Screening of water dipoles inside finite-length armchair carbon nanotubes (original) (raw)
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Radiowave dielectric investigation of water confined in channels of carbon nanotubes
The Journal of Chemical Physics, 2012
Structure and dynamics of water confined in channels of diameter of few nanometer in size strongly differ from the ones of water in the bulk phase. Here, we present radiowave dielectric relaxation measurements on water-filled single-walled carbon nanotubes, with the aim of highlighting some aspects on the molecular electric dipole organization of water responding to high spatial confinement in a hydrophobic environment. The observed dielectric spectra, resulting into two contiguous relaxation processes, allow us to separate the confined water in the interior of the nanotubes from external water, providing support for the existence in the confinement region of water domains held together by hydrogen bonds. Our results, based on the deconvolution of the dielectric spectra due to the presence of a bulk and a confined water phase, furnish a significantly higher Kirkwood correlation factor, larger than the one of water in bulk phase, indicating a strong correlation between water molecules inside nanotubes, not seen in bulk water.
Theoretical investigations on the tip-functionalised carbon nanotubes interacting with water
International Journal of Nanoparticles, 2008
Interactions between single-walled carbon nanotubes (SWNTs) and water molecules were studied using first principle calculations and molecular dynamics simulations. The SWNTs were modelled by varying the diameter ranging from the chiral vector (6, 0) to (9, 0) and by modifying the tube ends terminated with hydroxyl (-OH) and carboxyl (-COOH) functional groups. Water and SWNT molecules were modelled using the SPC model and a flexible model based on the OPLS force field respectively. The first principle NBO charges were used for describing the tube-water electrostatic interactions. The results indicate that the movement of water into the COOH-SWNT is rather different from the pristine and OH-functionalised nanotubes. Water molecules prefer to localise around the SWNT's tips than other parts. Hydrophilic behaviour of functionalised SWNT is improved over the pristine tube in agreement with experiments. The COOH-SWNT also shows the confinement of water molecules that may be useful for H 2 O transport.
Carbon nanotube screening effects on the water-ion channels
Applied Physics Letters, 2008
A self-consistent tight-binding method is used to investigate the screening effects of semiconducting and metallic single-wall carbon nanotubes (SWCNTs) when the water molecules and various charged ions pass through the nanotubes. The trajectories of ions and water molecules are obtained from molecular dynamics simulations. It is shown that metallic SWCNTs have much stronger screening abilities than semiconducting SWCNTs. Our results indicate that it is possible to distinctly identify different ions and also to differentiate between armchair and zig-zag nanotubes.
Electronic structure and dielectric behavior of finite-length single-walled carbon nanotubes
4th IEEE Conference on Nanotechnology, 2004.
The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied within a tight-binding model, which well captures the oscillation pattern of the band gap as the tube length increases. We find that: (1) the parallel screening constant || grows almost linearly with the length and shows little dependence on the band gap; (2) the perpendicular screening is strongly related to the band gap and ⊥ converges to its bulk value when the length exceeds tens of radius. Our method is employed to study the depolarization effect of a short (6,6) nanotube in a wet environment, when water is inside the tube. This situation is of interest for biomimetic uses of carbon nanotubes.
Journal of Chemical Sciences, 2007
We have carried out a series of molecular dynamics simulations of water containing a narrow carbon nanotube as a solute to investigate the filling and emptying of the nanotube and also the modifications of the density and hydrogen bond distributions of water inside and also in the vicinity of the outer surfaces of the nanotube. Our primary goal is to look at the effects of varying nanotube diameter, wall thickness and also solute-solvent interactions on the solvent structure in the confined region also near the outer surfaces of the solute. The thickness of the walls is varied by considering single and multi-walled nanotubes and the interaction potential is varied by tuning the attractive strength of the 12-6 pair interaction potential between a carbon atom of the nanotubes and a water molecule. The calculations are done for many different values of the tuning parameter ranging from fully Lennard-Jones to pure repulsive pair interactions. It is found that both the solvation characteristics and hydrogen bond distributions can depend rather strongly on the strength of the attractive part of the solute-water interaction potential. The thickness of the nanotube wall, however, is found to have only minor effects on the density profiles, hydrogen bond network and the wetting characteristics. This indicates that the long range electrostatic interactions between water molecules inside and on the outer side of the nanotube do not make any significant contribution to the overall solvation structure of these hydrophobic solutes. The solvation characteristics are primarily determined by the balance between the loss of energy due to hydrogen bond network disruption, cavity repulsion potential and offset of the same by attractive component of the solute-water interactions. Our studies with different system sizes show that the essential features of wetting and dewetting characteristics of narrow nanotubes for different diameter and interaction potentials are also present in relatively smaller systems consisting of about five hundred molecules.
Channelling of dipolar molecules through carbon nanotubes
Nanotechnology, 2007
We study the dynamic polarization of carbon nanotubes caused by the propagation of fast electric dipoles under channelling conditions. We specifically analyse the position and orientation dependences of the dipole self-energy, stopping force, and the torque about the dipole centre. It is found that a dipole is strongly attracted to the nanotube wall and shows a tendency to orient itself perpendicular to the direction of motion. The stopping force shows more complex behaviour, but is generally found to be larger close to the nanotube wall and when oriented in the perpendicular direction at higher speeds.
Dielectric relaxation of water inside a single-walled carbon nanotube
Physical Review B, 2009
We report a molecular dynamics study of anisotropic dynamics and dielectric properties of water confined inside a single-walled carbon nanotube (SWNT) at room temperature. The model includes dynamics of an SWNT described by a realistic potential function. A comparison with simulations assuming a rigid nanotube demonstrates that the popular assumption severely overestimates the dielectric constant for small diameter SWNTs. Simulations of water inside flexible SWNTs with various diameters reveal strong directional dependence of the dynamic and dielectric properties due to the confinement effect. The obtained dielectric permittivity spectra (DPS) identify two different dipolar relaxation frequencies corresponding to the axial and the cross-sectional directions, which are significantly smaller and larger than the single relaxation frequency of bulk water, respectively. The frequency variation increases as the SWNT diameter decreases. The results suggest that DPS can be used as a fingerprint of water inside SWNTs to monitor the water intrusion into SWNTs.
Electronic Sensitivity of Carbon Nanotubes to Internal Water Wetting
ACS Nano, 2011
We have constructed devices in which the interior of a single-walled carbon nanotube (SWCNT) field-effect transistor acts as a nanofluidic channel that connects two fluid reservoirs, permitting measurement of the electronic properties of the SWCNT as it is wetted by an analyte. Wetting of the inside of the SWCNT by water turns the transistor on, while wetting of the outside has little effect. These observations are consistent with theoretical simulations that show that internal water both generates a large dipole electric field, causing charge polarization of the tube and metal electrodes, and shifts the valance band of the SWCNT, while external water has little effect. This finding may provide a new method to investigate water behavior at nanoscale. This also opens a new avenue for building sensors in which the SWCNT simultaneously functions as a concentrator, nanopore and extremely sensitive electronic detector, exploiting the enhanced sensitivity of the interior surface.
Current Understanding of Water Properties inside Carbon Nanotubes
Nanomaterials
Confined water inside carbon nanotubes (CNTs) has attracted a lot of attention in recent years, amassing as a result a very large number of dedicated studies, both theoretical and experimental. This exceptional scientific interest can be understood in terms of the exotic properties of nanoconfined water, as well as the vast array of possible applications of CNTs in a wide range of fields stretching from geology to medicine and biology. This review presents an overreaching narrative of the properties of water in CNTs, based mostly on results from systematic nuclear magnetic resonance (NMR) and molecular dynamics (MD) studies, which together allow the untangling and explanation of many seemingly contradictory results present in the literature. Further, we identify still-debatable issues and open problems, as well as avenues for future studies, both theoretical and experimental.