Transport Of Aqueous Solutions Research Articles

Transport Properties in Multicomponent Systems Containing Cyclodextrins and Nickel Ions.

In this work, we propose a comprehensive experimental study of the diffusion of nickel ions in combination with different cyclodextrins as carrier molecules for enhanced solubility and facilitated transport. For this, ternary mutual diffusion coefficients measured by Taylor dispersion method are reported for aqueous solutions containing nickel salts and different cyclodextrins (that is, α-CD, β-CD, and γ-CD) at 298.15 K. A combination of Taylor dispersion and other methods, such as UV-vis spectroscopy, will be used to obtain complementary information on these systems. The determination of the physicochemical properties of these salts with CDs in aqueous solution provides information that allows us to understand solute-solvent interactions, and gives a significant contribution to understanding the mechanisms underlying diffusional transport in aqueous solutions, and, consequently, to mitigating the potential toxicity associated with these metal ions. For example, using mutual diffusion data, it is possible to estimate the number of moles of each ion transported per mole of the cyclodextrin driven by its own concentration gradient.

Production and dispersion of free radicals from transient cavitation Bubbles: An integrated numerical scheme and applications

As an advanced oxidation process with a wide range of applications, sonochemistry relies on acoustic cavitation to induce free radicals for degrading chemical contaminants. The complete process includes two critical steps: the radical production inside the cavitation bubble, and the ensuing dispersion of these radicals into the bulk solution. To grasp the physicochemical details in this process, we developed an integrated numerical scheme with the ability to quantitatively describe the radical production-dispersion behavior. It employs coupled simulations of bubble dynamics, intracavity chemical reactions, and diffusion–reaction-dominated mass transport in aqueous solutions. Applying this method to the typical case of argon and oxygen bubbles, the production mechanism for the main radicals is revealed. Moreover, the temporal-spatial distribution of the radicals in the liquid phase is presented. The results demonstrate that the enhanced radical production observed in oxygen bubbles can be traced to the initiation reaction O2 + H2O → OH+HO2, which requires relatively low activation energy. In the outside liquid region, the dispersion of radicals is limited by robust recombination reactions. The simulated penetration depth of OH is around 0.2 μm and agrees with reported experimental measurements. The proposed numerical approach can be employed to better capture the radical activity and is instrumental in optimizing the engineering application of sonochemistry.

Evaluation of the Global S-Entropy Production in Membrane Transport of Aqueous Solutions of Hydrochloric Acid and Ammonia.

The results of experimental studies of volume osmotic fluxes () and fluxes of dissolved substances () in a system containing a synthetic Nephrophan® membrane (Orwo VEB Filmfabrik, Wolfen, Germany) set in a horizontal plane are presented. The membrane separated water and aqueous HCl or ammonia solutions or aqueous ammonia and HCl solutions. It was found that for the homogeneity conditions of the solutions and depend only on the concentration and composition of the solutions. For concentration polarization conditions (where concentration boundary layers are created on both sides), and depend on both the concentration and composition of the solutions and the configuration of the membrane system. The obtained results of the and flux studies were used to assess the global production of entropy for the conditions of homogeneity of solutions (), while and —to assess the global production of entropy for concentration polarization conditions ). In addition, the diffusion-convective effects and the convection effect in the global source of entropy were calculated. The concentration polarization coefficient was related to modified concentration Rayleigh number, e.g., the parameter controlling the transition from non-convective (diffusive) to convective state. This number acts as a switch between two states of the concentration field: convective (with a higher entropy source value) and non-convective (with a lower entropy source value). The operation of this switch indicates the regulatory role of earthly gravity in relation to membrane transport.

Gating of Hydrophobic Nanopores with Large Anions.

Understanding ion transport in nanoporous materials is critical to a wide variety of energy and environmental technologies, ranging from ion-selective membranes, drug delivery, and biosensing, to ion batteries and supercapacitors. While nanoscale transport is often described by continuum models that rely on a point charge description for ions and a homogeneous dielectric medium for the solvent, here, we show that transport of aqueous solutions at a hydrophobic interface can be highly dependent on the size and hydration strength of the solvated ions. Specifically, measurements of ion current through single silicon nitride nanopores that contain a hydrophobic-hydrophilic junction show that transport properties are dependent not only on applied voltage but also on the type of anion. We find that in Cl--containing solutions the nanopores only conducted ionic current above a negative voltage threshold. On the other hand, introduction of large polarizable anions, such as Br- and I-, facilitated the pore wetting, making the pore conductive at all examined voltages. Molecular dynamics simulations revealed that the large anions, Br- and I-, have a weaker solvation shell compared to that of Cl- and consequently were prone to migrate from the aqueous solution to the hydrophobic surface, leading to the anion accumulation responsible for pore wetting. The results are essential for designing nanoporous systems that are selective to ions of the same charge, for realization of ion-induced wetting in hydrophobic pores, as well as for a fundamental understanding on the role of ion hydration shell on the properties of solid/liquid interfaces.

Reducing Adhesion for Dispensing Tiny Water/Oil Droplets and Gas Bubbles by Femtosecond Laser‐Treated Needle Nozzles: Superhydrophobicity, Superoleophobicity, and Superaerophobicity

AbstractThree‐level microstructures were formed on the stainless‐steel surfaces by simple femtosecond laser ablation. The structured surfaces exhibit superhydrophilicity in air and superoleophobicity/superaerophobicity in water. After further stearic acid modification, the surfaces turned to superhydrophobicity and underwater superoleophilicity/superaerophilicity. Through this technique, the nozzle of a needle is transformed to possess superwettabilities. When the nozzles were used to release liquid and gas, the sizes of the dispensed water and oil droplets and air bubbles were dramatically reduced. Particularly, we demonstrate that the underwater superaerophobic nozzle could dispense air bubbles in nanoliter volume without the need of reducing the nozzle diameter. The liquid retention at the opening of the needle was also effectively prevented. Therefore, the reduced droplet/bubble size and retention allow us to achieve a dramatically enhanced volume accuracy and resolution during manipulation and transport of aqueous solutions and gases. The femtosecond laser‐induced superwetting nozzles can be used in high‐resolution liquid transport, inkjet printing, 3D printing, pipettes, medical devices, cell engineering, biological detection, microchemical reactor, and reducing industrial gas emission.

Guanidinium Group Remains Protonated in a Strongly Basic Arginine Solution.

Knowledge of the acid dissociation constant of an amino acid has very important ramifications in the biochemistry of proteins and lipid bilayers in aqueous environments because charge and proton transfer depend on its value. The acid dissociation constant for the guanidinium group in arginine has historically been posited as 12.5, but there is substantial variation in published values over the years. Recent experiments suggest that the dissociation constant for arginine is much higher than 12.5, which explains why the arginine guanidinium group retains its positive charge under all physiological conditions. In this work, we use X-ray photoelectron spectroscopy to study unsupported, aqueous arginine nanoparticles. By varying the pH of the constituent solution, we provide evidence that the guanidinium group is protonated even in a very basic solution. By analyzing the energy shifts in the C and N X-ray photoelectron spectra, we establish a molecular level picture of how charge and proton transport in aqueous solutions of arginine occur.

A modified two-state empirical valence bond model for proton transport in aqueous solutions.

A detailed analysis of the proton solvation structure and transport properties in aqueous solutions is performed using classical molecular dynamics simulations. A refined two-state empirical valence bond (aTS-EVB) method, which is based on the EVB model of Walbran and Kornyshev and the anharmonic water force field, is developed in order to describe efficiently excess proton transport via the Grotthuss mechanism. The new aTS-EVB model clearly satisfies the requirement for simpler and faster calculation, because of the simplicity of the two-state EVB algorithm, while providing a better description of diffusive dynamics of the excess proton and water in comparison with the previous two-state EVB models, which significantly improves agreement with the available experimental data. The results of activation energies for the excess proton and water calculated between 300 and 340 K (the temperature range used in this study) are also found to be in good agreement with the corresponding experimental data.

Synthesis and incorporation of selenide in pyrite and mackinawite

Abstract According to performance assessment reports for high-level radioactive waste repositories, 79Se is a radionuclide that could represent a potential threat to the biosphere. Therefore knowledge of its geochemical behavior during its transport in aqueous solutions is fundamental to assess the safety of repository sites. Selenium is often associated with sulfides such as pyrite, a frequent minor constituent of host rocks and bentonite backfills considered for radioactive waste disposal. In this study, we investigated the uptake of Se by Fe sulfides synthesized in batch experiments under anoxic conditions. Results from X-ray diffraction and scanning electron microscopy analyses reveal the formation of pyrite and mackinawite. More than 98% of the Se added to solutions (initial concentration: 10−3–10−6 mol/l) was taken up by the Fe sulfide minerals. Focused ion beam analysis shows an inhomogeneous Se distribution with a higher accumulation in the center of the pyrite grains, probably due to the progressive depletion of Se from solution with regard to S. The results imply that pyrite and its most important precursor phase, mackinawite, are efficient in removing selenium from solution, which may contribute in reducing the mobility of 79Se released from radioactive waste.

Influence of a cellulose diacetate matrix on the complexation kinetics of tetraphenylporphin with Zn and Cd

The dependence of the reaction rate of tetraphenylporphin zinc and cadmium complexes in a polymer matrix on a base of cellulose diacetate and low-molecular model solutions was investigated. The characteristics of the diffusive transport of aqueous solutions of zinc and cadmium acetates through the cellulose diacetate membrane were obtained. The kinetic control of the porphyrin reaction incorporated into the polymer, and the determining influence of the steric limitations of the matrix of a rigid chain polymer on macroheterocycle deformation (and thus its reactivity) are shown.

A Novel Attempt to Calculate the Velocity Correlation Coefficients in Ternary Electrolyte Solution

This work gives estimated values of the velocity correlation coefficients VCCs for ternary electrolyte solutions (the system may have a tracer ion as one of the components), utilizing available measured transport coefficients. The VCCs originate from linear response theory and give a deeper insight into the microdynamic structure of complex ionic solutions. By assuming Onsager’s relation to be valid, ten sets of velocity correlation coefficients were calculated for a ternary system and were used to calculate the VCCs for 134Cs+ ion (present in trace amount) transport in aqueous solutions of CsCl and KCl at 25 ○C.

Role of Viscosity on Capillary Flow and Stress Corrosion Cracking Behavior

It is documented that the viscosity has a significant effect on stress corrosion cracking (SCC) behavior in terms of the K-da/dt relation. In order to better understand the role of viscosity and its effect on transport of aqueous solution to the crack tip due to capillary action at the crack tip, experiments were conducted using a glass-metal setup. The confined space between the crack-mouth faces was simulated using wedge-type geometry between a glass slide and 7475 aluminum plate. The space between the glass and aluminum crevice was carefully controlled using spacers. The effect of viscosity was modeled using water, glycerin, and its mixture. According to our best knowledge, this article presents the first simple model of experimental simulation of the capillary flow phenomenon with a goal of arriving at a better understanding of how the viscosity affects the SCC behavior. Experimental results of several materials taken from the literature support the role of viscosity on SCC behavior.

An Improved Multistate Empirical Valence Bond Model for Aqueous Proton Solvation and Transport

A new multistate empirical valence bond model (MS-EVB3) is developed for proton solvation and transport in aqueous solutions. The new model and its quantum version (qMS-EVB3) are based on the MS-EVB2 model [Day et al., J. Chem. Phys. 2002, 117, 5839] and recently developed flexible water models-the SPC/Fw model [Wu et al. J. Chem. Phys. 2006, 124, 24503] and the qSPC/Fw model [Paesani et al. J. Chem. Phys. 2006, 125, 184507]-for classical and quantum simulations, respectively. Using ab initio data as benchmarks, the binding energies and optimized geometries calculated with the new model for protonated water clusters, as well as the potential energy surface for proton shuttling between water molecules in a cluster environment, are improved in comparison to the MS-EVB2 model. For aqueous solutions, classical and quantum molecular dynamics simulations with the MS-EVB3 model yield a more accurate description of the solvation structure and diffusive dynamics of the excess proton. New insight is also provided into the proton solvation and hopping dynamics in water, as well as the "amphiphilic" nature of the hydrated proton that has been predicted to give rise to its enhanced concentration at aqueous interfaces and an effectively lower pH of the air-water interface [Petersen et al. J. Phys. Chem. B 2004, 108, 14804].

Investigation of loaded halite-SiO2 interfaces undergoing dissolution-precipitation processes

Deformation assisted by transport in aqueous solutions is important for the rheology of earth materials, and models commonly used to describe deformation by dissolution-precipitation creep assume a steady state process in a closed system which is driven by the potential energy of the system. Here, we studied the effect of uni-axial stress on the convergence of halite crystals in contact to SiO2 at dry conditions and in presence of saturated solution by optical interferometry. Adding saturated solution caused the convergence to increase strongly. Simultaneously, Linnik-based phase shift interference microscopy was used to in situ monitor the nano-scale morphology of the loaded surface of the crystal. These investigations revealed that the measured crystal convergence is not dominated by dissolution within the loaded halite-SiO2 interface but rather by an increased plasticity of the halite crystal due to the addition of saturated solution. Temporarily reducing the stress reduces the elastic strain energy of the crystal and potential energy of the system as driving force for dissolution, but increases the potentiality for material transport from the interface into the bulk fluid. Thus, mechanisms which cause a remanent excess energy contribute to increased solubility and material flux during periods of reduced stress. Local plastic deformation satisfies this condition. We expect from our results that episodic cycling of tectonic stress, pore pressure, or solute activity significantly enhances deformation rates in rocks.

Transport in aqueous solutions of Group IIB metal salts. Part 7.—Measurement and prediction of isotopic diffusion coefficients for iodide in solutions of cadmium iodide

Isotopic diffusion coefficients for iodide have been measured in aqueous solutions of cadmium iodide over the concentration range 0.1–1.0 mol dm–3, using the diaphragm cell technique. The iodide diffusion coefficients are shown to decrease smoothly but steeply from the infinite dilution value of 2.046 × 10–5 cm2 s–1 to less than half that value in the concentration range above 0.1 mol dm–3. This remarkable decline has been assigned to the presence of complexes of the type CdI+2–xx(x= 1, 2, 3, 4). The irreversible thermodynamic analysis developed previously for cadmium diffusion in this same system (part 4) has been extended to include isotopic diffusion of labelled ligands on multiply substituted complexes. Using this analysis the observed iodide diffusion coefficients have been predicted within close limits over the whole concentration range up to ≈ 0.5 mol dm–3.

Transport in aqueous solutions of group IIB metal salts at 298.15 K. Part 6.—Irreversible thermodynamic parameters for zinc chloride and verification of Onsager's reciprocal relationships

Transport in aqueous solutions of group IIB metal salts at 298.15 K. Part 6.—Irreversible thermodynamic parameters for zinc chloride and verification of Onsager's reciprocal relationships

Transport in aqueous solutions of group IIB metal salts (298.15 K). Part 4.—Interpretation and prediction of isotopic diffusion coefficients for cadmium in dilute solutions of cadmium iodide

A method for predicting isotopic diffusion coefficients for component ions in a self-complexed electrolyte has been developed. In an irreversible thermodynamic analysis the diffusion coefficient has been shown to be a function of the mobility coefficients of the free ion and its complexes together with the interionic coupling coefficients between labelled and unlabelled species. It is shown that these coefficients may be evaluated by an extension of the methods developed earlier to predict isothermal transport in such systems. Cadmium ion diffusion coefficients in aqueous cadmium iodide, Daa, have been predicted (0.003–0.10 mol dm–3). These describe the maximum anticipated experimentally. Observed and calculated Daa agree to within 3 % at 0.1 mol dm–3.

Transport in aqueous solutions of group IIB metal salts at 298.15 K. Part 5.—Irreversible thermodynamic parameters for zinc perchlorate and verification of Onsager's reciprocal relationships

The isothermal vectorial transport properties of zinc perchlorate have been measured over the concentration range 0.1–3.0 mol dm–3 at 298.15 K. Hittorf transport numbers were shown to agree with those measured earlier using concentration cells. Conductance and salt diffusion coefficients were also measured. These data were used to calculate mobility (Lik) and resistance (Rik) coefficients using irreversible thermodynamic theory. Analysis showed that the Onsager reciprocal relationships (O.R.R.) were obeyed.

Transport in aqueous solutions of group IIB metal salts at 298.15 K. Part 2.—Interpretation and prediction of transport in dilute solutions of cadmium iodide: an irreversible thermodynamic analysis

The transport data of Part 1 have been used to obtain the binary mobility coefficients (Lik) and corresponding resistance coefficients (Rik) of the salt in the range 0.05–0.60 mol dm–3. It is shown that these binary mobility coefficients are summations of the more fundamental mobility and coupling coefficients (lik) between the component ions of the complexed salt: Cd2+, CdI2–xx(x= 1, 2, 3, 4) and I–. The distribution of these complexes at each concentration have been obtained from stability constant data and used in an optimisation procedure to obtain equivalent ionic conductances of the complex ions at infinite dilution (λ°x). These data were used to estimate lik coefficients (using Pikal's method), to predict binary coefficients (Lik) and to predict the transport numbers, conductances and salt diffusion coefficients of the salt in dilute solutions. Predicted and observed data are in good agreement in dilute solutions.

Transport in aqueous solutions of group IIB metal salts at 298.15 K. Part 1.—Isothermal transport properties of cadmium iodide

The isothermal transport properties of aqueous cadmium iodide solutions have been measured in the range 0.05–0.60 mol dm–3. Transport numbers (t+) and solvent-fixed diffusion coefficients of the salt (Dv) were obtained, the former potentiometrically using cadmium amalgam concentration cells, with transference, and the latter by interferometry, using Rayleigh optics. In addition, electrical conductance measurements were made. The data are compared with existing, but incomplete, literature sources. Attention is drawn to the negative transport number of cadmium obtained in more concentrated solutions (> 0.28 mol dm–3).

Transport of Aqueous Solutions at a Mercury—Glass Interface, Induced by Electric Polarization

Transport of Aqueous Solutions at a Mercury—Glass Interface, Induced by Electric Polarization