A. S. Lileev

Orientational relaxation in hydrogen-bonded systems: aqueous solutions of electrolytes

A model of the rotational motion of water molecules within ion hydration sheaths is proposed in the present paper. This model is based on the concept of a ‘boundary’ ion, according to which the parameters of the structural surroundings, as well as the translational, rotational and librational motions of water molecules within the first sphere, are the same as those for water molecules in water. The wide-band absorption spectra, α(ν)(0 < ν/cm–1 < 400), and the complex dielectric permittivity spectrum measured for the concentrated electrolyte solutions, are described on the basis of the model proposed in this paper. It is shown that the confined rotator/extended diffusion (CR/ED) model, which has been advanced previously for liquid water, is applicable for spectral calculations of the electrolyte solutions studied in the present paper.The typical characteristics of ions having hydrophilic and hydrophobic hydration, as well as the distinctions between the hydration sheaths of ions with negative and positive hydrations, are discussed. A new method is proposed to study the molecular nature of these phenomena at the level of elementary processes. The complex dielectric permittivity of the concentrated LiCl, NaCl, Nal, KCl and KBr solutions has been measured in the range 7–25 GHz at 25 °C. For electrolyte solutions, the wide band (0 ⩽v/cm–1⩽ 1000) dielectric spectra and the parameters of the proposed model are calculated.

Microwave dielectric properties of aqueous solutions of potassium and cesium fluorides

The microwave dielectric properties of aqueous solutions of potassium and cesium fluorides are studied over a wide concentration range at frequencies of 13 to 25 GHz and temperatures of 288, 298, and 308 K. The static dielectric constant ɛs and the time τ and enthalpy of activation ΔHɛ++ of dielectric relaxation for the solutions are calculated. It is demonstrated that, for fluorides, the disruptive effect of ions on the hydrogen bond network of water is weaker than that for the other halogenides.

Temperature Changes of Dielectric Permittivity and Relaxation in Aqueous Lithium Iodide Solutions

The complex permittivity of aqueous LiI solutions is studied over a wide range of concentrations at temperatures of 288–323 K in the water permittivity dispersion region at seven frequencies in the range of 7.5–25 GHz. One relaxation region describable by the Debye or Cole-Cole equation is observed in these solutions. Dielectric relaxation time τ and static permittivity ɛs are studied as dependent on temperature and concentration. The time and enthalpy of activation of dielectric relaxation decrease in going from water to solutions, which corresponds to the distortion of the initial water structure and the increasing mobility of water molecules in hydration shells of ions. In the initial concentration range, the water activity is a linear function of 1/ɛs. The negative temperature dependence of ɛs disappears in going to concentrated solutions. At high concentrations, the static dielectric constant increases in response to increasing temperature. The new trends in ɛs and τ at elevated temperatures of 313–323 K are due to the formation of ion pairs and other ion-water groups having high dipole moments.

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.

Molecular dynamic simulations of terahertz spectra for water-methanol mixtures

Molecular dynamic (MD) simulations have been performed to probe the single molecule and collective dynamics in water–methanol mixtures. The MD simulations were carried out for mixtures with 0.0, 0.12, 0.21, 0.5 and 1.0 mol fraction of methanol at the temperature 298 K. Both translational and rotational densities of states for water and methanol molecules in the far infrared (IR) region are reported. A new method for the identification of discrete dielectric relaxation modes in molecular liquids is described. The method is based on the decomposition of autocorrelation functions (ACFs) in the time domain and enables one to obtain the distribution of characteristic times. In this work, the technique was applied to the dipole moment time ACFs for water–methanol mixtures, and the distributions of dielectric relaxation times are reported. Several distinct relaxation modes in the dielectric spectra of the mixtures are identified and the origin of composite (anomalous) dielectric spectra is discussed.

Effect of dielectric and structural properties of solutions on the polymerizability of diallylammonium-type monomers

New polymerization systems— N , N -diallyl- N -methylammonium trifluoroacetate (D1TFA) and N , N -diallylammonium trifluoroacetate (D2TFA)—exhibit phenomena that distinguish their behavior during radical polymerization (Scheme 1) from the known cases, in particular, from the quaternary N , N -diallyl- N , N -dimethylammonium chloride (D3C). These phenomena are evidence of a substantial effect of the medium on the basic polymerization characteristics of new cationogenic monomers: the initial polymerization rate V , the average length of the polymer chain P n , and the constant of chain transfer to the monomer C m [1].

Microwave dielectric permittivity and relaxation of aqueous potassium trimethylacetate solutions

The MW dielectric properties of aqueous potassium trimethylacetate (pivalate) solutions have been measured at six frequencies (10–25 GHz) at 288, 298, and 308 K. The static dielectric constants and dielectric relaxation times and activation parameters have been calculated. Trimethylacetate ion leads to the decrease in the mobility of water molecules and strengthening of their hydrogen bonds. These changes of water are similar to those in solutions of other carboxylates with a large number of nonpolar groups. The hydrophobic hydration of the trimethylacetate ion is maximal in this series.

Microwave dielectric properties of potassium hydroxide aqueous solutions

Microwave dielectric properties of potassium hydroxide aqueous solutions were studied at frequencies of 13 to 25 GHz over a wide range of concentrations and temperatures of 288 to 308 K. Experimental electrical conductivity data were used to determine ionic losses at high frequencies. The static dielectric permittivity σs, dielectric relaxation time τ, and thermodynamic activation parameters of dielectric relaxation (ΔHɛ++, ΔGɛ++, and ΔSɛ++) were calculated. These quantities decrease in transfer from water to solutions. Thereby we demonstrate that potassium hydroxide has a disturbing effect on the initial hydrogen-bond network of water.

Dielectric constant and dielectric relaxation in aqueous solutions of K2[PdCl4] and K2[PtCl4]

The MW-dielectric properties of aqueous solutions of K2[PtCl4] (I) and K2[PdCl4] (II) were studied at 298 and 313 K in the frequency range (12–25 GHz) corresponding to the maximum dielectric constant dispersion for water and aqueous solutions of these salts. The low-frequency conductivities were measured. The static dielectric constant, the dielectric relaxation time, and the enthalpy of activation of the dielectric relaxation of the solutions were determined. Compared to pure water, in solutions of salts I and II, the orientational mobility of water molecules is increased and the network of H-bonds is violated more strongly than that of most other ions with hydrophilic hydration. It was demonstrated for the first time that dielectric spectroscopy can be used for analyzing complexation processes in systems containing aqua and hydroxo chloride complexes of metals.