Transport Properties Of Solutions Research Articles

Transport Properties of Aqueous Solutions of Alkyltrimethylammonium Bromide Surfactants at 25°C

Intradiffusion coefficients, D, of n-alkyltrimethylammonium bromides [CH3–(CH2)n−1–N(CH3)3Br, CnTAB] (n=6, 8, 10, 12) in mixtures with heavy water were measured by the PGSE–NMR technique at 25°C. The experimental data permitted evaluation of the influence of the alkyl chain length on the surfactant self-aggregation process. For all the surfactants considered, the D trend showed a slope change corresponding to the critical micellar composition (cmc). In the premicellar composition range, D decreased linearly with the square root of the surfactant molality. The D values extrapolated at infinite dilution were related to the limiting mutual diffusion coefficients, determined through the Taylor dispersion technique. In the micellar composition range, solubilized tetramethylsilane (TMS) molecules were used to determine the micelle intradiffusion coefficient, DM, from which the aggregate radii and the aggregation numbers were obtained. The decreasing trend of DM with increasing surfactant molality was interpreted in terms of interparticle electrostatic repulsion. DM values allowed evaluation of the Gouy–Chapman layer thickness. The solvent intradiffusion coefficient in the heavy water–CnTAB mixtures, Dw, was also measured. It decreased with increasing surfactant molality. For n=8, 10, 12 the Dw trend presented a slope change at the cmc, which could be ascribed to the strong decrease in hydration of surfactant molecules upon micellization. Because of its short hydrophobic tail, C6TAB exhibited peculiar aggregation behavior. Its cmc, which is poorly marked, is lower than the value predicted by extrapolating the cmc values obtained for the other terms of the series. The C6TAB aggregates do not solubilize TMS molecules; the estimated aggregation number is extremely low (∼3). Finally, no abrupt slope change in the solvent intradiffusion coefficient trend was detected. This evidence suggests that C6TAB molecules do not micellize in aqueous solution, but form trimers in which the surfactant hydrophobic tails are not hidden from contact with water molecules.

Database and models of electrolyte solutions for lithium battery

Transport and thermodynamic properties of electrolyte solutions are very essential for development and design of lithium ion or lithium polymer batteries. An electrolyte database for lithium battery, which includes a quite number of organic solvents, lithium electrolytes and possible by-products (e.g. CO 2), has been compiled. Appropriate models have been evaluated for representing the variety of properties for solvents and electrolyte solutions, such as, conductivity, transference number, diffusivity, dissociation constant and so on. Particular attention has been given on conductivity in this paper, considering its essential importance for battery; several typical examples have been presented and discussed.

Predicting Drying in Multiple-Zone Ovens

In the coating industry, the drying of solvent-coated polymeric films takes place in convected heated dryers, which usually consist of a series of zones. The operating conditions of airflow, solvent partial pressure(s), and temperature at the entrance of each zone are chosen to minimize the drying time while maintaining an acceptable product quality. In this work, the drying behavior of polymer solutions in such oven configurations is predicted from binary and multicomponent drying models. Both models involve coupled heat- and mass-transfer equations that describe the changes in the concentration of each solvent, the temperature, and the thickness of the film throughout the drying. The model equations become highly nonlinear because of the strong and complicated concentration and temperature dependencies of the thermodynamic and transport properties of polymer solutions. These nonlinear equations are solved numerically using the finite difference approximation. The solutions show that multiple-zone ovens ...

A study of solute transport mechanisms using rare earth element tracers and artificial rainstorms on snow

Rare earth element (REE) tracers and three artificial rain‐on‐snow storms at the Central Sierra Snow Laboratory, California indicate that (1) tracers applied to the snow surface immediately prior to the storm quickly appear at the bottom of the pack, with the tracer traversing the pack faster when the snowpack is wetter; (2) unlike most previous studies in which low solute concentrations were observed at high flow in diurnal cycles, the concentrations of the REE tracers in the outflow are positively related with input water flux; and (3) at a constant input flux the concentrations of all the REE tracers decreased exponentially with time, and the rate of this decrease was greater at high flow than at low flow. These observations can be qualitatively simulated by partitioning liquid water in the snowpack into mobile and immobile phases. Transport of the mobile water phase is governed by the advection‐dispersion equations, while the immobile water only moves by exchanging with the mobile water. The rate of exchange between mobile and immobile waters follows first‐order kinetics. Unlike previous mobile‐immobile models for snow, the exchange rate coefficient is assumed to increase exponentially with the effective water saturation. The model successfully simulates the positive concentration dependency on input water flux. However, it remains unclear how the exchange rate coefficient varies with the nature of the medium and with hydrological conditions. These observations suggest that tracer concentrations in the outflow are largely dominated by solute transport via fast flow channels. This surprising result implies that a spatially averaged flow rate may not be adequate for modeling solute transport properties in unsaturated media.

Airway surface liquid osmolality measured using fluorophore-encapsulated liposomes.

The airway surface liquid (ASL) is the thin layer of fluid coating the luminal surface of airway epithelial cells at an air interface. Its composition and osmolality are thought to be important in normal airway physiology and in airway diseases such as asthma and cystic fibrosis. The determinants of ASL osmolality include epithelial cell solute and water transport properties, evaporative water loss, and the composition of secreted fluids. We developed a noninvasive approach to measure ASL osmolality using osmotically sensitive 400-nm-diam liposomes composed of phosphatidylcholine/cholesterol/polyethylene glycol-phosphatidylcholine (1:0.3:0.08 molar ratio). Calcein was encapsulated in the liposomes at self-quenching concentrations (30 mM) as a volume-sensitive marker, together with sulforhodamine 101 (2 mM) as a volume-insensitive reference. Liposome calcein/sulforhodamine 101 fluorescence ratios responded rapidly (< 0.2 s) and stably to changes in solution osmolality. ASL osmolality was determined from calcein/sulforhodamine 101 fluorescence ratios after addition of microliter quantities of liposome suspensions to the ASL. In bovine airway epithelial cells cultured on porous supports at an air-liquid interface, ASL thickness (by confocal microscopy) was 22 microm and osmolality was 325 +/- 12 mOsm. In anesthetized mice in which a transparent window was created in the trachea, ASL thickness was 55 microm and osmolality was 330 +/- 36 mOsm. ASL osmolality was not affected by pharmacological inhibition of CFTR in airway cell cultures or by genetic deletion of CFTR in knockout mice. ASL osmolality could be increased substantially to > 400 mOsm by exposure of the epithelium to dry air; the data were modeled mathematically using measured rates of osmosis and evaporative water loss. These results establish a ratio imaging method to map osmolality in biological compartments. ASL fluid is approximately isosmolar under normal physiological conditions, but can become hyperosmolar when exposed to dry air, which may induce cough and airway reactivity in some patients.

Effects of SNP, ouabain, and amiloride on electrical potential profile of isolated sheep pleura.

The fluid and solute transport properties of pleural tissue were studied by using specimens of intact visceral and parietal pleura from adult sheep lungs. The samples were transferred to the laboratory in a Krebs-Ringer solution at 4 degrees C within 1 h from the death of the animal. The pleura was then mounted as a planar sheet in a Ussing-type chamber. The results that are presented in this study are the means of six different experiments. The spontaneous potential difference and the inhibitory effects of sodium nitroprusside (SNP), ouabain, and amiloride on transepithelial electrical resistance (R(TE)) were measured. The spontaneous potential difference across parietal pleura was 0.5 +/- 0.1 mV, whereas that across visceral pleura was 0.4 +/- 0.1 mV. R(TE) of both pleura was very low: 22.02 +/- 4.1 Omega. cm2 for visceral pleura and 22.02 +/- 3.5 Omega. cm2 for parietal pleura. There was an increase in the R(TE) when SNP was added to the serosal bathing solution of parietal pleura and to the serosal or mucosal bathing solution in visceral pleura. The same was observed when ouabain was added to the mucosal surface of visceral pleura and to either the mucosal or serosal surface of parietal pleura. Furthermore, there was an increase in R(TE) when amiloride was added to the serosal bathing solution of parietal pleura. Consequently, the sheep pleura appears to play a role in the fluid and solute transport between the pleural capillaries and the pleural space. There results suggest that there is a Na+ and K+ transport across both the visceral and parietal pleura.

Fracture void structure: implications for flow, transport and deformation

This review focuses on studies of flow, transport and deformation processes at a scale of a single discontinuity. The paper provides an evaluation of: (1) various methods suggested for geometrical characterization of void structure; and (2) theoretical and practical problems arising from significant differences between the actual geometry of fracture void structure and its parallel plate representation. The use of an equivalent aperture concept is shown to be seriously misleading in: (a) evaluation of flow regime, and hence selection of appropriate flow laws; (b) correlating tracer and hydraulic tests, and assessment of solute transport properties; and (c) relating hydraulic and mechanical apertures, and predicting influence of stress perturbation and deformability.

Solute transport properties of compacted Ca-bentonite used in FEBEX project

The present Spanish concept of a deep geological high level waste repository includes an engineered clay barrier around the canister. The clay presents a very high sorption capability for radionuclides and a very small hydraulic conductivity, so that the migration process of solutes is limited by sorption and diffusion processes. Therefore, diffusion and distribution coefficients in compacted bentonite (i.e. in “realistic” liquid to solid ratio conditions) are the main parameters that have to be obtained in order to characterise solute transport that could be produced after the canister breakdown. Through-Diffusion (TD) and In-Diffusion (ID) experiments with HTO, Sr, Cs and Se were carried out using compacted FEBEX bentonite, which is the reference material for the Spanish concept of radioactive waste disposal. Experiments were interpreted by means of available analytical solutions that allow the estimation of diffusion coefficients and, in some cases, distribution coefficients. Analytical solutions are simple to use, but rely on hypotheses that do not hold in all the experiments. These experiments were interpreted also using an automatic parameter estimation code that overcomes the limitations of analytical solutions. Numerical interpretation allows the simultaneous estimation of porosity, diffusion and distribution coefficients, accounts for the role of porous sinters and time-varying boundary concentrations, and can use different types of raw concentration data.

ChemInform Abstract: Beyond the Classical Transport Laws of Electrochemistry: New Microscopic Approach to Ionic Conductance and Viscosity

The concentration dependence of the transport properties (i.e., the conductivity and the viscosity) of an electrolyte solution has been a subject of lively debate for a very long time. The foundation for understanding the transport properties of electrolyte solutions was laid down by Debye, Huckel, Onsager, and Falkenhagen who derived several limiting laws valid at low ion concentration. These classical laws have been rederived several times, although their extension to concentrated solutions has proven to be very difficult. We discuss a new microscopic approach toward understanding the transport laws of electrochemistry. This new approach is based on the general ideas of the mode coupling theory. We show that the mode coupling theory approach is appropriate in the present case because concentration effects arise from collective variables (like charge density and current) which are treated correctly by the mode coupling theory. The new theory can describe the crossover from the low to high concentration seamlessly. Our study yields microscopic expressions of both conductivity and viscosity in terms of static and dynamic structure factors of the charge and number densities of the electrolyte solution. The celebrated expressions of Debye, Huckel, and Onsager for static conductance, of Debye and Falkenhagen for frequency dependent electrolyte friction, and of Falkenhagen for the viscosity follow exactly from the present microscopic theory in the limit of very low ion concentration. Recently derived microscopic expressions of Chandra, Wei, and Patey for the frequency dependent conductivity can also be derived from the present scheme. The present theory is a self-consistent theory. For conductance, the agreement of the present theory with experimental results is satisfactory even up to one molar concentration. For viscosity, the theory seems to give the right trend and suggests directions for further improvement to explain the myriad of unexplained behavior known for a long time.

Organic-Inorganic Hybrid Materials with Specific Solute and Gas Transport Properties for Membrane and Sensor Applications

This paper is concerned with synthesis of hybrid materials for membrane applications. Examples of hybrid nanocomposites (type I) and hybrid polymers (type II) are presented. Dealing with type I, molecular sieves such as microporous silica beads or zeolite crystals were added to polymer matrices as an attempt to increase gas and vapor separation membrane performance. Also, specific organic molecules were inserted in a silica matrix as the active part of chemical sensors. Regarding type II materials, the arrangement at the molecular level of the organic and inorganic parts as well as their chemical composition have been investigated for facilitated transport of heavy metal ions or aminoacids in aqueous media, but also for separation of oxygen/nitrogen or volatile organic compounds from air. Processing of type II membranes is mainly based on the sol-gel method for which the synthesis of hybrid materials is undoubtedly one of the major advances. The specific advantages of this “chimie douce” method (low temperature chemical process, large variety of material precursors, material structure adaptability, and good film forming ability) are described here as a very suitable way to design and synthesize synthetic membranes with improved performance.

A Time Domain Reflectometry Method to Measure Immobile Water Content and Mass Exchange Coefficient

Physical nonequilibrium of water and solute transport in soil has been reported. One of the most common mechanistic models used to describe physical nonequilibrium transport phenomena is the mobile–immobile model (MIM). Two significant parameters in the MIM are immobile water content (θim) and mass exchange coefficient (α). Previously, a method for determining θim and α using sequential tracers (ST) has been used to characterize solute transport. In this work, we present and evaluate a method to estimate θim and α using time domain reflectometry (TDR). The TDR method was tested in laboratory experiments using three 20 cm long by 12 cm diameter undisturbed saturated soil columns. The method used TDR with an application of CaCl2 to obtain resident concentrations as a function of time. The data obtained from TDR were analyzed using a log‐linear equation developed based on the ST method to estimate θim and α. The θim and α estimates from the TDR method were compared with the estimates from the ST method and from effluent data. A conventional inverse curve fitting method (CXTFIT) was used to estimate parameters from effluent data. The means of θim/θ from the TDR method, ST method, and effluent data were 0.31, 0.30, and 0.26, respectively. The means of α from the TDR method, ST method, and effluent data were 0.03, 0.03, and 0.04 h−1, respectively. The values of θim/θ and α from the TDR method were very similar to the estimates from the ST method. In all three columns, the θim estimates from the TDR method were within the 95% confidence intervals (CI) of the estimates from the effluent data. In two of three columns, the α estimates from the TDR method were within the 95% CI of the estimates from the effluent data. The TDR method is relatively simple, rapid, and had advantages over the ST method and conventional methods for measuring solute transport properties.

Beyond the Classical Transport Laws of Electrochemistry: New Microscopic Approach to Ionic Conductance and Viscosity

The concentration dependence of the transport properties (i.e., the conductivity and the viscosity) of an electrolyte solution has been a subject of lively debate for a very long time. The foundation for understanding the transport properties of electrolyte solutions was laid down by Debye, Huckel, Onsager, and Falkenhagen who derived several limiting laws valid at low ion concentration. These classical laws have been rederived several times, although their extension to concentrated solutions has proven to be very difficult. We discuss a new microscopic approach toward understanding the transport laws of electrochemistry. This new approach is based on the general ideas of the mode coupling theory. We show that the mode coupling theory approach is appropriate in the present case because concentration effects arise from collective variables (like charge density and current) which are treated correctly by the mode coupling theory. The new theory can describe the crossover from the low to high concentration seamlessly. Our study yields microscopic expressions of both conductivity and viscosity in terms of static and dynamic structure factors of the charge and number densities of the electrolyte solution. The celebrated expressions of Debye, Huckel, and Onsager for static conductance, of Debye and Falkenhagen for frequency dependent electrolyte friction, and of Falkenhagen for the viscosity follow exactly from the present microscopic theory in the limit of very low ion concentration. Recently derived microscopic expressions of Chandra, Wei, and Patey for the frequency dependent conductivity can also be derived from the present scheme. The present theory is a self-consistent theory. For conductance, the agreement of the present theory with experimental results is satisfactory even up to one molar concentration. For viscosity, the theory seems to give the right trend and suggests directions for further improvement to explain the myriad of unexplained behavior known for a long time.

Potential of dual-skinned, high-flux membranes to reduce backtransport in hemodialysis

Potential backfiltration of cytokine-inducing material is a clinical concern during hemodialysis conducted with high-flux membranes. Novel hollow-fiber membranes were developed that had asymmetric convective solute transport properties, aimed at reducing the passage of potentially harmful molecules from dialysate to blood, while maintaining the desired fluid and solute movement from blood to dialysate. Sieving coefficient as a function of molecular weight was measured in vitro using polydisperse dextrans. Measurements were conducted using two different flat-sheet membranes in series or using hollow fiber membranes having two integrally formed skin layers. Based on measured experimental parameters, model calculations simulated the performance of a clinical-scale dialyzer containing these new membranes versus that of a commercially available high-flux dialyzer. Asymmetric convective solute transport was demonstrated using both commercial flat-sheet and newly developed hollow-fiber membranes. For two flat-sheet membranes in series, the extent of asymmetric transport was dependent on the order in which the solution was filtered through the membranes. For the hollow-fiber membranes, the nominal molecular weight cut-off was 20 kD in the blood-to-dialysate direction and 13 kD in the dialysate-to-blood direction. For this membrane, model calculations predict that clearance of a beta2-microglobulin-sized molecule (11,800 D) would be significantly greater from blood to dialysate than in the reverse direction, even under conditions of zero net ultrafiltration. A novel hollow-fiber dialysis membrane was developed that allows greater convective solute transport from blood to dialysate than from dialysate to blood.

Performance limitations of polymer electrolytes based on ethylene oxide polymers

Studies of polymer electrolyte solutions for lithium-polymer batteries are described. Two different salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium trifluoromethanesulfonate (LiTf), were dissolved in a variety of polymers. The structures were all based upon the ethylene oxide unit for lithium ion solvation, and both linear and comb-branch polymer architectures have been examined. Conductivity, salt diffusion coefficient and transference number measurements demonstrate the superior transport properties of the LiTFSI salt over LiTf. Data obtained on all of these polymers combined with LiTFSI salts suggest that there is a limit to the conductivity achievable at room temperature, at least for hosts containing ethylene oxide units. The apparent conductivity limit is 5×10 −5 S/cm at 25°C. Providing that the polymer chain segment containing the ethylene oxide units is at least 5–6 units long, there appears to be little influence of the polymer framework to which the solvating groups are attached. To provide adequate separator function, the mechanical properties may be disconnected from the transport properties by selection of an appropriate architecture combined with an adequately long ethylene oxide chain. For both bulk and interfacial transport of the lithium ions, conductivity data alone is insufficient to understand the processes that occur. Lithium ion transference numbers and salt diffusion coefficients also play a major role in the observed behavior and the transport properties of these polymer electrolyte solutions appear to be quite inadequate for ambient temperature performance. At present, this restricts the use of such systems to high temperature applications. Several suggestions are given to overcome these obstacles.

Simulation of calcium leaching and desorption in an acid forest soil

The aim of the study was to evaluate effects of mobile and immobile water and diffusion-limited transport on the binding and release of ions in soils. The desorption and leaching of calcium in a humic layer of a densely rooted acid forest soil under a beech stand was studied in laboratory experiments by leaching soil columns with a desorption solution and recycling the leachate through the columns. Radioactive tracers were added and monitored in the leachate to evaluate desorption and leaching characteristics of the soil. Parallel experiments were conducted with chloride and calcium to determine transport and desorption parameters independently. The experimental data were then analysed with a transport model, taking into account effects of mobile and immobile soil water fractions, and in the case of calcium assuming an equilibrium Langmuir adsorption isotherm. The transport was highly dependent on the mobility of the soil water, and in particular the fraction of the soil water to which the chemical was confined as a result of ionic properties. For chloride an excluded soil water phase had to be taken into account to explain the experimental findings. Immobile or mobile water and solute transfer and transport properties were not sufficient to explain non-equilibrium effects in the adsorption reactions. Desorption curves agreed with results from batch experiments, provided the leaching experiments were done in such a way that equilibration between the soil solution and the solid matrix adsorption sites was reached, otherwise desorption was delayed and the calculated isotherms do not represent actual equilibrium adsorption–desorption conditions.

Preferential Flow and Pedotransfer Functions for Transport Properties in Sandy Kandiudults

Soils with differences in argillic and kandic horizon clay content (12–28% clay), thickness of overlying sandy eluvial horizons (ranging from &lt;0.50 to &gt;1.0 m), and degree of structural development occur in upland Kandiudult soils in the Upper Coastal Plain of Georgia. Interest in agricultural site‐specific management necessitates more adequate characterization of solute transport properties between and within these soils. Undisturbed columns (15‐cm diam., ) were collected by horizon for three pedons typifying the extremes of the clay content in the argillic horizon. Breakthrough curves (BTCs) were conducted using a Br− tracer and were evaluated by fitting the single‐ and two‐region adaption of the convection–dispersion equation (CDE) to outflow measurements. Saturated hydraulic conductivity (Ks) measurements and methylene blue dye staining of conducting voids were also performed on the cores. Dye staining indicated differences in preferential flow occurred between surface (Ap), eluvial (E), and argillic and kandic (Bt) horizons. Retardation factors (R) were positively correlated with clay quantities, and horizons possessing relatively less clay (A and E horizons) possessed the highest α values (quickest solute exchange rates between mobile and immobile regions). Horizons with relatively higher clay quantities (Bts) had the lowest α and β (ratio of mobile water to the volumetric water content) values, but the highest effective dispersivity (λeff) values. Dye‐stained areas were correlated with β, which suggested β may be an approximation of the degree of preferential flow for these soils. For the three pedons studied, significant differences in α existed between the extremes, and thus they are interpreted to behave differently from a solute transport standpoint. Pedotransfer functions (PTFs) were developed for grossly estimating hydraulic and transport parameters.

Transport properties of urea and alkylureas aqueous solutions. A velocity correlation study.

Abstract Intradiffusion coefficients were measured at 25°C by the PGSE-NMR technique for the binary systems: water-urea, water-(N-methylurea), water-(N,N′-dimethylurea). The collected data have been combined with osmotic and mutual diffusion coefficients present in the literature to calculate the velocity correlation coefficients (VCC). The results have been interpreted in terms of molecular interactions, showing that alkylureas have a structuring effect on the aqueous medium. The hydration number of the solutes were estimated.

Electrolyte solutions for technology - new aspects and approaches

Abstract

Electrodeposition of copper from cuprous cyanide electrolyte

A model is developed for electrodeposition of copper from cuprous cyanide electrolyte onto a stationary disk electrode. The solutions examined are similar to those of copper strike-plating baths, in which cuprous may exist as Cu+ and Cu(CN)n(n−1)−, n=1–4. The effects of mass transport by diffusion and migration, multiple electrode reactions, and homogeneous complexation equilibria are considered. The model elucidates the influence of solution composition, transport properties, and kinetic constants on current distribution and polarization characteristics. Because cyanide is released upon discharge of the copper–cyanide complex, the distribution of copper-containing species shifts towards higher-order complexes near the electrode surface. Changes in solution composition which effect a greater percentage of copper complex in the more saturated cyanide state decrease the uniformity of the current distribution at a given fraction of the limiting current, which occurs because higher-order complexes have a lower diffusivity; and, if higher-order species are less electroactive, these changes decrease the current density at a given applied potential. Because copper–cyanide complexes have smaller diffusion coefficients than free cyanide, the concentration gradient of CN− causes the solution potential to increase near the electrode surface, and migration enhances the transport of anionic complexes. In most cases, the current distribution becomes increasingly non-uniform with applied potential; but under some circumstances that are elucidated here, the least non-uniform current distribution may occur at an intermediate fraction of the limiting current. In all studies, the current distribution approaches the highly non-uniform primary-like distribution as the limiting current is approached.

Modeling of multilayer drying of polymer films

A model was developed to predict the drying behavior of multilayer polymer films on inert substrates. The model considers simultaneous heat and mass transfer controlled by complex thermodynamic and transport properties of polymer solutions. Key components of the model are the incorporation of the free volume theory to predict diffusivities in each polymer layer, the use of heat and mass transfer coefficients to describe complex transport phenomena in the gas phase, the incorporation of exact equilibrium boundary conditions at polymer–polymer interface, and the use of the Flory–Huggins theory to describe both liquid–liquid and vapor–liquid equilibria. The model can be applied to guide processing, product formulation, scale-up, and oven design. As an example, the model is applied to simulate the drying of a two-layer coating of poly vinyl acetate (in toluene) over polystyrene (also in toluene) on a polyester substrate. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1665–1675, 1999