Narrow Carbon Nanotubes Research Articles

Tuning the magnetic properties of beryllium chains.

In this work we explore the effect of confining beryllium chains inside carbon nanotubes. Linear Ben systems are characterized by two states originating from the presence of edge orbitals localized at the chain extremities. The two spins occupying these orbitals are, in the gas phase, antiferromagnetically coupled, with the magnetic coupling J decaying exponentially as a function of increasing length of the chain. When inserted into narrow carbon nanotubes, the linear geometry is found to be more stable than the more compact cluster conformation favored for the isolated case: the lack of space inside the cavity prevents the chain from folding. Most importantly, the presence of the surrounding nanotube not only preserves the linear structure of Ben, but affects its magnetic properties too. In particular it was found that the magnetic coupling between the ground and the first excited state can be modulated according to the nanotube diameter as well as the chain length, and our calculations suggest a possible direct relationship between these parameters and J. This behavior can be exploited to engineer a composite Ben@CNT system with the magnetic coupling tuned by construction, with interesting potential applications.

Confinement effect of carbon nanotubes on the chain mobility of conjugated polymer poly(9,9-dioctylfluorenyl-2,7-diyl)

The conjugated polymer polyflourene has been well studied for its strong blue light emission ability and high quantum efficiency behavior. It has wide applications for light emitting diodes, sensors as well as photo-detectors. Therein the <inline-formula><tex-math id="Z-20181210033236-1">\begin{document}$ \beta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-1.png"/></alternatives></inline-formula> conformation of PFO crystals is more attractive due to its longer conjugation length, higher carrier mobility and better luminous efficiency. Therefore it is great essential to control the formation and stability of <inline-formula><tex-math id="Z-20181210033236-2">\begin{document}$ \beta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-2.png"/></alternatives></inline-formula> conformation of PFO crystals to develop new kind of photo-electronic devices. As is known, polymeric materials confined in a nanometer-sized space often exhibit unique properties compared with their bulk state, such as abnormal chain mobility, molecular assembly and phase transition behavior. These factors are of great significance to develop new kind of material and applications. Generally the confined condition includes quantum dot (zero-dimensional, 0D), nanowire or nanotube (1D), ultrathin film (2D) and nanoparticle (3D). In this paper, we design a unique 1D nanoconfined environment based on vertically aligned carbon nanotube (CNT) array structure. An ultra-high CNT density is achieved through a solvent-induced contraction process. The adjacent narrow carbon nanotube gap thus forms a quasi-1 confined nano-space with the tunable size ranging from 5 to 50 nm. Then we infiltrate the conjugated polymer poly(9,9-dioctylfluorene-2,7-diyl) (PFO) into those nano-gaps of carbon nanotube arrays through a solvent evaporation method to obtain the PFO infilled CNT array composite film. It is found that the chain mobility of PFO molecules in such a 1D nano-confined space of carbon nanotubes is significantly suppressed compared with the scenario of the spin-coated PFO film. The transition speed between different crystal forms of PFO declines greatly, which meanwhile improves the thermal stability of the <inline-formula><tex-math id="Z-20181210033236-3">\begin{document}$ \beta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-3.png"/></alternatives></inline-formula> conformation of PFO crystal. Additionally, the aligned carbon nanotubes have great effects on the orientation and distribution of PFO chains. The PFO crystals are confirmed to grow preferentially along the longitudinal direction of CNT array, which is potential to grow PFO crystals with high quality and excellent performance. Thus, such a PFO/CNT array composite film can have great potential to prepare PFO photovoltaic devices with excellent luminescent properties and high stability in the future.

Geometry-diversified Coulomb excitations in trilayer AAB stacking graphene

The lower-symmetry trilayer AAB-stacked graphene exhibits rich electronic properties and thus diverse Coulomb excitations. Three pairs of unusual valence and conduction bands create nine available interband excitations for the undoped case, in which the imaginary (real) part of the polarizability shows 1D square root asymmetric peaks and 2D shoulder structures (pairs of antisymmetric peaks and logarithm type symmetric peaks). Moreover, the low frequency acoustic plasmon, being revealed as a prominent peak in the energy loss spectrum, can survive in a narrow gap system with the large-density-of-states from the valence band. This type of plasmon mode is similar to that in a narrow gap carbon nanotube. However, the decisive mechanism governing this plasmon is the intraband conduction state excitations. Its frequency, intensity and critical momentum exhibit a non-monotonic dependence on the Fermi energy. The well-defined electron-hole excitation boundaries and the higher frequency optical plasmons are transformed by varying the Fermi energy. There remain substantial differences between the electronic properties of trilayer AAB, ABC, AAA and ABA graphene stackings.

Water in Narrow Carbon Nanotubes: Roughness Promoted Diffusion Transition

Diffusion of single-file water confined in carbon nanotubes (CNT) has been studied extensively via molecular dynamics simulations in the literature. However, very often, the simulation results do not provide a satisfactory insight to the fundamental mechanism, failing to explain the experimental trend. Sometimes, simulation results are even contradictory to each other. In this work, we first summarize factors that affect the diffusion calculation of single-file water confined in narrow CNTs. In particular, we investigate how the roughness of the CNT model affects diffusion properties of the confined water. A transition of ballistic to Fickian diffusion shall be observable when water is confined in (6, 6) CNTs with roughness. Our simulation results also reveal the single-file diffusion mechanism of confined water when the CNT has significant roughness. This is because the single-file water molecules confined in smooth CNTs move in a collective way, while the motion becomes random in CNTs with roughness. In...

High Interfacial Barriers at Narrow Carbon Nanotube-Water Interfaces.

Water displays anomalous fast diffusion in narrow carbon nanotubes (CNTs), a behavior that has been reproduced in both experimental and simulation studies. However, little is reported on the effect of bulk water-CNT interfaces, which is critical to exploiting the fast transport of water across narrow carbon nanotubes in actual applications. Using molecular dynamics simulations, we investigate here the effect of such interfaces on the transport of water across arm-chair CNTs of different diameters. Our results demonstrate that diffusion of water is significantly retarded in narrow CNTs due to bulk regions near the pore entrance. The slowdown of dynamics can be attributed to the presence of large energy barriers at bulk water-CNT interfaces. The presence of such intense barriers at the bulk-CNT interface arises due to the entropy contrast between the bulk and confined regions, with water molecules undergoing high translational and rotational entropy gain on entering from the bulk to the CNT interior. The intensity of such energy barriers decreases with increase in CNT diameter. These results are very important for emerging technological applications of CNTs and other nanoscale materials, such as in nanofluidics, water purification, nanofiltration, and desalination, as well as for biological transport processes.

Enhanced diffusion on oscillating surfaces through synchronization.

The diffusion of molecules and clusters under nanoscale confinement or absorbed on surfaces is the key controlling factor in dynamical processes such as transport, chemical reaction, or filtration. Enhancing diffusion could benefit these processes by increasing their transport efficiency. Using a nonlinear Langevin equation with an extensive number of simulations, we find a large enhancement in diffusion through surface oscillation. For helium confined in a narrow carbon nanotube, the diffusion enhancement is estimated to be over three orders of magnitude. A synchronization mechanism between the kinetics of the particles and the oscillating surface is revealed. Interestingly, a highly nonlinear negative correlation between diffusion coefficient and temperature is predicted based on this mechanism, and further validated by simulations. Our results provide a general and efficient method for enhancing diffusion, especially at low temperatures.

Modulation of thermal conductivity in single-walled carbon nanotubes by fullerene encapsulation: enhancement or reduction?

Fullerene encapsulation has been proven to be a powerful approach to enhance the mechanical and electronic properties of single-walled carbon nanotubes (SWCNTs). However, some discrepancies emerge in recent studies of the fullerene encapsulation effect on the thermal conductivity of SWCNTs. More specifically, most previous theoretical studies predicted slight enhancement in the thermal conductivity, but the recent experiment by Kodama et al. (Nat. Mat.16, 892, 2017) observed a clear reduction in the thermal conductivity of SWCNTs by fullerene encapsulation. We perform molecular dynamics simulations to revisit this issue, by comparatively investigating the thermal conductivity of the SWCNT (n, n) and the corresponding peapod (n, n) with n = 8, 9, 10, and 11. We find that the encapsulation can reduce the thermal conductivity of narrower SWCNTs with n = 8 and 9, but it can slightly enhance the thermal conductivity of thicker SWCNTs with n = 10 and 11. The underlying mechanisms for these opposite effects are explored by analyzing the encapsulation induced structural deformation and the variation in the phonon dispersion of the SWCNT. We illustrate that the reduction effect observed in the recent experiment is related to the mechanism for reduction of the thermal conductivity for narrower SWCNTs here.

Quantum dynamics of H2 in a carbon nanotube: Separation of time scales and resonance enhanced tunneling.

Quantum confinement effects are known to affect the behavior of molecules adsorbed in nanostructured materials. In order to study these effects on the transport of a single molecule through a nanotube, we present a quantum dynamics study on the diffusion of H2 in a narrow (8,0) carbon nanotube in the low pressure limit. Transmission coefficients for the elementary step of the transport process are calculated using the flux correlation function approach and diffusion rates are obtained using the single hopping model. The different time scales associated with the motion in the confined coordinates and the motion along the nanotube's axis are utilized to develop an efficient and numerically exact approach, in which a diabatic basis describing the fast motion in the confined coordinate is employed. Furthermore, an adiabatic approximation separating the dynamics of confined and unbound coordinates is studied. The results obtained within the adiabatic approximation agree almost perfectly with the numerically exact ones. The approaches allow us to accurately study the system's dynamics on the picosecond time scale and resolve resonance structures present in the transmission coefficients. Resonance enhanced tunneling is found to be the dominant transport mechanism at low energies. Comparison with results obtained using transition state theory shows that tunneling significantly increases the diffusion rate at T < 120 K.

Go with the flow

Membranes Enhanced water transport occurs in a number of narrow pore channels, such as biological aquaporins. Tunuguntla et al. thoroughly characterized molecular transport through narrow carbon nanotubes (CNTs) (see the Perspective by Siwy and Fornasiero). In contrast to previous studies, the authors focused on water and ion transport through relatively short (∼10-nm) fragments of CNTs embedded in lipid bilayer membranes. Strong confinement generated highly accelerated water flow compared with that observed in biological water transporters. A key factor in the transport rate was the tunable rearrangement of intermolecular hydrogen bonding. Furthermore, by changing the charges at the mouth of the nanotube, the authors were able to alter the ion selectivity. Science , this issue p. [792][1]; see also p. [753][2] [1]: /lookup/doi/10.1126/science.aan2438 [2]: /lookup/doi/10.1126/science.aao2440

Confined Water: Structure, Dynamics, and Thermodynamics.

Understanding the properties of strongly confined water is important for a variety of applications such as fast flow and desalination devices, voltage generation, flow sensing, and nanofluidics. Confined water also plays an important role in many biological processes such as flow through ion channels. Water in the bulk exhibits many unusual properties that arise primarily from the presence of a network of hydrogen bonds. Strong confinement in structures such as carbon nanotubes (CNTs) substantially modifies the structural, thermodynamic, and dynamic (both translational and orientational) properties of water by changing the structure of the hydrogen bond network. In this Account, we provide an overview of the behavior of water molecules confined inside CNTs and slit pores between graphene and graphene oxide (GO) sheets. Water molecules confined in narrow CNTs are arranged in a single file and exhibit solidlike ordering at room temperature due to strong hydrogen bonding between nearest-neighbor molecules. Although molecules constrained to move along a line are expected to exhibit single-file diffusion in contrast to normal Fickian diffusion, we show, from a combination of molecular dynamics simulations and analytic calculations, that water molecules confined in short and narrow CNTs with open ends exhibit Fickian diffusion because of their collective motion as a single unit due to strong hydrogen bonding. Confinement leads to strong anisotropy in the orientational relaxation of water molecules. The time scale of relaxation of the dipolar correlations of water molecules arranged in a single file becomes ultraslow, of the order of several nanoseconds, compared with the value of 2.5 ps for bulk water. In contrast, the relaxation of the vector that joins the two hydrogens in a water molecule is much faster, with a time scale of about 150 fs, which is about 10 times shorter than the corresponding time scale for bulk water. This is a rare example of confinement leading to a speedup of orientational dynamics. The orientational relaxation of confined water molecules proceeds by angular jumps between two locally stable states, making the relaxation qualitatively different from that expected in the diffusive limit. The spontaneous entry of water inside the hydrophobic cavity of CNTs is primarily driven by an increase in the rotational entropy of water molecules inside the cavity, arising from a reduction in the average number of hydrogen bonds attached to a water molecule. From simulations using a variety of water models, we demonstrate that the relatively simple SPC/E water model yields results in close agreement with those obtained from polarizable water models. Finally, we provide an account of the structure and thermodynamics of water confined in the slit pore between two GO sheets with both oxidized and reduced parts. We show that the potential of mean force for the oxidized part of GO sheets in the presence of water exhibits two local minima, one corresponding to a dry cavity and the other corresponding to a fully hydrated cavity. The coexistence of these two regimes provides permeation pathways for water in GO membranes.

Inhibitory Effect of Adsorbed Water on the Transport of Methane in Carbon Nanotubes.

We investigate the transport diffusion of methane at 300 K and pressures of up to 15 bar in dry and wetted carbon nanotubes (CNTs) having diameters ranging from 0.95 to 2.034 nm using nonequilibrium molecular dynamics (NEMD) simulation. Because of their strong hydrogen bonding, preadsorbed water molecules transport in the form of clusters and block the diffusion of methane, reducing the Onsager coefficient of methane dramatically compared to that in dry CNTs. The reduction in the methane Onsager coefficient is greater in narrower CNTs or at higher water densities. Because the diameter of the water clusters is almost invariant with water density, the Onsager coefficient of water in the (10, 10) CNT increases linearly with water density. It is further found that whereas decreasing the CNT diameter from 2.034 to 0.95 nm enhances the Onsager coefficient of pure methane by about 1 order of magnitude, the Onsager coefficient of water is almost independent of the CNT diameter at a water density of 0.05 g/cm3. We propose a theoretical model for the strong dependency of methane diffusion in wetted CNTs on the Onsager coefficient of water, the preadsorbed water density, and the CNT diameter. The model predicts the Onsager coefficients of the methane/water mixture from the Onsager coefficients of the pure components. Our study provides a basic understanding of the coupled diffusion of immiscible components in nanochannels and will facilitate progress in gas storage and carbon capture as well as nanofiltration and biomedical and biotechnological applications.

Atomic layer deposition of Al2O3 catalysts for narrow diameter distributed single-walled carbon nanotube arrays growth

Taking the importance of uniform size catalysts and the unfavorable effects of residual metal catalysts into consideration, herein, we develop a facile way which utilizes the typical and facile semiconducting technique namely atomic layer deposition (ALD) to prepare non-metallic Al2O3 catalysts for narrow diameter single-walled carbon nanotube (SWNT) arrays growth. As a result, we obtained SWNT arrays with narrow-diameter distribution of 1.26 ± 0.033 nm on the a-plane sapphire substrates. Moreover, the relationship between catalysts and SWNTs were explored. These optimized conditions pave an avenue for narrow diameter even chirality distribution in SWNTs growth, which promotes the development of structure-controlled and relative applications of SWNTs.

Effect of temperature and diameter of narrow single-walled carbon nanotubes on the viscosity of nanofluid: A molecular dynamics study

Equilibrium molecular dynamics simulations by all-atom model have been employed to investigate the adsorption properties and temperature dependence of the shear viscosity of ethanol molecules confined in narrow single-walled carbon nanotubes (SWCNTs). Since the properties of the narrow tubes (diameters < 7 Å) are strongly influenced by their curvature, the narrow SWCNTs with diameters ranging from 0.54 to 1.08 nm and the length of 2.5 nm in ethanol reservoir at 273.0, 298.0 and 323K and 1 bar have been studied. The results indicate that endo-adsorption occurs in nanotubes with the diameter larger than 0.81 nm and as a result ethanol nano-wires can be formed inside nanotubes.Calculations of shear viscosity of the nanofluid using Green–Kubo method reveal that the relative viscosity of the confined ethanol decreases with increasing temperature.All the CNT@ethanol fluids have lower viscosity than the base liquid ethanol at all temperatures and the viscosity increases with the increase of CNT radius and endo-adsorption.Chirality of the CNTs has minor effects on shear viscosity and endo-adsorption and the main factor is CNTs diameter.The results of the present work provide deep understanding of the viscosity changes with temperature at the nanofluids and can describe the mechanisms for base fluid property modifications caused by adding nanoparticles. These results are applicable in design and preparation of diesohols and fuel-grade ethanol.

Chirality effect on Lithiation of narrow carbon nanotubes; bond order MD and DFT studies

Bond order force field molecular dynamic simulation and also a complimentary density functional theory method are employed for lithiation of narrow carbon nanotubes (CNTs). Since interior region of the narrow tubes (diameters < 7 Å) is strongly influenced by their walls’ ‘curvature effect’, endo-lithiation occurs via formation of lithium chains. Whereas, in the case of exo-lithiation the absorbed lithium atoms form coaxial cylinders up to radiuses of 12 Å. Meanwhile, although to some extent chirality of the CNTs has minor effects on endo-litiation’s distribution, the main factor in the total lithium storage capacity is the diameter. In addition, to obtain more applicable results this study is extended also for a bundle of the CNTs and it is seen that the adsorption energy and also the storage capacity enhance about 1.5 times.

Optimal shape of entrances for a frictionless nanochannel

In a nearly frictionless channels such as narrow carbon nanotubes, flow is limited by the viscous dissipation occurring at the tube mouth. Using both numerical and analytical approaches, it is demonstrated that such end effects can be reduced to a considerable extent by adding an entrance of well-chosen shape.

Tunable Electronic and Magnetic Properties of Transition Metal-Cyclopentadiene Sandwich Molecule Wires Functionalized Narrow Single Wall Carbon Nanotubes

The structural, electronic, and magnetic properties of 1D organometallic molecule wires functionalized narrow single wall carbon nanotube, [TMCp]∞/SWCNTs (TM = Sc, V, Mn, Fe, Co, SWCNTs, (n, m) = (7,7), (10,0), (11,0)), are first studied by density functional theory calculations. In the case of the 1D [TMCp]∞ wires encapsulated in SWCNTs, the reaction between 1D [TMCp]∞ and SWCNTs are endothermic or exothermic depending on the diameters of SWCNTs, while the dimension confinement effect disappears through placing the organometallic molecular wires outside the SWCNTs. Moreover, obvious ionic bonding nature is identified in the systems by putting the 1D [TMCp]∞ wire in or outside of the SWCNTs. In contrast, stronger covalent bonding nature is found for the derivatives by desorption of one raw of hydrogen atoms in the cyclopentadiene ligands. In particular, diverse electronic and magnetic properties are introduced by the choice of SWCNTs and the functionalized 1D [TMCp]∞ wires, which allows the 1D [TMCp]∞/SWCNTs wires to function as a basic building block for potential application in electronic- and spintronic-based devices.

Effects of water-channel attractions on single-file water permeation through nanochannels

Single-file transportation of water across narrow nanochannels such as carbon nanotubes has attracted much attention in recent years. Such permeation can be greatly affected by the water-channel interactions; despite some progress, this issue has not been fully explored. Herein we use molecular dynamics simulations to investigate the effects of water-channel attractions on occupancy, translational (transportation) and orientational dynamics of water inside narrow single-walled carbon nanotubes (SWNTs). We use SWNTs as the model nanochannels and change the strength of water-nanotube attractions to mimic the changes in the hydrophobicity/polarity of the nanochannel. We investigate the dependence of water occupancy inside SWNTs on the water-channel attraction and identify the corresponding threshold values for drying states, wetting-drying transition states, and stably wetting states. As the strength of water-channel attractions increases, water flow increases rapidly first, and then decreases gradually; the maximal flow occurs in the case where the nanochannel is predominately filled with the 1D water wire but with a small fraction of ‘empty states’, indicating that appropriate empty-filling (drying-wetting) switching can promote water permeation. This maximal flow is unexpected, since in traditional view, the stable and tight hydrogen-bonding network of the water wire is the prerequisite for high permeability of water. The underlying mechanism is discussed from an energetic perspective. In addition, the effect of water-channel attractions on reorientational dynamics of the water wire is studied, and a negative correlation between the flipping frequency of water wire and the water-channel attraction is observed. The underlying mechanism is interpreted in term of the axial total dipole moment of inner water molecules. This work would help to better understand the effects of water-channel attractions on wetting properties of narrow nanochannels, and on single-file water permeation through nanochannels, which might be helpful in designs of high-flux nanochannels.

Chirality effect on nearly half-metallic properties in systematic endo-doping of 3d transition metals of narrow carbon nanotubes

Spin polarized density functional calculations were employed to study chirality effect on electronic and magnetic properties of 3d transition metals (TMs) endo-doped co-diameter (∼7Å) narrow (5,5) and (9,0) single walled carbon nanotubes (CNTs). Various magnetizations up to ∼6μB was obtained for different 3dTM-CNT systems (recall that the magnetization of fcc structure cobalt is ∼1.6μB). In addition nearly half-metallic magnetic behavior has been observed for the most of considered systems. These results would be useful for spintronic and nano-magnetic technology.

Salt Solutions in Carbon Nanotubes: The Role of Cation−π Interactions

Understanding the structure of aqueous electrolytes at interfaces is essential for predicting and optimizing device performance for a wide variety of emerging energy and environmental technologies. In this work, we investigate the structure of two common salt solutions, NaCl and KCl, at a hydrophobic interface within narrow carbon nanotubes (CNTs). Using a combination of first-principles and classical molecular dynamics simulations in conjunction with molecular orbital analysis, we find that the solvation structure of the cations in the CNTs can deviate substantially from the conventional weakly interacting hydrophobic picture. Instead, interactions between solvated ions and π orbitals of the CNTs are found to play a critically important role. Specifically, the ion solvation structure is ultimately determined by a complex interplay between cation−π interactions and the intrinsic flexibility of the solvation shell. In the case of K+, these effects result in an unusually strong propensity to partially desol...

From dimers to collective dipoles: Structure and dynamics of methanol/ethanol partition by narrow carbon nanotubes.

Alcohol partitioning by narrow single-walled carbon nanotubes (SWCNTs) holds the promise for the development of novel nanodevices for diverse applications. Consequently, in this work, the partition of small alcohols by narrow tubes was kinetically and structurally quantified via molecular dynamics simulations. Alcohol partitioning is a fast process in the order of 10 ns for diluted solutions but the axial-diffusivity within SWCNT is greatly diminished being two to three orders of magnitude lower with respect to bulk conditions. Structurally, alcohols form a single-file conformation under confinement and more interestingly, they exhibit a pore-width dependent transition from dipole dimers to a single collective dipole, for both methanol and ethanol. Energetic analyses demonstrate that this transition is the result of a detailed balance between dispersion and electrostatics interactions, with the latter being more pronounced for collective dipoles. This transition fully modifies the reorientational dynamics of the loaded particles, generating stable collective dipoles that could find usage in signal-amplification devices. Overall, the results herein have shown distinct physico-chemical features of confined alcohols and are a further step towards the understanding and development of novel nanofluidics within SWCNTs.