Non-linear dielectric polarization of water solutions in dioxane

The dielectric polarization and its change in an external electric field were measured for dioxane—water diluted solutions up to 0.3 molar fraction of water. The results were found to be qualitatively similar to those previously observed for dioxane—alcohols mixtures.     

Pseudospinodal curve for binary solutions determined from the non-linear dielectric effect

Non-linear dielectric effect (NDE) measurements were used to determine the pseudospinodal curves for nitrobenzene—hexane and benzonitrile—hexane solutions. Values obtained for universal magnitudes describing pseudospinodals are in good agreement with theoretical predictions and with experimental values found by other methods. The power exponent describing the temperature changes of NDE decreases with increasing distance from the critical concentration.     

The non-linear dielectric effect in liquid xenon

The non-linear dielectric effect (NLDE), that is the increase in the dielectric constant divided by the square of the applied field, is measured for a number of non-polar molecular liquids and for liquid xenon. The values of the NLDE are compared with results in the literature and with values predicted by theory. The agreement with other experiments is quite good, but with theory is very poor, the only exception being Liquid xenon, where agreement is good. A possible explanation is given. The prediction that the NLDE should increase strongly near the critical point due to the divergence of the isothermal compressibility could not be established by experiment. The conclusion is drawn that this failure is due to the reduction by the theory of second-order effects to first-order thermodynamic and molecular properties.     

Electrospray-ionization driven by dielectric polarization

A non-conductive piezo ceramic plate has been used to induce an electric field to generate an electrospray as ionization method for mass spectrometric determination. This technique decreases the risk of undesired discharges, induced by high electric currents. The applicability of the technique is demonstrated and compared with a commercial electrospray for mass spectrometric determination of reserpine and myoglobin.     

Dielectric polarization of a partially neutralized poly(methacrylic acid) in dilute aqueous solutions: Conformational transition

Dielectric permittivity ε′ (at a frequency of 1 MHz) of aqueous solutions of a partially neutralized poly(methacrylic acid) Na-PMAA was studied with varying the degree of ionization α_i from 0 to 0.78 and concentrations w ₂ (g/g) from 1.25 × 10^?4 to 6 × 10^?3 at 25°C. It was shown that the concentration dependence of ε′ for Na-PMAA aqueous solutions at all α_i values contains two regions corresponding to different changes in ε′, and the above regions are separated by the crossover point w*₂. In the first region, ε′ increases with the increasing concentration Δε′/Δw ₂ > 0; in the second region, ε′ decreases with the increasing concentration Δε′/Δw ₂ < 0. The sign inversion of Δε′/Δw ₂ is explained by different structures of water and mechanisms of hydration in regions I and II. In the region corresponding to the ascending branch of the ε′-w ₂ curve, the dipole moments of macromolecules per repeating unit, μ = (〈M ²〉/N)^1/2, were calculated according to the Buckingham theory. The μ value is high; as a macromolecule is saturated with ionized units, this value nonmonotonically changes from ～10 D at α_i = 0 to ～18 D at α_i ～ 0.24. This dependence peaks at ～30 D at α_i ～ 0.1. As is assumed, (〈M ²〉/N)^1/2 depends on the vector sum of partial dipole moments of hydrated nonionized monomer units (μ ～10 D) and fluctuation-induced dipole moments of ionized monomer units. The profile of μ as a function of the degree of ionization of Na-PMAA indicates the occurrence of the conformational transition in an individual macromolecule. This transition takes place at the degree of ionization α_i ～ 0.1. An analysis of molecular interactions in the (ionized coil)-solvent system explans the conformational transition in Na-PMAA.     

Dielectric relaxation in some polyacrylate solutions

The dielectric constant ?′ and loss factor ?″ of poly(butyl acrylate), poly(butyl methacrylate), and poly(isobutyl methacrylate) solutions are reported in the frequency region of 1 kHz to 24.42 GHz at four different temperatures of 27, 40, 50, and 60°C. Cole–Cole plots are plotted to obtain the distribution parameter and relaxation time. The activation energies are evaluated assuming dielectric relaxation to be a rate process in these solutions. A possible relaxation mechanism is discussed.     

The non-linear dielectric effect in xenon. The density dependence

The density dependence of the non-linear dielectric effect in xenon is measured. Experiments were performed along an isotherm with a reduced temperature T* = 1.01 in a reduced density range 0.1 to 1.8. There is a large disagreement with theory, which in first order leads to electrostriction. Arguments are given why experimental conditions and the construction of the measuring cell in our case exclude electrostriction. The results are explained in terms of first- and second-order effects. Use is made of the close relation with the theory of light scattering in first and second order. It is possible to write the non-linear dielectric effect as a sum of two terms, one linear in the density and the other increasing with σ*³. Quantitative estimates for the value of the coefficient of σ*³ cannot be given because of lack of knowledge of four-point correlation functions.     

Nonlinear dielectric effect in benzonitrile and lauronitrile solutions

The nonlinear dielectric effect, NDE, and the calculated correlation factors R^p and R^s are reported for binary solutions of benzonitrile and lauronitrile in benzene and cyclohexane. Substantial differences found for solutions in these two solvents have been explained in terms of critical phenomena in cyclohexane solution.     

Computer simulation of interfacial polarization in stratified dielectric systems

Time and frequency dependent dielectric properties of bilayer dielectrics are treated with components showing dielectric relaxation. The time dependent behaviour can be calculated using the Boltzmann superposition principle. The exact integro-differential equations are derived, and the boundary conditions discussed. The analytical formulae resulting for the frequency domain are an extension of those published for bilayer dielectrics with nonrelaxing components. For the time domain the numerical solution is preferred because the analytical solution is very complicated. After a short discussion of the numerical method some examples are presented, and the effect of various component parameters on the dielectric properties is studied.The main conclusion is that two types of interfacial polarization mechanisms must be distinguished: the classical ohmic, and the dielectric. The latter is the consequence of the polarizational surface charge density, and influences strongly the observed relaxation strengths of the components.Presented at the 20. Jahrestagung Organische Festkörper, July 1983, Brandenburg, German Democratic Republic     

Dielectric relaxation of nitroalkanes in dilute solutions

The relative permittivity at frequencies of 10kHz and 10GHz and the refractive indices have been measured for dilute solutions of (a) nitroethane, (b) 1-nitropropane, (c) 2-nitropropane, and (d) 1-nitrobutane in cyclohexane at 10°, 20°, 30° and 40°C. Materials (b) and (c) together with (e)2-nitro 1-propanol and (f) 2-nitro-l-butanol, have also been studied in different nonpolar solvents. The electric dipole moments, the dielectric relaxation times, and the molar activation energy parameters have been calculated. The results for nitroalcohols show the existence of internal hydrogen bonding between the hydroxyl group and an oxygen atom of the nitro group. The plots of log τ versus log η for materials (b) and (c) are linear for the solvents n-heptane, cyclohexane and decalin. The possibility of interaction of these materials with p-xylene, carbon tetrachloride and p-dioxane are discussed. Activation enthalpy (ΔH_ε) of these materials is observed to be higher in dilute solutions than in pure liquids, and also ΔH_ε for nitrobutane is significantly lower than for the other materials.     

Dielectric behaviour of Gelatin solutions and Gels

 Sol and Gel state properties of aqueous gelatin solutions of concentrations 4%, 6%, 8% and 10% (w/v) have been investigated through dielectric relaxation studies done at various temperatures in the range T=20–60 °C carried out over a frequency range f=20 Hz–10 MHz and no relaxation of any nature was observed. The sharp transition observed at the gelation temperature T _gel provided an excellent matching with the same measured through differential scanning calorimetry (DSC). The capacitance (C _p) values above f=100 kHz became increasingly negative as the gel was melted to the sol state. However, in the gel state C _p was found to be almost independent of temperature for frequencies above 100 kHz. At frequencies lower than 10 kHz, C _p measured was ∼10⁵ F, implying pronounced interfacial polarization either due to electro-chemical reaction or because of ions getting trapped at some interface within the bulk. Received: 10 February 1997 Accepted: 2 September 1997     

Dielectric relaxation of electrolyte solutions in acetonitrile

Complex permittivity spectra in the frequency range 0.95v (GHz)89 for acetonitrile and its solutions of LiBr, NaI, NaClO₄, and Bu₄NBr at 25°C show one Debye equation for the neat solvent whereas the superposition of a Debye process for the solute and a Cole-Cole distribution for the solvent is necessary to account for the dielectric relaxation behavior of the solutions. The reorientation of bulk acetonitrile is diffusive and only weakly coupled to viscosity. The number of solvent molecules irrotationally bound to the electrolyte is in good agreement with conventional solvation numbers for all electrolytes, when kinetic depolarization is assumed to be negligible. The solute relaxation process is dominated by the formation kinetics and reorientation of contact ion pairs. There is evidence for solvent-shared ion pairs in dilute NaClO₄ solutions.     

New formulation and implementation for volume polarization in dielectric continuum theory

In the use of dielectric continuum theory to model bulk solvation effects on the electronic structure and properties of a solute, volume polarization contributions due to quantum mechanical penetration of the solute charge density outside the cavity nominally enclosing it are known to be significant. This work provides a new formulation and implementation of methods for solution of the requisite Poisson equation. In previous formulations the determination of the surface polarization contribution required evaluation of the difficult to calculate electric field generated by the volume polarization. It is shown that this problematic quantity can be eliminated in favor of other more easily evaluated quantities. That formal advance also opens the way for a more efficient apparatus to be implemented for calculation of the direct contribution of volume polarization to the solvation energy. The new formulation and its practical implementation are described, and illustrative numerical results are given for several neutral and ionic solutes to study the convergence and precision in practice.     

Dielectric polarization and polarizability of 1-pentanol+n-octane mixtures from static dielectric constant and refractive index data at 0,25 and 45°C

Static dielectric constants and refractive indices of 1-pentanol+n-octane mixtures were measured in the temperature range between 0 and 45°C. Data discussed in terms of Kirkwood correlation factor and Lorentz-Lorenz molar refractivity give information on the short range intermolecular interactions between the components. The role played by the nonpolar n-octane in the destruction of 1-pentanol oligomers is also pointed out.