fermi level we are able to study the e-ph interaction in the metallic nanotube species only. The observed electron dynamics can be used to calculate e-ph scattering matrix elements for two likely scattering scenarios: forward scattering from twistons and backscattering by longitudinal acoustic phonons. The corresponding matrix elements reveal an intrinsically weak e-ph interaction approximately 50% smaller than predicted by tight-binding calculations.     

Finite element simulation for estimating the mechanical properties of multi-walled carbon nanotubes

A finite element simulation technique for estimating the mechanical properties of multi-walled carbon nanotubes is developed. In the present modeling concept, individual carbon nanotube is simulated as a frame-like structure and the primary bonds between two nearest-neighboring atoms are treated as beam elements, the beam element properties are determined via the concept of energy equivalence between molecular dynamics and structural mechanics. As to the simulation of the interlayer van der Waals force which has intrinsic nonlinearity and complicated applying region, a simplifying method is proposed that the interlayer pressure caused by van der Waals force instead of the force itself is to be considered, and we make use of the linear part of the interlayer pressure near the equilibrium condition to avoid the nonlinearity in problem, then linear spring elements whose stiffness is determined by equivalent force concept can be utilized to simulate the interlayer van der Waals force such that significant modeling and computing effort is saved in performing the finite element analysis. Numerical examples for estimating the mechanical properties of nanotubes, such as axial and radial Young’s modulus, shear modulus, natural frequency, buckling load, etc., are presented to illustrate the accuracy of this simulation technique. By comparing to the results found in the literature and the possible analytical solutions, it shows that the obtained mechanical properties of nanotubes by the present method agree well with their comparable results. In addition, the relations between these mechanical properties and the nanotube size are also discussed.     

Atomic particle channeling simulation in carbon nanotubes

The ion distributions of vibration and rotation energies, as well as of the degree of torsion at the nanotube outlet, have been calculated via mathematical simulation of molecular hydrogen ion channeling in a carbon nanotube. The observed resonance effects have been analyzed. It is found that the probability of ion detection increases near the axis of a chiral carbon nanotube.     

Raman spectroscopy of isolated carbyne chains confined in carbon nanotubes: Progress and prospects

Carbyne is an infinitely long linear chain of carbon atoms with sp¹ hybridization and the truly one-dimensional allotrope of carbon. While obtaining freestanding carbyne is still an open challenge, the study of confined carbyne, linear chains of carbon encapsulated in carbon nanotubes, provides a pathway to explore carbyne and its remarkable properties in a well-defined environment. In this review, we discuss the basics and recent advances in studying single confined carbyne chains by Raman spectroscopy, which is their primary spectroscopic characterization method. We highlight where single carbyne chain studies are needed to advance our understanding of confined carbyne as a material system and provide an overview of the open questions that need to be addressed and of those aspects currently under debate.     

Superconducting properties of carbon nanotubes

Metallic single wall carbon nanotubes have attracted much interest as 1D quantum wires combining a low carrier density and a high mobility. It was believed for a long time that low temperature transport was exclusively dominated by the existence of unscreened Coulomb interactions leading to an insulating behavior at low temperature. However experiments have also shown evidence of superconductivity in carbon nanotubes. We distinguish two fundamentally different physical situations. When carbon nanotubes are connected to superconducting electrodes, they exhibit proximity induced superconductivity with supercurrents which strongly depend on the transmission of the electrodes. On the other hand intrinsic superconductivity was also observed in suspended ropes of carbon nanotubes and recently in doped individual tubes. These experiments indicate the presence of attractive interactions in carbon nanotubes which overcome Coulomb repulsion at low temperature, and enables investigation of superconductivity in a 1D limit never explored before. To cite this article: M. Ferrier et al., C. R. Physique 10 (2009).     

Mechanical properties of carbon nanotubes

A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young’s moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young’s modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 29 July 1999     

Collective diffusion in carbon nanotubes: Crossover between one dimension and three dimensions

Using non-equilibrium molecular dynamics and Monte Carlo methods, we study the collective diffusion of helium in carbon nanotubes. The results show that the collective diffusion coefficient(CDC) increases with the dimension of the channel. The collective diffusion coefficient has a linear relationship with the temperature and the concentration. There exist a ballistic transport in short carbon nanotubes and a diffusive transport in long carbon nanotubes. Fick's law has an invalid region in the nanoscale channel.     

Transport properties of supercooled confined water

This article presents an overview of recent experiments performed on transport properties of water in the deeply supercooled region, a temperature region of fundamental importance in the science of water. We report data of nuclear magnetic resonance, quasi-elastic neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy, studying water confined in nanometer-scale environments. When contained within small pores, water does not crystallise, and can be supercooled well below its homogeneous nucleation temperature T_h. On this basis it is possible to carry out a careful analysis of the well known thermodynamical anomalies of water. Studying the temperature and pressure dependencies of water dynamics, we show that the liquid-liquid phase transition (LLPT) hypothesis represents a reliable model for describing liquid water. In this model, water in the liquid state is a mixture of two different local structures, characterised by different densities, namely the low density liquid (LDL) and the high-density liquid (HDL). The LLPT line should terminate at a special transition point: a low-T liquid-liquid critical point. We discuss the following experimental findings on liquid water: (i) a crossover from non-Arrhenius behaviour at high T to Arrhenius behaviour at low T in transport parameters; (ii) a breakdown of the Stokes-Einstein relation; (iii) the existence of a Widom line, which is the locus of points corresponding to maximum correlation length in the p-T phase diagram and which ends in the liquid-liquid critical point; (iv) the direct observation of the LDL phase; (v) a minimum in the density at approximately 70 K below the temperature of the density maximum. In our opinion these results represent the experimental proofs of the validity of the LLPT hypothesis.