Temperature Dependence Of Self-diffusion Coefficient Research Articles

Molecular-level insights into structure and dynamics in ionic liquids and polymer gel electrolytes

Designing new electrolytes requires a better understanding of the correlation between their transport properties and their molecular structure. In this work, we present a detailed study of ionic liquids and polymer gel electrolytes probing their structure and dynamics by nuclear magnetic resonance (NMR) spectroscopy. In particular, ammonium- and phosphonium-based ionic liquids (ILs) are combined with different LiTFSI concentrations, and then with different ratios of poly(methylmethacrylate) polymer. The temperature dependence of self-diffusion coefficients of mobile species, DLi+, DTFSI- and DP4441+ or DN4441+, measured by pulsed field gradient (PFG) NMR spectroscopy obeys the Arrhenius equation. Diffusivity of [P4441][TFSI] ILs is found to be greater than those of the [N4441][TFSI] ILs in both liquid and gel electrolytes. Solid state NMR experiments including 13C and 19F MAS, 13C{19F},13C{1H} CPMAS probe the local structure and molecular-level interactions between ions and polymer in gel electrolytes, particularly for samples with higher PMMA content (≥25 wt%). Finally, the fast field cycling relaxometry has been used to unveil the rotational and translational dynamics of P4441+ or N4441+ and TFSI− by measuring 1H and 19F R1 relaxation rate profiles at different temperatures. A comprehensive NMR analysis including relaxation studies at low magnetic field provides decisive new insights regarding the formation of ionic clusters and the interaction of ions with the polymer chain in the case of the gel electrolytes.

TMS self-diffusion coefficients in the binary solvent carbon tetrachloride – acetone-d6. 1H PGSE NMR experiment and random discrete displacements model of self-diffusion

Abstract The tetramethylsilane (TMS) self-diffusion coefficients in the binary solvent carbon tetrachloride (CTC) – acetone-d6 (A-d6) have been obtained by the pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) method at 278, 298, and 318 K. The TMS self-diffusion coefficients increase as the A-d6 concentration and temperature become higher. The temperature dependences of the TMS self-diffusion coefficients at various concentrations of the binary solvent have been analysed based on the random discrete displacements model of self-diffusion presented in this paper. Within the framework of the proposed model, it is shown that the Arrhenius type of the temperature dependence of the self-diffusion coefficient (which is observed for TMS in this work) is a special case when the diffusion activation energy ED > kBT. In the opposite case, the temperature dependence of the self-diffusion coefficient tends to the form of the equation obtained for an ideal gas.

Thermal performance of a binary carbonate molten eutectic salt for high-temperature energy storage applications

Molten carbonate eutectic salts are promising thermal storage and heat transfer fluid materials in solar thermal power plant with the feature of large specific heat capacity, wide operating temperature range and little corrosive. The high-temperature properties of molten carbonates should be determined accurately over the entire operating temperature for energy system design. In this paper, molecular dynamic simulation is used to study temperature and component dependence of microstructures and thermophysical properties of the binary carbonate molten salt. Negative linear temperature dependence of densities and thermal conductivities of binary mixtures of different components is confirmed with respect to the distances of ion clusters. Besides, positive linear temperature dependence of self-diffusion coefficient is also obtained. When temperature is constant, densities and thermal conductivities of binary mixtures are linearly related with components. Self-diffusion coefficients of CO32− firstly increase and then decrease with increasing mole fraction of Na2CO3. The temperature-thermophysical properties-composition correlation formulas are obtained, and the database of thermophysical properties of molten carbonate salts over the entire operating temperature is complemented, which will provide the essential data for heat transfer and storage system design, operation, and optimization in CSP.

Atomistic description of self-diffusion in molybdenum: A comparative theoretical study of non-Arrhenius behavior

According to experimental observations, the temperature dependence of self-diffusion coefficient in most body-centered cubic metals (bcc) exhibits non-Arrhenius behavior. The origin of this behavior is likely related to anharmonic vibrational effects at elevated temperatures. However, it is still debated whether anharmonicity affects more the formation or migration of monovacancies, which are known to govern the self-diffusion. In this extensive atomistic simulation study we investigated thermodynamic properties of monovacancies in bcc molybdenum, here taken as a representative model system, from zero temperature to the melting point. We combined first-principles calculations and classical simulations based on three widely used interatomic potentials for Mo. In our analysis we employ static and dynamic atomistic calculations as well as statistical sampling techniques and thermodynamic integration to achieve thorough information about temperature variations of vacancy formation and migration free energies and diffusivities. In addition, we carry out large-scale molecular dynamics simulations that enable direct observation of high-temperature self-diffusion at the atomic scale. By scrutinizing the results obtained by different models and methods, we conclude that the peculiar self-diffusion behavior is likely caused by strong temperature dependence of the vacancy formation energy.

Diffusional Motion of Solvated Ions in Super-Concentrated Electrolytes

The evolution of solvation structure and dynamics of aqueous LiTFSI based electrolytes with varying salt concentration and competing divalent (Zn2+, Mg2+ and Ca2+) and ammonium based (Me3EtN+) cations were studied using 7Li, 19F and 1H nuclear magnetic resonance (NMR) spectroscopy and pulsed-field gradient (PFG) NMR methods. The NMR peak intensity analysis (Figure 1(a)), reveals that more than half of Li+, TFSI- and H2O molecules are invisible in liquid NMR spectra, likely due to the loss of mobility (broader NMR line width) associated with formation of bigger solvate clusters at higher salt concentrations. The 7Li, 19F and 1H chemical shift values (Figure 1(b)), were shifted to the higher field (more negative chemical shift values) with salt concentration, indicating the interaction between Li+ cations and TFSI- anions became stronger, while the hydrogen bonding network between H2O molecules became weaker resulting from the localization of water clusters in the solutions. The mobility of the remaining species were analyzed through the PFG-NMR based diffusion measurements (Figure 1(c)). It showed that Li+ cation diffuses relatively faster than TFSI- anion (D H2O>D Li>D TFSI) for these aqueous electrolytes, and differ from non-aqueous electrolyte solutions which traditionally register higher anion diffusion rates (D anion > D Li) [1-4]. The D H2O/D TFSI diffusion ratio showed that the relative mobility of water molecules increases with LiTFSI concentration and by addition of multivalent (Zn2+, Mg2+ and Ca2+) cation salt. The D Li/D TFSI diffusion ratio reaches the maximum value of ~3.4 for the 20 m LiTFSI/H2O solution, and the addition of competing cations tends to minimally affect the lithium diffusion. The different behavior between D H2O/D TFSI and D Li/D TFSI values suggest that the localized water molecules diffuse freely in the higher concentration electrolytes, while the diffusion motions of Li+ cation and TFSI- anion depend strongly on the total composition of the competing ions in the solution. The structural and diffusional properties of high concentration electrolytes will be discussed based on diffusion and chemical shift analysis. References Frömling, T., et al., Enhanced Lithium Transference Numbers in Ionic Liquid Electrolytes. J. Phys. Chem. B, 2008. 112(41): p. 12985-12990.Hayamizu, K., Temperature Dependence of Self-Diffusion Coefficients of Ions and Solvents in Ethylene Carbonate, Propylene Carbonate, and Diethyl Carbonate Single Solutions and Ethylene Carbonate + Diethyl Carbonate Binary Solutions of LiPF6 Studied by NMR. J. Chem. Eng. Data, 2012. 57(7): p. 2012-2017.Hayamizu, K., et al., Pulse-Gradient Spin-Echo 1H, 7Li, and 19F NMR Diffusion and Ionic Conductivity Measurements of 14 Organic Electrolytes Containing LiN(SO2CF3)2. J. Phys. Chem. B, 1999. 103(3): p. 519-524.Wu, T.-Y., et al., Influence of LiTFSI Addition on Conductivity, Diffusion Coefficient, Spin–Lattice Relaxation Times, and Chemical Shift of One-Dimensional NMR Spectroscopy in LiTFSI-Doped Dual-Functionalized Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data, 2015. 60(3): p. 471-483. Figure 1

Effect of Temperature and Water Content on the Properties of Solid Protic Electrolyte of Tetra Calixarene Sulfonic Acid: NMR Study

The methods of 1H NMR and pulsed field gradient NMR are used to study the protic solid electrolyte of calix[4]arene-para-sulfonic acid in the temperature range of –15 to 24°C and water content λ of 1.6 to 5.7 H2O molecules per SO3H. Analysis of the 1H signal intensity in NMR spectra showed that no ice phase is formed in the whole studied temperature and water content range. The hydration numbers of H+(H2O)h complexes are calculated on the basis of the temperature dependences of chemical shift values. The pulsed field gradient NMR technique is used to determine self-diffusion coefficients. Activation energies Eact are calculated on the basis of the temperature dependences of self-diffusion coefficients. Good agreement of the data on diffusion Eact and protic conductivity are shown. A corollary of the Nernst–Einstein equation is used to calculate the values of protic conductivity on the basis of self-diffusion data. The calculated values of protic conductivity in the water content λ range of 1.6 to 5.7 agree with the data obtained experimentally.

Temperature dependence of Self-diffusion coefficient (SDC) of liquid aluminum using Embedded Atom Method-Finnis-Sinclair (EAMFS) potential

Atomistix tool kit force field calculations have been done, using the embedded atom method-Finnis-Sinclair potential as implemented in Virtual Nano Lab-Atomistix Tool Kit (VNL-ATK) to study the temperature dependence of self-diffusion coefficient of liquid aluminum. Also, we calculated the shear viscosity from the Sutherland-Einstein relation, and reports that, the calculated SDC and viscosity are sensitive to temperature. Results obtained at 980, 1020 and 1060K for SDC underestimated available experimental results, while the calculated results for viscosity at 1000 and 1200K overestimated experimental data available in the literature. The underestimation might be due to the shortrange order in liquid Al.Keywords: self-diffusion, viscosity, aluminum, temperature

The influence of NaCl concentration on the (LiCl-KCl) eutectic system and temperature dependence of the ternary system

To explore the complex correlation between local structure and properties in the alkali chlorides ternary system, simulations were systematically conducted for 11 different (Li, Na, K) Cl compositions from 900 K to 1200 K as the fundamental study of magnesium chloride electrolysis. For the ternary system, the density was calculated across the full composition and database was established. Furthermore, the structure simulation results revealed that the coordination of Li-Cl pair tended to be a distorted tetrahedron and the Na-Cl and K-Cl pairs tended to be an octahedron. The prediction of the properties was compared with available experiments and extrapolated analytical data, the deviations are acceptable. The temperature had no significant effects on the local structure and thermal conductivity. The results also showed that the Tosi−Fumi potential predicted positive temperature dependence of self-diffusion coefficients and ionic conductivity, and negative temperature dependence of the viscosity. In addition, the correlation between the local structure and transport properties was explored. The hydrodynamic radius of Li+ and K+ is similar in the ternary system, it can be found that whilst the K+ ion diffuses as an atomic species, the Li+ ion carries at least some of its coordinating Cl− ions in the diffusion process, giving the diffusing species a larger effective size than the bare ion.

Kinetic and thermodynamic properties of liquid zinc: An ab initio molecular dynamics study

In this paper, structure, dynamic and kinetics properties of the liquid zinc were calculated by ab initio molecular dynamics simulations. Temperature dependence of self-diffusion coefficient, shear viscosity and surface tension were investigated in the range from 420 to 550°C. The pair correlation functions calculated in this study are in good agreement with those previous results by other scholars. The calculated results indicate that both of self-diffusion coefficient and shear viscosity have very good compatibility with Arrhenius relationship. Moreover, the formula exhibiting temperature dependence of the surface tension had been established in order to evaluate the surface tension at any given temperature in this paper.

Melting properties of Pt and its transport coefficients in liquid states under high pressures

Molecular dynamics (MD) simulations of the melting and transport properties in liquid states of platinum for the pressure range (50–200 GPa) are reported. The melting curve of platinum is consistent with previous ab initio MD simulation results and the first-principles melting curve. Calculated results for the pressure dependence of fusion entropy and fusion volume show that the fusion entropy and the fusion volume decrease with increasing pressure, and the ratio of the fusion volume to fusion entropy roughly reproduces the melting slope, which has a moderate decrease along the melting line. The Arrhenius law well describes the temperature dependence of self-diffusion coefficients and viscosity under high pressure, and the diffusion activation energy decreases with increasing pressure, while the viscosity activation energy increases with increasing pressure. In addition, the entropy-scaling law, proposed by Rosenfeld under ambient pressure, still holds well for liquid Pt under high pressure conditions.

高压条件下简单金属熔体的输运性质及其熵标度关系

本文利用经典分子动力学方法研究了在高温高压条件下Fe，Mo，Ta，W，Ni和Cu六种金属熔体的自扩散系数、粘度系数以及对关联熵随温度和压强的变化，验证了Rosenfeld提出的输运系数熵标度关系在高压条件下对金属熔体的适用性。研究结果表明金属熔体的自扩散系数(粘度系数)在给定的压强下满足Arrhenius关系，并且扩散激活能和粘度激活能随压强的增大而增大；Rosenfeld提出的输运系数熵标度关系在高温高压条件下对金属熔体依然使用。为此，在高温高压条件下实验中很难测量得到的金属熔体的输运性质(自扩散系数和粘度)可以通过较容易测量得到的结构性质(对分布函数或结构因子)利用输运系数熵标度关系计算得到。 Molecular dynamic simulations are applied to study the temperature and pressure dependences of self-diffusion coefficient, viscosity and pair correlation entropy of the liquid Fe, Mo, Ta, W, Ni and Cu under high temperature and high pressure conditions. Our results suggest that the tem-perature dependences of self-diffusion coefficients and viscosity are well described by the Arrhenius law at given pressure and that the activation energy increases with increasing pressure. In particular, we find that the entropy-scaling laws proposed by Rosenfeld for self-diffusion coefficients and viscosity still hold well for the liquid metals under high temperature and pressure conditions. Using the entropy-scaling laws, we can obtain transport properties that are difficult to measure from the structural properties (the pair distribution functions or structural factor) which are easier to measure.

Transport Properties and the Entropy-Scaling Law for Liquid Tantalum and Molybdenum under High Pressure

Molecular dynamics simulations are applied to study the transport properties, including the self-diffusion coefficient and viscosity, of liquid tantalum and molybdenum under high pressure conditions. The temperature dependence of self-diffusion coefficient, viscosity and the pair correlation entropy under high pressure conditions are investigated. Our results show that the Arrhenius law well describes the temperature dependence of self-diffusion coefficients and viscosity under high pressure, and the diffusion activation energy decreases with increasing pressure, while the viscosity activation energy increases with increasing pressure. The temperature dependence of the pair correlation entropy is well described by 1/T scaling. Furthermore, we find that the entropy-scaling laws, proposed by Rosenfeld for self-diffusion coefficients and viscosity in simple liquids under ambient pressure, still hold well for liquid tantalum and molybdenum under high pressure conditions.

Temperature dependence of diffusion coefficient of carbon monoxide in water: A molecular dynamics study

In the present work, molecular dynamics simulations of a mixture of carbon monoxide (CO) gas in SPC/E water (H2O) with CO as a solute and water as a solvent have been performed to understand the self-diffusion coefficient of the components, i.e. CO and water along with the mutual diffusion coefficients and structural properties of the system by studying the radial distribution function (RDF) of the components present in the system at different temperatures of 293K, 303K, 313K, 323K, and 333K. The mole fraction of CO in the system is 0.018 and that of water is 0.982. The solvent–solvent, solute–solute and solute–solvent radial distribution functions have been estimated to study the structural properties of the system. The self-diffusion coefficient of CO is calculated using mean square displacement (MSD) and velocity autocorrelation function (VACF) and that of water is estimated using MSD method only. The self-diffusion coefficient of CO agrees within around 20% of the experimental results and that of water agrees within around 10% of the experimental results. The mutual diffusion coefficient of solute–solvent is calculated using Darken's relation. The temperature dependence of self-diffusion coefficients of CO and water and mutual diffusion coefficients of CO in water all follow the Arrhenius behavior from where we estimate the activation energy of the diffusion process. Thus estimated activation energies also agree to experimental values.

Self-diffusion in liquid lithium from coherent quasielastic neutron scattering

Abstract Using the method of quasielastic coherent neutron scattering by liquid lithium, the temperature dependence of self-diffusion coefficient is investigated and compared with analogous data extracted by the incoherent scattering method.

Temperature Dependence of Self-Diffusion Coefficients of Ions and Solvents in Ethylene Carbonate, Propylene Carbonate, and Diethyl Carbonate Single Solutions and Ethylene Carbonate + Diethyl Carbonate Binary Solutions of LiPF6 Studied by NMR

The self-diffusion coefficients, D, of lithium, anions, and solvents in four binary-solution electrolytes of ethylene carbonate (EC)–diethyl carbonate (DEC) and three single-solution electrolytes of EC, DEC, and propylene carbonate (PC) including 1 M LiPF6 were measured by 1H, 7Li, and 19F NMR spectroscopy from (353 to 243) K or above freezing for seven solution electrolytes. In the single DEC electrolyte, DLi and DPF6 had almost the same values at every temperature, whereas DLi was smaller than DPF6 in the EC and PC solutions. In the binary EC–DEC electrolytes, as the ratio of EC increased, DLi gradually became smaller, while DPF6 remained almost unchanged in the temperature range studied. At 303 K, the degree of ion dissociation α was evaluated from the ionic conductivity, DLi and DPF6. The α value increased from 0.17 to 0.71 as the EC ratio increased from (0 to 100) %.

The behavior of self-diffusion coefficient under conditions of varying isotope composition of crystal

The variation of diffusion parameters with varying isotope composition in both the high-temperature and low-temperature region is studied in view of the dependence of the parameters of interatomic potential on the atomic mass. It is demonstrated that the isotopic dependence of the coefficient of self-diffusion is insignificant at high temperatures. However, upon transition to low temperatures, the difference between the coefficients of self-diffusion in isotopically different crystals becomes appreciable. Calculations for diamond and lithium reveal that the coefficient of self-diffusion in the low-temperature region decreases by one-three orders of magnitude during transition from 12C to 13C and increases by an order of magnitude during transition from 7Li to 6Li. This effect is associated with quantum tunneling at low temperatures and is caused by the presence of “zero-point oscillations” of atoms. It is demonstrated that, in the high-temperature region, the inclusion of isotopic dependence of the parameters of interatomic potential has a marked effect on the self-diffusion coefficient. The temperature dependence of self-diffusion coefficient is calculated, and temperatures are estimated below which the Arrhenius law is no longer valid.

Temperature dependence of self-diffusion coefficient in several liquid metals

The temperature-dependent self-diffusion coefficient D(T) in liquid metals between the melting temperature Tm and boiling point Tb is modeled in terms of the relationship among D, liquid viscosity η, and liquid–vapor surface tension γlv. The model predictions for D(T) correspond to available experimental and molecular dynamics (MD) simulations results for liquid alkali metals Li, Na, Rb and Cs, semi-metal Al, transition and noble metals Ni, Cu, Ag and Au.

Dynamics of Supercooled Water and Glassy Water

Quasielastic neutron scattering of normal and supercooled water was measured in the temperature range 253-330K to investigate the possible anomaly expected to occur around 230K. Anomalous temperature dependence of self-diffusion coefficient, which may suggest a critical slowing-down, was found for the first time. Vapor-deposited glassy water (amorphous ice) and those doped with methanol (hydrogen-bond breaking impurity) and Xe and SF6 (both hydrogen-bond forming impurities) were prepared in a novel cryostat designed for this experiment. The in-situ neutron scattering of these samples was measured on a total scattering, smallangle scattering, and inelastic scattering spectrometers. A strong correlation among the ordering of hydrogenbond system, volume expansion, homogenization in a nano-scale range, and decrease of the excess lowenergy excitation was found in the experiments for the annealing and impurity effects. The future study on supercooled and glassy water was discussed along with high-intensity spectrometers at J-PARC.

A quasi-elastic neutron scattering study of the dynamics of supercritical water

Dynamics of supercritical water was studied by quasi-elastic neutron scattering. Two series of measurements, respectively, at constant temperature of 673 K and constant density of 0.578 g/cm 3 were carried out. Experimental data were fitted properly by the jump-diffusion model. The self-diffusion coefficient, typically in the interval 3.71–5.21 � 10 � 8 m 2 /s, depends both on temperature and density. The mean residence time is, however, fairly constant at 0.30 ps in all cases. From the temperature dependence of self-diffusion coefficient which is of Arrhenius type the activation energy Ea ¼ 2:25 kcal/mol is being estimated. 2003 Elsevier Science B.V. All rights reserved.

Temperature Dependence of Self-Diffusion Coefficient in Liquid Hg and Sn: a Modified Hard-Sphere Description

Article Temperature Dependence of Self-Diffusion Coefficient in Liquid Hg and Sn: a Modified Hard-Sphere Description was published on December 1, 2002 in the journal High Temperature Materials and Processes (volume 21, issue 4).