Chemical Potential Distribution Research Articles

Stacking pattern of multi-layer InAs quantum wires embedded in In 0.53Ga 0.47− xAl xAs matrix layers grown lattice-matched on InP substrate

Multi-layer InAs quantum wires were grown on, and embedded in In 0.53Ga 0.47− x Al x As (with x=0, 0.1, 0.3 and 0.48) barrier/spacer layers lattice matched to an InP substrate. Correlated stacking of the quantum wire arrays were observed with aluminum content of 0 and 0.1. The quantum wire stacks became anti-correlated as the aluminum content was increased to 0.3 and 0.48. The origin of such stacking pattern variation was investigated by finite element calculations of the chemical potential distribution for indium on the growth front surface of the capping spacer layer. It is shown that the stacking pattern transition is determined by the combined effect of strain and surface morphology on the growth front of the spacer layers.

Void Formation Induced by the Divergence of the Diffusive Ionic Fluxes in Metal Oxides Under Chemical Potential Gradients

When metal oxides are exposed to chemical potential gradients, ions are driven to diffusive mass transport. During this transport process, the divergence of ionic fluxes offers the formation/annihilation of oxides. Therefore, the divergence of ionic flux may play an important role in the void formation in oxides. Kinetic equations were derived for describing chemical potential distribution, ionic fluxes and their divergence in oxides. The divergence was found to be the measure of void formation. Defect chemistry in scales is directly related to the sign of divergence and gives an indication of the void formation behavior. The quantitative estimation on the void formation was successfully applied to a growing magnetite scale in high temperature oxidation of iron at 823 K.

D209 LSCF空気極の三次元数値解析による過電圧予測(OS4 水素・燃料電池),動力エネルギーシステム部門20周年,次の20年への新展開)

The overpotential in a three-dimensional La_<1-x>Sr_xCo_<1-y>Fe_yO_<3-δ> (LSCF) cathode structure obtained by a dual-beam focused ion beam-scanning electron microscope is predicted by the lattice Boltzmann method. Gaseous, ionic and electronic transport equations with electrochemical reaction at LSCF/pore boundary are solved with an assumption of local equilibrium in the solid oxide. The gas transport is modeled by a so-called dusty gas model. The numerical simulation is performed under the current density conditions of 0.01, 0.05, 0.1 and 0.2 A/cm^2. The cathode overpotentials predicted by this method agreed well with the experimental results. Three-dimensional chemical potential distributions inside a cathode microstructure are presented. The proposed method can be used for predicting polarization in mixed ionic electronic conductor electrode.

Void Formation in the Growing Scale Induced by the Divergence of the Diffusive Ionic Flux in High Temperature Oxidation of Metals

Voids are frequently generated and dispersed in oxide scales formed in high temperature oxidation of metals. The divergence of ionic flux may play an important role in the void formation in a growing scale. Kinetic equations were derived for describing chemical potential distribution, ionic fluxes and their divergence in the scale. The divergence was found to be the measure of void formation. Defect chemistry in scales is directly related to the sign of divergence and gives an indication of the void formation behavior. The quantitative estimation on the void formation was successfully applied to a growing magnetite scale in high temperature oxidation of iron at 823 K.

Profile of Chemical Potential in Pressure-Driven Membrane Processes Accompanied by Gel-Enhanced Concentration Polarization

A model for distribution of chemical potential and concentration polarization enhanced by gel accumulated on membrane surface has been proposed. It provides distribution of chemical potential and concentration in the liquid phase and within the gel layer. The model allows analyzing the influence of thickness of fouling gel layer on the CP degree, surface concentration and chemical potential. The model is based on the following assumptions: 1. process is accompanied by accumulation of gel layer at membrane surface along with concentration polarization; 2. diffusion layer and deposited gel consist of different components and these layers are characterized by different values of diffusivity coefficients; 3. correlation for effective hindered back diffusion coefficient within deposited layer is adopted from [Boudreau, Geochim. Cosmochim. Acta, 60, 1996]; 4. transverse transport is based on the following mechanisms: convection due to pressure difference and back diffusion owing to concentration gradient. The following conclusions have been drawn: (A) diffusion resistance within the gel layer is getting dominant and cannot be ignored; (B) In the presence of a gel layer the membrane surface concentration, C1M, is enhanced due to hindered back diffusion of salt ions that in turn, results in growth of osmotic pressure and chemical potential at the membrane surface. It provides elevated salt concentration in permeate and decreases the net driving force; (C) Analysis of calculated data indicates high sensitivity of CP degree to coefficient of hindered back diffusion within gel layer.

Impulsive effect on an elastic solid with generalized thermodiffusion

The theory of generalized thermoelastic diffusion with one relaxation time is employed to study the distribution of temperature, displacement components, stresses, concentration and chemical potential in a semi-infinite medium having an impulsive mechanical load at the origin. Using the joint Laplace and Fourier transforms, the governing equations are transformed into a vector–matrix differential equation which is then solved by the eigenvalue approach. The solution of the problem in the physical domain is obtained numerically using a numerical method for the inversion of the Laplace and Fourier transforms. Results of this work are presented graphically and are compared with the results of generalized thermoelasticity and classical elasticity deduced as special cases.

Plane Strain Deformation in Generalized Thermoelastic Diffusion

The present investigation is concerned with plane strain deformation in homogeneous isotropic generalized thermoelastic diffusion subjected to a normal force, thermal source, and chemical potential source. Laplace and Fourier transform techniques are employed to solve the problem. The integral transform have been inverted by using a numerical technique to obtain the displacements, stresses, temperature distribution, and chemical potential distribution. The numerical results of these quantities are illustrated graphically to depict the response of various sources in the theories of thermoelastic diffusion and thermoelasticity for a particular model. Some particular cases have been deduced from the present investigation.

Trivalent Metal Adsorption Properties on Synthesized Viscose Rayon Succinate

A viscose rayon succinate (VRS) was synthesized using viscose rayon, succinic anhydride and DMSO. The VRS was well characterized by C13 nuclear magnetic resonance, Fourier transform infrared analysis and properties of the VRS up taking trivalent metals from aqueous solution were investigated. Both esterification and carboxyl bonding of the VRS were assigned essentially at 1729 and 1693 cm−1, respectively. And the essential band of bonding between metal and the material was determined at 1605–1639 cm−1. The available adsorption capacity, degree of substitution and pKa of the VRS were 6.2mequiv/g, 2.5 and 3.72, respectively. The adsorption of metal ions on the VRS follows the order of Cr3+>Al3+>Fe3+ with maximum adsorptions capacities 1.48, 1.059 and 1.029 mmol/g. An equilibrium modeling, which is obtained from chemical potential and Boltzmann distribution, was demonstrated trivalent metal adsorption on the VRS in different pHs. Surface potential, Ψ0, an effective ratio of surface equilibrium constants, Keffect, the probability factor P(A) and a degree of protonation, χ represent the physicochemical interactions between carboxyl group and metal ions.

Dynamical behavior of generalized thermoelastic diffusion with two relaxation times in frequency domain

A general solution to the field equations of homogeneous isotropic generalized thermoelastic diffusion with two relaxation times (Green and Lindsay theory) has been obtained using the Fourier transform. Assuming the disturbances to be harmonically time.dependent, the transformed solution is obtained in the frequency domain. The application of a time harmonic concentrated and distributed loads have been considered to show the utility of the solution obtained. The transformed components of displacement, stress, temperature distribution and chemical potential distribution are inverted numerically, using a numerical inversion technique. Effect of diffusion on the resulting expressions have been depicted graphically for Green and Lindsay (G-L) and coupled (C-T) theories of thermoelasticity.

“Chessboard” effect and mass transfer in interfacial media of organic and inorganic nature

The paper reviews our previous research work on the origin of mass transfer through interfaces of solids and biological membranes. Using the thermodynamic approach of physical mesomechanics we conclude that the propagation of transport flows through interfaces and membranes in organic and inorganic nature is based on structural phase transformations in nanostructural states at interfaces of heterogeneous media. Such states arise at interfaces and in membranes under a chessboard-like distribution of stresses, strains and chemical potentials of components of conjugated dissimilar media. The practical applications of the developed approach in biology and modern materials science are considered.

Thermomechanical response of generalized thermoelastic diffusion with one relaxation time due to time harmonic sources

A general solution to the field equations of generalized thermodiffusion in an elastic solid has been obtained, in the transformed form, using the Fourier transform. Assuming the disturbances to be harmonically time dependent, the transformed solution is obtained in the frequency domain. As an application, concentrated and distributed sources have taken to illustrate the utility of the approach. The transformed solutions are inverted numerically, using a numerical inversion technique to invert the Fourier transform. The variations of concentration distribution, chemical potential distribution and effect of diffusion on the normal stress and temperature distribution have been depicted graphically for Lord and Shulman (L–S) and coupled thermoelastic (C-T) theories of thermoelasticity.

Void Formation in Magnetite Scale Formed on Iron at 823 K -Elucidation by Chemical Potential Distribution-

Estimation of void formation in oxide scale is important for predicting exfoliation of the oxide scale. Void formation in magnetite scale formed on iron at 823 K has been elucidated by chemical potential distribution, flux of oxide ion and its divergence. This calculation also estimates a effective diffusion coefficient, which includes both lattice diffusion and grain boundary diffusion in magnetite scale. The resulting effective diffusion coefficients give the quantitative elucidation of the morphology of the magnetite scale. The divergence of oxide ion explains well a position and an amount of void in magnetite scale.

Simulation estimates of cloud points of polydisperse fluids

We describe two distinct approaches to obtaining the cloud-point densities and coexistence properties of polydisperse fluid mixtures by Monte Carlo simulation within the grand-canonical ensemble. The first method determines the chemical potential distribution mu(sigma) (with the polydisperse attribute) under the constraint that the ensemble average of the particle density distribution rho(sigma) match a prescribed parent form. Within the region of phase coexistence (delineated by the cloud curve) this leads to a distribution of the fluctuating overall particle density n, p(n), that necessarily has unequal peak weights in order to satisfy a generalized lever rule. A theoretical analysis shows that as a consequence, finite-size corrections to estimates of coexistence properties are power laws in the system size. The second method assigns mu(sigma) such that an equal-peak-weight criterion is satisfied for p(n) for all points within the coexistence region. However, since equal volumes of the coexisting phases cannot satisfy the lever rule for the prescribed parent, their relative contributions must be weighted appropriately when determining mu(sigma). We show how to ascertain the requisite weight factor operationally. A theoretical analysis of the second method suggests that it leads to finite-size corrections to estimates of coexistence properties which are exponentially small in the system size. The scaling predictions for both methods are tested via Monte Carlo simulations of a polydisperse lattice-gas model near its cloud curve, the results showing excellent quantitative agreement with the theory.

Implications of the detailed fluctuation theorem for the sources of irreversibility in interfacial charge transfer processes

We investigate from basic principles of nonequilibrium statistical mechanics the general reasons why electron transfer across an interface is associated with irreversible elements (resistances) in equivalent circuit modeling. We apply the detailed fluctuation theorem [C. Jarzynski, J. Stat. Phys. 98, 77 (2000)] to a simple model of an interface between two different materials. The elementary transition rates are interpreted in terms of the evolution of a microstate, and obey a ratio that is related to the heat absorbed from the phonon bath while promoting an electron to a higher energy level. The amount of irreversibility (the entropy production), and also the macroscopic current density, can be both obtained with the additional constraint that the system belongs in a particular mesostate, determined by the distribution of chemical and electrostatic potential.

Study of thermodynamic parameters in amphiphilic systems by lattice Monte Carlo: effect of tails and heads

Results from three-dimensional lattice Monte Carlo simulations of amphiphile–solvent mixtures are presented. The chemical potential is derived from the monomer distribution in different clusters rather than using a Widom particle insertion approach. The effect of tail and head characteristics on the non-ideality of these systems, aggregation number, and premicellar phenomena is considered. The aggregation number and CMC behavior of the simulated amphiphilic systems are compared with existing experimental results for non-ionic amphiphiles. Two kinds of polydispersity changing with total concentration of surfactants are observed which are related to phase transition phenomena. Shape variations in clusters are studied by calculating the eigenvalues of the gyration matrix; it is shown that large clusters are non-spherical. With the Maclaurin’s expansion of activity coefficient into volume fraction, the distribution of excess chemical potential with changing aggregation number is considered. Study of the degree of non-ideality of these amphiphiles reveals that asymmetric amphiphiles are characterized by greater non-ideality than symmetric amphiphiles. Goldstein’s parameters are calculated taking non-ideality into consideration. The difference between the phenomenological model and the simulation data is investigated.

Liquid-vapor interface of a polydisperse fluid

We report a grand canonical Monte Carlo simulation study of the liquid-vapor interface of a model fluid exhibiting polydispersity in terms of the particle size sigma. The bulk density distribution, rho0(sigma), of the system is controlled by the imposed chemical potential distribution mu(sigma), the form of which is specified such that rho0(sigma) assumes a Schulz form with associated degree of polydispersity approximately = 14%. By introducing a smooth attractive wall, a planar liquid-vapor interface is formed for bulk state points within the region of liquid-vapor coexistence. Owing to fractionation, the pure liquid phase is enriched in large particles, with respect to the coexisting vapor. We investigate how the spatial variation of the density near the liquid-vapor interface affects the evolution of the local distribution of particle sizes between the limiting pure phase forms. We find [as previously predicted by density-functional theory, Bellier-Castella, Phys. Rev. E 65, 021503 (2002)] a segregation of smaller particles to the interface. The magnitude of this effect as a function of sigma is quantified via measurements of the relative adsorption. Additionally, we consider the utility of various estimators for the interfacial width and highlight the difficulty of isolating the intrinsic contribution of polydispersity to this width.

Fractionation effects in phase equilibria of polydisperse hard-sphere colloids

The equilibrium phase behavior of hard spheres with size polydispersity is studied theoretically. We solve numerically the exact phase equilibrium equations that result from accurate free energy expressions for the fluid and solid phases, while accounting fully for size fractionation between coexisting phases. Fluids up to the largest polydispersities that we can study (around 14%) can phase separate by splitting off a solid with a much narrower size distribution. This shows that experimentally observed terminal polydispersities above which phase separation no longer occurs must be due to nonequilibrium effects. We find no evidence of reentrant melting; instead, sufficiently compressed solids phase separate into two or more solid phases. Under appropriate conditions, coexistence of multiple solids with a fluid phase is also predicted. The solids have smaller polydispersities than the parent phase as expected, while the reverse is true for the fluid phase, which contains predominantly smaller particles but also residual amounts of the larger ones. The properties of the coexisting phases are studied in detail; mean diameter, polydispersity, and volume fraction of the phases all reveal marked fractionation. We also propose a method for constructing quantities that optimally distinguish between the coexisting phases, using principal component analysis in the space of density distributions. We conclude by comparing our predictions to Monte Carlo simulations at imposed chemical potential distribution, and find excellent agreement.

Chemical Potential Distribution and Void Formation in Magnetite Scale Formed in Oxidation of Iron at 823K

Chemical Potential Distribution and Void Formation in Magnetite Scale Formed in Oxidation of Iron at 823K

Capacitance dependence of chemical potential distribution in supported nanoclusters

We investigate the capacitance dependence of the chemical potential distribution of Au nanoclusters supported on hexanedithiol/Au(1 1 1) substrate by scanning tunneling spectroscopy. It is shown that the average of the chemical potentials, which correspond to the electron affinity and the ionization potential of the cluster, distributes around the level nearly equal to the Fermi energy of the grounded substrate. The total capacitance of the clusters towards the environment significantly affects the deviation of the distribution, which becomes smaller with decreasing total capacitance. The analysis in the capacitance range of 0.1 aF–2 aF in detail clearly exhibits the transition in the charge neutrality of the supported clusters.

Physical Chemical Principles of Photovoltaic Conversion with Nanoparticulate, Mesoporous Dye-Sensitized Solar Cells

We review the status of the understanding of dye-sensitized solar cells (DSSC), emphasizing clear physical models with predictive power, and discuss them in terms of the chemical and electrical potential distributions in the device. Before doing so, we place the DSSC in the overall picture of photovoltaic energy converters, reiterating the fundamental common basis of all photovoltaic systems as well as their most important differences.