Dielectric Relaxation Parameters Research Articles

Dielectric Properties of the Free Water in Hydroxypropyl Cellulose

We performed dielectric measurements of aqueous solutions of hydroxypropyl cellulose (HPC) with various concentrations in the temperature range between 25 °C and -20 °C. A primary relaxation process due to the motion of free water restricted by HPC molecules is observed at GHz region. The relaxation time and shape parameter of the primary process strongly depend on the concentration of HPC. The change of the dielectric relaxation parameters is interpreted by the results of the formation of a cholesteric phase structure of the HPC molecules.

Dielectric properties of thermally degraded chloroprene rubber

We performed dielectric measurements on thermally aged carbon-black-filled chloroprene rubber (CR). Primary and secondary processes were observed in unaged and thermally aged CR. The primary process is due to the cooperative motion of chloroprene chains in CR, and the secondary process is due to the local motion of chloroprene chains. For the primary process, the relaxation time slightly increases and symmetric shape parameter of the loss spectrum decreases with increasing aging time. For the secondary process, the relaxation strength decreases with increasing aging time, and reaches zero after 50 h. These changes in the dielectric relaxation parameters are due to the progress of the dehydrochlorination reaction at the chloroprene chains.

On a universal relation for defect data in solids

We show that the defect data parameters related to various defect processes, e.g., formation, migration, dielectric relaxation parameters, obey a universal law. In particular, the defect entropies scale with the defect enthalpies irrespective of the process considered. A concrete example is given here for SrF 2 by considering the dielectric relaxation parameters ( R 1 relaxation mechanism) for crystals doped with trivalent ions of Ce, Eu, and Gd, parameters for the anion-Frenkel formation as well as for the migration of anion vacancy and the anion interstitial motion.

Dielectric Relaxation of Water in Hydration Shells of Ions

Microwave spectroscopy has been used to study the dielectric properties of aqueous electrolyte solutions over a wide range of concentrations, the frequency range (7 to 25 or 7 to 120) GHz, and the temperature range (283 to 313 or 288 to 308) K. The static dielectric permittivity, dielectric relaxation time, and activation enthalpy have been calculated for 46 binary systems. General relations between dielectric relaxation parameters and structural effects in aqueous salt solutions are considered. The increase in the order of complementary structural organization for water in the bulk and hydration shells of ions gives rise to the molecular-kinetic stabilization of water and to the structure-making effect. This explains the difference between dielectric relaxation characteristics for a wide variety of electrolyte solutions. We present systematic dielectric data for aqueous electrolytes with hydrophilic and hydrophobic hydration of cations and anions. The temperature effect is also examined. On the basis of ...

10.1007/s11498-008-3005-8

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.

Dielectric relaxation and dispersion studies of mixtures of 1-propanol and benzonitrile in pure liquid state at radio and microwave frequencies

Complex permittivity of 1-propanol, benzonitrile and their binary mixtures over a range of concentrations was obtained in radio and microwave frequency range at various temperatures. Vector network analyzer (VNA) operating in the frequency range 0.3 MHz to 3.0 GHz was used to obtain complex permittivity spectra. Complex permittivity of the liquid samples at two spot frequencies 9.1 GHz and 19.61 GHz were also measured using standard microwave benches. Dielectric constant at optical frequency ( ∈ ∞) was measured using Abbe's refractometer. Measured values of the dielectric loss ( ∈″) have been plotted against dielectric constant ( ∈′) in a complex plane for 1-propanol, benzonitrile and their mixtures. Various dielectric relaxation parameters like relaxation time ( τ), static dielectric constant ( ∈ 0) and high frequency limiting values of dielectric constant ( ∈ ∞1) were obtained from these curves. Dielectric relaxation parameters thus obtained were used to evaluate excess inverse relaxation time (1/ τ) E, excess static permittivity ( ∈ 0 E), Kirkwood correlation factor ( g), angular correlation factor ( g eff) and thermodynamic parameters. Molecular interaction between the molecular species of the liquid mixtures was interpreted in terms of these parameters.

Influence of long-range cation order on relaxor properties of dopedPb(Mg1/3Nb2/3)O3ceramics

The 1:1 $B$-site cation order in $\text{Pb}({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}){\text{O}}_{3}$ relaxor ferroelectric ceramics was significantly enhanced by doping of minor amounts of ${\text{La}}^{3+}$, ${\text{Sc}}^{3+}$, or ${\text{W}}^{6+}$ (less than $3\text{ }\text{at}\text{.}\text{ }%$) combined with a slow cooling procedure. Transmission electron microscopy examination confirmed the size increase of the cation-ordered regions embedded in a disordered matrix in the samples that were slowly cooled after sintering. The average cation ordering parameter $(S)$ determined from x-ray diffraction data in these partially ordered samples was about 0.3--0.4. The ferroelectric properties and dielectric relaxation were compared in partially ordered and disordered $(S=0)$ samples with the same composition. It was found that typical relaxor behavior was preserved in partially ordered ceramics. Furthermore, the temperature and diffuseness of the characteristic relaxor permittivity peak and the parameters of dielectric relaxation (in particular, the distribution of relaxation times and the Vogel-Fulcher freezing temperature) were practically independent of $S$. In contrast, the diffuseness of the phase transition from the ferroelectric phase (induced by external electric field) to the ergodic relaxor phase appeared to be much larger in the disordered samples than in the partially ordered ones (this diffuseness was assessed using pyroelectric current and ferroelectric hysteresis loops). These results suggest that cation ordering did not influence the behavior of polar nanoregions which are responsible for the dielectric response in the ergodic relaxor phase but significantly influenced the ferroelectric phase transition. The results are interpreted in terms of different types of polar regions in the disordered matrix and cation-ordered domains.

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.

The Dipole Moment and Molecular Mobility of Cholesteryl-Containing Monomers in Solution: Association and Gel Formation

The permittivity, molecular dipole moment, and dielectric relaxation parameters (relaxation time and activation energy) of cholesteryl esters of alkyl-, methacryloyl-ω-oxy-, and aminocarboxylic acids were studied in dilute solutions in toluene. The influence of the chemical structure of molecules on these characteristics was considered. The presence of NH groups and cholesteryl radicals (responsible for H-bonding and specific dispersion interactions) and an increase in the length of methylene chains in molecules substantially influenced dipole moments and dipole polarization relaxation times and contributed to the development of structuring processes (association and gel formation) in solutions of these compounds.

Dynamics of Water in Partially Crystallized Polymer/Water Mixtures Studied by Dielectric Spectroscopy

The dielectric relaxation process of water was investigated for polymer/water mixtures containing poly(vinyl methyl ether), poly(ethyleneimine), poly(vinyl alcohol), and poly(vinylpyrrolidone) with a polymer concentration of up to 40 wt % at frequencies between 10 MHz and 10 GHz in subzero temperatures down to -55 degrees C. These polymer/water mixtures have a crystallization temperature TC of water at -10 to -2 degrees C. Below TC, part of the water crystallized and another part of the water, uncrystallized water (UCW), remained in a liquid state with the polymer in an uncrystallized phase. The dielectric relaxation process of UCW was observed, and reliable dielectric relaxation parameters of UCW were obtained at temperatures of -26 to -2 degrees C. At TC, the relaxation strength, relaxation time, and relaxation time distribution change abruptly, and their subsequent changes with decreasing temperature are larger than those above TC. The relaxation strength of UCW decreases, and the relaxation time and dynamic heterogeneity (distribution of relaxation time) increase with decreasing temperature. These large temperature dependences below TC can be explained by the increase in polymer concentration in the uncrystallized phase C(p,UCP) with decreasing temperature. C(p,UCP) is independent of the initial polymer concentration. In contrast to the relaxation times above TC, which vary with the chemical structure of the polymer and its concentration, the relaxation times of UCW are independent of both of them. This indicates that the factor determining whether the water forms ice crystals or stays as UCW is the mobility of the water molecules.

Broadband dielectric spectroscopy of nanostructured maleated polypropylene/polycarbonate blends prepared by in situ polymerization and compatibilization

The miscibility and molecular dynamics of nanostructured maleated polypropylene (mPP)/polycarbonate (PC) blends prepared by in situ polymerization of macrocyclic carbonates with polypropylene modified with 0.5 wt% of maleic anhydride-reactive groups were investigated over a wide range of frequencies (10 −2–0.5 × 10 7 Hz) at different constant temperatures using broadband dielectric spectroscopy and scanning transmission electron microscope (STEM). The molecular dynamics of the glass relaxation process of the blend (α-relaxation process) appeared at a lower temperature range compared with that of the pure PC. This shift in the molecular relaxation process is attributed to the partial miscibility of the two polymer components in the blends as previously confirmed by the morphology via STEM. Nanoscale morphologies with average domain diameters as small as 50 nm were obtained for the different blend compositions studied. The STEM photographs show that the graft mPP- g-PC prefers to locate at the interfaces as previously reported. The relaxation spectrum of pure PC and mPP/PC blends was resolved into α- and β-relaxation processes using the Havriliak–Negami equation and ionic conductivity. The dielectric relaxation parameters, such as relaxation peak broadness, maximum frequency, f max, and dielectric strength, Δ ɛ (for the α- and β-relaxation processes), were found to be blend composition dependent. The kinetics of the α-relaxation processes of the blends were well described by Vogel–Fulcher–Tammann (VFT) equation. The local process of PC was resolved into two relaxation processes β 1 and β 2, associated with the carbonyl groups' motion and the combined motions of carbonyl and phenylene groups, respectively. Only β 2 shifted to lower frequency in the blend while β 1 was relatively not affected by blending. The electric modulus of the blends was used to get a sufficient resolution of the different relaxation processes in the samples, i.e., α-, β-relaxation processes, ionic conductivity, and interfacial polarization. In addition, the blending method used was found to increase the d.c. conductivity without affecting the charge carrier transport mechanism, making it possible to develop novel polymer blends with tunable dielectric properties and morphology from existing polymers.

Dielectric spectroscopy analysis in employing liquid crystal phthalonitrile derivative in nematic liquid crystals

Dielectric anizotropy and relaxation properties of 2,3-dicyano-1,4-di[3,4,5-tri(dodecyloxy)phenylcarbonyloxy] benzene (DCDPB)-doped E7 and E7 liquid crystal have been investigated by the dielectric spectroscopy method. Dielectric anisotropy property of the LCs changes from the positive type to negative type. Dielectric relaxation properties suggest that LCs exhibit a monodispersive dielectric property. The relaxation frequency of E7 and E7/DCDPB liquid crystals was calculated by means of Cole–Cole plots. Consequently, DCDPB dopant changes the dielectric anizotropy and relaxation parameters of E7 LC.

Dielectric relaxation of dioxane-water mixtures using time domain technique

The complex permittivity of dioxane in water mixtures for various concentration and temperatures have been measured as a function of frequency between 10 MHz to 20 GHz using time domain reflectometry technique. Dielectric relaxa-tion parameters i.e. static dielectric constant and relaxation time were obtained from the complex permittivity spectra using the nonlinear least square fit method. The relaxation behaviour of these mixtures are explained by the Debye model. The Debye relaxation time of the mixture shows a maxima for the mixture with 40% of water by volume. This suggests that the tendency to form cluster between water and dioxane molecules is maximum for this mixture. The Kirkwood correlation factor, excess permittivity and Bruggeman factor have been determined at various concentration of water in dioxane.

Simulation of dielectric relaxation in periodic binary systems of complex geometry

Dielectric relaxation in binary mixtures containing particles or lamellae with complex geometry has been simulated within the quasielectrostatic approximation by a three-dimensional finite-difference method. The method was tested using simple models corresponding to water-in-oil (W/O) and oil-in-water (O/W) emulsions with volume fraction P up to 0.5. The dielectric spectra calculated by the finite difference method agreed with those expected from Wagner's equation at P ⩽ 0.3 and approached those from Hanai's equation at P > 0.4 . This method was applied to more complicated binary mixtures of oil and water: a bicontinuous cubic structure, a suspension of particles with projections, and a planar bilayer with a rippled or interdigitated interface. The bicontinuous phase that is supposed to appear near the transition between W/O and O/W emulsions showed dielectric properties similar to those of the O/W emulsion. The undulation of the particle surface and the interface of the planar bilayer affected all parameters of dielectric relaxation, especially the relaxation intensity.

Analysis of Dielectric Relaxation Parameters in the Range of Glass Transition

The apparent activation energy W, the temperature Ta at which the molecular movement is assumed frozen (the relaxation time is infinitely large) and the preexponential factor t0 were determined for Nylon 11 using the data obtained by fractional polarization thermally stimulated discharge current technique. The aim was to investigate the temperature dependence of the relaxation time in the range of the glass transition temperature. An experimental thermogram can be analyzed equally well using the Vogel-Fulcher-Tammann-Hess relationship or the Arrhenius equation. Experimental results and simulations, for nearby peaks, demonstrate that the relaxation time at peak temperature changes from about 100 to 500 s revealing a very narrow distribution in relaxation times. On contrary, W and especially t0 varies in large limits and the values for t0 are in many situations physically meaningless. It was found that the temperature at which the molecular movement can be assumed frozen for electric effects is about 150 K below the glass transition temperature in Nylon 11. A small change in W (in the limit ± kTm which represents the minimum uncertainty interval in W) induces a change in t0 of about two decades, indicating (i) that any analysis assuming t0 constant should be avoided and (ii) the selectivity limit of the method.

Dielectric Relaxation in Glycine–Water and Glycine–Ethanol–Water Solutions Using Time Domain Reflectometry

Dielectric relaxation measurements on water–ethanol–glycine ternary system were carried out using time domain reflectometry (TDR) at 25, 30, 35, and 40°C in the frequency range from 10 MHz to 10 GHz. Glycine–ethanol–water solutions are prepared with different concentrations of ethanol (0, 5, 10, 15, 20, and 30%) and also for different glycine molar concentrations (0, 0.2, 0.4, 0.6, 0.8, and 1 M). The dielectric relaxation parameters are measured for aqueous glycine solutions also to compare the results with those for the glycine–ethanol–water ternary system. For all the mixtures considered, only one relaxation peak was observed in this frequency range. All the mixtures display a Cole–Davidson dispersion. The relaxation peaks shift to lower frequency with an increase in glycine concentration and also with ethanol concentration. The logarithm of the relaxation time log(τ) shows a nonlinear relation with glycine concentration which implies a change of relaxation mechanism with glycine concentration. The dielectric strength Δe for these mixtures shows a nearly linear relation with glycine molar concentration.

Dielectric Studies of Glycine–Ethylene Glycol–Water Solutions Using Time Domain Reflectometry

Time domain reflectometry (TDR) has been used for dielectric relaxation measurements on the glycine–ethylene glycol–water ternary system (TDR) at 25, 30, 35, and 40°C in the frequency range from 10 MHz to 10 GHz. Glycine–ethylene glycol–water solutions are prepared with different concentrations of ethylene glycol (0, 5, 10, 15, 20, and 30%) and also for different glycine molar concentrations (0, 0.2, 0.4, 0.6, 0.8, and 1 M). The dielectric relaxation parameters are measured for aqueous glycine solutions also to compare the results with those for the glycine–ethylene glycol–water ternary system. For all the solutions considered, only one relaxation peak was observed in this frequency range. The complex permittivity spectra for the aqueous glycine solutions can be well described by the Cole–Davidson expression, whereas that for the ternary system can be well described by the Havriliak–Negami expression. The logarithm of the relaxation time log(τ) shows a nonlinear relation with the glycine molar concentration that implies a change in the relaxation mechanism with glycine concentration. The dielectric strength Δe increases with an increase in glycine molar concentration, whereas it decreases with an increase in ethylene glycol concentration.

Influence of molecules with chloro group on the associative liquid methanol: A dielectric relaxation approach

The dielectric relaxation parameters, viz., static dielectric constant, ɛ, and relaxation times, τ, have been determined for chlorobenzene-methanol (CB-MET), 1,2 dichloro ethanemethanol (DE-MET) and dimethylene chloride-methanol (DC-MET) mixtures with thirteen different concentrations at three temperatures, viz., 15, 25 and 45°C. The experimental technique used for this work was the time domain reflectometry (TDR) in the frequency range of 10 MHz to 20 GHz using the Hewlett Packard HP 54750 sampling oscilloscope. The information regarding hydrogen bonding structural behavior in MET due to CB, DE and DC are obtained by using the theoretical models based on the excess properties. The data suggest that CB and DE are not influenced by hydrogen bonding in MET whereas DC is influenced by the hydrogen bonding mechanism in MET. It appears that the behavior of DC on MET is different from CB and DE in MET.

Non-Debye dielectric relaxation in complex materials

Abstract The paper considers several examples of non-Debye dielectric response in complex heterogeneous media. The percolation phenomenon and Cole–Cole relaxation in disordered matter are discussed in detail. The proposed models are illustrated by different sample systems: ionic microemulsions, porous glasses, porous silicon, polymer–water mixtures, and polymer–microcomposite materials. The models enable us to establish the relationship between the parameters of dielectric relaxation broadening, structural properties of the media and transport features of charge carriers in the considered systems. In addition, the origins of “strange kinetic” phenomena were discussed based on statistical physics and fractional time evolution ideas.

The symmetric broadening of the water relaxation peak in polymer–water mixtures and its relationship to the hydrophilic and hydrophobic properties of polymers

The dielectric relaxation of water molecules in polymer–water mixtures is discussed. The memory function approach and scaling relationships are used as a basis for the model of symmetric dielectric spectrum broadening. The correspondence between the relaxation time, the geometrical properties, the self-diffusion coefficient, and the Cole–Cole exponent is established. The relationship between the hydrophilic and hydrophobic properties of the polymers and the dielectric relaxation parameters is discussed.