Preparation of ultra-and nanoporous glasses and study of their structural and electrokinetic characteristics in 1: 1 electrolyte solutions

Nano-and ultraporous glass membranes with pore radii of 4.5–150 nm are prepared from sodium borosilicate glasses of various compositions. Structural parameters (structure resistance coefficient, volume porosity, and filtration factor) and electrokinetic characteristics (conductivity, counterion transport numbers, and electrokinetic potential ζ _α ^* ) of membranes are determined at various KCl and NaCl solution concentrations (10^?4?10^?1 M) in a neutral pH region. The passage from nano-to ultraporous glasses is accompanied by an increase in |ζ _α ^* | values, which is apparently related to a decrease in the thickness of a gel layer due to the removal of ion-permeable secondary silica from pore channels. The comparison of electrokinetic characteristics of glass membranes (counterion transport numbers, efficiency coefficients, and electrokinetic potentials) measured in NaCl and KCl solutions indicates a higher specificity of K⁺ counterions as compared to Na⁺ ions.     

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.     

Electrokinetic characteristics of initial porous glasses and those modified with titanium- and aluminum-oxide particles

The structural (volume porosity, structural resistance coefficient, and average pore radius) and electrokinetic (specific electrical conductivity, ion-transport numbers, and electrokinetic potential) characteristics of macroporous glass membranes obtained from two-phase sodium-borosilicate glasses with different times of thermal treatment have been studied in solutions of hydrochloric acid and potassium chloride. The properties of the initial membranes have been compared with the characteristics of the same membranes modified by filtering through them suspensions of aluminum- and titanium-oxide nanoparticles with different weight concentrations. It has been shown that, at low degrees of pore channel surface coverage with nanoparticles (<0.1), the structural parameters of the membranes remain almost unchanged. In addition, it has been found that the presence of positively charged nanoparticles on the negatively charged surface increases the surface conductivity and the absolute value of the electrokinetic potential.     

Structural and Electrosurface Properties of Porous Glasses of Various Composition in 1 : 1 Electrolyte Solutions

Complex studies of structural (the specific surface area, the volume porosity, the structural resistance coefficient, and the average pore radius), adsorption and electrokinetic (the electrical conductivity, the ion transport numbers, and the electrokinetic potential) characteristics as functions of pH and the concentration of KCl solution were carried out on porous glasses (PGs) with or without lead oxide and leached under various conditions. It was established that temperature of the leaching solution affects the colloidochemical parameters of PGs, while the addition of salt to the leaching solution exerts practically no influence on the PG behavior. It was shown that the addition of lead oxide results in the formation of membranes with thinner pores and higher surface charge.     

Colloido-chemical characteristics of nanoporous glasses with different compositions in solutions of simple and organic electrolytes. 2. Equilibrium electrochemical characteristics of membranes

The regularities of variations in the electrokinetic potential and surface charge of nanoporous glass membranes with different compositions have been studied as depending on the type of an electrolyte (sodium, potassium, ammonium, tetramethylammonium, and tetraethylammonium chlorides) and the structure of pore space. It has been shown that, in solutions containing specifically sorbed organic counterions, the range of positive values of electrokinetic potential arises due to the superequivalent absorption of counterions in the Stern layer. It has been found that the influence of the specific adsorption of counterions on the electrokinetic potential of porous glasses increases with the amount of secondary silica in the pore space. The effects of the counterion specificity, pore channel sizes, and composition of a porous glass on the value of the surface charge have been analyzed. The absolute value of the surface charge has been shown to significantly increase in the presence of organic counterions in comparison with inorganic ions throughout the examined range of background electrolyte concentrations.     

Low‐voltage efficient electroosmotic pumps with ultrathin silica nanoporous membrane

In this work, an efficient electroosmotic pump (EOP) based on the ultrathin silica nanoporous membrane (u‐SNM), which can drive the motion of fluid under the operating voltage as low as 0.2 V, has been fabricated. Thanks to the ultrathin thickness of u‐SNM (～75 nm), the effective electric field strength across u‐SNM could be as high as 8.27 × 10⁵ V m^?1 in 0.4 M KCl when 1.0 V of voltage was applied. The maximum normalized electroosmotic flow (EOF) rate was as high as 172.90 mL/min/cm²/V, which was larger than most of other nanoporous membrane based EOPs. In addition to the ultrathin thickness, the high porosity of this membrane (with a pore density of 4 × 10¹² cm^?2, corresponding to a porosity of 16.7%) also contribute to such a high EOF rate. Moreover, the EOF rate was found to be proportional to both the applied voltage and the electrolyte concentration. Because of small electrokinetic radius of u‐SNM arising from its ultrasmall pore size (ca. 2.3 nm in diameter), the EOF rate increased with increasing the electrolyte concentration and reached the maximum at a concentration of 0.4 M. This dependence was rationalized by the variations of both zeta potential and electrokinetic radius with the electrolyte concentration.     

Electrokinetic Characteristics of Porous Glasses in Solutions of Sodium and Iron(III) Chlorides

The structural (structural resistance coefficient, bulk porosity, average pore radius, and specific surface area) and electrokinetic (surface conductivity and electrokinetic potential) characteristics of high-silica micro- and macroporous glasses produced from two-phase sodium borosilicate glass have been compared in solutions of an indifferent electrolyte (sodium chloride) and iron(III) chloride containing iron ions, which have a high specificity to silica surfaces. It has been shown that, in the presence of iron ions, the electrokinetic behavior of porous glasses is governed by two factors. First, the superequivalent adsorption of these ions in the Stern layer leads to positive values of the electrokinetic potential, and, second, their mobility in the pore space decreases, thereby resulting in the appearance of equilibrium solution concentration ranges, in which the specific conductivity of a pore solution becomes lower than that of a free solution.     

Colloid chemical characteristics of nanoporous glasses with different compositions in solutions of simple and organic electrolytes. 3. Calculation of electrochemical characteristics of membranes in terms of a homogeneous model

The electrosurface characteristics of nanoporous glass membranes–ion concentrations in pores with taking into account the specificity of counterions, electrokinetically mobile charge, the convective component of pore solution electrical conductivity, electroosmotic mobility of a liquid in the field of streaming potential and ion mobilities in pore space–were calculated within the homogeneous model. The effects of the type of counterion (sodium, potassium, ammonium, tetramethylammonium, and tetraethylammonium ions), solution concentration, glass composition, and pore size on the equilibrium and transport characteristics of membrane systems have been analyzed. A method for the determining of electrolyte activity coefficients in the membranes has been proposed.     

The Effect of Thermal Treatment on the Structural and Electrokinetic Properties of Porous Glass Membranes

The properties of porous glass membranes prepared by acid leaching of sodium borosilicate glasses 8B and 8V and also 8B glass containing small amounts of fluorine and phosphorus (SFP) are comprehensively studied. The effect of the composition and conditions of thermal treatment of the original and porous glasses on their structural (specific surface area, structure resistance coefficient, average pore radius, volume porosity, and filtration factor) and electrokinetic characteristics (conductivity, counterion transport numbers, and electrokinetic potential) in KCl solutions at neutral pH values is studied. It is shown that an increase in thermal treatment temperature T _TT of the porous glasses from 120 to 750°C leads to a decrease in structure resistance coefficient β of 8B membranes. For membranes prepared from SFP glass, β values, efficiency coefficients, and counterion transport numbers are virtually independent of T _TT at 120–600°C and increase at T _TT = 750°C. Specific surface area and volume porosity decrease with a rise in T _TT for all studied membranes. The observed regularities of variations in the membrane characteristics are explained by the increasing fraction of large pores because of sintering of small pores with an increase in T _TT and by the different amounts of secondary silica in the pore space of porous glasses.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 299–307.Original Russian Text Copyright © 2005 by Volkova, Ermakova, Sidorova, Antropova, Drozdova.     

Investigation of the interaction of a polyelectrolyte with low molecular weight electrolytes containing nonidentical counterions by differential refractometry

If the counterion of a polyelectrolyte is not identical with any of the ions of a low molecular weight electrolyte added to the solution, the system may be regarded as a four-component system. Relations for the refractive index increments have been derived which allow the determination of the coefficient of selective sorption of the added electrolyte from the refractive index increments of the components independent of the original counterion of the polyelectrolyte. Equilibrium dialysis and differential refractometry were used to study the interaction of KCl, KBr and NaI with poly[-1(2-hydroxyethyl)pyridiniumbenzenesulfonate methacrylate] or with an analogous polymer containing a toluenesulfonate counterion in aqueous solutions. The coefficient of selective sorption increases in the series Cl^? < Br^? < I^? from strongly negative to strongly positive values; the specific interaction of these counterions with the macroion increases in the same order.     

静电位阻模型在纳滤膜跨膜电位解析中的应用

采用静电位阻模型对纳滤膜的跨膜电位进行了理论解析, 考察了溶液体积通量密度、原料液浓度、阴阳离子扩散系数比、膜孔半径和膜体积电荷密度对KCl(1-1型电解质)和MgCl2(2-1型电解质)中的纳滤膜跨膜电位的影响. 研究结果表明, 随着通量密度的增大, KCl和MgCl₂的跨膜电位线性程度增强; 两种电解质的跨膜电位均随着原料液浓度和膜孔半径的增大而下降; 在不同的考察范围内, 阴阳离子扩散系数比对1-1型和2-1型电解质的跨膜电位的影响差别较大; KCl的跨膜电位随着膜体积电荷密度的变化关于零点呈现出对称性, 而MgCl₂的跨膜电位零点则出现在膜体积电荷密度为负的条件下.     

Structure and Electrosurface Properties of Porous Glasses with Different Compositions in KCl and NaCl Solutions

For porous glasses with and without small amounts of fluorine and phosphorus, structural (specific surface area, structure resistance coefficient, and mean pore radius) and electrosurface characteristics (adsorption of potential-determining ions, conductivity, counterion transport numbers, and electrokinetic potential) in sodium and potassium chloride solutions are compared. Results of measuring the equilibrium and transport characteristics of membranes are used to calculate the constants of surface reactions and adsorption potentials of ions within the framework of the 2-pK model of oxide surface charging. Within the framework of the homogeneous model, electrochemical characteristics of porous glasses, namely, concentrations of co- and counterions in a pore-confined liquid, Donnan potentials, convective component of the conductivity of a pore-confined solution, and mobility of counterions in the membranes, are calculated.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 342–351.Original Russian Text Copyright © 2005 by Ermakova, Medvedeva, Volkova, Sidorova, Antropova.     

Irreversible adsorption of latex particles on fibrinogen covered mica

Physicochemical properties of bovine plasma fibrinogen (Fb) in electrolyte solutions were characterized. These comprised the diffusion coefficient (hydrodynamic radius), determined by the DLS method, electrophoretic mobility and the isoelectric point. The hydrodynamic radius of Fb was 12 nm for pH<5. The number of uncompensated (electrokinetic) charges on the protein N _c was calculated from the electrophoretic mobility data. It was found that for pH<5.8 the electrokinetic charge was positive, independently of the ionic strength and negative for pH>5.8. For pH=3.5 the value of N _c , was 26 for 10^?3 M. Similar electrokinetic measurements were performed for the mica substrate using the streaming potential cell. It was shown that for pH=3.5 and 10^?3 M, the zeta potential of mica remained negative (?50 mV). This promoted an irreversible, electrostatically driven adsorption of Fb, which was confirmed in experiments carried out under diffusion-controlled transport. The surface concentration of Fb on mica was determined directly by AFM counting. By adjusting the time of adsorption, Fb monolayers of desired coverage were produced. Independently, the presence of Fb on mica was determined quantitatively by the colloid enhancement method, in which negatively charged latex particles were used, having the diameter of 800 nm. It was found that for Fb coverage below 0.05 the method was more sensitive than other indirect methods. The experimental data obtained in latex deposition experiments were adequately interpreted in terms of the random site model used previously for polyelectrolytes. It was shown that adsorption sites consisted of a cluster of two Fb molecules. It was concluded that the colloid enhancement method can be successfully used for detecting the presence of proteins at solid substrates and to determine the uniformity of monolayers in the nanoscale.     

A radioanalytical phantom for assessing the efficacy of electrokinetic decontamination of entrained radioactivity within concrete media

A phantom for the evaluation of electrokinetic remediation of radioactive species from water saturated concrete is described. The phantom has been designed to be a general analogue for environments where structural concrete is saturated by radioactive aqueous solutions and where electrokinetic remediation may be deployed. It is also a specific analogue for the walls of storage ponds for legacy spend nuclear fuel pins where the pond water comprises a large volume of hazardous active waste that may penetrate the pond wall. The fabricated phantom was evaluated using a fixed electrical potential to monitor the rate of cationic transport of K⁺ through concrete samples of different thickness (20 and 35 mm respectively). Results of the evaluation show K⁺ diffusion coefficients of 5.20 × 10^?13 and 7.61 × 10^?13 m² s^?1 for the 20 mm and 35 mm samples, consistent with those seen in literature for the transport of caesium through concrete of similar thickness. The phantom offers a means of experimental validation of computational electrokinetic models as well as providing a basis to test the effects of electrode material on ionic transport rates, to interrogate the effects of pH on all components of the system, and as a basis for instruction, education and training in nuclear decommissioning and waste treatment.     

Effects of solvent and counterion on ion pairing and observed charge states of diquaternary ammonium salts in electrospray ionization mass spectrometry

Two diquaternary ammonium chloride salts have been used to examine the roles of solvent and counterion in determination of the degree of ion pairing in solution and the resultant charge state distributions in electrospray ionization mass spectrometry (ESI-MS). Three series of solvents, that is, alcohol, polar aprotic, and chlorinated solvents, have been employed to test the influence of solvent polarity and other parameters on the desorption behavior of diquaternary ammonium ions observed in ESI-MS. Solvents of higher polarity were found to yield gas-phase ions of higher charge states, in accordance with their reduced tendency toward ion pairing in solution. Counterion effects were investigated via the following approaches: (1) increase the diquaternary ammonium salt concentration; (2) increase the concentration of an external electrolyte that contained the common counterion Cl^?; (3) replace Cl^? with trifluoroacetate (TFA_c ^?); (4) increase the concentration of an external electrolyte that contained TFAc^?. These experiments indicate that variation of the specific counterion employed alters the degree of influence that the counterion exerts (via ion pairing) on electrospray ionization mass spectra. Increasing amounts of trifluoroacetate ions in a variety of solvent systems invariably led to a progressive shift of the observed ESI-MS charge states of diquaternary ammonium ions toward lower values.     

Electrokinetic studies on testosterone/aqueous electrolyte interface : Part 1. Electro-osmosis,electrophoresis, streaming potential and streaming current

The electrical properties of testosterone interfaces were investigated. For this purpose, measurements of electro-osmosis, hydrodynamic permeation, streaming potential and streaming currents of metabolically important solutions of the electrolytes NaCl, KCl and MgCl₂ (in the concentration range 10^?4?10^?3 mol/l) across a testosterone plug were carried out. Electrophoretic mobility of testosterone particles suspended in these electrolyte solutions was also studied. The data were analysed from the viewpoint of nonequilibrium thermodynamics. Phenomenological coefficients were evaluated from the linear transport equations and Saxen's relationship was verified. Dependence of phenomenological coefficients on electrolyte concentration was examined. Electro-osmotic and electrophoretic transport coefficients were found to vary linearly with concentration, whereas hydrodynamic permeation and membrane conductance coefficients show non-linear variation. The results are explained on the basis of structural modifications occurring during the passage of the permeating species through the membrane. The nature of the electrical double layer formed at the testosterone/solution interface was ascertained on the basis of the direction of electro-osmotic permeation and electrophoretic migration of testosterone particles.Zeta potentials were estimated in order to obtain a plausible picture of the electrical double layer at the testosterone/solution interfaces. Dependence of zeta potentials on concentration was examined and membrane parameters calculated. The double layer thickness was estimated, which reveals that the diffuse double layer is more compact in the case of MgCl₂ than in that of KCl.     

T-x diagram and transport properties of the GeSe-GeI2 solid electrolyte

The T-x diagram for the GeSe-GeI₂ system was plotted based on DTA, XRD, and conductivity data. The diagram features a simple eutectic and a limited region of solid solutions with prevalent GeSe content. It was established that, in the region of solid solutions, the properties of the GeSe-GeI₂ solid electrolyte are substantially dependent on the concentration of the GeI₂ dopant. The highest conductivity (10^?3?10^?4 S/cm at 150°C), lowest activation energy of electric conduction (0.3–0.4 eV), and lowest electronic (hole) transport numbers (10^?5?10^?7 at 150°C) at high ionic (～1.0) and cationic (0.9–1.0) transport numbers were observed at a GeI₂ concentration of 3–6 mol %. In the two-phase region, the transport properties (conductivity and activation energy of conduction) only slightly depend on the dopant concentration.     

Note on nonaqueous electrokinetic transport in charged porous media

A model for electrokinetic transport in charged capillaries is compared with experiments using nonaqueous lithium chloride solutions. The electrokinetic parameters considered are the pore fluid conductivity and the concentration potential. Methanol/water mixtures were the solvent, and track-etched mica membranes with a well-characterized pore structure were the porous medium. The electrolyte concentrations used were such that the Debye lengths of solutions in pores ranged from much smaller to much larger than the radius of pores. The space-charge model is found to be capable of qualitatively describing the trend of the electrokinetic data, but as expected, at higher concentrations the model fails, probably because the assumption that ion—ion interactions are negligible no longer holds. The experimental results show that the pore fluid conductivity depends strongly on the dielectric constant of the solvent, that the absolute value of the pore wall charge tends to decrease with the lowering of the solvent dielectric constant, and that the wall charge tends to increase with the concentration of the chloride ion.     

Structural and Electrosurface Characteristics of Sulfonated Cation-Exchange Perfluoropolymer Membranes in 1 : 1 Electrolyte Solutions

The equilibrium (the exchange capacity, the structural resistance coefficient, and contact angles) and transport (the conductivity) characteristics of differently obtained sulfonated cation-exchange perfluoropolymeric membranes in 1 : 1 electrolyte solutions were investigated. It was shown that the transformation of membranes from the Na⁺form to the K⁺form sharply decreases their moisture content, which is accompanied by an increase in the structural resistance coefficient and the counterion concentration in membranes. Experimental data were used for calculating the electrochemical characteristics of membranes: efficiency coefficients, ion mobilities and transfer numbers of ions in the intramembrane liquid, as well as Donnan potentials. Measurements of the wettability of fluoroplastic ion-exchange membranes with water and electrolyte solutions showed that the presence of strongly acidic ionogenic groups significantly decreases contact angles as compared with that of the polytetrafluoroethylene surface. It was also established that, for the investigated systems, the contact angle is virtually independent of the composition of the liquid phase.     

A comparison of electrochemical and electrokinetic parameters determined for cellophane membranes in contact with NaCl and NaNO3 solutions

Electrochemical and electrokinetic characterizations of cellophane membrane samples have been carried out by measuring membrane potential, salt diffusion, and tangential streaming potential, which allow the determination of different characteristic membrane parameters. Experiments were made with the membrane samples in contact with NaCl and NaNO(3) solutions at different concentrations and under different external conditions (concentration gradients), in order to obtain differences in transport and membrane characteristic parameters, depending on the electrolyte considered. Salt permeability across the membrane, which was obtained from diffusion measurements, is about twice as high for NaCl solutions as for NaNO(3) solutions, which is attributed to the different sizes of the electrolytes. Membrane potential measurements keeping the concentration ratio constant (C(1)/C(2)=2) were used to determine both the effective fixed charge concentration in the membrane, X(f), and the average value of transport numbers, t(i); taking into account these values, concentration dependence of membrane potential under a different external condition (C(1)=cte=0.01 M, 5 x 10(-3)< or =C(M)< or =5 x 10(-2)) was predicted. Results show that cellophane membrane behaves as a weak cation-exchange membrane and its permselectivity to cations is practically independent of the electrolyte considered. From electrokinetic results, assuming a Langmuir-type adsorption of anions on the cellophane surface, the number of accessible sites per surface unit was obtained, which is higher for Cl(-) than for NO(3)(-), in agreement with the small radii of chlorine ions; however, no significant differences in the specific adsorption free energy were found (DeltaG(Nacl)=-22.0 x 10(3) J/mol) and (DeltaG(NaNO(3))=-23.2 x 10(3) J/mol).