Concentrated Aqueous NaCl Solutions Research Articles

Enhanced Durability and Antireflective Performance of Ag-Based Transparent Conductors Achieved via Controlled N-Doping.

Ag-based transparent conductors (TCs) are often proposed as an alternative to ITO coatings. However, while their performance has been widely demonstrated, their environmental durability is frequently overlooked or addressed with the use of highly specific encapsulating layers. In this work, the durability and antireflective performance of Ag-based TCs are simultaneously enhanced. To do so, a transfer matrix modeling approach is used to determine the general requirements for high performance antireflective properties as a function of Ag thickness and dielectric refractive indices, offering more widely applicable insight into stack optimization. Coating durability is investigated as a function of the Ag microstructure, which is modified by altering the N2 concentration used for doping of the Ag layer and the selection of the seed layer. Increasing N2 concentration during Ag deposition was found to decrease grain size and durability of Ag coatings deposited on Si3N4 whereas all coatings on ZnO(Al) showed higher stability. Significantly higher durability is found when specifically combining intermediate N2 concentrations in the sputtering gas mixture (Ag(N):5%, compared to 0% and 50%) and a ZnO(Al) seed layer, and a mechanism accounting for this increased durability is proposed. The addition of NiCrNx protective coatings increases the system durability without altering these trends. These findings are combined to fabricate a highly performant Ag-based TC (TV = 89.2%, RVFS = 0.23%, 21.4 Ω), which shows minimal property changes following corrosion testing by immersion in a heated and highly concentrated aqueous NaCl solution (200 g/L, 50 °C).

Dielectric Response and Linear Absorption Spectroscopy of Ionic Systems.

Time-dependent electric fields applied to ionic systems can induce both a dielectric and a conductive response, leading to the generation of macroscopic polarization and current, respectively. It has long been recognized that it is not possible to determine the two types of responses separately. However, this aspect is often not adequately accounted for in dielectric and absorption spectroscopies of ionic systems. To clarify this, we theoretically investigate the dielectric and conductive responses of ionic systems containing polyatomic ions based on linear response theory. We derive general expressions for the frequency-dependent dielectric functions, conductivity, and absorption coefficient, including those measured experimentally. Furthermore, we show that the dielectric and conductive responses cannot be uniquely distinguished even at the theoretical level and, therefore, cannot represent experimentally measured quantities. Instead, dielectric and absorption spectra of ionic systems should be expressed in terms of the generalized dielectric function that encompasses both dielectric and conductive responses. We propose a computational method to calculate this generalized dielectric function reliably. Model calculations on concentrated aqueous solutions of NaCl, a monatomic salt, and LiTFSI, a polyatomic salt, show that the dielectric and linear absorption spectra of the two systems based on the generalized dielectric function are significantly different from purely dielectric counterparts in the far-IR, terahertz, and lower-frequency regions. Moreover, the spectra are mainly determined by the autocorrelations of total dipole and total current, but dipole-current cross-correlation can also significantly contribute to the spectra of the LiTFSI solution. The present theoretical approach could be extended to nonlinear spectroscopy of ionic liquids and electrolyte solutions.

Cluster-size distribution of ions in concentrated aqueous NaCl solutions: Molecular dynamics simulations

Recently, the properties of screening phenomena in concentrated electrolytes have attracted considerable attention. Molecular dynamics (MD) simulations were performed on an aqueous NaCl solution, and the cluster-size distribution of cations and anions was clarified. The cluster-size distribution exhibited approximately power-law decay behavior with a sufficiently high concentration. In addition, the fraction of isolated ions without pairing or clustering was also investigated. In concentrated electrolytes, the number of isolated ions does not significantly depend on the electrolyte concentration. This study clarifies the statistical physics of the cations and anions in concentrated electrolytes.

Amphiphilicity and salt-tolerance of ethoxylated and propoxylated anionic surfactants

The aqueous solubility of anionic surfactants is generally limited by their Krafft point. However, the insertion of non-ionic spacers such as ethoxy or propoxy groups between the alkyl chain and the anionic head is known to improve the water solubility of these surfactants in pure water or in the presence of electrolytes. In this work, the amphiphilicity of a series of ethoxylated or propoxylated sulfate surfactants is assessed by the PIT-slope method. Then, the phase behavior of these surfactants in concentrated aqueous solutions of NaCl or CaCl2 is investigated and compared with that of the typical nonionic (C12EO7) and ionic (SDS) surfactants. Surprisingly, sodium dodecyl sulfate presents a cloud point at high salinities and temperatures. Adding ethoxy or propoxy groups greatly enhances the resistance to electrolytes due to the “disordered” structure of non-ionic spacers that hinders crystallization, leading to Krafft point under 0 °C. Increasing the number of hydrophilic ethoxy groups increases the salt tolerance in contrast with the decrease observed with the slightly hydrophobic propoxy groups. Finally, the salt effect of CaCl2 and Ca(NO3)2. are compared pointing out the salting-out effect of Cl− and showing a weak salting-in effect of Ca2+ on nonionics and its strong interaction with sulfate anionic function.

Impact of nitrate on the redox chemistry and solubility of Tc(IV) in alkaline, dilute to concentrated aqueous NaCl solutions

The impact of nitrate on the redox behaviour and solubility of 99Tc(IV) was investigated in 0.1–5.0 M NaCl–NaNO3–NaOH solutions with 0.1 M ≤ [NO3−] ≤ 1.0 M and 8.5 ≤ pHm ≤ 14.5 (with pHm = –log [H+]) in the presence or absence of reducing agents (as Fe powder, Na2S2O4, Sn(II)). The evolution of the redox conditions as a function of time (for t ≤ 450 days) was investigated: (i) in the absence of technetium (inactive samples), (ii) in the presence of 99Tc(IV) (added as 1–2 mg of TcO2∙0.6H2O(am)), and (iii) in the presence of 137Cs(I) (and absence of 99Tc). All experiments were conducted in an Ar-glovebox (O2 < 1 ppm) at T = (22 ± 2) °C. An improved understanding of Tc redox processes in nitrate-rich alkaline solutions is relevant to predict Tc behaviour in specific nuclear waste disposal scenarios and a topic of fundamental scientific interest.Nitrate induces a clear increase in Eh over time in the investigated aqueous solutions both in the presence and absence of reducing agents. In the case of Fe powder, this increase is observed almost immediately whereas in the presence of Na2S2O4 or Sn(II) the oxidizing effect is only observed after several months in inactive systems (absence of Tc). In the presence of technetium, the increase in Eh occurs within a few days (5–50, depending upon reducing system, pHm and ionic strength). The evolution of Eh in the presence of 137Cs (with similar β– dose as in solubility experiments with 99Tc) was analogous to that in the inactive systems. These observations indicate that the solid TcO2∙0.6H2O(am) may play a role in catalysing nitrate reduction and radiation induced reactions have no significant impact in our experiments. Liquid-liquid extraction and XANES measurements confirm that technetium in the aqueous phase is mostly present as Tc(VII). Colorimetric nitrate/nitrite tests show the formation of nitrite, confirming that the oxidation of Tc(IV) to Tc(VII) is coupled to the reduction of nitrate. Our experimental observations support that, although kinetically hindered, nitrate can effectively oxidize Tc(IV).

Measurements of the complex permittivity of highly concentrated aqueous NaCl solutions and ferrofluid employing microwave cylindrical cavities

Few resonance cavities operating on different modes have been used for the accurate multi-frequency determination of the complex permittivity of highly concentrated aqueous NaCl solutions at a frequency range of 2.5 GHz to 24 GHz. It has been shown that the use of the perturbation method would lead to significant measurement uncertainties especially for lossy samples and should be avoided especially for TE0n1 mode cavities. At frequencies that are smaller than 15 GHz the imaginary part of the permittivity of NaCl solutions increases while at frequencies larger than 15 GHz it decreases, with the increasing conductivity of the electrolyte. In the last case the total dielectric losses for the saturated electrolyte are noticeably smaller than for pure water. The complex permittivity and complex permeability of ferrofluid, liquid that exhibits diamagnetic properties at microwave frequencies, were measured by employing two cylindrical cavities operating on complementary modes.

Dielectric properties and high-frequency conductivity of the sodium chloride-water system

An analysis has been performed of the dielectric characteristics and high-frequency (hf) electrical conductivity (EC) of aqueous solutions of NaCl. A method of the estimation of the static dielectric constant and of the time of dipole relaxation of concentrated aqueous solutions of NaCl in a wide range of concentrations and temperatures has been suggested. It has been shown that the limiting hf EC of the solutions and the hf EC at the frequency of 2455 MHz decrease with increasing salt concentration and differently change with increasing temperature: the limiting hf EC increases, whereas the hf EC at the frequency of 2455 MHz decreases. The decrease in the hf EC leads to a reduction of the rate of the hf heating of the NaCl solution with increasing salt concentration.

Synthesis of porous poly[oligo(ethylene glycol) methyl ether methacrylate] gels that exhibit thermosensitivity in highly concentrated aqueous NaCl solution

The polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) in 20 wt% aqueous ethanol solution and oligo(ethylene glycol) methyl ether methacrylate (OEGMA300, Mn = 300 g mol−1) in water was carried out in the presence of a crosslinker. Polymerization at temperatures above the lower critical solution temperature (LCST) yielded the corresponding porous poly[oligo(ethylene glycol) methyl ether methacrylate] gels by polymerization-induced phase separation. The resulting porous gels showed rapid swelling-deswelling in water. The temperature dependency of the equilibrium swelling ratio of the gels was investigated in several concentrated aqueous NaCl solutions. At 20 °C, the equilibrium swelling ratios of the POEGMA300 gel obtained from OEGMA300 were largely unaffected by NaCl concentration; however, above 30 °C, they decreased with increasing NaCl concentration. Therefore, the POEGMA300 gel showed sharp and high thermosensitivity in highly concentrated aqueous NaCl solutions. Similar swelling behaviors were observed for PMEO2MA gel, which was prepared from MEO2MA.

Microstructural evolution during experimental albitization of K-rich alkali feldspar

Crystals of K-feldspar (C2/m), in contact with highly concentrated aqueous NaCl solutions at 500°C and 200 MPa, are pseudomorphically replaced by high albite $$ (C\bar{1}) $$ as a result of an interface-coupled dissolution/reprecipitation process. The reaction occurs at an extremely sharp reaction front (<10 nm) and involves the complete breakdown of the initial framework structure. This results in the release of tetrahedrally incorporated elements such as Fe3+ and Ti4+ and a significant increase in Si/Al disorder across the reaction interface. The evolving microstructure is controlled by crystallographic relations between the phases. This leads to highly anisotropic, sawtooth-shaped intergrowths of albite and initial K-feldspar, resulting in the least structural misfit between the two framework structures. As a result, the newly formed interfaces appear to be semicoherent, and cracks across the reaction fronts even indicate elastic strain. The reaction produces 2 distinctive albite types (albite-1 and albite-2). Both are polycrystalline, with albite-2 showing significantly larger subgrain sizes. This indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product. The reaction also produces a highly porous rim. However, the porosity is not evenly distributed resulting in a porous albite-1 and a non-porous albite-2 that mostly surrounds large, euhedral pores. Despite the substantial volume fraction of porosity in albite-1, no significant 3D interconnectivity could be detected, making the presence of a pervasive porosity unlikely. However, the result of coarsening is the continuous modification of the 3D porosity distribution. This could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved.

Structural features of concentrated aqueous NaCl solution in the sub- and supercritical state at different densities

The structural properties of 4.37 m NaCl(aq) at sub- and supercritical conditions (1. p = 25 MPa, Т = 450–750 K, ρ = 1.054–0.188 g/cm 3; 2. p = 250 MPa, Т = 823 K, ρ = 0.867 g/cm 3) are studied by the extended RISM integral equation method. The behavior of pair correlation functions and partial coordination numbers is analyzed. The structural features of the investigated system are discussed in the framework of a clustering hypothesis. According to the obtained results the solution structure transforms from a state characterized by hydrated ions and contact ion pairs (in the subcritical region) to a structure where non-H-bonded water molecules and low-molecular weight cluster conformations predominate (in the low density supercritical region). The structural features of the highly dense supercritical NaCl solution can be defined by free H 2O molecules and larger clusters.

Copper(I) π‐Complexes with 2‐Butyne‐1,4‐diol. Synthesis and Crystal Structure of Na[CuCl2(HOCH2C≡CCH2OH)]·2H2O

AbstractCrystals of anionic Na[CuCl2(HOCH2C≡CCH2OH)]·2H2O π‐complex have been synthesized by interaction of 2‐butyne‐1,4‐diol with CuCl in a concentrated aqueous NaCl solution and characterized by X‐ray diffraction at 100 K. The crystals are triclinic: space group $P{\bar 1}$, a = 7.142(3), b = 7.703(3), c = 10.425(4) Å, α = 105.60(3), β = 99.49(3), γ = 110.43(3)°, V = 495.9(4) Å3, Z = 2, R = 0.0203 for 3496 reflections. The structure is built of discrete [CuCl2(HOCH2C≡CCH2OH)]− anionic stacks and polymeric $\rm [Na^{+}(H_{2}O)_{2}]_{\infty}$ cations among the stacks. The CuI atom adopts trigonal planar coordination of two Cl− anions and the C≡C bond of 2‐butyne‐1,4‐diol, Cu–(C≡C) distance is equal to 1.903(3) Å. Na+ cations environment is octahedral and consists of O and Cl atoms. The crystal packing is governed by strong hydrogen bonds of O–H···Cl and O–H···O types.

Effects of ion concentration on the hydrogen bonded structure of water in the vicinity of ions in aqueous NaCl solutions

Molecular dynamics simulations of dilute and concentrated aqueous NaCl solutions are carried out to investigate the changes of the hydrogen bonded structures in the vicinity of ions for different ion concentrations. An analysis of the hydrogen bond population in the first and second solvation shells of the ions and in the bulk water is done. Although essentially no effect of ions on the hydrogen bonding is observed beyond the first solvation shell of the ions for the dilute solutions, for the concentrated solutions a noticeable change in the average number of water-water hydrogen bonds is observed in the second solvation shells of the ions and even beyond. However, the changes in the average number of hydrogen bonds are found to be relatively less when both water-water and ion-water hydrogen bonds are counted. Thus, the changes in the total number of hydrogen bonds per water are not very dramatic beyond the first solvation shell even for concentrated solutions.

Forces between Mica Surfaces, Prepared in Different Ways, Across Aqueous and Nonaqueous Liquids Confined to Molecularly Thin Films

We have measured normal and lateral interactions across a range of different liquids between mica surfaces using a surface force balance (SFB). The mica surfaces were prepared either by melt cutting using Pt wire and standard procedures in our laboratories or by tearing sheets (that had not been exposed to Pt) off from a freshly cleaved sheet of mica. AFM micrographs revealed the substantial absence of Pt nanoparticles on the melt cut and torn-off mica surfaces. Normal-force versus surface-separation (D) profiles and shear force versus D measurements for purified water (no added salt), for concentrated aqueous NaCl solutions, and for cyclohexane revealed that in all cases the behavior of the highly confined liquids between melt-cut and between torn-off mica sheets was identical within experimental scatter. These results demonstrate directly that interactions measured between melt-cut mica surfaces as routinely prepared using established procedures in our laboratories and in other laboratories are free of the effect of any Pt contamination.

Large ionic clusters in concentrated aqueous NaCl solution

The stability of the local structure of aqueous 1.0 M NaCl solution at 293 K was investigated by molecular dynamics simulations. The mean and maximum life-times of the ion pairs were determined to be 0.13, 0.14 and 0.27 ps for negatively charged, neutral and positively charged ions pairs, respectively. The stability of non-neutral ion pairs was studied from the structure of the anion–cation radial distribution function and other structural functions. We found that non-neutral ions pairs are stabilized by at least one counter-ion forming in this way large ionic clusters that include the hydration molecules. About 25% of the ions are included in neutral clusters formed by a minimum of four ions. The existence of these large clusters obfuscates the commonly accepted chemical reaction scheme for the interconvention of ion pairs in aqueous solutions.

Structure of concentrated aqueous NaCl solution: A Monte Carlo study

The structure of aqueous NaCl 1 M solution was studied by Monte Carlo simulation data obtained with 2117 rigid water molecules 40 Na+ and 40 Cl− at 293 K. The structural features were determined from the usual radial distribution functions, angular-radial distribution functions, angular correlations and the mean force potential. The ion hydration structure was obtained as such as the structure of ions associations. The first hydration shell structure is almost not affected by the finite concentration. The second shell is concentration dependent mainly with respect to the tilt angle. The cation hydration is less affected than the anion hydrated shell. Anion–cation, anion–anion and cation–cation pairs were detected. A fraction 0.46 of the cations and 0.32 of the anions are associated in pairs formed by two ions sharing, at least, two water molecules in their solvation shells. The idealized structures of all pairs include two to four water molecules located in such a way that the attractive energies are increased and the repulsive ones decreased. The structure of 1 M NaCl is also determined by recovering the water tetrahedral structure around the solute ions and by the stabilizing influence of water molecules that are shared by the ions. The last conclusion is that about 20% of the water molecules lose some degree of freedom because they solvate directly the solute. Almost all the water molecules are involved to some degree in the ion solvation.

Measurement and correlation of the activity coefficients of H+ and HSO3- in concentrated aqueous solutions of NaCl.

The activity coefficients of HSO3– and H+ were determined in concentrated aqueous solutions of NaCl in order to provide a theoretical basis for using sea water as a solvent in flue gas desulfurization processes.The activity coefficient of HSO3– was determined at 313 K and 323 K by measuring the pH of mixtures of NaCl, H2O and small amounts of NaHSO3 at a known partial pressure of SO2. The activity coefficient of H+ was determined over a temperature range of 296 K–333 K by measuring the pH of mixtures of NaCl, H2O and small amounts of HCl.As the ionic strength increased, the activity coefficient of HSO3– decreased while that of H+ increased. The Pitzer Equation could correlate the activity coefficients of both species with reasonable accuracies for practical use.

The photoelastic behaviour of swollen networks of polymethacrylic acid

The visoelastic photoelastic behaviour of cross-linked polymethacrylic acid, swollen to equilibrium in variously concentrated aqueous NaCl solutions ( c x = 0.05-1.5 M), was studied. In the rubber-like region, stress and birefringence relaxation at various elongations (λ) can be separated into the deformation- and time-dependent parts. Both the extrapolated equilibrium modulus ( G r ) and the interaction parameter (χ) strongly depend on the degree of swelling of the gel. One of the most interesting findings is that the exponent of the volume fraction of the polymer ( ν 2) in the dependence of the modulus G e on ν 2 is much higher than 1/3 as predicted by the theory of Gaussian networks, if the concentration of the crosslinking agent c is low. The same is true for the Mooney-Rivlin constant ( C 1) even if the ratio C 2 C 1 approaches zero at lower ν 2. The values of the stress-optical coefficient ( C e ) increase with both increasing swelling and decreasing content of the cross-linking agent in the gel; the most pronounced increase in C e is connected with the largest decrease in G e . The same dependence of C e on the modulus in the dry state ( G d ), irrespective of the concentration of the cross-linking agent and c s , suggests the conclusive role played by the macroform contribution to birefringence. The effects found are probably due to the disappearance of the secondary structure of PMA chains with increasing swelling and concentration of the cross-linking agent.

Embrittlement of polycrystalline silver chloride

The first page of this article is displayed as the abstract.

ON THE SOLUBILITY OF ANHYDROUS CALCIUM SULPHATE AND OF GYPSUM IN CONCENTRATED SOLUTIONS OF SODIUM CHLORIDE AT 25 °C, 30 °C, 40 °C, AND 50 °C

The solubilities of anhydrous CaSO4 and CaSO4.2H2O in concentrated aqueous solutions of NaCl at a series of temperatures—25 °C, 30 °C, 40 °C, and 50 °C, have been determined. It was found that the transition temperature for the reaction[Formula: see text]which in pure water has a value of 42 °C, is shifted progressively to lower temperatures with increasing NaCl concentration. It was also found that the variation of the transition temperature with NaCl concentration could be adequately represented by the equation[Formula: see text]where ΔG, ΔH, and ΔS are the Gibbs free energy, enthalpy, and entropy of the reaction and P0 and P are the vapor pressures of pure water and the solution respectively at the absolute temperature T.