scholarly journals Effect of Layer Charge Density on Hydration Properties of Montmorillonite: Molecular Dynamics Simulation and Experimental Study

2019 ◽  
Vol 20 (16) ◽  
pp. 3997 ◽  
Author(s):  
Jun Qiu ◽  
Guoqing Li ◽  
Dongliang Liu ◽  
Shan Jiang ◽  
Guifang Wang ◽  
...  
Keyword(s):  
Charge Density ◽  
The Self ◽  
Dynamics Simulation ◽  
Central Axis ◽  
Layer Charge ◽  
Water Molecules ◽  
Hydration Properties ◽  
Self Diffusion ◽  
Simulation Results ◽  
Self Diffusion Coefficient

Four kinds of Ca-montmorillonite with different layer charge density were used to study the effect of charge density on their hydration properties by molecular dynamics simulation and experiments. The research results of Z-density distribution of water molecules, Hw (hydrogen in water molecules), and Ca in the interlayer of montmorillonite show that the hydration properties of montmorillonite are closely related to its layer charge density. If the charge density is low, the water molecules in the interlayers are mainly concentrated on the sides of the central axis about –1.3 Å and 1.5 Å. As the charge density increases from 0.38semi-cell to 0.69semi-cell, the water molecules are distributed −2.5 Å and 2.4 Å away from the siloxane surface (Si-O), the concentration of water molecules near the central axis decreases, and at the same time, Ca2+ appears to gradually shift from the vicinity of the central axis to the Si-O surface on both sides in the montmorillonite layer. The simulation results of the radial distribution function (RDF) of the Ca-Hw, Ca-Ow (oxygen in water molecules), and Ca-Ot (the oxygen in the tetrahedron) show that the Ca2+ and Ow are more tightly packed together than that of Hw; with the increase of the charge density, due to the fact that the negative charge sites on the Si-O surface increase, under the action of electrostatic attraction, some of the Ca2+ are pulled towards the Si-O surface, which is more obvious when the layer charge density of the montmorillonite is higher. The results of the RDF of the Ot-Hw show that with the increase of charge density, the number of hydrogen bonds formed by Ot and Hw in the interlayers increase, and under the action of hydrogen bonding force, the water molecules near the central axis are pulled towards the two sides of Si-O surface. As a result, the arrangement of water molecules is more compact, and the structure is obvious. Correspondingly, the self-diffusion coefficient shows that the higher the layer charge density, the lower the self-diffusion coefficient of water molecules in interlayers is and the worse the hydration performance of montmorillonite. The experimental results of the experiments fit well with the above simulation results.

A Molecular Dynamics Simulation of the Transport Properties of Molten (La1/3, K)Cl

2005 ◽  
Vol 60 (3) ◽  
pp. 187-192 ◽  
Author(s):  
Masahiko Matsumiya ◽  
Koichi Seo
Keyword(s):  
Molecular Dynamics ◽  
Charge Asymmetry ◽  
The Self ◽  
Dynamics Simulation ◽  
Alkali Chloride ◽  
Self Diffusion ◽  
Dynamical Properties ◽  
Experimental Values ◽  
Dynamics Simulations ◽  
Self Diffusion Coefficient

Molecular dynamics simulations of molten (La1/3, K)Cl at 1123 K have been performed in order to investigate the correlation between simulated dynamical properties such as the self-exchange velocity (ν), the self-diffusion coefficient (D) and the electrical conductivity (κ) and the corresponding experimental values. The simulated results revealed that v and D of potassium decrease with increasing mole fraction of lanthanum, as expected from the experimental internal cation mobilities, b. The decrease of bK, νK and DK is ascribed to the tranquilization effect by La3+, which strongly interacts with Cl−. In contrast, bLa, νLa, and DLa increase with increasing concentration of La3+. The distorted linkage of the network structure of [LaCl6]3− units was disconnected with increasing the concentration of the alkali chloride. This might be attributed to the stronger association of La3+ with Cl− due to the enhanced charge asymmetry of the two cations neighboring Cl−. The sequence of the calculated v’s, D’s, and κ’s is consistent with those of the referred experimental results.

Self Diffusion in Liquid Titanium: Quasielastic Neutron Scattering and Molecular Dynamics Simulation

2009 ◽  
Vol 289-292 ◽  
pp. 609-614 ◽  
Author(s):  
Andreas Meyer ◽  
Jürgen Horbach ◽  
O. Heinen ◽  
Dirk Holland-Moritz ◽  
T. Unruh
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Neutron Scattering ◽  
The Self ◽  
Dynamics Simulation ◽  
Self Diffusion ◽  
Quasielastic Neutron ◽  
Liquid Titanium ◽  
Quasielastic Neutron Scattering ◽  
Self Diffusion Coefficient

Self diffusion in liquid titanium was measured at 2000K by quasielastic neutron scattering (QNS) in combination with container less processing via electromagnetic levitation. At small wavenumbers q the quasielastic signal is dominated by incoherent scattering. Up to about 1.2 °A−1 the width of the quasielastic line exhibits a q2 dependence as expected for long range atomic transport, thus allowing to measure the self diffusion coefficient DTi. As a result the value DTi = (5.3± 0.2)× 10−9 m2s−1 was obtained.With a molecular dynamics (MD) computer simulation using an embedded atom model (EAM) for Ti, the self diffusion coefficient is determined from the mean square displacement as well as from the decay of the incoherent intermediate scattering function at different q. By comparing both methods, we show that the hydrodynamic prediction of a q2 dependence indeed extends up to about 1.2 °A−1. Since this result does not depend significantly on the details of the interatomic potential, our findings show that accurate values of self diffusion coefficients in liquid metals can be measured by QNS on an absolute scale.

scholarly journals Nano-metering of Solvated Biomolecules Or Nanoparticles from Water Self-Diffusivity in Bio-inspired Nanopores

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Luca Bergamasco ◽  
Matteo Alberghini ◽  
Matteo Fasano
Keyword(s):  
Diffusion Coefficient ◽  
Liquid System ◽  
The Self ◽  
Water Molecules ◽  
Indirect Measure ◽  
Self Diffusion ◽  
Pore Liquid ◽  
Time Required ◽  
Practical Feasibility ◽  
Self Diffusion Coefficient

Abstract Taking inspiration from the structure of diatom algae frustules and motivated by the need for new detecting strategies for emerging nanopollutants in water, we analyze the potential of nanoporous silica tablets as metering devices for the concentration of biomolecules or nanoparticles in water. The concept relies on the different diffusion behavior that water molecules exhibit in bulk and nanoconfined conditions, e.g., in nanopores. In this latter situation, the self-diffusion coefficient of water reduces according to the geometry and surface properties of the pore and to the concentration of suspended biomolecules or nanoparticles in the pore, as extensively demonstrated in a previous study. Thus, for a given pore-liquid system, the self-diffusivity of water in nanopores filled with biomolecules or nanoparticles provides an indirect measure of their concentration. Using molecular dynamics and previous results from the literature, we demonstrate the correlation between the self-diffusion coefficient of water in silica nanopores and the concentration of proteins or nanoparticles contained therein. Finally, we estimate the time required for the nanoparticles to fill the nanopores, in order to assess the practical feasibility of the overall nano-metering protocol. Results show that the proposed approach may represent an alternative method for assessing the concentration of some classes of nanopollutants or biomolecules in water.

scholarly journals Molecular dynamics study of diffusion of xenon in water at different temperatures

2018 ◽  
Vol 16 (2) ◽  
Author(s):  
Niraj Kumar ◽  
Narayan Prasad Adhikari
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Structural Properties ◽  
The Self ◽  
Dynamics Simulation ◽  
Velocity Autocorrelation Function ◽  
Arrhenius Behavior ◽  
Self Diffusion ◽  
Different Temperatures ◽  
Self Diffusion Coefficient

Molecular Dynamics simulation was performed using 2 xenon atoms as solute and 300 water molecules as solvent. We have studied the structural properties as well as transport property. As structural properties, we have determined the radial distribution function (RDF) of xenon-xenon, xenon-water, and water-water interactions. Study of RDF of xenon-xenon and oxygen-oxygen interactions of water shows that there is hydrophobic behavior of xenon in the presence of water. We have studied the self diffusion coefficient of xenon, water, and mutual diffusion coefficients of xenon in water. The self diffusion coefficient of xenon was estimated using both mean-squared displacement (MSD) and velocity autocorrelation function (VACF), while only MSD was used for water. The temperature dependence of the diffusion coefficient of xenon and water were found to follow the Arrhenius behavior. The activation energies obtained are 12.156 KJ/mole with MSD and 14.617 KJ/mole with VACF in the temperature range taken in this study.

A Nonequilibrium Approach for Self-Diffusion in Unbounded Rapid Granular Flows

2000 ◽  
Vol 627 ◽  
Author(s):  
Payman Jalali ◽  
Piroz Zamankhan ◽  
William Polashenski
Keyword(s):  
Diffusion Coefficient ◽  
Kinetic Theory ◽  
Diffusion Problem ◽  
The Self ◽  
Spherical Particles ◽  
Self Diffusion ◽  
Granular Shear ◽  
Simulation Results ◽  
Self Diffusion Coefficient ◽  
Simulation Scheme

ABSTRACTA nonequilibrium simulation scheme is introduced to investigate the transverse diffusive motion in unbounded shear flows of smooth, monodisperse, inelastic spherical particles. A certain labeling algorithm is used in this scheme to extract a one-way particle mass flux which results a concentration gradient for the labeled particles. The self-diffusion coefficient can then be obtained from Fick's law. Using this scheme, one may find that the self-diffusion phenomenon across any layer inside the granular shear flow is analogous to the classic diffusion problem across a membrane. Under steady conditions, the current simulation results revealed that the particle diffusivity can be described by a linear law. This finding justifies the assumption of a linear law relationship in the kinetic theory type derivation of an expression for self-diffusivity. Moreover, it is shown that the results of self-diffusion coefficient obtained from the computer simulations are in agreement with the predictions of kinetic theory formulations in the range of solid volume fractions less than 0.5.

scholarly journals Effect of Layer Charge Characteristics on the Distribution Characteristics of H2O and Ca2+ in Ca-Montmorillonites Interlayer Space: Molecular Dynamics Simulation

Materials ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2318 ◽  
Author(s):  
Jun Qiu ◽  
Guoqing Li ◽  
Dongliang Liu ◽  
Shan Jiang ◽  
Guifang Wang ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Charge Density ◽  
Interlayer Space ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Layer Charge ◽  
Water Molecules ◽  
Isomorphic Substitution ◽  
Distribution Characteristics

The charge characteristics of montmorillonite have significant effects on its hydration and application performances. In this study, a molecular dynamics simulation method was used to study the influence of the charge position and charge density of montmorillonite on the distribution of H2O and Ca2+ in layers. The results showed that when the layer charge is mainly derived from the substitution among ions in the tetrahedron, a large number of Hw and Ot are combined into a hydrogen bond in the interlayer, thus the water molecules are more compactly arranged and the diffusion of water molecules among the layers is reduced. In addition, the Ca2+ are diffused to the sides by a concentrated distribution in the central axis of the layer. As the charge density of the montmorillonite increases, the polarity of the Si–O surface increases, which lesds to the deterioration of the diffusibility of the water molecules and the structure of the water molecules in the interlayers is more stable. The increase in the layer charge density lesds to the expansion of the isomorphic substitution range of the crystal structure, which results in a more dispersed distribution of Ca2+ among the layers under the action of electrostatic attraction between the substituted negative sites and the Ca2+.

Simulation of the Properties of 1-Ethyl-3-Methyl-Imidazolium Chloride/Chloroaluminate Ionic Liquids: Concentration and Temperature Dependence

2012 ◽  
Vol 457-458 ◽  
pp. 249-252
Author(s):  
Guo Cai Tian ◽  
Ding Wang ◽  
Ya Dong Li
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Molar Fraction ◽  
Chemical Properties ◽  
The Self ◽  
Dynamics Simulation ◽  
Imidazolium Chloride ◽  
Self Diffusion ◽  
Conductivity Increase ◽  
Self Diffusion Coefficient

Influences of the molar fractions of AlCl3and temperature on room temperature molten salts 1-ethyl-3-methyl-imidazolium Chloride /Chloroaluminate [Emim]Cl/AlCl3are studied by molecular dynamics simulation. The physical and chemical properties such as density, diffusion coefficients, viscosity, conductivity of [Emim]Cl/AlCl3with different molar fraction of AlCl3are calculated. The density is obtained as 1.1744g/cm3for [Emim]Cl, which agree well with the experimental value (1.186g/cm3). It was shown that the density and conductivity increase, whereas the viscosity decreases with the increasing of molar fraction of AlCl3. The self-diffusion coefficients of [Emim]+, Cl-and AlCl3increases and the changes of self-diffusion coefficient of AlCl3is the biggest as to molar fraction increase. It is shown that the conductivity, the self-diffusion coefficient of particles all increase, and the changes of AlCl3is the biggest with the increasing of temperature, whereas the density and viscosity reduce.

Self-Diffusion Coefficient of Molecular Fluid in Porous Media

2011 ◽  
Vol 312-315 ◽  
pp. 417-422 ◽  
Author(s):  
Vladimir Andryuschenko ◽  
Valery Rudyak
Keyword(s):  
Porous Media ◽  
Diffusion Coefficient ◽  
Hard Sphere ◽  
The Self ◽  
Dynamics Simulation ◽  
Fluid Density ◽  
Adsorption Time ◽  
Self Diffusion ◽  
Velocity Autocorrelation ◽  
Self Diffusion Coefficient

The paper deals with the molecular-dynamics simulation of the self-diffusion of fluid molecules in porous media using the hard-sphere potential. A study is made of the velocity autocorrelation functions of the molecules and dependences of the self-diffusion coefficient on the pore sizes, po-rosity, fluid density, and adsorption time.

Sign in / Sign up

Export Citation Format

Share Document