Dielectric Increment Research Articles

Fluctuation mechanism of the dielectric polarization of water-in-oil microemulsions with ionic surfactant

A statistical model is proposed to describe the dielectric polarization of ionic microemulsions at a region far below percolation in which the microemulsions consist of spherical single droplets with water in the central core surrounded by a layer of surfactant molecules. The model describes the effect of temperature and dispersed phase content on the behavior of the dielectric polarization of ionic water-in-oil microemulsions and explains the experimentally observed increase of the static dielectric permittivity as a function of temperature. The microemulsions formed with surfactant sodium bis(2-ethylhexyl) sulfosuccinate have been analyzed with the help of this model. The systems are considered to consist of nanometer-sized spherical noninteracting water droplets of equal size with negatively charged head groups, staying at the interface, and positive counterions, distributed in the electrical diffuse double layer of the droplet interior. It is shown that the droplet polarizability is proportional to the mean-square fluctuation dipole moment of the droplet. This mean-square dipole moment and the corresponding value of the dielectric increment depend on the equilibrium distribution of counterions within a diffuse double layer. The density distribution of ions is determined by the degree of the dissociation of the ionic surfactant. The relationship between the dielectric permittivity, the constant of dissociation of surfactant, the content of the dispersed phase, and the temperature has been ascertained.

Nonlinear dielectric relaxation in non-interacting dipolar systems

The frequency dependence of the nonlinear dielectric effect caused by the Langevin dipolar saturation has been studied for dilute benzene solutions of 4,4′-n-hexylcyanobiphenyl and 4-(trans-4′-n-hexylcyclohexyl)isothiocyanatobenzene. The nonlinear dielectric increment induced by the coupling between the static electric field of high strength (107 V/m) and a field of small intensity and changeable frequency (1 MHz–3 GHz) shows a relaxation which is interpreted by Coffey theory.

Dielectric studies of a 5-n-alkyl-2-(4'-isothiocyanatophenyl)- 1,3-dioxane (nDBT) homologous series (n=4-10)

The results of dielectric studies of seven members of a 5-n-alkyl-2-(4'-isothiocyanatophenyl)- 1,3-dioxane (nDBT) homologous series (n=4-10) in the isotropic and smectic A phases are presented. The complex dielectric permittivity, epsilon* (nu) = epsilon'(nu) - iepsilon'' (nu), was measured with the aid of two experimental set-ups: an impedance analyser (10kHz-13 MHz) and a dielectric time domain spectrometer (TDS, 10 MHz-4 GHz). This allowed two main relaxation processes in both the phases studied to be separated: the low frequency (l.f.) process connected with molecular reorientations around the short axes, and the high frequency (h.f.) process connected with the rotations around the long axes. The measured dielectric increments enabled us to estimate the value and direction of the dipole moment of the nDBT molecules. The l.f. relaxation process in the isotropic and smectic A phases of the nDBT compounds exhibits some peculiar features which distinguish the materials from other similar substances. The observed decrease of the relaxation times and activation enthalpy with increasing n is discussed in relation to the molecular arrangements in the smectic layers.

Scaling Behavior of Physical Properties of Food Polysaccharide Solutions: Dielectric Properties and Viscosity of Sodium Alginate Aqueous Solutions

The dielectric properties of a typical ionic food polysaccharide, alginates with different chemical compositions and molecular sizes, were investigated with special relevance to the solution viscosity. The dielectric relaxation around 1 MHz due to the fluctuation of bound counterions was analyzed. The polymer concentration, C, dependence of the dielectric increment, Δe, and that of the relaxation time, τ, are summarized as Δe ∝ C1/3 and τ ∝ C-2/3 at the dilute region and as Δe ∝ C0 and τ ∝ C -1 at the semidilute region for all of the samples, in good agreement with the scaling relations predicted by polyelectrolyte solution theories. The crossover concentration, C*, from the dilute to the semidilute region was determined as the concentration at the intersection of the two regions. The concentration dependence of the relative viscosity, ηrel, was also expressed by two scaling equations: (ηrel − 1) ∝ C1 at low concentration and ηrel ∝ C1/2 at high concentration. The crossover concentration, C*, determined ...

Dynamical Properties of Two Ferroelectric Phases of Epoxy Compound

Dielectric methods (FDDS and TDS) were used to study collective and molecular processes of two ferroelectric phases of 4′-[(S,S)-2,3-epoxy-hexyloxy] phenyl 4-decyloxy benzoate (EHPDB) which shows the following phase sequence: Is-N*-SmC*-S3-Cr. In our previous study of this material it has been shown that the S3 phase is also a ferroelectric one. In this study new dielectric measurements have been done using gold coated cells which allowed to observe the soft mode in the N*-SmC* pretransition region. The Goldstone mode was observed for the SmC* and S3 phases, however, the S3 phase appears to be a metastable one. The measurements of spontaneous polarization confirm this, too. Spontaneous polarization as well as critical frequencies and dielectric increments are presented for all processes observed and discussed in terms of the mean-field model.

Dielectric analysis of interaction between polyelectrolytes and metal ions within food gels

The dielectric constant, ε, of food gels containing metal ions was measured in the frequency range 10 3–10 6 Hz. Dielectric relaxation was observedfor ionic gels but not for nonionic gels. For ionic gels, the dielectric increment, Δ ε, increased with an increase in material concentration and the amount of the ionic groups in the system. By analyzing the data for the dielectric relaxation, the concentration of counterions bound to polyelectrolytes in the gel, N b , and the fluctuation length of the bound counterions, d, were obtained. These results indicate that the investigation of the dielectric relaxation for ionic gels is an effective method for analyzing the interaction between polyelectrolytes and metal ions within gels quantitatively.

Dielectric analysis of food polysaccharides in aqueous solution

The dielectric properties of typical ionic food polysaccharides, alginate and κ-carrageenan, were investigated in the frequency range from 10 3 Hz to 10 7 Hz. For both polymers, two kinds of dielectric relaxation processes were observed; the higher-frequency relaxation being analyzed. The concentration dependence of the dielectric increment, Δε H, and that of the relaxation time, τ H, agreed well with the scaling law derived from polyelectrolyte solution theory. This result indicates that the mechanism of the high-frequency relaxation is ascribed to fluctuation of the loosely bound counterions to the polyelectrolyte within the range of the correlation length, ξ. Using the dielectric relaxation data, the crossover concentration from the dilute to the semi-dilute region for polysaccharide solutions was estimated. In addition, the fluctuation length of the bound counterions, d, and the concentration of counterions bound to the polyelectrolytes, N b, were evaluated. The dielectric relaxation measurement was an effective method for analyzing the polymer chain distribution and the counterion binding nature in the polysaccharide solutions. The dielectric relaxation of typical ionic food polysaccharides, alginate and κ-carrageenan, were investigated in the frequency range from 10 3 Hz to 10 7 Hz. The concentration dependence of the dielectric increment and that of the relaxation time agreed well with the scaling law derived from the polyelectrolyte solution theory, the relaxation being ascribed to the fluctuation of the loosely bound counterions to the polyelectrolyte.

Dielectric relaxation of non-conducting colloidal particles in non-binary solutions: mutual enhancement of adsorption oscillations

This paper deals with the low-frequency dielectric dispersion (LFDD) of colloidal suspensions with non-binary electrolyte solutions as dispersion media. Starting from the theory of double-layer concentration polarization in AC fields, it is demonstrated that counterions can undergo significant adsorption oscillations which can increase to a large extent the dielectric increment of the suspensions. It is also shown that such oscillations can also affect the characteristic relaxation frequency of the dielectric spectrum, ω cr. This quantity can be either larger or smaller than it would be in a purely binary electrolyte, in which adsorption oscillations do not occur. The predictions of the theory are compared to experimental LFDD data reported in the literature.

The cure and diffusion of water in halogen containing epoxy/amine thermosets

Dielectric measurements were performed to determine the effect of chlorine, methyl and trifluoromethyl substituents on the cure of bis[ N,N-bis(2,3-epoxypropyl)-4-aminophenyl]methane with 4,4′-diaminodiphenylsulfone and 4,4′-bis[1,4-phenylenebis(1-methylethylidene)]-bis[2,6-dimethyl]benzamine, and the data were analysed to give gelation and vitrification points. Infra-red measurements were also carried out during the cure process to monitor the consumption of epoxy groups. Dynamic mechanical thermal analysis and density measurements were carried out on the N,N-diglycidylaniline system and a reduction in the glass transition temperature was observed to occur with the incorporation of a trifluoromethyl group into the resin structure. Dielectric and gravimetric studies are reported on the absorption of water by these resins. In agreement with gravimetric data for water absorption, dielectric data obtained at 10 Hz showed that trifluoromethyl substitution increases the diffusion coefficient whereas chlorine substitution decreased it. The chlorinated resin exhibited a higher than expected initial dielectric increment, which has been attributed to the effect of a micro-porous surface structure of the resin. Atomic force microscopy of the resins surfaces indicates that the chlorinated and fluorinated resins have greater surface roughness than the protonated analogues, consistent with the dielectric observations. Analysis of the amount of ‘bound’ and ‘free’ water in the resin systems shows that the halogenated resins have a lower percentage of bound water and more of the water is in the ‘free’ state.

Dielectric relaxation in ‘diluted’ siloxanes with swallow-tailed side groups

Abstract Polysiloxanes consisting of 36-SiCH3Z-O- units, where Z is a swallow-tailed liquid crystal moiety S or a CH3 group, were synthesized. Dielectric constants and relaxation frequencies were measured from 0.1 Hz to 10 MHz for four different molar ratios of CH3 and S groups and compared with the data for the respective monomeric liquid crystal material. In all cases a δ- and α-relaxation were detected. The relaxation frequencies f R of the α-process increase with increasing degree of dilution and can be related to the decreasing glass temperature. The δ-process approaches the f R-values of the monomer by dilution. Both the dielectric increments of the δ-process, as well as the static dielectric constants parallel to the director, prove that the swallow-tailed units are strongly antiparallel oriented. This correlation cannot be destroyed by dilution.

A comparative study of the high‐frequency dielectric properties of poly(α‐glutamate) and poly(γ‐glutamate) aqueous solutions

The dielectric properties of poly(α-glutamic acid) and poly(γ-glutamic acid) aqueous solutions in the fully ionized state have been investigated in the frequency range from 1 MHz to 1 GHz by means of frequency-domain dielectric spectroscopy measurements. In this frequency range, micro-Brownian dynamics and internal motion of side-chain polar groups give rise to nonexponential relaxation processes resulting in an intermediate dielectric relaxation between that due to the counterion atmosphere polarization and that due to the orientational polarization of the water molecules. In this work, we study the influence of the polymer concentration in the dilute-semidilute regime on the dielectric parameters, i.e., the dielectric increment Δϵ and the relaxation time τ, and discuss their relevance in the light of some scaling pictures recently proposed by Dobrynin, Colby, and Rubinstein to describe the unentangled regime of flexible polyelectrolyte solutions. © 1997 John Wiley & Sons, Inc. Biopoly 40: 485–494, 1996

Dielectric studies of ion fluctuation and chain bending in native DNA

The high-frequency dielectric dispersion exhibited by solutions of native DNA is characterised as a function of electrolyte concentration, counterion type, temperature and pH. The data are interpreted in terms of counterion fluctuation along short segments (subunits) of the DNA chain. From calculation of the subunit length from dielectric relaxation time and increment, information is derived regarding the static and dynamic bending of the DNA chain. Activation enthalpies for the ion fluctuation process are obtained from temperature-dependent dielectric data.

Dielectric properties of a surface stabilized ferroelectric liquid crystal in cells of various thickness

Abstract Measurements of the complex dielectric permittivity have been performed in the frequency range of the collective director modes (101–106 Hz) in the vicinity of the S*C↔S*A phase transition of the compound 4-[(R)(-)-(2-chloro-3-methylbutanoyloxy)]-phenyl-[4n-decyloxy]benzoate and revealed that a dielectric relaxation process due to collective director fluctuations is active in the helically unwound S*C as well in the S*A phase, if the formation of the S*c helix is suppressed. A twisted and bent director configuration (splayed state) occurs in thin, planar oriented samples with various cell gaps (2–27 μm). The observed mode of Debye type was characterized as a function of temperature and cell thickness. By a decrease of the cell thickness the dielectric increment is lowered in the S*C phase but enhanced in the S*A phase. This Debye mode is only in part suppressed by the application of a bias electric field. With decreasing cell thickness its relaxation frequency decreases in the S*A phase, but incr...

Local order in protein solutions

Nonlinearity of the dielectric increment of protein solutions as a function of concentration can be explained by the existence of local order. This local order can be expressed in Saupe order parameters. Using a simple mean field theory, it is shown how these order parameters can be obtained. Two cases from the literature are used to illustrate the method.

Dielectric relaxation in polystyrene suspensions. Effect of ionic strength

The study of the conductivity and dielectric response of colloidal suspensions in a.c. fields of frequency ω can help in improving our understanding of the electrical characteristics of the solid—liquid interface in colloidal systems. In fact, the strong dielectric dispersion shown by such systems at low frequencies is intimately related to the polarization of the double layer surrounding the particles. In this work, we present recent data on the real and imaginary parts of the conductivity and dielectric constant of spherical polystyrene suspensions as a function of the frequency of the applied field, and of KCl concentration in the dispersion medium. The conductivity and dielectric increments are compared to the predictions of accepted theoretical models. The qualitative agreement between both types of data is excellent, although the experimental results are significantly higher than the theoretical ones. Reasons for such discrepancies are discussed in the light of recently reported determinations.

Dielectric relaxation of electrolyte solutions: Molecular dynamics and theoretical results for ions in simple dipolar solvents

Computer simulation and theoretical results are given for the frequency dependent dielectric function of model electrolyte solutions. The influences of salt concentration, ionic charge, and solvent dipole moment are discussed. It is found that a substantial salt induced dielectric decrement persists up to the dispersion frequency. At higher frequencies, however, the dielectric constant of the solution is larger than that of the solvent giving a salt induced dielectric increment.

Dielectric properties of human blood and erythrocytes at radio frequencies (0.2-10 MHz); dependence on cell volume fraction and medium composition.

The dielectric properties of human erythrocytes (red blood cells) suspended in whole blood and in isotonic media at various volume fractions (haematocrits) have been studied in the frequency range 0.2-10 MHz, in which the so-called beta-dispersion due to the Maxwell-Wagner effect is known to occur. The capacitance and conductance at 25 degrees C were measured by an instrument interfaced to a computer. The rectangular sample cavity (1 ml volume) contained four pure gold electrode pins, and the sample could be circulated by a roller pump. The frequency-dependence of the permittivity and conductivity were fitted by non-linear least squares regression. Corrections were applied for non-linearity in the dielectric increment at high haematocrit, and for electrode polarisation when diluting the blood in saline. Data were interpreted in terms of a simple equivalent resistor-capacitor circuit. From the measured haematological values the specific membrane capacitance (Cm) and the conductivities internal and external to the cells (sigma i' and sigma o' respectively) were estimated. The conductivities behaved in a predictable manner with a mean of 0.458 S.m-1 (s.d. +/- 0.044) for sigma i', whereas the value of Cm (and indeed the actual capacitance of the suspension) was dependent on the amount of plasma present. Hence, in stationary normal (anticoagulated) whole blood samples, Cm was as high as 2.98 mu F.cm-2 (s.d. +/- 0.40), in contrast to about 0.9 mu F.cm-2 in blood diluted more than two-fold (to less than 20% hct) in isotonic media. The high value remained when the diluent was plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental Study of Nonlinear Dielectric Relaxation Spectra of Ferroelectric Liquid Crystals in the Smectic C* Phase

Nonlinear dielectric relaxation spectra of two kinds of ferroelectric liquid crystals (FLC) are investigated in the chiral smectic C (SmC*) phase. The linear spectrum shows the relaxation of Debye type and the third-order nonlinear spectrum also shows the relaxation of Debye type generalized to the nonlinear case. The third-order nonlinear dielectric increment is found to be negative, which indicates that the dielectric nonlinearity of FLCs in the SmC* phase mainly originates from the saturation of molecular dipole moments induced by the applied electric field. The profiles of linear and nonlinear spectra remain almost unchanged throughout the SmC* phase. In the vicinity of the SmA-SmC* phase transition temperature, the linear spectrum shows the critical behavior of Curie-Weiss type and the third-order spectrum shows a sharp peak.

Dielectric measurements on electro-manipulation media

The permittivity and conductivity of solutions of sugars and sugar alcohols, such as are suitable for electric-field work on cells, were measured. The range of concentrations was 0–3 M (subject to solubility), and the frequency range was not commonly used in dielectrophoresis prior to electrofusion (200 kHz–2 MHz). This was widened to 30 kHz–12MHz, when dispersive behaviour was found. A parallel-plate impedance chamber with variable electrode-spacing, suited to stable measurements in these low-conductivity aqueous media, was used. Errors due to electrode polarisation were effectively removed by linear regression of the series parameters against electrode distance, as well as by subtraction of data obtained on KCl solutions of comparable conductivity. The permittivity of the sugar solutions decreased as only approximately linear functions of concentration, so that a description in terms of both first- and second-order molar dielectric increments ( δ 1 and δ 2) provided a better description of the behaviour than a single linear increment (δ). Sugar solutions of concentration of 1.2 M or less showed no change in permittivity or conductivity over the measured frequency range (i.e., were dispersion-free). On the other hand, various high-density media showed dispersion. The stabilised silica sol ‘Percoll’ showed dispersion over the whole frequency range; solutions of sucrose (at above 1.2 M concentration), as well as of proprietary high-density solutes (‘Metrizamide’ at above 0.5 M and ‘Nycodenz’ at above 0.75 M) showed dispersion above 0.6 MHz. Although these media are of interest for electro-manipulation (they can be used to prevent sedimentation), their dispersive properties may make them unsuitable for use with radio-frequency fields.

Complex Dielectric Permittivity of Di-propyloxyazoxybenzene (3.OAOB) and Racemic Methylbutyl-phenyl-hexyloxybenzoate (CE6) on the Basis of the Nordio-Rigatti-Segre Theory

Abstract Results of dielectric relaxation studies of two thermotropic liquid crystal substances, 3.OAOB and racemic CE6, are discussed on the basis of the Nordio-Rigatti-Segre theory. Due to the anisotropy of the molecular structure, different contributions of the longitudinal and transversal components of the permanent dipole moment to the dielectric spectra can be observed. Theoretical values for the dielectric increment of the four basic relaxation modes are calculated in two different ways and compared with the experimental results.