Molecular Dynamics Simulations Of Transport Research Articles

Molecular Dynamics Simulation of Transport and Structural Properties of CO2–Alkanes

Carbone dioxide emissions have imposed serious threats on the environment and health. As such, industrially viable CO2 storage and utilization technologies are of high demand. This study by perform...

Molecular dynamics simulation of transport of water/DMSO and water/acetone mixtures through boron nitride nanotube

The transport properties of fluids are significant quantities needed in engineering application. In this research, transport of water/dimethyl sulfoxide (DMSO) and water/acetone mixtures through armchair boron nitride nanotubes (BNNTs) was investigated using molecular dynamics simulations technique. The studied systems were composed of (6,6) BNNTs, water/DMSO or water/acetone mixtures. External pressures were applied in these systems along the x axis of the simulation cell. These simulations allow us to explore the mechanisms of transport and separation of solvents as organic contaminants. Without an applied pressure, DMSO or acetone molecules enter and occupy inside the BNNT, but their passing was not significant. For complete analysis of the systems, we calculated the density profiles of species, the radial distribution function of molecules, the retention time of solvents and their hydrogen bonds. The results showed that the transport of solvents through the BNNT was dependent on the amount of applied pressure.

Molecular Dynamics Simulation of Transport and Separation of Carbon Dioxide–Alkane Mixtures in a Nanoporous Membrane Under Sub- and Supercritical Conditions

Extensive nonequilibrium molecular dynamics simulations were carried out to study the transport and separation of binary mixtures of $$\hbox {CO}_2$$ and n-alkane chains in a molecular pore network model of nanoporous carbon molecular-sieve membrane. Separation of both sub- and supercritical mixtures was studied. The membrane was generated atomistically by the Voronoi tessellation of the space, using tens of thousands of atoms. The simulations indicate that there is an optimal pressure drop for separation of mixtures of $$\hbox {CO}_2$$ and n-alkanes, when the mixtures enter the membrane under supercritical conditions. In addition, separation of $$\hbox {CO}_2$$ from n-alkanes becomes increasingly more efficient as the size of the alkane increases.

Distinguishing Single DNA Nucleotides Based on Their Times of Flight Through Nanoslits: A Molecular Dynamics Simulation Study

Transport of single molecules in nanochannels or nanoslits might be used to identify them via their transit (flight) times. In this paper, we present molecular dynamics simulations of transport of single deoxynucleotide 5'-monophoshates (dNMP) in aqueous solution under pressure-driven flow, to average velocities between 0.4 and 1.0 m/s, in 3 nm wide slits with hydrophobic walls. The simulation results show that, while moving along the slit, the mononucleotides are adsorbed and desorbed from the walls multiple times. For the simulations, the estimated minimum slit length required for separation of the dNMP flight time distributions is about 5.9 μm, and the minimum analysis time per dNMP is about 10 μs. These are determined by the nature of the nucleotide-wall interactions, channel width, and by the flow characteristics. A simple analysis using realistic dNMP velocities shows that, in order to reduce the effects of diffusional broadening and keep the analysis time per dNMP reasonably small, the nucleotide velocity should be relatively high. Tailored surface chemistry could lead to further reduction of the analysis time toward its minimum value for a given driving force.

Molecular dynamics simulations of transport and separation of supercritical carbon dioxide-alkane mixtures in supported membranes

The results of extensive nonequilibrium molecular dynamics (MD) simulations of flow and transport of several binary mixtures of CO 2 and an n -alkane chain, from CH 4 to C 4 H 10 , through a model porous membrane composed of three pores in series with significantly different sizes and in the presence of an external pressure gradient, are reported. The technique that we use for the simulations is a combination of the configurational-bias Monte Carlo method (used for efficient generation of molecular models of n -alkane chains) and the dual control-volume grand-canonical MD method. The selectivity of the membrane changes qualitatively as the length of the alkane chain increases, resulting in high separation factors in favor of the alkanes. Moreover, we find that, under supercritical conditions, unusual phenomena occur that give rise to direction- and pressure-dependent permeabilities for the fluids. The results, which are also in agreement with a continuum formulation of the problem, indicate that the composite nature of the membrane gives rise to the direction-dependent permeabilities. Hence, modeling flow and transport of supercritical fluid mixtures in porous materials with the type of morphology considered in this paper (such as supported porous membranes) would require using effective permeabilities that depend on both the external pressure drop and the direction along which it is applied to the materials.

5021 カーボンナノチューブ内部での水の輸送と相変化に関する分子動力学シミュレーション(S51-1 マイクロ・ナノスケールの熱流体現象とその応用(1),S51 マイクロ・ナノスケールの熱流体現象とその応用)

5021 カーボンナノチューブ内部での水の輸送と相変化に関する分子動力学シミュレーション(S51-1 マイクロ・ナノスケールの熱流体現象とその応用(1),S51 マイクロ・ナノスケールの熱流体現象とその応用)

Molecular dynamics simulations of transport and separation of carbon dioxide-alkane mixtures in carbon nanopores.

The configurational-bias Monte Carlo method, which is used for efficient generation of molecular models of n-alkane chains, is combined for the first time with the dual control-volume grand-canonical molecular-dynamics simulation, which has been developed for studying transport of molecules in pores under an external potential gradient, to investigate transport and separation of binary mixtures of n-alkanes, as well as mixtures of CO2 and n-alkanes, in carbon nanopores. The effect of various factors, such as the temperature of the system, the composition of the mixture, and the pore size, on the separation of the mixtures is investigated. We also report the preliminary results of an experimental study of transport and separation of some of the same mixtures in a carbon molecular-sieve membrane with comparable pore sizes. The results indicate that, for the mixtures considered in this paper, even in very small carbon nanopores the energetic effects still play a dominant role in the transport and separation properties of the mixtures, whereas in a real membrane they are dominated by the membrane's morphological characteristics. As a result, for the mixtures considered, a single pore may be a grossly inadequate model of a real membrane, and hence one must resort to three-dimensional molecular pore network models of the membrane.

Nonequilibrium molecular dynamics simulations of transport and separation of supercritical fluid mixtures in nanoporous membranes. I. Results for a single carbon nanopore

The results of extensive nonequilibrium molecular dynamics simulations of transport of a supercritical fluid mixture through a carbon nanopore, in the presence of an external pressure gradient, are reported. If the downstream pressure is large enough, a pore packing phenomenon occurs in which several layers of the fluids fill the pore. We also find that the fluid molecules form dynamic clusters that travel the length of the pore, with cluster sizes that oscillate with the time. In addition, the simulations indicate that there may be an optimal pore size and an optimal applied pressure gradient for maximum separation of a supercritical fluid mixture into its components.

Nonequilibrium molecular dynamics simulations of transport and separation of gas mixtures in nanoporous materials

The nonequilibrium molecular dynamics simulations of transport and separation of a binary gas mixture through a porous membrane with interconnected pores of distributed sizes are reported. The membrane is modeled by a three-dimensional disordered molecular network of interconnected pores consisting of tens of thousands of atoms, based on a Voronoi tessellation of space. Results are presented for transport and adsorption of the gases, including the existence of an optimal pore structure for maximum separation of the gases.

Nonequilibrium molecular dynamics simulation of transport and separation of gases in carbon nanopores. II. Binary and ternary mixtures and comparison with the experimental data

We present the results of extensive nonequilibrium molecular dynamics simulations of transport and separation characteristics of binary and ternary gas mixtures consisting of CO2, CH4, and H2 through a carbon nanopore, in the presence of an external chemical potential gradient. The gas molecules are represented as Lennard-Jones (LJ) hard spheres. The effect of the various factors, such as the temperature, feed composition, and the pore size, on the transport, adsorption, and separation characteristics is investigated in detail. The simulations’ predictions are compared with experimental data obtained with a carbon molecular-sieve membrane. In some cases, there is good agreement between the predictions and the experimental data, while in other cases the simulations’ results and the data do not agree. Possible causes for the (dis)agreement are discussed, including the crucial interplay between two main factors in gas separation in a pore space, namely, adsorption on the pores’ walls versus the morphology (the pores’ interconnectivity and size distribution) of the porous material. Improved models are thus suggested.

Nonequilibrium molecular dynamics simulation of transport and separation of gases in carbon nanopores. I. Basic results

We present the results of extensive nonequilibrium Molecular Dynamics simulations of transport of a binary gas mixture of CO2 and CH4 through a carbon nanopore, in the presence of an external chemical potential or concentration gradient. The CH4 molecules are represented as Lennard-Jones (LJ) hard spheres, while the CO2 molecules are modeled both as LJ hard spheres, as well as three-site linear structures to account for their quadrupole moments. The effect of the various factors, including the structure of the pore walls, temperature, feed composition, and the molecular models and their parameters, on the transport, adsorption, and separation of the gases is investigated in detail. While the structure of the pore walls has virtually no effect on the separation factor, the temperature of the system, the pore size, and the molecular models and their parameters strongly influence it.

Nonequilibrium Molecular Dynamics Simulation of Transport of Gas Mixtures in Nanopores

The results of the first nonequilibrium molecular dynamics simulation of transport of a gas mixture through a carbon nanopore, in the presence of an external chemical potential gradient, are reported. While the structure of the pore walls and the composition of the mixture have essentially no effect on the separation factor, the temperature of the system and the pore size strongly influence it. The results are in qualitative agreement with the new experimental data that are presented in this Letter.

Molecular Dynamics Simulation of Transport in Diamond and GaN: Role of Collective Excitations

ABSTRACTIn this paper we consider the role of collective excitations in transport of charge carriers in the conduction band of diamond and GaN. The present molecular dynamics simulation uses a Monte Carlo algorithm to determine the time between collisions with scattering rates calculated quantum mechanically using the Fermi Golden Rule. For very thin films (L=0.01 μm) and for low fields (F<10 V/μm), the energy spectra of both diamond and GaN contain a series of peaks which are attributed to the absorption and emission of discrete plasmons. In diamond. the intervalley LA, LO and TO scattering becomes increasingly more important at higher fields while electron-plasmon interactions decrease. For thicker diamond films (L=0.1 μm), there is hot electron transport for F∼10 V/μm and quasi-ballistic transport for F-100 V/μm. In GaN with L=0.01 μm and fields F∼10 V/μm, there is a discrete series of peaks in the energy spectrum corresponding to excitations associated with polar optical scattering.