Boiling temperatures and excess thermodynamic functions of 2-propanol-n-alkyl propanoate solutions

Boiling temperatures of five binary systems are measured by ebuliometer in the pressure range of 5.333?C101.3 kPa. The compositions of equilibrium vapor phases in the systems are calculated using the constructed saturated vapor pressure isotherms as a base. The excess Gibbs energies, excess enthalpies, and excess entropies of solutions are calculated from our data on liquid-vapor equilibria. Regularities in the changes of phase equilibria and thermodynamic properties of solutions with the composition and temperature of the system are established. Vapor-liquid equilibria in the systems are described by the Wilson and NRTL equations.     

On the relation between thermodynamic,transport and structural properties of electrolyte solutions

The relation between thermodynamic, transport and structural properties of electrolyte solutions is explored for volumes and radii of ions in solution, water structure making and breaking by ions, ion pairing, and electromotive force of cells with transport, and preferential solvation of ions in mixed solvents. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 1, pp. 18–31. The text was submitted by the authors in English.     

On the thermodynamic equilibrium between ice and electrolyte solutions in the conditions of confined geometry

For a small volume (of about 10⁻⁶ cm³) of NaCl and other electrolyte solutions (C = 0.1 and 1 M) in thin (r = 5/10 μm) single quartz capillaries, dependencies of the column length l of frozen solutions on the temperature t were measured using comparator IZA-2 in a thermostated chamber. At temperatures range t > −4 °C (for C = 0.1 M) and t > −8 °C (for C = 1 M) the l(t) dependencies are reversible and therefore correspond to establishment of an equilibrium between ice-1 and the solution.

From the constants mass condition of the dissolved salt in a frozen column, the l(t) expression was derived, which includes thermodynamic relation between solution concentration in an equilibrium with ice, C_s, and the temperature t for bulk systems. Deviations from the data known for bulk solutions were observed in thin capillaries when temperature t decreased to −3 °C (for 0.1 M NaCl) and to −6 °C for 1 M NaCl solution.

This effect may be a result of strong adhesion of the ice column to capillary walls. In this case, some internal stresses arise in frozen solution resulting in a deviation from thermodynamic equilibrium conditions for bulk systems. When approaching the temperature of ice melting, adhesion forces decrease due to formation of a thin non-freezing water interlayer on the capillary wall. In this temperature range the experimental data are in agreement with the predictions for bulk systems. It was supposed that the observed deviation in thin capillaries may be caused by formation of an amorphous ice phase with higher density as compared with the ice-1 during rapid freezing, or by an effect of ice microlenses formation. Both effects will result in a deviation from the phase diagram corresponding to a bulk solution.     

Effect of the electrolyte concentration on cation binding in aqueous surfactant solutions.

Electrospray ionisation mass spectrometry (ESI-MS) is used for the qualitative and quantitative study of ion binding to interfaces. The ESI-MS measurements are carried out in aqueous solutions of sodium dodecyl sulphate (SDS) in the presence of NaCl, NH(4)ClO(4) , KCl, or Mg(ClO(4))(2) . The effect of the electrolyte concentration on the fractions, y(cation(+) ), of the DS(-) monomers bound to the cations is shown. Moreover, the binding stability of different cations with DS(-) monomers is determined versus the electrolyte concentration. This stability and the y(Na(+) ) values (the Na(+) ions derived from SDS), estimated in the presence of a given electrolyte, are quantitatively correlated with the electrolyte cation effect on the water structure. We also present calibration curves from which the molar concentrations of the sodium ions (derived from SDS) and of the other cations (derived from the electrolyte), bound to the SDS-micelle surface at a given electrolyte concentration, can be obtained. Besides, specific ion effects (Hofmeister effects) are considered for 1:1 electrolytes.     

Symmetrical radial distribution functions in the potentially theory of electrolyte solutions

A symmetrical radial distribution function g_ij in electric double layer theory has been proposed by Féat and Levine. We adopt their work to the electrolyte bulk to show how a symmetrical g_ij may be obtained in the potential theory of electrolyte solutions.     

Dielectric analysis of nanofiltration membrane in electrolyte solutions: influences of electrolyte concentration and species on membrane permeation

Dielectric properties of a nanofiltration membrane immersed in dilute aqueous electrolyte solutions were measured, and frequency dependence of capacitance and conductance of the systems was analyzed, based on the interfacial polarization theory, giving values of permittivity and conductivity of the membrane and the solutions. Permittivity, epsilon m, of the membrane slightly decreased whereas conductivity, km, of the membrane increased with increasing electrolyte concentration, as a result of entrance of ions into the membrane. The ratio of membrane/solution conductivity, km/kw, also depended on the electrolyte concentration, showing that distribution of ions in the membrane and in solutions follow Donnan equilibrium, due to the presence of negative fixed charges in the membrane. New expressions were derived from Donnan equilibrium principle to explain this phenomenon, and negative fixed charge concentration ce of the membrane was obtained; thus the Donnan potential, DeltaPhi Don, of the membrane in solutions at various concentrations could be calculated. The new expressions could be expected to be usable to analyze ion permeation property through membrane.     

Consideration of the volume changes in describing concentration front migration in electrolyte solutions

It is possible to avoid certain difficulties in describing the diffusion in electrolyte solutions by taking into account the process of spatial rearrangement of species that accompanied the concentration variations and was recently introduced into consideration. The experimental substantiation of taking into account this process is the different concentrations of solvent, i.e., water, observed in solutions of different concentrations.     

The thermodynamic characteristics of hydrogen peroxide in H2SO4-H2O solutions

The paper presents experimental data and an analysis of literature data on hydrogen peroxide forms in concentrated solutions of sulfuric acid, H₂O₂(aq), H₃O ₂ ⁺ (aq), and HSO ₅ ^? (aq). The thermodynamic constants of the parallel equilibria $\begin{array}{*{20}c} {H_2 O_2 (aq) + H_3 O^ + (aq) \Leftrightarrow H_3 O_2^ + (aq) + H_2 O (K_1 (298) = 8 \times 10^{ - 4} ),} \\ {H_2 O_2 (aq) + HSO_4^ - (aq) \Leftrightarrow HSO_5^ - (aq) + H_2 O (K_2 (298) = 1.2 \times 10^{ - 2} )} \\ \end{array} $ were determined. The activity coefficients of H₂O₂ and Henry constants for solutions of H₂O₂ in sulfuric acid were calculated.     

The thermodynamic functions of 4f metal dichlorides in the condensed state

The temperature dependences of heat capacity were obtained for solid 4f metal dichlorides LnCl₂ (Ln = La, …, Lu) in the quasi-harmonic approximation over the temperature range from 0 K to the melting point T _m . The correction for systematic underestimation of the lattice heat capacity component in this approximation was determined from high-temperature EuCl₂ heat capacity measurements. The literature data were analyzed to select the temperatures and enthalpies of phase transitions and estimate the heat capacities of the substances in the liquid state. The thermodynamic functions of LnCl₂ in the condensed state were calculated over the temperature range 298.15–2000 K. The calculations were performed taking into account excited electronic states whose energies did not exceed 10000 cm^?1.     

Effects of electrolyte concentration and counterion valence on the microstructural flow regimes in dilute cetyltrimethylammonium tosylate micellar solutions

The shear thickening behavior and the transition to shear thinning are examined in dilute cetyltrimethylammonium tosylate (CTAT) micellar solutions as a function of surfactant concentration and ionic strength using electrolytes with different counterion valence. Newtonian behavior at low shear rates, followed by shear thickening and shear thinning at higher shear rates, are observed at low and intermediate surfactant and electrolyte concentrations. Shear thickening diminishes with increasing surfactant concentration and ionic strength. At higher surfactant or electrolyte concentration, only a Newtonian region followed by shear thinning is detected. A generalized flow diagram indicates two controlling regimes: one in which electrostatic screening dominates and induces micellar growth, and another, at higher electrolyte and surfactant concentrations, where chemical equilibrium among electrolyte and surfactant counterions controls the rheological behavior by modifying micellar breaking and reforming. Analysis of the shear thickening behavior reveals that not only a critical shear rate is required for shear thickening, but also a critical deformation, which appears to be unique for all systems examined, within experimental error. Moreover, a superposition of the critical shear rate for shear thickening with surfactant and electrolyte concentration is reported.     

Isobars of the boiling temperature and isotherms of excess thermodynamic functions of isobutanol-alkyl ketone solutions

The boiling temperatures for solutions of five binary systems are measured via ebulliometry in the pressure range of 5.333–101.3 kPa. The isotherms constructed for the pressure of saturated vapor serve as the base for computing the compositions of equilibrium vapor phases of the systems. The excess Gibbs energies, enthalpies, and entropies of solutions are computed from the data on liquid-vapor equilibrium. The laws of changes in the phase equilibria and thermodynamic properties of solutions are determined depending on the composition and temperature of the systems. The vapor-liquid equilibrium of the systems is described by Wilson and NRTL equations.     

Experimental and theoretical study of the displacement process between two electrolyte solutions in a microchannel

Displacement of one electrolyte solution by another in a microchannel is required in many biolab chip devices. The objective of this paper is to develop a better understanding of the displacement process between two electrolyte solutions under an applied electric field in a cylindrical microchannel in terms of the traveling distance of the interface between these two electrolyte solutions. In order to develop a general model to predict the location of the interface, two different situations are considered; one model assumes the presence of a sharp interface between the two solutions and the other model considers a mixing zone between the two solutions. Carefully conducted experiments were carried out to obtain the current-time relationship, which is used in the model to predict the location of the interface. In these experiments, deionized ultrafiltered water (DIUF water), 10 mM KCl, 0.1 mM KCl, and 0.1 mM LaCl3 solutions were used as the testing liquids. Polyamide-coated silica capillary tubes of internal diameter 100 mum and length 10 cm were employed in this study. The relationship between traveled distance of the interface and time was predicted by a developed model based on the measured current-time relationship for such a displacement process under a constant applied electric field. The characteristics of the nonlinear change of the traveling distance with the time were also discussed in this paper.     

The thermodynamic characteristics of formation of ternary sulfides MeLn2S4 and solid solutions based on them

The thermodynamic characteristics of formation of ternary sulfides CaGd₂S₄ and BaTm₂S₄ from Ca(Ba)S and Gd₂(Tm₂)S₃ binary sulfides were determined using various modifications of the electromotive force method. Activity and cationic and anionic transfer numbers in extended phases based on MeLn₂S₄ were studied simultaneously. CaGd₂S₄ and BaTm₂S₄ were found to be stable over the electrolytic temperature range 653–723 K. The stability boundaries of phases based on CaY₂S₄. BaTm₂S₄, CaPr₂S₄, and CaSm₂S₄ were determined. A vacancy mechanism of defect formation with predominantly sulfide ion transfer was suggested for sequential doping of ternary with binary sulfides.     

The effect of pH,chloride ion and background electrolyte concentration on the SERS of acidified pyridine solutions

Surface enhanced Raman spectra of pyridine are reported as a function of pH, halide concentration and background electrolyte concentration. The assignments of pyridinium bands are given in the range 100–4000 cm^?1, and the low frequency band around 235 cm^?1 is discussed. It is found that to obtain a pyridinium spectrum, the presence of halide is necessary. Background electrolyte concentration does not affect the intensity of the pyridine spectrum but greatly affects that of pyridinium. On the basis of the dependence of the intensity of pyridinium on chloride and background electrolyte concentrations, pyridinium is considered not be directly adsorbed on the electrode surface but rather located in the diffuse double layer and associated with specifically adsorbed chloride to form an ion pair.The in-situ measurement of pH and the SERS of pyridine and pyridinium during a pH titration reveal a linear relation between surface pH and bulk pH. Specifically adsorbed chloride causes a decrease in the surface pH. This decrease is explained by a shift of the electrostatic potential at the outer Helmholtz plane caused by specific adsorption of chloride.     

Effect of NiO nanofiller concentration on the properties of PEO-NiO-LiClO4 composite polymer electrolyte

Composite polymer electrolyte films comprising polyethylene oxide (PEO) as the polymer host, LiClO₄ as the dopant, and NiO nanoparticle as the inorganic filler was prepared by solution casting technique. NiO inorganic filler was synthesized via sol-gel method. The effect of NiO filler on the ionic conductivity, structure, and morphology of PEO-LiClO₄-based composite polymer electrolyte was investigated by AC impedance spectroscopy, X-ray diffraction, and scanning electron microscopy, respectively. It was observed that the conductivity of the electrolyte increases with NiO concentration. The highest room temperature conductivity of the electrolyte was 7.4?×?10^?4 S cm^?1 at 10 wt.% NiO. The observation on structure shows the highest conductivity appears in amorphous phase. This result has been supported by surface morphology analysis showing that the NiO filler are well distributed in the samples. As a conclusion, the addition of NiO nanofiller improves the conductivity of PEO-LiClO₄ composite polymer electrolyte.