Transport Properties Of Solutions Research Articles

Large-scale tracer profiles in a deep claystone formation (Opalinus Clay at Mont Russelin, Switzerland): Implications for solute transport processes and transport properties of the rock

Natural tracers (Cl − and stable water isotopes) in pore water of the Opalinus Clay and adjacent formations were studied in the motorway tunnel at Mont Russelin, Switzerland. The Opalinus Clay occurs in the core of an anticline which is cut by a complex system of thrust faults. Concentration profiles of natural tracers were taken from 17 boreholes along a 363 m long section. Pore waters of drillcore samples were analysed with indirect and direct methods. The Cl − and stable water isotope distribution in the pore water shows a regular and well defined profile, with a conspicuous decrease towards the overlying Dogger limestone aquifer. The highest Cl − values (approximately 23,000 mg/L) are found in the core of the anticline in Liassic claystones underlying the Opalinus Clay. To quantify the large-scale transport properties of the Opalinus Clay formation, a 2D transport model was constructed and used to reproduce the observed concentration profiles. The calculations indicate that the observed tracer distributions are consistent with diffusion as the dominant transport process. Groundwater flow in the overlying Dogger aquifer was initiated about 2–4 Ma ago, which is long after the folding of the Jura Mountains and probably coincides with the exposure of the aquifer to freshwater recharge following continued erosion of the anticline. The calculations suggest that tracer distributions are controlled by 1) the timing of freshwater recharge in the overlying limestone aquifer, 2) the shape of the anticline and 3) the magnitude and the anisotropy ratio of diffusion coefficients.

Transport properties of multi-cations doped cerium oxide

The transport properties of members of the solid solution (100−x)CeO2·xLa0.6Sr0.4CoO3 (CexLSC), where x=5, 7.6, and 10.6mol% have been investigated under oxidising and mildly reduce atmospheres. The single phase solid solutions CexLSC have fluorite-type structure (space group Fm3¯m) with Ce replaced by La, Sr, and Co. The unit cell volume expands with increasing degree of substitution. The CexLSC compositions exhibit thermally activated conductivity behaviour over a temperature range of 150–900°C. The bulk conductivity increases up to 5–6 orders of magnitudes. In contrast to the undoped CeO2, the grain boundary conductivity determines the transport properties of the CexLSC solid solutions only below 200°C. The total conductivity of the CexLSC compositions with x>5mol% seems to be enhanced due to the increase in the concentration of oxygen vacancies and the emergence of the hole charge carriers. Results obtained in the present study demonstrate that the fabrication method does not greatly influence the transport properties of the CexLSC solid solutions.

Transport properties of aqueous solutions of sodium alginate at 298.15 K

Mutual diffusion coefficients (interdiffusion coefficients) of sodium alginate in aqueous dilute solutions, at concentrations from 0.001 to 0.500 g mL −1 and at 298.15 K, alone and in combination with caffeine, using an open-ended conductimetric capillary cell, have been measured. These results are discussed in the light of structural analysis conducted by means of theoretical calculations (molecular mechanics). Based on such results, the equivalent conductance at infinitesimal concentration of the alginate ion in the referred solutions, at 298.15 K, has been estimated. These studies, complemented by some density and viscosity measurements, and carried out at the same range of concentrations, permit us to have a better understanding of the structure of these systems and the thermodynamic behaviour of sodium alginate in different media, that is, improving the know how of the physical and chemical interactions of those two important food chemistry components.

Comparison of Three Methods for Determination of Root Hydraulic Conductivity of Maize ( Zea mays L.) Root System

Three techniques of root pressure probe, pressure chamber and high pressure flow meter were used to measure the hydraulic conductivities ( Lp r ) of whole root systems of young maize ( Zea mays L.) seedlings grown hydroponically under either drought or normal water conditions. Compared to normal water conditions, drought stress simulated by polyethylene glycol 6 000 (osmotic potential = −0.2 MPa) reduced Lp r in the root system by over 50%. It indicated that water permeability in the roots decreased significantly when plants suffered from water shortages. Moreover, there was no significant difference ( P < 0.05) on the Lp r values in the root systems developed under a given water stress regime among the three techniques used. Therefore, all three methods are acceptable to study the hydraulic conductivity of maize seedling root systems. We have also highlighted some of the technical limitations of each method. It can be inferred that the root pressure probe is preferable for young maize seedlings because it is subtle and has the additional ability to determine solute transport properties, but the method is time consuming. Other advantages and disadvantages of each technique are discussed in order to acquaint researchers with basic information that could contribute to their choice of an appropriate technique for future studies.

Systematic Study of the Simple Predictive Approaches for Thermodynamic and Transport Properties of Multicomponent Solutions

The densities, viscosities, and conductivities were measured for the ternary solution NaCl + urea + H2O, the quintuple solution NaCl + Na2SO4 + KCl + K2SO4 + H2O, and their binary subsystems at 298.15 K. The results together with the densities, viscosities, and conductivities of multicomponent solutions reported in the literature were used to study the predictability of the Young’s rule for density and conductivity, the rule of Patwardhan and Kumar for density, Hu’s equation for the viscosity of mixed electrolyte solutions based on the Eyring’s absolute rate theory and the rule of Patwardhan and Kumar, and the semiideal solution theory for thermodynamic and transport properties. The results show that all the tested equations can provide comparable and accurate predictions for the densities of multicomponent electrolyte solutions. The semiideal solution theory is applicable to the aqueous solutions of electrolytes and nonelectrolytes, and its predictions for the densities of the examined solutions are in n...

Modeling of Infrared Drying of Polymer Solutions

This work presents the dynamic modeling of drying behavior of polymer solutions in an infrared-convective oven. Two study cases were considered for the drying process. The first one deals with the drying of a coated polymer solution on a fixed substrate while the second one includes drying of the same solution on a moving substrate in an infrared (IR) oven. Both models involve simultaneous heat and mass transfer equations that describe changes in the solvent concentration and the polymer temperature during the drying process. The set of partial differential equations (PDEs) arising from the mass and energy balances constitute a highly nonlinear system due to inter-dependence of the thermodynamic and transport properties of polymer solutions. The models were numerically solved and were validated using published experimental data. The models were employed to simulate the drying of a polyvinyl acetate coating (in toluene) on a polyester substrate. Results obtained from the derived model demonstrated the importance of parameters such as web velocity, heater temperature, and inlet air velocity in the IR drying process. In general, high temperature and air velocity cause rapid drying of the polymer coating, while high substrate velocity resulted in drying. This model can be applied on any industrial applications that include continuous IR drying process of polymer-coated layers to predict the drying behavior of the coated product.

Anisotropic Solute Diffusion Tensor in Porcine TMJ Discs Measured by FRAP with Spatial Fourier Analysis

A new method solely based on spatial Fourier analysis (SFA) was developed to completely determine a two-dimensional (2D) anisotropic diffusion tensor in fibrous tissues using fluorescence recovery after photobleaching (FRAP). The accuracy and robustness of this method was validated using computer-simulated FRAP experiments. This method was applied to determine the region-dependent anisotropic diffusion tensor in porcine temporomandibular joint (TMJ) discs. The average characteristic diffusivity of 4 kDa FITC-Dextran across the disc was 26.05 ± 4.32 μm²/s which is about 16% of its diffusivity in water. In the anteroposterior direction, the anterior region (30.99 ± 5.93 μm²/s) had significantly higher characteristic diffusivity than the intermediate region (20.49 ± 5.38 μm²/s) and posterior region (20.97 ± 2.46 μm²/s). The ratio of the two principal diffusivities represents the anisotropy of the diffusion and ranged between 0.45 and 0.51 (1.0 = isotropic). Our results indicated that the solute diffusion in TMJ discs is inhomogeneous and anisotropic. These findings suggested that diffusive transport in the TMJ disc is dependent on tissue composition (e.g., water content) and structure (e.g., collagen orientation). This study provides a new method to quantitatively investigate the relationship between solute transport properties and tissue composition and structure.

A fundamental study of the transport properties of aqueous superacid solutions.

An extensive investigation of the transport properties of aqueous acid solutions was undertaken. The acids studied were trifluoromethanesulfonic (CF(3)SO(3)H), bis(trifluoromethanesulfonyl)imide [(CF(3)SO(2))(2)NH], and para-toluenesulfonic (CH(3)C(6)H(4)SO(3)H), of which the first two are considered superacids. NMR measurements of self-diffusion coefficients (D), spin-lattice relaxation times (T(1)), and chemical shifts, in addition to ionic conductivity (sigma), viscosity (eta), and density measurements, were performed at 30 degrees C over the concentration range of 2-112 water to acid molecules. Results showed broad maxima in sigma for all three acids in the concentration range of 12-20 water to acid molecules. This coincided with minima in anion Ds and is attributed to a local molecular ordering, reduced solution dielectric permittivity, and increased ionic interactions. The location of the maxima in sigma correlates with what is observed for hydrated sulfonated perfluoropolymers such as Nafion, which gives a maximum in ionic transport when the ratio of water to acid molecules is about 15-20. Of the three acids, bis(trifluoromethanesulfonyl)imide was found to be the least dependent on hydration level. The occurrence of the anticorrelation between the ionic conductivity maximum and the anion self-diffusion minimum supports excess proton mobility in this region and may offer additional information on the strength of hydrogen bonding in aqueous media as well as on the role of high acid concentration in the Grotthuss proton transport mechanism.

Solute dispersion in oscillating electro-osmotic flow with boundary mass exchange

Mass transfer in an oscillatory electro-osmotic flow (EOF) is theoretically studied, for the case of a cylindrical tube with a reactive wall. An expression for the dispersion coefficient, reflecting the time-averaged mass flux of an electrically neutral solute, is derived analytically. Under the influence of a reversible solute-wall mass exchange, the dispersion coefficient exhibits a complex dependence on the various parameters representing the effects of the electric double-layer thickness, oscillation frequency, solution transport properties, solute partitioning, and reaction kinetics. Our results suggest that, in the presence of a reversible mass exchange at the wall, an oscillatory EOF may be used for separation of species. It is found that optimal conditions for separation are achieved for a thin double-layer, where an inert solute, or one with slow exchange kinetics, experiences virtually no dispersion while the dispersion is maximized for the reactive solute exhibiting fast kinetics.

ChemInform Abstract: Electrolyte Solutions for Technology - New Aspects and Approaches

The use of chemical models is shown for the calculation of thermodynamic and transport properties of concentrated electrolyte solutions. Comparison is made with empirical approaches. Molecular ions with delocalized charges abolishing the concept of ionic point charges for the calculation of short range interactions are considered in the framework of chemical models. Novel lithium salts for technical applications are presented and the influence of electron withdrawing substituents at the anions on ion-pair formation, conductivity and anodic stability limit is studied to illustrate the role of molecular ions with delocalized charges.

Volumetric, Ultrasonic, and Transport Properties of an Aqueous Solution of Polyethylene Glycol Monomethyl Ether at Different Temperatures

The density, speed of sound, and dynamic viscosity of the aqueous solutions of polyethylene glycol monomethyl ether at T = (283.15 to 323.15) K have been measured experimentally over the entire range of compositions at atmospheric pressure. From these experimental data, the excess molar volume, isentropic compressibility, deviation in isentropic compressibility, deviation in speed of sound, and viscosity deviation have been determined for each composition. The calculated values of these quantities have favorably been fitted to two different variable-degree polynomial equations.

Influence of variable hydrodynamic interaction strength on the transport properties of coiled polymers

We have computed the hydrodynamic radius Rh and intrinsic viscosity [eta] of a large number of random coil polymer models by path integration. We examine the effects of chain length, solvent quality, monomer size and shape, and chain stiffness on the approach of these transport properties to the limit of large molecular mass. For many of the models, we have also calculated the ensemble-averaged solvent velocity field in the vicinity of the coil as it moves with constant drift velocity under the action of an external force. Naive scaling arguments predict alpha=nu and beta=3(nu-1) , where alpha , beta , and nu are the exponents controlling the chain length behavior of Rh , [eta] , and Rg , respectively. We present evidence for a "draining crossover" that quantifies the slow convergence of the transport properties to their asymptotic scaling behavior. Indeed, the convergence is so slow that effective alpha and beta exponents rarely agree with the naive predictions at typical molecular masses. For the same chain models, Rg converges rapidly to its asymptotic behavior, indicating that the effect is not due to a crossover from theta to swollen behavior, as often stated. Solvent quality, monomer size, and chain stiffness all influence the draining crossover. Our results call into question the common practice of extracting metrical data, e.g., characteristic ratios, directly from polymer solution transport properties.

Explicit numerical method for prediction of transport properties of aqueous glycol solutions

AbstractAmong various gas dehydration processes, absorption is the most commonly employed technique, wherein the water vapour in the gas stream gets absorbed in the glycol. In the present work, a numerical method is developed to predict the viscosity and thermal conductivity of aqueous glycol solutions as a function of temperature and glycol mole fraction. The adjusted coefficients of correlations have been optimised through an efficient and reliable algorithm by minimising the standard deviation of predicted values in comparison with the experimental data by solving the system of linear equations. The numerical results are compared with the reliable experimental data where the obtained results illustrate good agreement with the experimental data. The proposed method appears to be superior owing to its accuracy and clear numerical background, wherein the relevant coefficients can be retuned if new and more accurate data are available in the future. The proposed method predicts the transport properties of ...

Interplay between the Transport of Solutes Across Nanofiltration Membranes and the Thermal Properties of the Thin Active Layer

The thin active layer (TAL) of seven nanofiltration (NF) membranes was studied using differential scanning calorimetry, and the membranes were classified into two groups according to the polymer physical state (amorphous or semicrystalline). NF membrane performance in terms of permeate volume flux density and rejection of neutral solutes was investigated in temperature cycles. The modeling of rejection using a hindered transport theory showed irreversible and opposite pore size changes for the two groups of NF membranes when the maximum operating temperature of the cycle exceeded the glass-transition temperature of the TAL. A mechanism of pore deformation is proposed to explain the variation of the solute transport properties as a function of the temperature and the polymer physical state in the TAL.

Onset of natural convection in the electrochemical cell with horizontal electrodes under non-steady-state conditions: A numerical study

The disturbance of mechanical equilibrium of stagnant electrolyte containing three types of ions and the onset of natural convection in the electrochemical cell with plane horizontal electrodes under the non-steady-state conditions are studied theoretically. The Navier-Stokes equations in the Boussinesq approximation, the equations of ionic transfer of electrolyte components, which is caused by diffusion, convection, and migration, and the electroneutrality condition were used as the mathematical model of the process. Using the numerical simulation, the regularities of the onset of natural convection of electrolyte solution with the formation of convective cells are studied. The effect of transport properties of solution on the critical time of onset of convection and on the time before the current starts to increase due to the onset of natural convection, on the sizes and shape of convective cells and the mass-transfer rate is investigated by the example of cathodic deposition of metal at the limiting current.

Deterministic Analysis and Upscaling of Bromide Transport in a Heterogeneous Vadose Zone

Conservative solute transport experiments were conducted at a field plot and on an undisturbed soil core from the same site. The hydraulic and solute transport properties were extensively characterized so that the data could be analyzed from a deterministic perspective. To investigate the influence of scale and conceptual model on solute transport in the relatively homogeneous upper soil profile of the field site, breakthrough curves that were collected at different depths in the undisturbed column and in the field experiments were compared and analyzed. The mobile‐immobile model provided a physically realistic description of the column data that was largely independent of the transport distance, and upscaling from the undisturbed core to the field plot was relatively successful. Mean and variance of the Br− travel times were controlled by plot‐scale variability in soil water content and heterogeneity, which was overcome by averaging the concentration values from four locations at the same depth and time, and analyzing the Br− transport behavior as a one‐dimensional process. Differences between the measured and simulated mass balances, average concentration, and the variations in concentration were predicted reasonably well across depth and time. Although prediction of the exact concentration information at a given point was not achieved, this study demonstrates that area‐average Br− transport in a heterogeneous vadose zone can be deterministically quantified.

Ion-Rejection, Electrokinetic and Electrochemical Properties of a Nanoporous Track-Etched Membrane and Their Interpretation by Means of Space Charge Model

Due to their straight cylindrical pores, nanoporous track-etched membranes are suitable materials for studies of the fundamentals of nanofluidics. In contrast to single nanochannels, the nano/micro interface, in this case, can be quantitatively considered within the scope of macroscopically 1D models. The pressure-induced changes in the concentration of dilute KCl solutions (salt rejection phenomenon) have been studied experimentally with a commercially available nanoporous track-etched membrane of poly (ethylene terephthalate) (pore diameter ca. 21 nm). Besides that, we have also studied the concomitant stationary transmembrane electrical phenomenon (filtration potential) and carried out time-resolved measurements of the electrical response to a rapid pressure switch-off (within 5-10 ms). The latter has enabled us to split the filtration potential into the streaming potential and membrane potential components. In this way, we could also confirm that the observed nonlinearity of filtration potential, as a function of the transmembrane volume flow, was primarily caused by the salt rejection. The results of experimental measurements have been interpreted by means of a space charge model with the surface charge density being a single fitting parameter (the pore size was estimated from the membrane hydraulic permeability). By using the surface charge density fitted to the salt rejection data, the results of electrical measurements could be reproduced theoretically with a typical accuracy of 10% or better. Taking into account the simplifications made in the modeling, this accuracy appears to be good and confirms the quantitative applicability of the basic concept of space charge model to the description of transport properties of dilute electrolyte solutions in nanochannels of ca. 20 nm.

Relationship between solute transport properties and tissue morphology in human annulus fibrosus

Poor nutritional supply to the intervertebral disc is believed to be an important factor leading to disc degeneration. However, little is known regarding nutritional transport in human annulus fibrosus (AF) and its relation to tissue morphology. We hypothesized that solute diffusivity in human AF is anisotropic and inhomogeneous, and that transport behaviors are associated with tissue composition and structure. To test these hypotheses, we measured the direction-dependent diffusivity of a fluorescent molecule (fluorescein, 332 Da) in three regions of AF using a fluorescence recovery after photobleaching (FRAP) technique, and associated transport results to the regional variation in water content and collagen architecture in the tissue. Diffusivity in AF was anisotropic, with higher values in the axial direction than in the radial direction for all regions investigated. The values of the diffusion coefficient ranged from 0.38 +/- 0.25 x 10(-6) cm(2)/s (radial diffusivity in outer AF) to 2.68 +/- 0.84 x 10(-6) cm(2)/s (axial diffusivity in inner AF). In both directions, diffusivity decreased moving from inner to outer AF. Tissue structure was investigated using both scanning electron microscopy and environmental scanning electron microscopy. A unique arrangement of microtubes was found in human AF. Furthermore, we also found that the density of these microtubes varied moving from inner to outer AF. A similar trend of regional variation was found for water content, with the highest value also measured in inner AF. Therefore, we concluded that a relationship exists among the anisotropic and inhomogeneous diffusion in human AF and the structure and composition of the tissue.

Surface Homogeneity of Anion Exchange Membranes: A Chronopotentiometric Study in the Overlimiting Current Range

Electrotransport of sodium chloride near and through the ASV anion exchange membrane was first investigated. Chronopotentiometric and current-voltage characteristics results have shown that the ASV membrane acts as a totally conducting plane with respect to the transport of NaCl electrolyte. SEM and AFM images contributed to confirm the overall homogeneous surface of the membrane. Further chronopotentiometric studies of the membrane were evaluated in the presence of different alkaline chloride solutions in order to explore the influence of alkali co-ions on the transport phenomena. Membrane characterization led to determine the transport number of chloride counterion in the membrane. It is reported in this work that chronopotentiometry using the Sand equation toward the homogeneous ion exchange membrane is a simple and efficient method for determination of the diffusion coefficient of the electrolytes in the bulk solution. Discussions on the transport properties of the electrolyte solutions in relation with the hydrated ion sizes allowed us to verify the diffusion coefficient of the electrolytes determined by means of chronopotentiometric method.

Synthesis processes and transport properties of solid solutions in the Bi2O3-GeO2-V2O5 system

The results of studies of solid solutions with the overall composition of Bi4V2 − xGexO11 − δ and Bi4Ge3 − xVxO12 + δ are presented. The process of phase formation are studied during the synthesis of solid solution using the ceramic method and through liquid precursors. Crystallochemical parameters of the obtained compounds are determined. The size distribution of the particles is studied. Conductivity of annealed of polycrystalline samples as a function of temperature and composition is studied using the impedance spectroscopy method. The shape of impedance complex plane plots of the samples obtained in different ways is studied and analyzed.