On the application of concentrated solution theory to the forced convective flow of excess supporting electrolyte

A recent model for electrolysis with forced convection in a channel and an excess of dilute supporting electrolyte is extended using concentrated solution theory. Mean Spherical Approximation theory is used to calculate the necessary Onsager coefficients and ionic activities. Using asymptotic methods, we demonstrate the surprising similarities between the leading order equations for the dilute and concentrated theories. In addition, in deriving the extension, certain omissions in the original work are highlighted: an oversight in the Butler-Volmer law used in the original work is corrected, and the systematic use of similarity-like variables in electrochemical problems that do not have a similarity solution along the entire length of the diffusion layer adjacent to an electrode is demonstrated. This helps to explain the manner in which the solutions for the anode and cathode boundary layers and the bulk region decouple from each other at limiting current, enabling a much simpler solution strategy.     

电化学双电层电容器动态模拟：离子尺寸及扩散系数的优化

电化学双电层电容器的低能量密度限制了其在储能动力等领域的应用,而有机电解液作为提升器件能量密度的关键因素,研究其导电电解质的特性具有重要的意义。通过构建电化学双电层电容器的动态模型,模拟了电化学双电层电容器的循环伏安曲线,并定量探究和解析了离子溶剂化尺寸和扩散系数对电容性能的影响。模拟结果表明：在低扫描速率情况下,电容性能主要受控于双电层结构特性,比电容随着离子溶剂化尺寸的减小而增大,而离子扩散系数对其电容性能没有影响;在高扫描速率情况下,电容性能会受控于离子传质过程,比电容随着离子溶剂化尺寸和离子扩散系数的增大而增大。并基于模拟计算和分析结果提出了理性设计和优化电化学双电层电容器的策略。     

Ion-cement hydrate interactions govern multi-ionic transport model for cementitious materials

The main objective of this investigation is to describe the interaction between cement hydrates and electrolyte solution to understand multi-ionic transport in cementitious materials. A surface complexation model in PHREEQC including an electrostatic term is used to simulate the ionic adsorption on the calcium silicate hydrate (C–S–H) surface. The equilibrium constants for the adsorption of ions on C–S–H surfaces are obtained by fitting experimental data to the model. The adsorption of both divalent and mono-valent cations, and also anions significantly changes the surface charges of hydrated paste. Chloride is being held in a chemical binding as Friedel's salt and bound mainly by the adsorptive action of C–S–H. An integrated modelling approach employing a phase-equilibrium model, a surface complexation model, and a multi-component diffusion model has been developed in PHREEQC to simulate the multi-ionic transport through hydrated cement paste. It was found that the physical adsorption of ions on C–S–H, the size of pores, and the surface site density of C–S–H govern the rate of penetration of ionic species. Finally, the proposed model has been validated against chloride profiles measured in this study as well as with data available in the literature for hydrated cement paste.     

Role of Interfacial Interactions in the Deposition of Colloidal Clay Particles in Porous Media

Colloidal clay particle transport under saturated conditions is believed to be controlled by its interactions with the surrounding environment. The dominating forces among these interactions are electrostatic forces that are determined by colloidal clay particle and porous medium surface charge density and Lifshitz–van der Waals forces that are determined by colloidal clay particle and porous medium surface thermodynamic properties. Electrostatic forces are greatly affected by solution chemistry in terms of solution ionic strength and pH. In this research, electrostatic and Lifshitz–van der Waals forces of natural colloidal clay particles with a model porous medium of silica sand were quantified at different ionic strength and pH conditions. At the same time, colloidal clay particle transport in the model medium of silica sand was conducted in a laboratory column. The maximum electrostatic forces, F ^EL (max), which occurred when the separation distance between colloidal clay particles and the porous medium was in the range of the sum of the double layer thicknesses of the colloidal clay particles and the porous medium, was found to be the determinant factor for colloidal clay particle deposition in the porous medium. Colloidal clay particle desorption in the porous media was related to the net effect of attractive Lifshitz–van der Waals forces and repulsive electrostatic forces, evaluated at the equilibrium distance where physical contact between the colloidal clay particle and silica sand actually occurred (i.e., affix force). Higher colloidal clay particle desorption was found to coincide with smaller affix force values.     

Influence of the solution cation mobility on the water uptake estimation of PVC Plastisol freestanding films by EIS

In this work, the influence of the outer solution cation mobility on the electrochemical behaviour of PVC Plastisol freestanding films was studied. For that purpose, the paint films were immersed in 0.5 M and 0.05 M chloride solutions with different cations (Na⁺, K⁺, Cs⁺). The electrochemical impedance spectroscopy (EIS) was the technique chosen for this study and estimated values of film capacitance and resistance were calculated.

For PVC Plastisol films, it was observed that the ion diffusion depends on the outer solution concentration. To explain such results different mechanisms for the ionic diffusion were considered. For higher concentration solutions the ions of the outer solution must diffuse into the film, while for lower concentration solutions the dissolution inside the film occurs followed by ionic diffusion from the film to the outer solution.

The water uptake was determined by EIS and gravimetry techniques. The Brasher and Kingsbury (BK) and the low frequency solution (LF) models were used to estimate this parameter by the EIS technique. A direct dependency between water uptake and solution concentration was obtained by this technique, while by gravimetry an inverse relation was obtained. However, the LF model presented water uptake values better correlated with the gravimetric ones comparatively to the BK equation. For the more concentrated solutions, the cation mobility influenced the water uptake estimated by EIS, whereas, such dependency was not observed with the gravimetric technique.

The results obtained in this work suggest that the outer solution resistivity and consequently the film resistance influence the water uptake measurements and should take part in any improved model used for water uptake determination.     

Influence of the solution cation mobility on the water uptake estimation of PVC Plastisol freestanding films by EIS

In this work, the influence of the outer solution cation mobility on the electrochemical behaviour of PVC Plastisol freestanding films was studied. For that purpose, the paint films were immersed in 0.5 M and 0.05 M chloride solutions with different cations (Na⁺, K⁺, Cs⁺). The electrochemical impedance spectroscopy (EIS) was the technique chosen for this study and estimated values of film capacitance and resistance were calculated.For PVC Plastisol films, it was observed that the ion diffusion depends on the outer solution concentration. To explain such results different mechanisms for the ionic diffusion were considered. For higher concentration solutions the ions of the outer solution must diffuse into the film, while for lower concentration solutions the dissolution inside the film occurs followed by ionic diffusion from the film to the outer solution.The water uptake was determined by EIS and gravimetry techniques. The Brasher and Kingsbury (BK) and the low frequency solution (LF) models were used to estimate this parameter by the EIS technique. A direct dependency between water uptake and solution concentration was obtained by this technique, while by gravimetry an inverse relation was obtained. However, the LF model presented water uptake values better correlated with the gravimetric ones comparatively to the BK equation. For the more concentrated solutions, the cation mobility influenced the water uptake estimated by EIS, whereas, such dependency was not observed with the gravimetric technique.The results obtained in this work suggest that the outer solution resistivity and consequently the film resistance influence the water uptake measurements and should take part in any improved model used for water uptake determination.     

Diffusion in polyelectrolyte solutions

Diffusion in polyelectrolyte solutions was studied. The mass transfer was determined by an electrochemical technique which involved transport from the fluid to the tube wall. It was found that diffusion behavior depended on the ionic nature of the diffusing species. Neutral molecules showed an increase in diffusion coefficients. This was apparently due to both solvation of solvent molecules and extension of polymer molecules. Ionic diffusing species showed a decrease in diffusion coefficients. The greater the ionic strength, the greater the decrease. The effect was most likely due to ionic interaction with the polyelectrolyte molecules.     

Nomenclature for transport phenomena in electrolytic systems

The document deals with the transport phenomena of importance to electrochemists and electrochemical engineers. In the absence of a report on mass transport at large, the first section presents general definitions of mass flux, of flux density and of phenomonological coefficients, as appearing in the relationships of irreversible thermodynamics, which express the proportionality between the driving forces and the fluxes. the main part is concerned with electrolytic systems, in particular with ideal dilute solutions. Mass transport by diffusion, by convection and by migration of ions under the influence of an electric field is considered. The diffusion coefficient of a species is distinguished from that of an electrolyte. A section is devoted to the transport of charges, including transport numbers, the flow of current through the solution and through the electrode, current efficiency, and current distribution. The report also discusses the precise meaning of concepts related to mass transport, such as the Nernst diffusion layer, mass transport control, interfacial concentrations, concentration overpotential, mass transport coefficients and diffusion potentials. However, the diffusion in solid electrolytes and surface diffusion are not treated.Recommendations for symbols and definitions are given. In many cases, it is endeavoured to clarify by a brief discussion the concept itself.     

Electrically modulated transport of diclofenac salts through hydrogels of sodium alginate,carbopol, and their blend polymers

The electrically modulated transdermal migration of diclofenac sodium (DS), diclofenac potassium (DP), and diclofenac diethylammonium (DD) drugs from the hydrogels of sodium alginate (NaAlg), carbopol (CP), and blends of NaAlg with CP prepared in 2:1, 2:1.5, and 2:2 ratios was investigated. The release of DS, DP, and DD was investigated through excised rat skin to study the effects of viscosity, pH, and the ionic strength of the receptor medium under the influence of an electrical current in a switch‐on and switch‐off mode. A pulsatile pattern of transport was observed that depended on the presence or absence of an electrical current. Drug transport was dependent on the electrical current, the ionic nature of drugs, and the ionic strength of the diffusion medium. Drug transport followed the sequence DS > DP > DD. A decrease in viscosity and an increase in the pH of the hydrogel were observed when an electrical current was applied. CP was more responsive to an electrical stimulus, but the rate of transport was higher for NaAlg. Increasing the amount of CP in the blends increased the electrical responsiveness. The blend hydrogel with a high CP content showed the highest enhancement in drug transport, whereas the NaAlg hydrogel showed the least. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 301–311, 2005     

Charge transport and glassy dynamics in ionic liquids

Ionic liquids (ILs) exhibit unique features such as low melting points, low vapor pressures, wide liquidus temperature ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. As a result, they show promise for use in variety of applications: as reaction media, in batteries and supercapacitors, in solar and fuel cells, for electrochemical deposition of metals and semiconductors, for protein extraction and crystallization, and many others. Because of the ease with which they can be supercooled, ionic liquids offer new opportunities to investigate long-standing questions regarding the nature of the dynamic glass transition and its possible link to charge transport. Despite the significant steps achieved from experimental and theoretical studies, no generally accepted quantitative theory of dynamic glass transition to date has been capable of reproducing all the experimentally observed features. In this Account, we discuss recent studies of the interplay between charge transport and glassy dynamics in ionic liquids as investigated by a combination of several experimental techniques including broadband dielectric spectroscopy, pulsed field gradient nuclear magnetic resonance, dynamic mechanical spectroscopy, and differential scanning calorimetry. Based on Einstein-Smoluchowski relations, we use dielectric spectra of ionic liquids to determine diffusion coefficients in quantitative agreement with independent pulsed field gradient nuclear magnetic resonance measurements, but spanning a broader range of more than 10 orders of magnitude. This approach provides a novel opportunity to determine the electrical mobility and effective number density of charge carriers as well as their types of thermal activation from the measured dc conductivity separately. We also unravel the origin of the remarkable universality of charge transport in different classes of glass-forming ionic liquids.     

DRYING GRANULAR POROUS MEDIA: GRAVITATIONAL EFFECTS IN THE ISENTHALPIC REGIME AND THE ROLE OF DIFFUSION MODELS

In this paper we have examined the influence of gravity on the moisture transport process during the isenthalpic drying period, and we have considered the use of diffusion models both to predict saturation pro- files and to extract apparent diffusivities from experi- mental data. For granular or unconsolidated porous media, the one-dimensional moisture transport process can be characterized by two dimensionless groups that account for capillary forces, gravitational forces and viscous forces. Detailed numerical solutions of the saturation transport equation indicate under what circumstances the diffusion model can be used with confidence, and under what circumstances the diffusion model can be used to predict saturation profiles even though it is an incorrect representation of the moisture transport process. In addition to exploring the predictive capabilities of the diffusion model, we have     

THE TRANSPORT OF CARBON DIOXIDE IN HIGH MOLECULAR WEIGHT BUFFER SOLUTIONS

The diffusion of carbon dioxide in biological media such as tissues and blood is an important physiological phenomenum. Transport of carbon dioxide in aqueous biological media causes, through chemical reactions, the simultaneous flux of several ionic species. The reversible reactions of CO₂ are coupled to amino acid dissociations of the protein species which have a large buffer capability. Due to the great difference in mobility of bicarbonate and protein, a diffusion potential evolves, which has a considerable influence upon the total CO₂ transport in the medium. The electrical potentials impede the carrier-facilitated CO₂transfer associated with the bicarbonate flux. New data on carbon dioxide transport in hemoglobin solutions are presented which clearly show the large reduction of CO₂ transport due to the electrical potentials. The experimental results correlate with diffusion potential data obtained previously. A theoretical model correctly predicts both the CO₂ transport and diffusion potential data as a function of The ionic composition of the solution. It is concluded that applied or electrical fields can have a significant effect on CO₂ transport in reactive biological media.     

Thermodynamics,a good theory for the study of electrochemistry in non-isothermal systems. A specific application: thermal diffusion

We present here a short survey on general non-equilibrium thermodynamics when the external forces are especially of electrostatical nature. Such a development provides a very well-adapted frame to analyse many irreversible processes as thermal diffusion in ionic media. This phenomena, so-called Soret effect in fluid mixtures, has greatly been studied by various experimental methods. Among these, the electrochemical ones give valuable information on quantities such as entropies and heats of transfer.     

Examination of the fundamental relation between ionic transport and segmental relaxation in polymer electrolytes

Replacing traditional liquid electrolytes by polymers will significantly improve electrical energy storage technologies. Despite significant advantages for applications in electrochemical devices, the use of solid polymer electrolytes is strongly limited by their poor ionic conductivity. The classical theory predicts that the ionic transport is dictated by the segmental motion of the polymer matrix. As a result, the low mobility of polymer segments is often regarded as the limiting factor for development of polymers with sufficiently high ionic conductivity. Here, we show that the ionic conductivity in many polymers can be strongly decoupled from their segmental dynamics, in terms of both temperature dependence and relative transport rate. Based on this principle, we developed several polymers with “superionic” conductivity. The observed fast ion transport suggests a fundamental difference between the ionic transport mechanisms in polymers and small molecules and provides a new paradigm for design of highly conductive polymer electrolytes.     

Polylactide (PLA)-Based Electrospun Fibrous Materials Containing Ionic Drugs as Wound Dressing Materials: A Review

The effect of the electrospinning process parameters on the morphology, alignment, and self-organization of the fibers into bundles and/or yarns are outlined. The fabrication of polylactide materials containing ionic drugs by electrospinning is emphasized. The main approaches used for the preparation of electrospun drug-loaded materials: electrospinning of a mixed solution containing the polymer(s) and the drug(s) or dual spinneret electrospinning of separate drug-containing solutions are compared. The latter approach allows the obtaining of drug-loaded fibrous materials while avoiding the drug interaction. The potential application of the obtained materials containing ionic drugs as wound dressings is outlined.     

Chitosan–polyelectrolyte complexation for the preparation of gel beads and controlled release of anticancer drug. II. Effect of pH‐dependent ionic crosslinking or interpolymer complex using tripolyphosphate or polyphosphate as reagent

Chitosangel beads were prepared using an in‐liquid curing method by ionotropic crosslinking or interpolymer linkage with tripolyphosphate (TPP) or polyphosphate (PP). The ionic interaction of chitosan with TPP or PP is pH‐dependent due to the transition of “ladder‐loop” complex structures. Chitosan gel beads cured in a pH value lower than 6 of a TPP solution was a controlled homogeneous ionic‐crosslinking reaction, whereas chitosan gel beads cured in a lower pH PP solution was a nonhomogeneous interpolymer complex reaction due to the mass‐transfer resistance for the diffusion of macromolecular PP. According to the results of FTIR and EDS studies, it was suggested that significantly increasing the ionic‐crosslinking density or interpolymer linkage of a chitosan–TPP or chitosan–PP complex could be achieved by transferring the pH value of curing agent, TPP or PP, from basic to acidic. The swelling behavior of various chitosan beads in acid medium appeared to depend on the ionic‐crosslinking density or interpolymer linkage of the chitosan–TPP or chitosan–PP complex, which were deeply affected by the in‐liquid curing mechanism of the chitosan gel beads. By the transition of the in‐liquid curing mechanism, the swelling degree of chitosan–TPP or chitosan–PP beads was depressed and the disintegration of chitosan–TPP or chitosan–PP beads did not occur in strong acid. The drug‐release patterns of the modified chitosan gel beads in simulated intestinal and gastric juices were sustained for 20 h. These results indicate that the sustained release of anticancer drugs could be achieved due to the variation of the reaction mechanism of a chitosan–polyelectrolyte pH‐dependent ionic interaction. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1093–1107, 1999     

Electrochemical characterization and assessment of performance of zirconium phosphate and zinc modified zirconium phosphate membranes in aqueous sodium chloride solutions

Prepared membranes, zinc-zirconium phosphate (M-1 and M-2) and zirconium phosphate (M-3) were electrochemically characterized by membrane potential and membrane conductance measurements using aqueous sodium chloride solution of varying compositions. The data have been used for the estimation of transport number of ions and solvent in the membrane phase in addition to permselectivity and membrane fixed charge density. Membrane conductance data were used to estimate the ionic permeability and verify diffusion controlled criteria endowed with the membrane phase. Solute and co-ion permeabilities were compared and found that their values were comparable. Solute rejection of membranes was examined for limiting and intermediate cases of solute–solvent interaction in the membrane phase along with positional solute rejection. Zirconium phosphate membrane showed considerable polarization index deviation from unity indicates its minor perspective than zinc-zirconium phosphate membrane. Results show that zinc modified zirconium phosphate membranes reflected modified elastic properties than zirconium phosphate membrane. The well-known Teorell–Meyer–Sievers (TMS) theory, which describes the membrane potential for charged membranes, was considered as a frame work.     

Transport phenomena in electrolyte solutions: Nonequilibrium thermodynamics and statistical mechanics

The theory of transport phenomena in multicomponent electrolyte solutions is presented here through the integration of continuum mechanics, electromagnetism, and nonequilibrium thermodynamics. The governing equations of irreversible thermodynamics, including balance laws, Maxwell's equations, internal entropy production, and linear laws relating the thermodynamic forces and fluxes, are derived. Green–Kubo relations for the transport coefficients connecting electrochemical potential gradients and diffusive fluxes are obtained in terms of the flux–flux time correlations. The relationship between the derived transport coefficients and those of the Stefan–Maxwell and infinitely dilute frameworks are presented, and the connection between the transport matrix and experimentally measurable quantities is described. To exemplify the application of the derived Green–Kubo relations in molecular simulations, the matrix of transport coefficients for lithium and chloride ions in dimethyl sulfoxide is computed using classical molecular dynamics and compared with experimental measurements.     

Ag(I)/Ag electrode reaction in amide-type room-temperature ionic liquids

Ag(I)/Ag electrode reaction was investigated in some amide-type room-temperature ionic liquids composed of different cations. The morphology of silver deposits and the electrochemical behavior were not sensitive to the difference in the cations of ionic liquids. On the other hand, it was suggested that the adsorption of bis(trifluoromethylsulfonyl)amide (TFSA⁻) is more important for electrodeposition of silver in both ionic liquids and aqueous solutions. The diffusion coefficients of silver cation in the ionic liquids indicated the silver cation is surrounded by TFSA⁻ to form a bulky species. The rate of crystal growth of silver particles in the ionic liquids by electrochemical Ostwald ripening was much slower than that in a nitrate aqueous solution, suggesting the charge transfer in the ionic liquids is slower than that in the aqueous solution.