Concentrated Aqueous Salt Solutions Research Articles

Experimental verification of increased electronic excitation energy of water in hydrate-melt water by attenuated total reflection-far-ultraviolet spectroscopy.

The demand for Li secondary batteries is increasing, with the need for batteries with a higher level of performance and improved safety features. The use of a highly concentrated aqueous electrolyte solution is an effective way to increase the safety of batteries because it is possible to use "water-in-salt" (WIS) and "hydrate-melt" (HM) electrolytes for practical applications. These electrolytes exhibit a potential window of >3.0V, which is attributed to the difference between the HOMO and the LUMO energies of the n orbital of the pure water molecules and that of the water molecules in the hydration shells of a metal ion, according to theoretical predictions. Thus, in the present study, the attenuated total reflectance (ATR)-far-ultraviolet (FUV) spectra of water and super-concentrated aqueous solutions, such as WIS and HM using a Li salt, were experimentally investigated. The effects of anions, cations, and deuteriums on the ATR-FUV spectra were examined. The ATR-FUV method is an excellent means of studying highly concentrated aqueous salt solutions. The results suggest that the transition energy of water molecules in an ultrahighly concentrated aqueous electrolyte containing HM and WIS increased by nearly 0.4eV (corresponding to an energy shift of over 10nm) compared to an aqueous electrolyte with a typical water concentration. It was also revealed that the transition energy of water changes depending on the environment of the non-bonding electron, which is directly connected with or affected by hydrogen bonding with other water molecules or directly connected with Li+.

Cationic Sterically Stabilized Diblock Copolymer Nanoparticles Exhibit Exceptional Tolerance toward Added Salt.

For certain commercial applications such as enhanced oil recovery, sterically stabilized colloidal dispersions that exhibit high tolerance toward added salt are desirable. Herein, we report a series of new cationic diblock copolymer nanoparticles that display excellent colloidal stability in concentrated aqueous salt solutions. More specifically, poly(2-(acryloyloxy)ethyltrimethylammonium chloride) (PATAC) has been chain-extended by reversible addition-fragmentation chain transfer aqueous dispersion polymerization of diacetone acrylamide (DAAM) at 70 °C to produce PATAC100-PDAAMx diblock copolymer spheres at 20% w/w solids via polymerization-induced self-assembly. Transmission electron microscopy and dynamic light scattering (DLS) analysis confirm that the mean sphere diameter can be adjusted by systematic variation of the mean degree of polymerization of the PDAAM block. Remarkably, DLS studies confirm that highly cationic PATAC100-PDAAM1500 spheres retain their colloidal stability in the presence of either 4.0 M KCl or 3.0 M ammonium sulfate for at least 115 days at 20 °C. The mole fraction of PATAC chains within the stabilizer shell was systematically varied by the chain extension of various binary mixtures of non-ionic poly(N,N-dimethylacrylamide) (PDMAC) and cationic PATAC with DAAM to produce ([n] PATAC100 + [1 - n] PDMAC67)-PDAAMz diblock copolymer spheres at 20% w/w. DLS studies confirmed that a relatively high mole fraction of cationic PATAC stabilizer chains (n ≥ 0.75) is required for the dispersions to remain colloidally stable in 4.0 M KCl. Cationic worms and vesicles could also be synthesized using a binary mixture of PATAC and PDMAC precursors, where n = 0.10. However, the vesicles only remained colloidally stable up to 1.0 M KCl, whereas the worms proved to be stable up to 2.0 M KCl. Such block copolymer nanoparticles are expected to be useful model systems for understanding the behavior of aqueous colloidal dispersions in extremely salty media. Finally, zeta potentials determined using electrophoretic light scattering are presented for such nanoparticles dispersed in highly salty media.

Electrochemical Behavior of Stainless Steels in Highly Concentrated Electrolytes

Due to the superior mechanical properties and corrosion resistance of stainless steels, their application as exterior material and current collector has been examined. Recently, concentrated aqueous solutions of lithium salts are highly expected as a novel electrolyte because they allow the safe operation of lithium ion batteries, different from conventional organic solvent based electrolytes. Therefore, understanding on the electrochemical behavior of stainless steels in concentrated aqueous solutions is crucial to judge the applicability of stainless steels to lithium ion batteries. It is well-known that electrochemical behavior of metals in concentrated aqueous solution is different from that in dilute aqueous solution. The difference is considered to be attributed to chemical state of water molecules. In the present work, electrochemical behavior of stainless steels in highly concentrated aqueous solution of lithium trifluoromethanesulfonate was examined.

Electrostatic Screening Length in Concentrated Salt Solutions

Thin films (0-30 nm) of very concentrated aqueous monovalent salt solutions (2-10 M of LiCl, NaCl, and CsCl) were examined to determine how ionic strength affects the screening length of the electrostatic potential. Measurements were consistent with a screening length in the range of 3-12 nm. The screening length increased monotonically as a function of salt concentration, and the rate of increase was a function of the monovalent salt type. The results were incompatible with the Debye length of Poisson-Boltzmann theory but consistent with previous measurements of surface forces. The screening length was determined from the surface excess of fluorescein, a dianion under basic conditions, which was present in trace amounts in the thin film and detected via its fluorescence emission. That is, we directly observed that the ion concentration in very concentrated solutions is perturbed far from an interface.

Plasma Polishing of Stainless Steels – The Electrolyte Concentration Vs. Gloss Level

Abstract The technology of plasma polishing in electrolyte is considered as environmental friendly alternative to the common electrochemical polishing process. The solutions of the electrolyte use no acids or toxicants, but the environmental safe, low concentrated aqueous solutions of various inorganic salts are used instead. The dependence of the gloss level of the treated surface upon the electrolyte concentration as well as upon the voltage is examined in this paper. The specimens of stainless steel were used for plasma polishing in ammonium sulphate based electrolyte. The influence of the voltage on the overall properties of the process is discussed, as well.

Aerosol Brown Carbon from Dark Reactions of Syringol in Aqueous Aerosol Mimics

We performed a laboratory investigation of the chemical processing of syringol, a representative model phenolic compound emitted from wood burning, in concentrated aqueous salt solutions mimicking tropospheric aerosol particles. For solutions containing chloride salts, we observed the formation of light-absorbing organic products (“brown carbon”), accompanied by a phase separation, within 10 h under dark conditions. Products were characterized at the molecular level using ultraperformance liquid chromatography interfaced to diode array detection and high-resolution quadrupole time-of-flight mass spectrometry equipped with electrospray ionization and matrix-assisted laser desorption/ionization interfaced to high-resolution time-of-flight mass spectrometry. The ultraviolet–visible spectra, together with high-resolution mass spectra results, suggest that syringol can be oxidized by dissolved oxygen, and the presence of Cl– promotes this reaction. Our results provide new insights into the evolution of aerosol...

High-Voltage Aqueous Supercapacitors Based on Natfsi

Replacing the acetonitrile-based electrolyte in state-of-the-art supercapacitors by an aqueous electrolyte could make these devices environmentally more benign, improve operational safety, and render supercapacitors potentially more cost efficient. The narrow electrochemical stability window of water (~1.23 V) is the main challenge in order to increase the energy density of water based devices. Recently it was reported that ultra-highly concentrated aqueous salt solutions can provide stability windows up to 3 V1. Salt concentrations higher than 21 mol kg-1 lead to increased kinetic stability, but result in reduced ionic conductivities of typically less than 10 mS cm-1. This renders such systems unsuitable for high power applications such as supercapacitors. In a recent study, we report beneficial effects in terms of electrochemical stability and conductivity for a moderately concentrated 8m NaTFSI aqueous solution2. Following a stringent test procedure, the stability window was determined to be 1.8 V and an ionic conductivity of 48 mS cm-1 was obtained, the latter being on par with modern organic electrolytes. A 1.8 V carbon/carbon supercapacitor displayed high maximum energy density of 14.4 Wh kg-1 on the activated carbon mass level and stable cycling over 100,000 cycles. Redox active potassium iodide was added to the system in order to boost its maximum specific energy to the very high value of 37.8 Wh kg-1, which is comparable to the performance of currently available commercial acetonitrile based supercapacitors. Suo, L.; Borodin, O.; Gao, T.; Olguin, M.; Ho, J.; Fan, X.; Luo, C.; Wang, C.; Xu, K., "Water-in-salt" electrolyte enables high-voltage aqueous lithium-ion chemistries. Science 2015, 350, 938. Reber, D.; Kühnel, R.-S.; Battaglia, C., High-voltage aqueous supercapacitors based on NaTFSI. Sustainable Energy Fuels 2017, doi: 10.1039/C7SE00423K

Preferential solvation, ion pairing, and dynamics of concentrated aqueous solutions of divalent metal nitrate salts.

We have investigated the characteristics of preferential solvation of ions, structure of solvation shells, ion pairing, and dynamics of aqueous solutions of divalent alkaline-earth metal nitrate salts at varying concentration by means of molecular dynamics simulations. Hydration shell structures and the extent of preferential solvation of the metal and nitrate ions in the solutions are investigated through calculations of radial distribution functions, tetrahedral ordering, and also spatial distribution functions. The Mg2+ ions are found to form solvent separated ion-pairs while the Ca2+ and Sr2+ ions form contact ion pairs with the nitrate ions. These findings are further corroborated by excess coordination numbers calculated through Kirkwood-Buff G factors for different ion-ion and ion-water pairs. The ion-pairing propensity is found to be in the order of Mg(NO3)2 < Ca(NO3)2 < Sr(NO3)2, and it follows the trend given by experimental activity coefficients. It is found that proper modeling of these solutions requires the inclusion of electronic polarization of the ions which is achieved in the current study through electronic continuum correction force fields. A detailed analysis of the effects of ion-pairs on the structure and dynamics of water around the hydrated ions is done through classification of water into different subspecies based on their locations around the cations or anions only or bridged between them. We have looked at the diffusion coefficients, relaxation of orientational correlation functions, and also the residence times of different subspecies of water to explore the dynamics of water in different structural environments in the solutions. The current results show that the water molecules are incorporated into fairly well-structured hydration shells of the ions, thus decreasing the single-particle diffusivities and increasing the orientational relaxation times of water with an increase in salt concentration. The different structural motifs also lead to the presence of substantial dynamical heterogeneity in these solutions of strongly interacting ions. The current study helps us to understand the molecular details of hydration structure, ion pairing, and dynamics of water in the solvation shells and also of ion diffusion in aqueous solutions of divalent metal nitrate salts.

Огнетушащая эффективность пены, полученной из концентрированных солевых растворов

Приведены результаты, полученные в ходе систематических экспериментальных исследований процесса тушения пламени нефтепродуктов подачей пены, полученной из концентрированных солевых растворов, в основание резервуара. Определены зависимости коэффициента растекания водно-солевого раствора по поверхности гептана и гептана по водно-солевому раствору пенообразователя с содержанием хлорида аммония. Выявлено, что с ростом концентрации хлорида аммония в растворе пенообразователя происходит увеличение минимального удельного расхода раствора фторированного пенообразователя более чем в 2 раза и оптимальной интенсивности подачи пены в 1,5 раза. Показана зависимость времени тушения пламени гептана от интенсивности подачи пены, полученной из водно-солевого раствора пенообразователя. Выявлено, что снижение способности горючего растекаться по раствору пенных пленок приводит к повышению огнетушащей эффективности, что выражается в снижении минимального удельного расхода раствора пенообразователя и оптимальной интенсивности подачи пены.

Salts Forming Low-Melting Eutectics with Water: BET Parameters

The BET parameters r for the number of sites and e for the excess molar enthalpy for adsorption of water on the salts, were obtained from their osmotic coefficients in concentrated aqueous salt solutions, as functions of their molalities, from the literature. The salts dealt with are those that form low melting eutectics with water that have not been studied in this respect previously. Most of the data pertain to 298.15 K, but a few data at other temperatures could also be dealt with.

Polymerization of vinyl fluoride in ionic liquid and ionic solutions

Poly(vinyl fluoride) films are extensively used as protective, easy-clean materials in the photovoltaic and aerospace industries. However, polymerization of vinyl fluoride (VF) monomer typically requires high pressures (>5000 psi) due to the low solubility of VF monomer in the aqueous polymerization medium. VF was found to exhibit high solubilities in fluorinated ionic liquids and concentrated aqueous ionic salt solutions at low pressures (<1000 psi). Polymerization of vinyl fluoride in the presence of ionic liquids or ionic salt solutions was pursued as a means of reducing the pressure needed to achieve high monomer conversion and molecular weight. The use of traditional ionic liquids possessing alkylimidazolium cations paired with fluorinated anions as solvents for VF polymerization resulted in poor conversion of vinyl fluoride, likely due to hydrogen atom abstraction from the alkyl substituents on the imidazolium cations. Polymerization of VF in the presence of lithium salts of the ionic liquid anions (trifluoromethylsulfonyl imide [Tf2N], triflate, and trifluoroacetate), on the other hand, resulted in high VF conversion and production of high molecular weight polymer at low VF pressures. The morphology of the resultant polymer consisted of fractal-like aggregates, and mixtures of the polymer with the aqueous ionic salt solutions formed viscous pastes.

Tube-Super Dielectric Materials: Electrostatic Capacitors with Energy Density Greater than 200 J·cm-3.

The construction and performance of a second generation of super dielectric material based electrostatic capacitors (EC), with energy density greater than 200 J·cm−3, which rival the best reported energy density of electric double layer capacitors (EDLC), also known as supercapacitors, are reported. The first generation super dielectric materials (SDM) are multi-material mixtures with dielectric constants greater than 1.0 × 105, composed of a porous, electrically insulating powder filled with a polarizable, ion-containing liquid. Second-generation SDMs (TSDM), introduced here, are anodic titania nanotube arrays filled with concentrated aqueous salt solutions. Capacitors using TiO2 based TSDM were found to have dielectric constants at ~0 Hz greater than 107 in all cases, a maximum operating voltage of greater than 2 volts and remarkable energy density that surpasses the highest previously reported for EC capacitors by approximately one order of magnitude. A simple model based on the classic ponderable media model was shown to be largely consistent with data from nine EC type capacitors employing TSDM.

Mechanisms of Acceleration and Retardation of Water Dynamics by Ions

There are fundamental and not yet fully resolved questions concerning the impact of solutes, ions in particular, on the structure and dynamics of water, which can be formulated as follows: Are the effects of ions local or long-ranged? Is the action of cations and anions on water cooperative or not? Here, we investigate how the reorientation and hydrogen-bond dynamics of water are affected by ions in dilute and concentrated aqueous salt solutions. By combining simulations and analytic modeling, we first show that ions have a short-ranged influence on the reorientation of individual water molecules and that depending on their interaction strength with water, they may accelerate or slow down water dynamics. A simple additive picture combining the effects of the cations and anions is found to provide a good description in dilute solutions. In concentrated solutions, we show that the average water reorientation time ceases to scale linearly with salt concentration due to overlapping hydration shells and structural rearrangements which reduce the translational displacements induced by hydrogen-bond switches and increase the solution viscosity. This effect is not ion-specific and explains why all concentrated salt solutions slow down water dynamics. Our picture, which is demonstrated to be robust vis-a-vis a change in the force-field, reconciles the seemingly contradictory experimental results obtained by ultrafast infrared and NMR spectroscopies, and suggests that there are no long-ranged cooperative ion effects on the dynamics of individual water molecules in dilute solutions.

Simulation study of ion pairing in concentrated aqueous salt solutions with a polarizable force field

The accuracy of empirical force fields is critical for meaningful molecular dynamics simulations of concentrated ionic solutions. Current models are typically developed on the basis of single ion properties such as the monohydrate energy in the gas phase, or the absolute hydration free energy at infinite dilution. However, the failure of these models to represent accurately the properties of concentrated solutions cannot be excluded. Here, these issues are illustrated for a polarizable potential based on classical Drude oscillators. To model accurately concentrated ionic solutions, the parameters of the potential functions are optimized to reproduce osmotic pressure data. The sodium-chloride potential of mean force in solution calculated from the empirically-adjusted model is consistent with the results from that calculated from ab initio CPMD simulations.

Speciation in Aqueous Solutions of Nitric Acid Estimated Within the Binding mean Spherical Approximation (BiMSA)

This work is aimed at a description of the thermodynamic properties of highly concentrated aqueous solutions of nitric acid salts at 25¡C. The predictive capability of the binding mean spherical approximation (BIMSA) was examined. First, Raman spectroscopy was used to study the proportion of associated nitric acid as a function of concentration. The corresponding apparent association constant values were compared with literature values. Besides, the BIMSA model led to an assessment of the degree of association. The so-calculated amount of associated nitric acid coincides accurately with our Raman experimental results up to a high concentration of acid.

Mussel-Inspired Chemistry for Robust and Surface-Modifiable Multilayer Films

In this article, we report a bioinspired approach to preparing stable, functional multilayer films by the integration of mussel-inspired catechol oxidative chemistry into a layer-by-layer (LbL) assembly. A polyanion of poly(acrylic acid-g-dopamine) (PAA-dopamine) bearing catechol groups, a mussel adhesive protein-mimetic polymer, was synthesized as the building block for LbL assembly with poly(allylamine hydrochloride) (PAH). The oxidization of the incorporated catechol group under mild oxidative condition yields o-quinone, which exhibits high reactivity with amine and catechol, thus endowing the chemical covalence and retaining the assembled morphology of multilayer films. The cross-linked films showed excellent stability even in extremely acidic, basic, and highly concentrated aqueous salt solutions. The efficient chemical cross-linking allows for the production of intact free-standing films without using a sacrificial layer. Moreover, thiol-modified multilayer films with good stability were exploited by a combination of thiols-catechol addition and then oxidative cross-linking. The outstanding stability under harsh conditions and the facile functionalization of the PAA-dopamine/PAH multilayer films make them attractive for barriers, separation, and biomedical devices.

Temperature‐concentration oscillations as a result of nanoheterophase structure of concentrated aqueous solutions of salts

AbstractDetailed precision investigation of aqueous solutions of NaBr·2H2O, KBr, RbNO3, and K2SO4 salts showed oscillations of crystal‐solution phase equilibria in the temperature range of 15–45 °C. The maximum deviations from the smooth correlation between the saturation temperature and the salt concentration (up to 4% of concentration and up to 10 °C) were found to correspond to simplest salt‐water ratios. Recently, similar trends were observed for NaNO3, KNO3 and K2CrO4 solutions. Oscillation amplitudes for saturation temperature in the investigated series decreased in the following orders: Na+→K+, Rb+, NH4+ (nitrate systems), CrO42–→SO42– and Br–→NO3– (potassium systems), and NO3–→Br– (sodium systems). Increase in total content of impurities (2‐4‐fold) in solution results in 1.5‐2‐fold elevation of the oscillation amplitudes. A concept of nanoheterophase solution was suggested to account for the observed temperature‐concentration oscillations. The concept is based on the original experimental data on interrelated variation of different properties of aqueous salt solutions depending on their concentrations. Characteristic features of the phase diagrams are discussed and influence of the oscillations on crystal growth is elucidated. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Ternary system H2O-CO2-NaCl at high T-P parameters: An empirical mixing model

New experimental data on the solubility of NaCl in gaseous CO2 were obtained at pressures (P) of 30–70 MPa and temperatures of 623 and 673 K on experimental equipment making possible to sample a portion of the gas in the course of the experiment. The new measures have demonstrated that the NaCl solubility increases with increasing temperature (T) and pressure and is approximately four to five orders of magnitude higher than the saturated vapor pressure of NaCl at the corresponding temperature. The paper also reports newly obtained experimental data on the equilibrium conditions of the reaction of talc decomposition into enstatite and quartz at a variable H2O/NaCl ratio in the fluid. The results of the experiments validate the empirical equations previously suggested for H2O and NaCl activities in concentrated aqueous salt solutions that can be used in describing silica-saturated fluids at high T-P parameters. A new empirical equation is suggested for the Gibbs free mixing energy in the H2O-CO2-NaCl ternary system, with the parameters of the equation calibrated against experimental data on phase equilibria in marginal binary systems and on the location of the boundary of the region of homogeneous three-component fluid according to data on synthetic fluid inclusions in quartz.

Nitric acid: modeling osmotic coefficients and acid–base dissociation using the BIMSA theory

This work is aimed at a description of the thermodynamic properties of highly concentrated aqueous solutions of nitric acid salts at 25 °C within the binding mean spherical approximation (BIMSA) theory. The predictive capability of this model was examined. First, Raman spectroscopy was used to study the proportion of associated nitric acid as a function of concentration. The corresponding apparent association constant values were compared with literature values. Besides, the BIMSA model, taking into account complex formation, was used to represent literature experimental osmotic coefficient variation with concentration. This theoretical description led to an assessment of the degree of association. The so calculated amount of associated nitric acid coincides accurately with our Raman experimental results up to a high concentration of acid.

Mixing behaviour of charged and non-charged surfactants described by BET isotherms

We analysed various sets of published results concerning the mixing behaviour of charged and non-charged surfactants, beyond their aggregation threshold, by means of the BET model modified by Stokes and Robinson. This approach, which is mainly used to account for properties of concentrated aqueous salt solutions, provides a good description of the properties of mixed micelles across the complete scale of compositions between the two pure surfactants. We use analyses of the behaviour of several systems reported in the literature for illustration. We consider the significance of the parameters C and r introduced in the BET model. For mixed micelle solutions in the presence of a support electrolyte, the value of the solvation enthalpy of the charged amphiphile by the non-ionic surfactant is small ( C close to one). This model is compared to the regular solution theory (RST).