Hydration and dielectrical properties of aqueous pyrrolidinium trifluoroacetate solutions

Results from microwave measurements of the dielectrical properties of aqueous pyrrolidinium trifluoroacetate solutions at maximum water dispersion frequencies (13–25 GHz) and temperatures of 288, 298, and 308 K are given. The static dielectrical constants, times, and activation parameters of the dielectrical relaxation of solutions are calculated. The enthalpy and time of dielectrical relaxation activation are increased by deceleration of the motion of water molecules in the hydrate shells of ions. The changes in dielectrical parameters are in this case minimal in a series of aqueous solutions of diallylammonium salts with cations of different structures and degrees of substitution. It is shown that pyrrolidinium ions are characterized by weak hydrophobic hydration.     

Two-sided Runge-Kutta method accurate to sixth order for second-order ordinary differential equations

A family of two-sided Runge—Kutta formulas accurate to sixth order is constructed for numerical solution of the Cauchy problem for second-order ordinary differential equations, which are solved for the highest derivative and have a sufficiently smooth right-hand side. Two-sided approximations to the sought solution are obtained after up to nine evaluations of the right-hand side of the differential equation in each integration step. The efficiency of the proposed formula is demonstrated in application to two test examples.Sumy Teachers' College. Kiev Teachers' College. Translated from Vychislitel'naya i Prikladnaya Matematika, No. 68, pp. 45–51, 1989.     

Polarization effects in thin layers of SiO2 and Al2O3

For film metal-dielectric-metal and hybrid-metal-dielectric-semiconductor systems based on pyrolytic fully grown films of SiO₂ and Al₂O₃ the dependence of the remanent polarization coefficient on the magnitude of the field in the films and the short circuit time was investigated. The nature of relaxation processes related to remanent polarization effects was analyzed.The authors take the opportunity to express their gratitude to A. S. Bashakidze for help in carrying out the measurements.     

Structural Specifics of the Concentration Dependence of Sound Velocity in Aqueous Solutions of Electrolytes

The concentration dependences of sound velocity in aqueous solutions of electrolytes are analyzed over a wide range of concentrations (with extrapolation to 100% salt). For many systems, the concentration dependence of the square of sound velocity is linear up to the values corresponding to overcooled salt melts. For these solutions, an expression for partial molar compressibility of salts in infinitely dilute solutions is derived based on the additivity of the squares of sound velocities of the solution components, where the salt component is an overcooled melt. For alkali halides, there is good agreement between the values of calculated in this way and the values obtained by extrapolation of the apparent molar compressibility in the low-concentration region using the concentration dependences of density and the solution compressibility coefficient. For systems of this type, where hydration is the dominant process, sound velocity in hydration shells and complex ion groups is constant (i.e., independent of concentration). The effects are interpreted in terms of the concept of redistribution of the fixed structural groups in two concentration zones of a solution, where 1) the hydration groups are built in the structure of water in a complementary way; 2) the fragments of hydration spheres and the ionic clusters are united with each other in a complementary way.     

Effect of dielectric properties and structure of aqueous solutions of diallylammonium salts on their reactivity in radical polymerization

The complex dielectric permittivity in the frequency range 7.5–25.0 GHz and the low-frequency specific conductivity of aqueous solutions of diallylammonium salts (diallylammonium and diallylmethylammonium trifluoroacetates and diallyldimethylammonium chloride) were measured at 293–308 K over a wide concentration range. On the basis of the results, the parameters of dielectric relaxation were calculated. The number of water molecules in the solvation shell of the salts was estimated. The concentration behavior of the initial rate of radical polymerization of diallylammonium salts and the rate constant of bimolecular chain termination was correlated with the specific features of the structure of aqueous monomer solutions. The role of “free” water in the initial salt solutions was revealed, a species whose presence in the system determines the character of concentration behavior of the rate constants for the elementary steps of polymerization, such as propagation, chain transfer to the monomer, and bimolecular chain termination.     

Microwave dielectric properties of aqueous potassium iodide solutions as a function of temperature

The complex dielectric permittivity of aqueous KI solutions was studied for molalities of 0.50–4.01 m and temperatures of 288–323 K in the region of water dielectric permittivity dispersion. The values of high-frequency of dielectric permittivity (ε) and dielectric losses (ε″) were obtained at seven frequencies ranging between 7.5 and 25 GHz. The low-frequency electrical conductivity of the aforementioned solutions was measured for calculating ionic losses. A single relaxation process is observed in these solutions, fitted by the Debye or Cole-Cole equation with small distribution parameters. The static dielectric constant and dielectric relaxation time were studied as functions of temperature and concentration; the activation enthalpy of dielectric relaxation was calculated. The temperature dependence of the static dielectric constant was found to disappear in highly concentrated solutions. The structure-breaking effect on water caused by K⁺ and I⁻ ions was affirmed, this effect disappearing in going to elevated temperatures.     

The IR Absorption Spectra of Aqueous Solutions of Dimethylsulfoxide over the Frequency Range 50–300 cm−1 and the Mobility of Water Molecules

The IR absorption spectra of aqueous solutions of dimethylsulfoxide (DMSO) with concentrations from 100% H₂O to 100% DMSO were recorded over the frequency range 50–500 cm^?1. The absorption spectra were described using the theoretical scheme of hindered rotators. A model was developed according to which orientation relaxation in solution was related to separate rotations of H₂O and DMSO molecules through fixed small and (or) large angles in a unified network of H-bonds consisting of several subsystems ordered to various degrees. The calculated absorption spectra were in agreement with the experimental data in the far IR region. Elementary motions of molecules were found to slow down in the passage from pure dimethylsulfoxide to its aqueous solutions. The special features of the hydrophilic and hydrophobic hydration of DMSO polar and nonpolar groups were considered.