Kinetic Diffusion Coefficients Research Articles

Piezoresistive fibers with record high sensitivity via the synergic optimization of porous microstructure and elastic modulus

Although different kinds of microengineering have been developed in piezoresistive fibers recently, it is still challenging to achieve a high-pressure sensitivity in these fibers. This is because these microstructures can only geometrically increase the conducting paths under pressure. In this work, via the theoretical calculation and practical experiments, we firstly demonstrated that not only the conducting paths but also the fibers’ elastic moduli of compression exhibit key roles in improving the sensitivities in fibers. Typically, by adjusting the kinetic diffusion coefficient between the spinning dope and the coagulation solution in wet-spinning, various structured (solid, hollow, porous, and hollow-porous) thermoplastic polyurethane (TPU) fibers with variable elastic moduli of compression were developed in this work. As a result, the piezoresistive fiber with a uniform and through porous structure (porous in both the core and the surface) exhibited the highest sensitivity of 0.67 kPa−1 due to its synergic improvement in conducting paths and contact area (with a low elastic modulus of compression of 6.98 kPa) under pressure. To the best of our knowledge, it is the recorded highest sensitivity in the piezoresistive fibers. Beyond the pressure sensing, we also proved the as-prepared porous fibers with an ultra-high stretchability of 2110%, a high performance in strain sensing, and a good candidate in humidity and gas sensing. At last, we successfully applied the piezoresistive fibers in our daily life for wearable sensing, demonstrating its high potential in practical application.

The Improved Interfacial and Thermal Stability of Nickel‐Rich LiNi0.85Co0.10Mn0.05O2 Cathode in Li‐Ion Battery via Perovskite La4NiLiO8 Coating

AbstractCapacity attenuation caused by Ni dissolution and interface instability during cycling is a major challenge because it limits the application of high Ni ternary cathode materials in Li‐ion batteries. In this paper, ternary LiNi0.85Co0.10Mn0.05O2 cathode with high nickel content was prepared by co‐precipitation method, and then was coated with perovskite La4NiLiO8 via the simple thermochemical method. The analysis of the images of transmission electron microscope (TEM) showed that the coating is uniformly covered on the surface of NCM85 material with a thickness of 5 nm. Compared to uncoated sample, the La4NiLiO8‐coated LiNi0.85Co0.10Mn0.05O2 material shows lower electrochemical impedance and better cyclic stability, the initial kinetic diffusion coefficient and the interface stability of the prepared material are greatly improved. Meanwhile, the problems of Li+/Ni2+ mixing are also been solved. This work provides a new strategy for improving the interface and thermal stability of the nickel cathode material of Li‐ion battery in the future.

Segregation of an intruder in a heated granular dense gas

A recent segregation criterion [Phys. Rev. E 78, 020301(R) (2008)] based on the thermal diffusion factor Λ of an intruder in a heated granular gas described by the inelastic Enskog equation is revisited. The sign of Λ provides a criterion for the transition between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE). The present theory incorporates two extra ingredients not accounted for by the previous theoretical attempt. First, the theory is based upon the second Sonine approximation to the transport coefficients of the mass flux of the intruder. Second, the dependence of the temperature ratio (intruder temperature over that of the host granular gas) on the solid volume fraction is taken into account in the first and second Sonine approximations. In order to check the accuracy of the Sonine approximation considered, the Enskog equation is also numerically solved by means of the direct simulation Monte Carlo method to get the kinetic diffusion coefficient D(0). The comparison between theory and simulation shows that the second Sonine approximation to D(0) yields an improvement over the first Sonine approximation when the intruder is lighter than the gas particles in the range of large inelasticity. With respect to the form of the phase diagrams for the BNE-RBNE transition, the kinetic theory results for the factor Λ indicate that while the form of these diagrams depends sensitively on the order of the Sonine approximation considered when gravity is absent, no significant differences between both Sonine solutions appear in the opposite limit (gravity dominates the thermal gradient). In the former case (no gravity), the first Sonine approximation overestimates both the RBNE region and the influence of dissipation on thermal diffusion segregation.

Concentration kinetics of intercalation systems

The description of the concentration kinetics in the lattice fluid model used the local equilibrium representation of the distribution function of nonequilibrium states. A set of nonlinear differential-difference equations was formulated to describe the evolution of the concentration field in the system. The calculation of the correlation functions and chemical potentials applied the quasichemical approximation for nonequilibrium states. In the linear approximation, the differential equations were derived for the density region and order parameter, where the former naturally includes the kinetic diffusion coefficient and the latter includes the time of relaxation to the equilibrium state. The initial set of nonlinear difference equations was used to study the processes with high concentration gradients. The examples of these processes include a discharge of intercalation power source and phase stratification, provided that the average density in the system corresponds to unstable state in the field of the condensed-rarefied phase transition.

Ab initio calculation of intrinsic diffusion coefficients for boron in silicon at finite temperatures

By determining the specific diffusion mechanism, the intrinsic diffusion coefficients for B in Si over a wide temperature range are calculated with an effective and reliable ab initio method under the condition of thermodynamics equilibrium. All the variables entering diffusion coefficients in the form of Arrhenius expression are determined. The calculated diffusion parameters and kinetic coefficients show excellent agreement with the accurate measurements. The good agreement between the calculational and experimental data confirms the interstitialcy mechanisms of B diffusion in Si and furthermore provides a straightforward and encouraging method to predict the kinetic diffusion coefficients and other properties of dopant in Si at finite temperatures.

Mass transport of impurities in a moderately dense granular gas

Transport coefficients associated with the mass flux of impurities immersed in a moderately dense granular gas of hard disks or spheres described by the inelastic Enskog equation are obtained by means of the Chapman-Enskog expansion. The transport coefficients are determined as the solutions of a set of coupled linear integral equations recently derived for polydisperse granular mixtures [Garzó, Phys. Rev. E 76, 031304 (2007)]. With the objective of obtaining theoretical expressions for the transport coefficients that are sufficiently accurate for highly inelastic collisions, we solve the above integral equations by using the second Sonine approximation. As a complementary route, we numerically solve by means of the direct simulation Monte Carlo method (DSMC) the inelastic Enskog equation to get the kinetic diffusion coefficient D0 for two and three dimensions. We have observed in all our simulations that the disagreement, for arbitrarily large inelasticity, in the values of both solutions (DSMC and second Sonine approximation) is less than 4%. Moreover, we show that the second Sonine approximation to D0 yields a dramatic improvement (up to 50%) over the first Sonine approximation for impurity particles lighter than the surrounding gas and in the range of large inelasticity. The results reported in this paper are of direct application in important problems in granular flows, such as segregation driven by gravity and a thermal gradient. We analyze here the segregation criteria that result from our theoretical expressions of the transport coefficients.

Statistical mechanical description and Monte Carlo simulation of diffusion in two-component lattice systems

Two different approaches based on linear response theory are considered in this paper. One of them results in quite general and exact expressions for kinetic diffusion coefficients in terms of mean square particle displacements that do not explicitly use any information concerning lattice gas dynamics or interparticle interactions. Relations between kinetic and chemical diffusion coefficients are considered as well. The other approach invokes the lattice gas master equation. It leads to a representation of the kinetic diffusion coefficient as a sum of static and memory-dependent terms. For the former, a closed form expression is derived in the case of thermally activated particle jumps in the model of traps. On this basis, the thermodynamic and memory aspects of multicomponent diffusion are considered. Monte Carlo (MC) simulation and calculation results are discussed. It is shown that memory effects are more pronounced as compared to one-component systems.

Statistical–mechanical description of diffusion in interacting lattice gases

A Mori-type equation for the lattice concentration of an interacting lattice gas is constructed on the basis of the master equation in the framework of the nonequilibrium statistical ensemble method due to Zubarev. The general expression for the diffusion coefficient, which takes into account particle jumps of arbitrary length, spatial dispersion and memory effects is derived. In contrast to systems with reversible dynamics the relevant or quasiequilibrium distribution significantly contributes to the diffusion coefficient. This contribution is represented by two cofactors, namely the kinetic diffusion coefficient and the correlation function of concentration fluctuations. For lattice gases with thermally activated hopping dynamics in hydrodynamic (zero frequency and long wave) limit the former is reduced to Zhdanov's form that reflects an important role of equilibrium characteristics, i.e. the chemical potential and the two-site vacancy distribution function. The self-consistent diagram approximation is used to evaluate these characteristics for a two-dimensional lattice gas with nearest-neighbor attractive interaction on a square lattice. Results for the diffusion coefficient coincide within a few per cent with Monte-Carlo simulation data.

A Molecular Dynamical Study of the Mutual Diffusion Coefficient and Cooperative Motion in a 2-Dimensional Aqueous Solution

Abstract Constant-temperature constant-pressure molecular dynamics simulations of a two-dimensional aqueous solution-like system are performed at many temperatures under a constant pressure. The total number of molecules in the system is 576, and the mole fraction of the solute is 0.5. The mutual diffusion coefficient, the kinetic diffusion coefficient, and the velocity correlation between different molecules are thus obtained. The reduced kinetic diffusion coefficient has a maximum at an intermediate temperature under a constant pressure. This feature is consistent with the temperature dependence of the mean-square-concentration fluctuations. The lifetime of the local structure is estimated from the cross-correlation function of displacement, which is computed from the time-averaged configurations, where the average period is several times longer than the velocity-autocorrelation time. The correlation length of the local concentration fluctuations is obtained and compared with the snapshots of the configurations at several temperatures. The dynamical properties are qualitatively in agreement with those of an alcohol–water mixture.

The Enskog theory for multicomponent mixtures. III. Transport properties of dense binary mixtures with one tracer component

The transport properties of dense binary fluid mixtures with one tracer component are discussed in the context of the revised Enskog theory (RET). Except for the mutual and thermal diffusion coefficients, the transport coefficients are those of the excess component alone. The kinetic diffusion coefficient is given exactly by its low density (Boltzmann) value divided by the magnitude of the radial distribution function at contact. The values of the mutual and thermal diffusion coefficients can be estimated to within 1% for all mass ratios μ. A comparison with earlier work on the limiting cases of the Rayleigh ( μ=∞) and Lorentz ( μ=0) gases is made.

Light scattering measurement and theoretical interpretation of mutual diffusion coefficients in binary liquid mixtures

Mutual diffusion coefficients for eleven binary systems of simple organic liquids have been measured by laser light scattering. By separating the mutual diffusion coefficient into a kinetic diffusion coefficient and a thermodynamic factor, we have been able to analyze the dynamical information contained in the kinetic coefficient in terms of a simple hard sphere theory of molecular motion. The hard sphere model of the kinetic diffusion coefficient is shown to be accurate for ideal and moderately nonideal solutions, and for both spherical and very nonspherical molecules. Only for extremely nonideal solutions were we unable to interpret diffusion coefficient data by our methods of analysis.