Investigation of small inhibitor effects on methane hydrate formation in a carbon nanotube using molecular dynamics simulation.

In this work, we simulated water molecules in fixed and rigid (15,0) CNTs and the confined water molecules formed a hexagonal ice nanotube in the CNT. After the addition of methane molecules in the nanotube, the hexagonal structure of confined water molecules disappeared and were replaced by almost all the guest methane molecules. The replaced molecules formed a row of water molecules in the middle of the hollow space of the CNT. We also added five small inhibitors with different concentrations (0.8 mol% and 3.8 mol%) to methane clathrates in CNT: benzene, 1-ethyl-3-methylimidazolium chloride ionic liquid ([emim+][Cl-] IL), methanol, NaCl, and tetrahydrofuran (THF). We investigated the thermodynamic and kinetic inhibition behaviors of the different inhibitors on the methane clathrate formation in the CNT using the radial distribution function (RDF), hydrogen bonding (HB), and angle distribution function (ADF). Our results showed that the [emim+][Cl-] IL is the best inhibitor from both aspects. It was also shown that the effect of THF and benzene is better than that of NaCl and methanol. Furthermore, our results showed that the THF inhibitors tended to aggregate in the CNT, but the benzene and IL molecules were distributed along the CNT and can affect the inhibitor behavior of THF in the CNT. We have also examined the effect of CNT chirality using the armchair (9,9) CNT, the effect of CNT size using the (17,0) CNT, and the effect of CNT flexibility using the (15,0) CNT by the DREIDING force field. Our results showed that the IL has stronger thermodynamic and kinetic inhibition effects in the armchair (9,9) and the flexible (15,0) CNT than the other systems, respectively.

Structure, dynamics, and morphology of nanostructured water confined between parallel graphene surfaces and in carbon nanotubes by applying magnetic and electric fields.

Water molecules experience certain changes in their properties when they feel an external magnetic or electric field. These changes are significant in different applications, such as biological and biotechnological processes, nano-pumping, and water treatment. In this work, we have performed molecular dynamics (MD) simulations to investigate the different thermodynamics, structure, and dynamics of water molecules confined between two parallel surfaces and also confined in carbon nanotubes (CNTs). We have also applied different electric and magnetic fields in different directions to the confined molecules. In the graphene system, no polygonal shape was formed in either low or high electric fields, whereas rhombic and pentagonal shapes were formed in low and high magnetic fields. In the CNT system, applying electric fields in all three dimensions made the pentagonal shape disappear and the confined water molecules formed a ring shape when the electric field was applied in the axial direction. Applying the electric field perpendicular to the graphene surfaces increases the self-diffusion of the confined molecules, whereas applying the electric and magnetic fields along the CNT axis decreases the self-diffusion of the confined water molecules. In the graphene system, applying the electric field perpendicular to the graphene surfaces decreases the average number of hydrogen bonds (〈HB〉) whereas the magnetic field has little effect on the 〈HB〉. In the CNT system, applying Ex also leads to a smaller number of HBs. Also, applying the magnetic field along the x-direction (along the CNT direction) leads to a greater number of HBs than the other fields.

Phase transitions in nanostructured water confined in carbon nanotubes by external electric and magnetic fields: a molecular dynamics investigation.

Applying electric and magnetic fields on water molecules confined in carbon nanotubes (CNTs) has important applications in cell biology and nanotechnology-based fields. In this work, molecular dynamics (MD) simulations were carried out to examine the probable phase transitions in confined water molecules confined in (14,0) CNTs at 300 K by applying different electric and magnetic fields in the axial direction. We have also studied some thermodynamics and structural properties of the confined water molecules in the different fields. Our results showed that the confined water molecules experience. Some phase (shape) transitions from the pentagonal to twisted pentagonal, spiral and circle-like shapes by increasing the electric field from 104 (V m-1) to 107 (V m-1). Also, applying the magnetic field with different intensities has small effects on the pentagonal shape of confined water molecules but applying the highest magnetic field (300 T) makes the pentagonal shape more ordered. These phase transitions have not been reported before. Our results also indicated that the ring-like shapes obtained in the presence of the electric field form more hydrogen bonds (HBs) than the other structures. The phase transitions of confined water molecules have been also proved by radial distribution function (RDF) and angle distribution function (ADF) analyses.

Molecular dynamics simulation of anticancer drug delivery from carbon nanotube using metal nanowires.

In this study, we have investigated delivery of cisplatin as the anticancer drug molecules in different carbon nanotubes (CNTs) in the gas phase using molecular dynamics simulation. We examined the shape and composition of the releasing agent by using the different nanowires and nanoclusters. We also investigated the doping effect on the drug delivery process using N-, Si, B-, and Fe-doped CNTs. Different thermodynamics, structural, and dynamical properties have been studied by using the pure and different doped CNTs in this study. Our results show that the doping of the CNT has significant effect on the rate of the drug releasing process regardless of the composition of the releasing agent. © 2019 Wiley Periodicals, Inc.

Molecular dynamics simulation of liquid water and ice nanoclusters using a new effective HFD-like model.

We have determined a new two-body interaction potential of water by the inversion of viscosity collision integrals of water vapor and fitted to achieve the Hartree-fock dispersion-like (HFD-like) potential function. The calculated two-body potential generates the thermal conductivity, viscosity, and self-diffusion coefficient of water vapor in an excellent accordance with experimental data at wide temperature ranges. We have also used a new many-body potential as a function of temperature and density with the HFD-like pair-potential of water to improve the two-body properties better than the SPC, SPC/E, TIP3P, and TIP4P models. We have also used the new corrected potential to simulate the configurational energy and the melting temperatures of the (H2 O)500 , (H2 O)864 , (H2 O)2048 , and (H2 O)6912 ice nanoclusters in good agreement with the previous simulation data using the TIP4P model. The extrapolated melting point at the bulk limit is also in better agreement with the experimental bulk data. The self-diffusion coefficients for the ice nanoclusters also simulated at different temperatures. © 2017 Wiley Periodicals, Inc.

Au@void@AgAu Yolk-Shell Nanoparticles with Dominant Strain Effects: A Molecular Dynamics Simulation.

Au@void@AgAu yolk-shell nanoparticles with different morphologies were studied by classical molecular dynamics simulation. The results indicated that all of simulated yolk-shell nanoclusters with ∼3.8 nm size and different morphologies are unstable at room temperature, and collapse of the shell atoms into the void space completely fills it and creates more stable Au@AgAu core-shell structures. Also, it was observed that thermodynamic stabilities of the created core-shell structures strongly depend on the morphology of nanocluster, for which competition between strain and surface energy effects plays the key role in this phenomenon. Within this competition, strain effect is dominant and helps the stability of the created core-shell structure. Herein, the icosahedral nanocluster with the lowest strain effect exhibits the highest thermodynamic stability. By comparing the simulation results with experimental data, it was concluded that the essential factor that controls the stability of these nanoparticles is their size.

Delivery of Cisplatin Anti-Cancer Drug from Carbon, Boron Nitride, and Silicon Carbide Nanotubes Forced by Ag-Nanowire: A Comprehensive Molecular Dynamics Study.

In this work, liberation of cisplatin molecules from interior of a nanotube due to entrance of an Ag-nanowire inside it was simulated by classical molecular dynamics method. The aim of this simulation was investigation on the effects of diameter, chirality, and composition of the nanotube, as well as the influence of temperature on this process. For this purpose, single walled carbon, boron nitride, and silicon carbide nanotube were considered. In order for a more concise comparison of the results, a new parameter namely efficiency of drug release, was introduced. The results demonstrated that the efficiency of drug release is sensitive to its adsorption on outer surface of the nanotube. Moreover, this efficiency is also sensitive to the nanotube composition and its diameter. For the effect of nanotube composition, the results indicated that silicon carbide nanotube has the least efficiency for drug release, due to its strong drug-nanotube. Also, the most important acting forces on drug delivery are van der Waals interactions. Finally, the kinetic of drug release is fast and is not related to the structural parameters of the nanotube and temperature, significantly.

A molecular dynamics study of the effect of the substrate on the thermodynamic properties of bound Pt-Cu bimetallic nanoclusters.

In this work confinement of the Pt708Cu707 bimetallic nanocluster in single-walled carbon, boron nitride, and silicon carbide nanotubes was investigated using molecular dynamics simulation. The results of the calculations showed that at 50% composition, a eutectic-like behavior is seen during the melting-freezing process. Also, the Pt708Cu707 bimetallic nanocluster tends to have a core-shell like structure with a Pt-rich core and a Cu-rich shell, except for boron nitride nanotubes in which the nanocluster exhibits a completely different pattern on the tube wall. The Pt-Cu nanoclusters confined in boron nitride nanotubes are extremely extended on the tube wall in such a way that most of the nanotube-nanocluster interface is covered by a monolayer metal coating which can promise unique physical and chemical properties for these types of nanocomposites. Also, extension of the nanocluster on the substrate surface reduces its melting point.

Investigation of thermal evolution of copper nanoclusters encapsulated in carbon nanotubes: a molecular dynamics study.

We have studied the heating and cooling processes of CuN nanoclusters encapsulated in CNTs with different diameters and chiralities in the range of 100-1700 K. We have investigated all of the possible effects: the effects of the nanocluster size, CNT diameter, and CNT chirality on the thermodynamic, structural, and dynamic properties during the melting process. Our thermodynamic results showed that the melting temperatures of the confined nanoparticles tend to increase with the nanoparticle size. Our energy results also showed that the melting temperature of the nanocluster decreases upon decreasing the CNT diameter, which is due to the greater nanocluster-CNT wall interactions in the smaller nanotube which make the cluster to expand more easily on the interface. The results also showed that the encapsulation of the nanocluster in the zigzag CNT has lower energy values than the armchair one, which is due to the greater interaction of the nanocluster and the zigzag CNT wall. We have also recognized a hysteresis in the course of the cooling process, which can be due to the fact that the nanoclusters and the nanotube make a coherent interface structure with more stability. Using the radial distribution function, it has been shown that the structural change with temperature is irreversible. Our dynamical results indicated that the bigger nanocluster has slower dynamics than the smaller cluster. It is also shown that the nanocluster on the smaller and zigzag CNTs has slower dynamics than the bigger and armchair tubes.

Investigation of thermodynamic, dynamic, and structural properties of H2 adsorption on a Ag-Au nanoalloy with a carbon nanotube support.

We have performed MD simulations to investigate H(2) adsorption on Ag-Au nanoclusters with the different Au mole fractions supported on the carbon nanotubes with the different diameters. Our thermodynamic results shown that the saturation value of coverage and the enthalpy of adsorption increases as the mole fraction of Au is increased. Our structural results showed that the presence of the H(2) gas exerts a significant effect on the nanocluster surface atoms and tends to stabilize the surface atoms on the nanocluster. Also, the structural changes are irreversible in such a way that by gradually decreasing the pressure to zero, the nanocluster geometry is not reversed to its initial structure in vacuum conditions. We have also shown that the nanoclusters have smaller values of the self-diffusion coefficients in presence of H(2) molecules than those values in the initial state (vacuum), which is due to the increasing of the interface structure between the nanocluster and the nanotube.