Ranges of frequency dispersion for the shear viscosity coefficients of aqueous solutions of electrolytes

The range of frequency dispersion for dynamic coefficient of shear viscosity η _S (ω) of electrolyte solutions obtained through kinetic equations under the condition of recovering the steady-state structure of a liquid exponentially or according to the diffusion law is considered. Numerical calculations of η _S (ω) are performed for an aqueous solution of NaCl depending on density ρ, temperature T, concentration C, and frequencies ω to select the potential of intermolecular interaction Φ _ab (|r|) and equilibrium radial distribution function g _ab (|r|). It is noted that the calculated theoretical results of η _S (ω) are in quantitative accordance with the experimental data. It is shown that the range of frequency dispersion η _S (ω) based on the diffusion mechanism is broad (～10⁵ Hz) and is narrow in the case of exponential attenuation of the viscous stress tensor (～10² Hz); this corresponds to both acoustic measurements and results from phenomenological theory.     

Temperature and concentration dependences of the activity coefficients of electrolytes

A model has been suggested that describes the interaction of hydrated ions in electrolytes and allows the calculation of the main physical effects. The model explains the character of the curves of the activity coefficients. Binary solutions of uni-univalent electrolytes at concentrations from zero to several moles per liter and at temperatures from zero to a few dozens of degrees were studied. The results of simulation were verified by comparing them with many literature data.     

The frequency dispersion of dynamic transfer coefficients and elastic moduli of magnetic liquids

The analytic equations for viscosity coefficients and the corresponding elastic moduli obtained in [3] were used to calculate these values over a wide range of reduced frequency values (ω* ≈ 10^?7?10). The volume η _v (ω) and shear η _s (ω) viscosity coefficients decreased as the frequency increased. The dispersions η _v (ω) and K _r (ω) were only caused by the contribution of structural relaxation, and the dispersions η _s (ω) and μ(ω), by translational and structural relaxation. The shear elastic modulus μ(ω) and relaxation volume elastic modulus K _r (ω) increased as the frequency grew. The results obtained were in satisfactory agreement with the conclusions from general relaxation theory.     

On the adequacy of modeling the concentration dependences of the activity coefficients for the components of solutions

An analysis of the accepted methods for calculating the activity coefficients for the components of binary aqueous solutions was performed. It was demonstrated that the use of the osmotic coefficients in auxiliary calculations decreases the accuracy of estimates of the activity coefficients. The possibility of calculating the activity coefficient of the solute from the concentration dependence of the water activity was examined. It was established that, for weak electrolytes, the interpretation of data on heterogeneous equilibria within the framework of the standard assumption that the dissociation is complete encounters serious difficulties.     

Nonmonotonic concentration dependences of elastic light scattering and its fluctuations in aqueous solutions

A nonmonotonic bimodal dependence of elastic, Rayleigh scattering on the potassium phenosan concentration in an aqueous solution has been revealed. A similar dependence has been found, for the first time, for scattering amplitude fluctuations. The observed correlation is indicative of structural transitions in hydration shells of potassium phenosan, which are responsible for the increase and scatter of their size comparable with the wavelength (527 nm) of a laser spectrometer.     

The temperature dependences and methods for the functional representation of the rates of proton magnetic relaxation in aqueous solutions of electrolytes

The paper presents the results of temperature dependence measurements for the rate of proton relaxation (1/T ₁) in sea water with salinity 35‰ over the temperature range −22−+120°C at atmospheric pressure and in some salt solutions at two concentrations (0.5 and 1 mol/l). The possibility of approximating the temperature dependences of magnetic relaxation rates by various functions in pure water, sea water, and solutions of salts with various concentrations was studied. The parameters of these dependences and trends of their variations under the influence of salt components are reported. The most well grounded method for the functional representation of the temperature dependences of 1/T ₁ is the use of the sum of exponents with the number of terms depending on solution concentration. This representation takes into account structural changes in solutions as the concentration grows and corresponds to the Frenkel model of the thermal motion of molecules in aqueous solutions of electrolytes. The combined use of the parameters of the temperature dependences of the rate of relaxation represented by various functions can be a mutually augmenting method for studying the dynamic properties of aqueous solutions of electrolytes with low and moderate concentrations.     

Dependence of the frequency dispersion of the bulk viscosity coefficient of solutions of electrolytes on the nature of the decay of relaxing fluxes

The region of the frequency dispersion of the bulk viscosity coefficient η_V(ω) of solutions of electrolytes is studied as a function of the nature of the decay of the stress tensor in the momentum and configuration space, the analytical expressions of which are derived by means of kinetic equations. Numerical calculations of η_V(ω) for a water solution of NaCl are performed over a wide range of frequencies, temperatures, and densities using a selection of the potentials of intermolecular interaction Φ{in{itab}}(|\(\vec r\)|) and radial distribution function {itg}{in{itab}}(|\(\vec r\)|). It is shown that the region of frequency dispersion η_V(ω) based on the power law of the decay of the stress tensor is wide (~10⁵ Hz), while the region based on the exponential law is narrow (~10² Hz).     

Phase diagrams and the thermodynamic Flory-Huggins interaction parameter of deformed solutions of polymers

It is assumed that the interaction parameter used in the Flory-Huggins theory may depend on the mechanical field. The effect of deformation on phase transitions in polymer solutions is considered under this assumption. An expression relating the thermodynamic parameter of interaction between the components to deformation conditions is proposed. Quantitative relations describing shifts in liquidus lines and spinodals of polymer-solvent systems in mechanical fields are derived.     

Preparation of high damping elastomer with broad temperature and frequency ranges based on ternary rubber blends

Based on the blends of chlorinated butyl rubber (CIIR), nitrile butadiene rubber (NBR) and chloroprene rubber (CR), a kind of high damping elastomer with broad temperature and frequency ranges is prepared. CIIR/NBR binary blend is prepared to take advantage of the immiscibility and the large difference in cross‐link density of the different phases caused by the curatives and accelerators migration. The dynamic mechanical analysis reveals that the binary blend was immiscible and its loss factor (tanδ) versus temperature curves show two separated and expanded loss peaks when compared with those of pure cured CIIR and NBR. In order to improve its damping properties at room temperature, the third component CR with the polarity between CIIR and NBR was blended into the binary blend. The resulted CIIR/NBR/CR ternary blend has gained effective damping properties (tanδ > 0.3) in the temperature range of ?86.4 to 74.6°C and the frequency range of 10^?2 to more than 10⁹ Hz. Other effects on the damping properties of the ternary rubber were also studied. Copyright © 2013 John Wiley & Sons, Ltd.     

Calculations of the thermodynamic properties of dimethylsulfoxide-water solutions on the basis of the cluster solvation model

The thermodynamic functions of dimethylsulfoxide mixtures with water were analyzed over the whole composition range using the cluster solvation model taking into account the distribution of clusters over solvation numbers. The equations of the model were shown to correctly describe the concentration dependences of saturated vapor pressure and excess enthalpy and volume on the assumption of dimethylsulfoxide hydration. The hydration numbers of dimethylsulfoxide and the variance of the distribution of hydrates over stoichiometric numbers were shown to increase as the temperature decreased.     

Effect of temperature on thermodynamic characteristics of the dissociation of glycylglycine in aqueous solutions of electrolytes

Heats of reaction of glycylglycine with nitric acid and potassium hydroxide solutions are determined by two calorimetric procedures at 288.15, 298.15, 308.15 K and an ionic strength of solution of 0.25, 0.50, and 0.75 in the presence of KNO₃. Standard thermodynamic characteristics (Δ_r H°, Δ_r G°, Δ_r S°, and Δ_p C°) are calculated for the acid-base reactions in aqueous peptide solutions. The effects of the concentration of background electrolyte and temperature on the heats of dissociation of glycylglycine are considered.     

Effect of simple electrolytes on the thermodynamic properties of room temperature ionic liquids in aqueous solutions

Density, sound velocity and conductivity measurements are carried out on 1-heptyl-3-methylimidazolium bromide ([C₇mim][Br]) in pure water and in aqueous solutions of sodium di-hydrogen citrate, di-sodium hydrogen citrate and tri-sodium citrate over a range of temperatures at atmospheric pressure. The experimental density and sound velocity data are used to calculate the apparent molar volume and isentropic compressibility as a function of temperature and concentration. The effects of temperature and charge on the anion of sodium citrate salts on the apparent molar volume and isentropic compressibility of [C₇mim][Br] are studied. It was found that both of the apparent molar volume and isentropic compressibility of [C₇mim][Br] in aqueous sodium citrate solutions are larger than those in pure water and increase by increasing temperature. The effects of temperature and charge on the anion of sodium citrate salts on the conductivity behavior of the investigated IL solutions are also studied.     

Thermodynamics of aqueous NH4Br solutions over wide ranges of concentrations and temperatures

The enthalpies of solution and dilution of aqueous solutions of NH₄Br at electrolyte concentrations lower than 6 mol/kg solvent are measured at 277 and 288 K. The generalized equation for the enthalpy as a function of concentration and temperature is derived using the data for 298 and 313 K. The thermodynamic properties of NH₄Br solutions at concentrations up to saturated solutions and at temperatures of 273, 298, 323, and 348 K are discussed.     

Lewis-Randall to McMillan-Mayer conversion for the thermodynamic excess functions of solutions. Part III. Common-ion mixtures of two electrolytes

Derivations are given for the equations expressing the thermodynamic coefficients that characterize the process of mixing two electrolytes with a common ion in the McMillan-Mayer system in terms of the coefficients for the corresponding process in the Lewis-Randall system, together with correction terms made up of various Lewis-Randall thermodynamic coefficients of the solutions. In the former case, the solutions are mixed at fixed molar ionic strength (i.e., fixed Debye kappa), fixed temperature, and fixed chemical potential of the solvent. In the latter case they are mixed at fixed molal ionic strength, fixed temperature, and fixed total pressure on the solutions.