Analytical theories of transport in concentrated electrolyte solutions from the MSA

Ion transport coefficients in electrolyte solutions (e.g., diffusion coefficients or electric conductivity) have been a subject of extensive studies for a long time. Whereas in the pioneering works of Debye, Hückel, and Onsager the ions were entirely characterized by their charge, recent theories allow specific effects of the ions (such as the ion size dependence or the pair association) to be obtained, both from simulation and from analytical theories. Such an approach, based on a combination of dynamic theories (Smoluchowski equation and mode-coupling theory) and of the mean spherical approximation (MSA) for the equilibrium pair correlation, is presented here. The various predicted equilibrium (osmotic pressure and activity coefficients) and transport coefficients (mutual diffusion, electric conductivity, self-diffusion, and transport numbers) are in good agreement with the experimental values up to high concentrations (1-2 mol L(-1)). Simple analytical expressions are obtained, and for practical use, the formula are given explicitly. We discuss the validity of such an approach which is nothing but a coarse-graining procedure.     

Comparative investigations of ion-exchange membranes

The equilibrium and transport properties (conductivity, transport number, diffusion) of crosslinked ionomer membranes based on sulfinated and sulfonated PSU in aqueous solutions of HCl, NaCl and KCl have been investigated and compared with a Nafion 117 membrane. It has been found that these membranes are more compact and their conducting paths are of smaller dimension than that of the Nafion 117. The influence of length of crosslinking chain, changing from –(CH₂)₄– to –(CH₂)₁₂–, is particularly indicated by the diffusion coefficients; the conductivity and transport numbers of counterions are influenced only slightly. Practically no dependence of this effect on the transport number of H⁺ has been found.     

Verification of a capillary model for the electroosmotic transport of a free solvent in ion-exchange membranes of different natures

It has been shown that the transport of a free solvent through ion-exchange membranes of different structural types in NaCl solutions can be calculated within the framework of the capillary model for electroosmotic transport on the basis of data on pore-radius distribution, exchange capacity, internal specific surface area, and concentration dependences of membrane electrical conductivity. The electrolyte-solution concentration range has been determined in which the convergence is observed between the data calculated in terms of the model and the results of the independent experimental determination of the numbers of water transport through the membranes. The fraction of through pores in the structure of an ion-exchange membrane has been found, and it has been shown that this fraction depends on the structural type of a polymer film alone.     

Electrochemical characterization of an asymmetric nanofiltration membrane with NaCl and KCl solutions: influence of membrane asymmetry on transport parameters

Electrochemical characterization of a nanofiltration asymmetric membrane was carried out by measuring membrane potential, salt diffusion, and electrical parameters (membrane electrical resistance and capacitance) with the membrane in contact with NaCl and KCl solutions at different concentrations (10(-3)< or =c(M)< or =5 x 10(-2)). From these experiments characteristic parameters such as the effective concentration of charge in the membrane, ionic transport numbers, and salt and ionic permeabilities across the membrane were determined. Membrane electrical resistance and capacitance were obtained from impedance spectroscopy (IS) measurements by using equivalent circuits as models. This technique allows the determination of the electrical contribution associated with each sublayer; then, assuming that the dense sublayer behaves as a plane capacitor, its thickness can be estimated from the capacitance value. The influence of membrane asymmetry on transport parameters have been studied by carrying out measurements for the two opposite external conditions. Results show that membrane asymmetry strongly affects membrane potential, which is attributed to the Donnan exclusion when the solutions in contact with the dense layer have concentrations lower than the membrane fixed charge (X(ef) approximately -0.004 M), but for the reversal experimental condition (high concentration in contact with the membrane dense sublayer) the membrane potential is practically similar to the solution diffusion potential. The comparison of results obtained for both electrolytes agrees with the higher conductivity of KCl solutions. On the other hand, the influence of diffusion layers at the membrane/solution interfaces in salt permeation was also studied by measuring salt diffusion at a given NaCl concentration gradient but at five different solutions stirring rates.     

Structural and Electrosurface Properties of Iron-Containing Porous Glasses in NaCl Solutions. I. Structural and Transport Characteristics of Porous Glasses

The structural (structural resistance coefficient, volume porosity, average pore radius, and specific surface area) and transport (specific electrical conductivity and counterion transport numbers) characteristics of high-silica micro- and macroporous glasses with different compositions (magnetite-free and magnetite- containing glasses) have been compared in solutions of an indifferent electrolyte (sodium chloride). It has been shown that the incorporation of iron(III) oxide into basic sodium-borosilicate glass changes the structure of the pore space of both microporous glasses produced by acidic leaching and macroporous glasses obtained from the microporous samples by additional alkaline treatment. Moreover, it has been found that the transport characteristics of microporous glasses with different compositions are similar, while, for magnetite- phase-containing macroporous glasses, the specific conductivity of a pore solution and counterion transport numbers are increased.     

Electrical conductivity of graphite suspensions in potassium chloride solutions in direct- and alternating-current electric fields

Electrical conductivity of graphite dispersions in aqueous KCl solutions has been measured. The measurements have been performed in alternating- (1000 Hz) and direct-current electric fields. In an alternating-current electric field, at electrolyte concentrations of 0.0005–0.01 М, the conductivity increases as depending on the mass fraction of the dispersed phase. In 0.1 М solutions, a decrease in the conductivity of the suspension is followed by an increase at dispersed phase contents of higher than 15 wt %. In a direct-current electric field, the conductivity of graphite suspensions (0.001–0.01 М KCl) varies slightly and increases at dispersed phase contents of higher than 15 wt %. In 0.1 М solutions, the specific conductivity of the suspension initially decreases and, then, increases at dispersed phase concentrations above 15 wt %. The unusual electrical properties of the suspensions have been explained as being results of variations in the capacitive and active components of the conductivity of graphite dispersions in electrolytes within the framework of a topological model. Particle polarization and a relatively high capacitive component of the conductivity mainly contribute to an increase in the conductivity of the suspensions in 0.0005–0.01 М electrolytes in the alternating-current electric field. A decrease in the conductivity of suspensions in 0.1 М electrolytes is due to a negative difference between the capacitive and active components of the specific conductivity. It has been assumed that the aggregation of graphite particles yields conducting structures at dispersed phase concentrations above 15 wt %.     

Determination of the ascorbate content of photographic developer solutions using miniaturised isotachophoresis on a planar chip

The use of miniaturised isotachophoresis, performed on a planar poly(methyl methacrylate) device with integrated platinum conductivity electrodes, for the analysis of the ascorbate content of photographic developer solutions has been investigated. An electrolyte system has been developed which enabled the analysis to be made without interference from any of the other components in the developer solution, a number of which were present at significantly higher concentrations than that of the ascorbate ions. Using this system, the ascorbate content of the developer solutions could be analysed in under 6 min. The limit of detection for ascorbate using miniaturised isotachophoresis was calculated to be 0.011 mmol dm(-3).     

Colloido-chemical characteristics of porous glasses with different compositions in KNO3 solutions. 1. Structural and electrokinetic characteristics of membranes

The structural (specific surface area, liquid-filtration coefficient, average pore radius, volume porosity, and structural-resistance coefficient) and electrokinetic (counterion transport numbers, specific electrical conductivity, and electrokinetic potential) characteristics of porous glasses with different compositions have been determined in potassium nitrate solutions with concentrations of 10^?3–10^?1 M. All the membranes under investigation have been shown to exhibit the dependences of efficiency coefficients and counterion transport numbers on electrolyte concentration and pore size that are predicted by the theory of an electrical double layer. It has been established that, at a constant electrolyte concentration, the absolute values of electrokinetic potential increase with the average pore radius because of variations in the slipping-plane position.     

New ion exchange membrane derived from sulfochlorated polyether sulfone for electrodialysis desalination of brackish water

The purpose of this work is to study the desalination of brackish water using a new ion exchange membrane, made from sulfochlorated polyethersulfone (Cl‐PES), and crosslinked using aminated polyethersulfone (NH2‐PES) as a crosslinking reagent. This membrane, named ClNH2 membrane, has been obtained by reaction between Cl‐PES with 1.3 SO₂Cl groups per monomer unit and 0.2 equivalent amount of NH2‐PES. ClNH2 membrane has been characterized in terms of contact angle, transport number, intrinsic conductivity, and water uptake (as a function of temperature). Electrodialysis performances of the newly synthetized membranes have been measured using an electrodialysis cell at a laboratory scale and compared to commercial membranes. All the experiments have been performed using synthetic brackish water solutions prepared from sodium chloride salts with different concentrations (varying from 0.5 to 5.0 g/L). The concentration of different water samples obtained has been found to be below the amount recommended by the World Health Organization (WHO) for drinking water.     

Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants 10. Behavior in aqueous solution at concentrations below the critical micellization concentration: an electrical conductivity study

Ion pairing and premicellar association have been often invoked to explain results obtained in studies of aqueous solutions of ionic dimeric surfactants (gemini surfactants), mainly by means of surface tension and electrical conductivity, at concentrations below the critical micellization concentration (cmc). The present work was undertaken in an attempt to find out under which conditions these effects come into play. For this purpose the electrical conductivity of solutions of many dimeric surfactants of the type spacer-alpha,omega-bis(alkyldimethylammonium bromide) have been measured. The alkyl chain contained m=10-18 carbon atoms. The spacer group was either an alkanediyl with s carbon atoms (m-s-m surfactants) or a xylylene m-xylyl-m surfactants). The results show that ion pairing occurs in solutions of m-s-m dimers with m< or =10, mostly as a result of their high cmc values. The results for 12-s-12 dimers with s< or =10 and for 12-xylyl-12 showed no evidence of either ion pairing or premicellar association. Premicellar association was present for 12-s-12 dimers with s> or =12, for m-8-m dimers with m> or =14, and for 16-xylyl-16. It showed through a positive curvature of the specific conductivity versus concentration plot and the presence of a maximum in the equivalent conductivity vs (concentration)(0.5) plot at concentrations below the cmc. The free energy associated with the premicellar association of m-8-m dimers has been estimated from the available cmc and micelle ionization degree data.     

Comparison of three methods for the determination of the electrical conductivity of ion-exchange polymers

The development of ion-exchange membranes techniques using an electrical potential gradient incite often to define the electrical conductivity of this category of functional polymers. The investigation methods of this conductivity did not stop to vary, to such a point that some results can be contradictory. So we have determined this dynamic characteristic in comparing three recent methods. This has been done with three ion-exchange membranes often used in industrial applications: CM1 and CM2, made from sulfonated and crosslinked polystyrene, and Nafion^® 117 made from sulfonated uncrosslinked polytetrafluoroethylene. Measurements were achieved in sodium chloride solutions, at concentrations from 0.1 to 2 mol l⁻¹. The results show, whatever the polymer microstructure, non-negligible disparities between the three methods.     

Reformulating the permselectivity-conductivity tradeoff relation in ion-exchange membranes

Polymer membranes used in separation applications exhibit a tradeoff between permeability and selectivity. That is, membranes that are highly permeable tend to have low selectivity and vice versa. For ion-exchange membranes used in applications such as electrodialysis and reverse electrodialysis, this tradeoff is expressed in terms of membrane permselectivity (i.e., ability to selectively permeate counter-ions over co-ions) and ionic conductivity (i.e., ability to transport ions in the presence of an electric field). The use of membrane permselectivity and ionic conductivity to illustrate a tradeoff between counter-ion throughput and counter-ion/co-ion selectivity in ion-exchange membranes complicates the analysis since permselectivity depends on the properties of the external solution and ionic conductivity depends on the transport of all mobile ions within a membrane. Furthermore, the use of these parameters restricts the analysis to ion-exchange membranes used in applications in which counter-ion/co-ion selectivity is required. In this study, the permselectivity-conductivity tradeoff relation for ion-exchange membranes is reformulated in terms of ion concentrations and diffusion coefficients in the membrane. The reformulated framework enables a direct comparison between counter-ion throughput and counter-ion/co-ion selectivity and is general. The generalizability of the reformulated tradeoff relation is demonstrated for cation-exchange membranes used in vanadium redox flow batteries.     

Modulating the emission intensity of poly-(9,9-bis(6'-N,N,N-trimethylammonium)hexyl)-fluorene phenylene) bromide through interaction with sodium alkylsulfonate surfactants

The interaction between the cationic HTMA-PFP (Poly-(9,9-bis(6'-N,N,N-trimethylammonium)hexyl-fluorene phenylene) bromide) and oppositely charged sodium n-alkyl sulfonate surfactants of different chain lengths has been studied in DMSO-water solutions (4% v/v) by UV-visible absorption, fluorescence spectroscopy, fluorescence lifetimes, electrical conductivity, and (1)H NMR spectroscopy. Polymer-surfactant interactions lead to complex spectroscopic behaviors which depends on surfactant concentration. At low surfactant concentrations, the observed strong static fluorescence quenching of fluorescence seems to be associated with formation of aggregates between polymer chains neutralized through interaction with surfactants. This is supported by conductivity and by analysis of absorption spectra deconvoluted at each surfactant concentration using an adapted iterative method. In contrast, above the surfactant critical micelle concentration, there is a strong fluorescence enhancement, leading in some cases to higher intensities than in the absence of surfactants. This is attributed to the transformation of the initially formed aggregates into some new aggregate species involving surfactant and polymer. These changes in HTMA-PFP fluorescence as a function of n-alkyl sulfonate concentration are important for the general understanding of polymer-surfactant interactions, and the aggregates formed may be important as novel systems for applications of these conjugated polyelectrolytes.     

Assessing the selectivity of composite ion-exchange membranes within the framework of the extended three-wire model of conduction

The possibility of assessing the selectivity of composite perfluorated membranes MF-4SK modified with polyaniline (PANI), based on the concentration dependence of their specific conductivity in terms of the extended three-wire model of conduction of ion-exchange materials is investigated. To check the reliability of results obtained, the transport numbers of ions are calculated based on the electrodiffusion coefficients of counter ions and coions determined from concentration dependences of conductivity and diffusion permeability of ion-exchange membranes. The transport numbers of hydrogen ions found by these two methods are shown to coincide with high accuracy throughout the whole range of concentrations of HCl solutions for the original MF-4SK membrane and membranes with the fixed thickness of the modified polyaniline layer on their one side. For the MF-4SK sample the with gradient distribution of polyaniline, which exhibits asymmetrical transport characteristics, the deviation between the transport numbers of ions calculated with the use of electrodiffusion coefficients of counter ions and coions and those determined in terms of the extended three-wire model of conduction is shown to increase with the increase in solution concentration but not exceed 4%.     

Prediction of the Conductance of Strong Electrolytes and the Calculation of the Ionization Constant of Weak Electrolytes in a Dilute Solution by a New Equation

In order to predict the conductance for dilute 1-1 valent electrolyte solutions,a new conductance equation was proposed based on the Onsager and Onsagar-Fuoss-Chen conductance equation.It has only one parameter A,which can be obtained directly from the data of ionic limiting molar conductivity Λ∞m,and its expression is very simple.The new equation has been verified by the experimental molar conductivities of some single strong electrolyte and mixed electrolyte solutions at 298.15 K reported in literatures.The results are in good agreement with the experimental data.Meanwhile the ionization constants of some weak electrolyte solutions were calculated by a modified equation of this new equation,and it was also found that the calculation results are in good agreement with the data in the literature.     

The influence of the concentration and size of silver nanoparticles on the conductivity of ring-shaped deposits resulting from evaporation of colloidal solution droplets

The conductivity of ring-shaped deposits formed at the periphery of evaporating droplets of silver nanoparticle colloidal solutions has been studied. The dependence of the resistance of the ring-shaped deposits on nanoparticle size has been shown to exhibit a percolation transition. The specific conductivity of the deposits has been estimated in relation to their geometric shapes. The conductivity has been established to nonmonotonically depend on nanoparticle sizes. It has been noted that, in rather strong fields, the conductivity of the composite layers dramatically increases after some induction period. The X-ray spectra of silver have been revealed to alter for samples the conductivity of which has increased under the action of an external electric field.     

Effects of concentration, relative permittivity, and temperature on the solution behavior of sodium carboxymethylcellulose as probed by electrical conductivity

Precise measurements on the electrical conductivity of solutions of sodium salt of carboxymethylcellulose in acetonitrile/water mixed-solvent media containing 10, 20, and 40 vol % of acetonitrile are reported as a function of temperature. The degree of substitution of carboxymethylcellulose used was 0.70, and the concentrations were varied from approximately 1 x 10(-4) to approximately 1 x 10(-2) equiv L(-1). The results showed a decrease in the equivalent conductivity with increasing polyelectrolyte concentration. The applicability of Manning's theory for salt-free polyelectrolyte solutions was examined, and a major discrepancy against the theory was observed. The calculated values of the equivalent conductivity deduced on the basis of this theory were found to be higher than the experimental ones. Possible reasons for this discrepancy have been discussed. The fractions of uncondensed counterions were evaluated, and these were found to depend on the polyelectrolyte concentration. The effects of the temperature and relative permittivity of the medium on the equivalent conductivity as well as on the fraction of uncondensed counterions were also investigated.     

传递性质的自由体积模型对方阱流体的应用

对简单分子构成的稀薄气体的传递性质已有较严格的分子动力学理论，但对稠密流体，尤其是液体，严格的理论方法尚难以解决实际问题词．实用中仍以经验或半经验模型为主．半经验模型以Eyring的绝对反应速率理论[1，2]和自由体积理论[3-11]为典型代表．由于自由体积模型可以同时反映温度和压力的影响，其应用潜力更大，值得进一步研究．对理论模型的检验一般用实际物系的测定数据．这种检验虽然直接可靠，但往往受到实验条件的限制，例如高温高压；近年来迅速发展的计算机分子模拟为建立和验证理论模型提供了一个有效手段．由于计算机模拟数…     

A thermodynamic study of the aggregation process of oxacillin sodium salt in aqueous solution

The aggregation characteristics of oxacillin in aqueous solutions have been examined by means of conductivity measurements over the temperature range 288.15-313.15 K and by static light scattering measurements at 298.15 K. Two critical concentrations were detected in conductivity and light scattering over the concentration range 0-0.35 mol kg^-1. Light scattering measurements indicate the formation of dimers at the first critical concentration (0.024 mol kg^-1) and the subsequent formation of aggregates with an aggregation number of 8 at the second critical concentration (0.104 molkg^-1). The thermodynamic parameters of aggregation were derived from the critical concentration data using a mass-action model that has been modified for application to systems of low aggregation number. Values for the enthalpy of aggregate formation calculated by this method showed that the aggregation became increasingly exothermic with increasing temperature. The values of the two critical concentrations show that this penicillin, oxacillin, is more hydrophobic than other molecules of similar structure.     

Electrical conduction in olefin oxide polymers

The electrical conductivities in vacuo of poly(ethylene oxide) and two higher olefin oxide polymers have been found to be ～9 orders higher than for other saturated organic polymers. The possibility of ionic transport resulting from the presence of impurities (including water) has been eliminated, and it is proposed that an inherent ionic process is operative, involving the generation of protons and then subsequent transport by a handing-on process. The two general requirements are the presence of proton-accepting atoms (in this case oxygen) in the polymer chains; and proximity to the melting point to ensure adequate chain-mobility. These requirements are met by poly(ethylene oxide), poly(trimethylene oxide), and poly(tetramethylene oxide), which are all close to their melting points at room temperature. poly(methylene oxide), with a melting point of ～180°C., on the other hand, has the low conductivity of a typical insulator.