Dielectric Increment Research Articles

Dielectric Behavior of Lipid Vesicles: The Case ofL-α-Dipalmitoylphosphatidylcholine Vesicles as a Function of Size and Temperature

We present an extensive set of radio wave dielectric relaxation spectroscopy measurements of aqueous suspensions of different size unilamellar L-alpha-dipalmitoylphosphatidylcholine (DPPC) vesicles, in a temperature range between 15 and 55 C, where the lipidic bilayer experiences structural transitions from the gel to the rippled phase (at the pretransition temperature) and from the rippled to the liquid phase (at the main transition temperature). The dielectric spectra have been analyzed in the light of the Cole-Cole relaxation function, and the main dielectric parameters-the dielectric increment Deltaepsilon and the mean relaxation frequency omega(0)--have been evaluated as a function of temperature. These parameters display a very complex phenomenology, depending on the structural arrangement of the lipid-water interface. The structural parameters that govern the dielectric behavior of these systems associated with the lipid bilayer have been recognized within a recent dynamic mean-field model we have proposed, aimed to predict the dipolar relaxation of an array of strongly interacting dipoles anchored to a flat or corrugated surface. They are the prefactor A(T) of the distance-dependent part of the effective dipolar interaction energy, the term Gamma(vis), that takes into account the damping of the dipolar motion, the average dipolar distance related to the area a(0) per polar head, and the bilayer thickness. The present analysis furnishes, from a phenomenological point of view, the dependence of these parameters on the temperature and on the vesicle size.

Dielectric dispersion of short single-stranded DNA in aqueous solutions with and without added salt

Dielectric spectroscopy measurements were performed for aqueous solutions of short single-stranded DNA with 30 to 120 bases of thymine over a frequency range of 10;{5} to 10;{8}Hz . Dielectric dispersion was found to include two relaxation processes in the ranges from 10;{5} to 10;{6} and from 10;{6} to 10;{8}Hz , respectively, with the latter mainly discussed in this study. The dielectric increment and the relaxation time of the high-frequency relaxation of DNA in solutions without added salt exhibited concentration and polymer-length dependences eventually identical to those for dilute polyion solutions described in previous studies. For solutions with added salt, on the other hand, those dielectric parameters were independent of salt concentration up to a certain critical value and started to decrease with further increasing salt concentration. This critical behavior is well explained by our newly extended cell model that takes into account the spatial distribution of loosely bound counterions around DNA molecules as a function of salt concentration.

Influence of the anisotropic polarizability on the anomalous dielectric relaxation spectra

The nonlinear dielectric response due to the application of a strong dc bias electric field superimposed on a weak ac electric field is considered in the context of the anomalous diffusion (subdiffusion). A perturbation procedure is used to derive analytical expressions for the first three harmonic components of the electric polarization of an assembly of both polar and anisotropically polarizable symmetric-top molecules. To accomplish that, an infinite hierarchy of multiterm (21) differential-recurrence equations of noninteger order for the moments is established and solved for the stationary regime. The results so obtained are illustrated in the form of Argand diagrams and three-dimensional relaxation spectra for the complex nonlinear dielectric increment extracted from the first harmonic component of the electric susceptibility. These plots show the role and importance played by the fractional exponent α and the parameter P measuring the influence of the dipole moment over the permanent one.

Determination of the nonlinear dielectric increment in the Cole-Davidson model

The problem of the nonlinear dielectric relaxation of complex liquids is tackled in the context of the Cole-Davidson [J. Chem. Phys. 19, 1484 (1951)] model. By using an appropriate time derivative of noninteger order, an infinite hierarchy of differential-recurrence relations for the moments (expectation values of the Legendre polynomials) is obtained. The solution is established for the stationary regime of an ensemble of polar and symmetric-top molecules acted on by a strong dc bias electric field superimposed on a weak ac electric field. The results for the first three nonlinear harmonic components of the electric susceptibility are analytically established and illustrated with the help of Argand diagrams for the nonlinear dielectric increment and three-dimensional dispersion and absorption spectra for the second and the third harmonic components as a function of the anomalous exponent beta</=1, the value of which gives rise to skewed arcs (Argand plots) and asymmetric shapes (loss spectra) in the high-frequency domain.

Dielectric dispersion for short double-strand DNA

A complex dielectric constant for double-strand DNA molecules with a length of not greater than 120 base pairs in an aqueous solution containing 30 mM NaCl was systematically measured as a function of chain length in such a way that experimental uncertainties associated with the molecular-weight distribution of specimens were virtually excluded. In contrast to the past experimental and theoretical studies for much longer DNA molecules, both the molar specific dielectric increment and the relaxation time are proportional to the chain length. These scaling rules cannot be accounted for by any theory so far proposed that gives analytical expressions for those two quantities in the long-chain limit.

Structure and properties of 2-cyanopyridinium perchlorate[2-CNPyH][ClO4

The crystal structure of 2-cyanopyridinium perchlorate,[2-CNPyH][ClO4], has been determined at 100 (phase II) and 293 K (phase I). It is monoclinicP 21 at 100 K andorthorhombic P 212121 at 293 K. The dynamic properties of the crystal were studied by differentialscanning calorimetry, dilatometry, pyroelectric, dielectric, proton(1H NMR),chlorine (35Cl NMR) magnetic resonance spectroscopies and the infrared method. The crystal undergoesa structural phase transition () at 170 K characterized by a complex mechanism involving both ‘order–disorder’ and‘displacive’ contributions. It reveals pyroelectric properties below 170 K. The dielectric relaxationexisting over phase I is due to the motion of the cyano group, whereas the dynamics of the[ClO4]− anions is reflected in the significant dielectric increment around the phase transition.

Incubation Temperature and Hemoglobin Dielectric of Chicken Embryos Incubated Under the Influence of Electric Field

Eggs from a layer-type breeder flock (Baladi, King Saud University) between 61 and 63 weeks of age were used in 3 trials to study the effects of electric field (EF) during incubation on the internal temperature of incubation, and eggs and hemoglobin (Hb) dielectric of chicken embryos at 18 days of age. Dielectric relative permittivity (ε′) and conductivity (σ) of Hb were examined in the range of frequency from 20 to 100 kHz. The values of dielectric increment (Δε′) and the relaxation times (τ) of Hb molecules were calculated. The internal temperature of eggs was measured in empty (following the removal of egg contents) and fertilized eggs in trials 1 and 2, respectively. The level of the EF was 30 kV/m, 60 Hz. EF incubation of embryos influenced the temperature of incubation and electrical properties of Hb molecules and did not influence the temperature of incubation and internal environment of eggs when empty eggs were incubated. EF incubation of fertilized eggs significantly raised the temperature of incubation, egg air cell, and at the surface of the egg yolk by approximately 0.09, 0.60, and 0.61°F, respectively and Hb ε′, σ, Δε′, and τ as a function of the range of frequency of 20 to 100 kHz when compared with their counterparts of the control group. It was concluded that the exposure of fertilized chicken eggs to EF of 30 kV/m, 60 Hz, during incubation altered dielectric properties of Hb and that probably affected cell to cell communication and created the right environment for enhancing the growing process and heat production of embryos consequently increasing the temperature of the internal environment of the egg, and incubation.

Enhancement of electroosmotic flow using zwitterionic additives

Zwitterionic additives provide a means of altering the EOF without increasing conductivity. The magnitude of the EOF in a bare silica capillary increased by as much as 69% upon addition of 500 mM of zwitterion to the running buffer. The EOF enhancement increases linearly with the zwitterion concentration. With zwitterionic additives of the form +NH3-(CH2)n-COO-, the magnitude of the EOF increase is directly related to the number of methylene groups, (n), which ranges from n = 1 to 7. The endgroups on the zwitterions also affect the EOF enhancement. The effect of Z1-methyl (+N(CH3)3CH2CH2CH2SO3-) on EOF was not a function of either the buffer cation or pH. The EOF enhancement is a function of the dielectric increment of the additive and the nature of the amine functionality.

Solvent quality influence on the dielectric properties of polyelectrolyte solutions: A scaling approach

The dielectric properties of polyelectrolytes in solvent of different quality have been measured in an extended frequency range and the dielectric parameters associated with the polarization induced by counterion fluctuation over some peculiar polyion lengths have been evaluated. Following the scaling theory of polyelectrolyte solutions and the recent models developed by Dobrynin and Rubinstein that explicitly take into account the quality of the solvent on the polyion chain conformation, we have reviewed and summarized a set of scaling laws that describe the dielectric behavior of these systems in the dilute and semidilute regime. Moreover, for poorer solvents, where theory of hydrophobic polyelectrolytes predicts, and computer simulation confirms, a particular chain structure consisting of partially collapsed monomers (beads) connected by monomer strings, we derived a scaling law. These predictions are compared with the results obtained from the dielectric parameters (the dielectric increment delta epsilon and the relaxation time tau(ion)) of the "intermediate" frequency relaxation of two partially charged polymers, which possess a carbon-based backbone for which water is a poor solvent and ethylene glycol is a good solvent. By varying the solvent composition (a water-ethylene glycol mixture), we have tuned the quality of the solvent, passing from poor to good condition and have observed the predicted scaling for all the systems investigated. These findings give a further support to the scaling theory of polyelectrolyte solutions and to the necklace model for hydrophobic polyelectrolytes in poor solvents.

Synthesis, Characterization, Spontaneous Polarization and Dielectric Relaxation Studies in the Antiferroelectric and Ferroelectric Phases of an Achiral Banana Liquid Crystal: Bent-16

Synthesis and textural characterization along with spectroscopic (IR) confirmation (of supra molecular bond formation) are reported for an achiral Banana Liquid Crystal (BLC) Bent-16, viz., 1,3-phynylene bis(4-hexadecylbenzoate). Bent-16 exhibits a B 2 phase which undergoes a paramorphotic change to B 2 (FE) phase with decreasing temperature. The intra-B 2 i.e., AF to FE transition is confirmed through double peaked spontaneous polarization profiles. Results of calorimetry (T c and ▵H from DSC) agree with polarization thermal microscopy (TM) and confirm first order nature of Isotropic to B 2 phase transition. Low-frequency (5 Hz–12 MHz) dielectric measurements of capacitance C (T) and capacitance dC/dT agree with TM and DSC. Two orientational relaxations viz., a low-frequency (LF ∼ 1 KHz) and a high frequency (HF ∼ 1 MHz) corresponding to a slow and fast time regimes respectively are reported. Arrhenius shift of relaxation frequency f R in LF and HF regions infer comparable activation energy in Antiferroelectric phases with the estimated energies from other experiments in other BLCs. The temperatures trend of dielectric increment ▵ ϵ and α-parameter estimated from off-centred Debye's dispersion in both the B 2 phases (LF and HF mechanism) support relative confinement of the dipole.

Collective dielectric relaxation in smectic A and smectic C⋆ phases near transition temperature of electroclinic liquid crystals

The collective dielectric relaxation processes of electroclinic liquid-crystal materials have been investigated in a thin (3.5μm) planar cell in the frequency range of 1 Hz–10 MHz. Measurement of complex dielectric permittivity versus temperature has been taken on aligned samples filled with different electroclinic liquid-crystal materials. The dielectric data were collected by using the measuring electric field perpendicular to the smectic layer planes. The behavior of the collective dielectric modes has been studied in smectic C*(SmC*) and smectic A(SmA) phases. However, near the transition temperature of SmC*-SmA phase, the dielectric permittivity due to the Goldstone mode and soft mode could not be separated. It has also been observed that the dielectric permittivity increases with temperature before the transition temperature of SmC*-SmA phase under bias field. Temperature dependence of dielectric increments before the transition temperature under bias field and relaxation frequency suggests that the electroclinic liquid crystal shows transitional behavior over a wide temperature range and does not obey the Curie–Weiss law near the transition temperature like in other ferroelectric liquid-crystal materials.

Dielectric and Piezoelectric Properties of BiScO3-PbTiO3 Crystals with Morphotropic Phase Boundary Composition

The room temperature dielectric permittivity of [100] oriented 0.37BiScO3-0.63PbTiO3 (BSPT63) crystals with a morphotropic phase boundary (MPB) composition was found to be 1400, lower than that of BSPT57 crystals with rhombohedral phase (∼3000), but much higher than that of the tetragonal crystal BSPT66 (∼200). The Curie temperature of BSPT63 single crystals along [100] was found to be about 443°C, while the values were around 440°C and 445°C for [110] and [111] oriented crystals, respectively. Evidence of a ferroelectric–ferroelectric phase transformation temperature was associated with a dielectric anomaly occurring around 310–350°C for different orientations, indicating a strong curvature of the MPB. The coercive fields (Ec) were found to be 20 kV/cm for [100] oriented crystals, 24 kV/cm and 27 kV/cm for [110] and [111] directions, respectively. The piezoelectric response for [100] oriented samples (d33 = 900 pC/N) is weaker than that in rhombohedral phase (d33 = 1200 pC/N) but much higher than that in tetragonal phase (d33 = 200 pC/N). The strain piezoelectric d33 improved with the temperature increasing owing to dielectric permittivity increment, while the voltage piezoelectric g33 is independent of temperature (g33 ∼0.074 m2/C). Evidence of a monoclinic phase for BSPT63 crystals is inferred using the X-ray powder diffraction (XRD), and the lattice parameters were calculated to be a=4.0751 Å, b=3.9765 Å, c=3.9893 Å and β=90.166°.

Nonlinear alternating current responses of dipolar fluids.

The frequency-dependent nonlinear dielectric increment of dipolar fluids in nonpolar fluids is often measured by using a stationary relaxation method in which two electric fields are used: The static direct current (dc) field of high strength causing the dielectric nonlinearity, and the probing alternating current (ac) field of low strength and high frequency. When a nonlinear composite is subjected to a sinusoidal electric field, the electric response in the composite will, in general, consist of ac fields at frequencies of higher-order harmonics. Based on the Fröhlich model, we present a theory to investigate the nonlinear ac responses of dipolar fluids containing both polarizable monomers and dimers. In the case of monomers only, our theory reproduces the known results. We obtain the fundamental, second-, and third-order harmonics of the Fröhlich field by performing a perturbation expansion. The even-order harmonics are induced by the coupling between the ac and dc fields, although the system under consideration has a cubic nonlinearity only. The harmonics of the Fröhlich field can be affected by the field frequency, temperature, dispersion strength, and the characteristic frequency of the dipolar fluid, as well as the dielectric constant of the nonpolar fluid. The results are found to be in agreement with recent experimental observations.

Apparent non-linear dielectric effect in liquids containing ions

Addition of ions into ethanol + p-xylene mixtures lead to an apparent, negative non-linear dielectric increments (a difference between an electric permittivity obtained at strong and at weak electric fields). The electrode polarisation phenomena were supposed to be responsible for the observed effect.

Dielectric spectroscopy of an antiferroelectric liquid crystal showing an antiferroelectric–ferrielectric transition

We report the dielectric relaxation behaviour in the antiferroelectric SmCA* and ferrielectric SmCγ* phases of the antiferroelectric liquid crystal 4-[5-(4-octloxyphenyl)-2-pyrimidinyl]phenyl 4,4,4-trifluoro-3-(methoxyphenyl)butanoate which shows an antiferroelectric transition at around 88±0.1°C. In the SmCA* phase, two dielectric relaxation modes have been found, namely the usual antiferroelectric Goldstone mode and another arising from molecular rotation around its short axis. In the SmCγ* phase, one dielectric relaxation mode has been observed due to the ferrielectric Goldstone mode. Dielectric increments and relaxation frequencies of the antiferroelectric and ferrielectric phases are estimated from the fits of the Cole–Cole function of the dielectric spectrum. The dependence of the bias field in the ferrielectric phase is also discussed.

Non-linear a.c. dielectric response of symmetric-top molecules by use of Wigner D-functions

The time evolution equation of the ensemble averages of the Wigner D-functions is used for describing the non-linear dielectric relaxation of an assembly of polar molecules in the context of the non-inertial rotational diffusion model. These functions are needed when one considers the case where the direction of the dipole moment makes some angle (different from zero) with the long molecular axis of the symmetric-top molecule. Moreover, it is assumed that the external perturbation acting on the liquid medium is due to the simultaneous application of a strong d.c. bias field superimposed on a weak a.c. electric field. Analytical expressions for the first three harmonic components of the electric polarization are derived and the first one is chosen as example of illustration by means of three-dimensional relaxation spectra and Cole–Cole diagrams. These figures clearly show the existence of two distinct relaxation processes along the short and the long molecular axes, respectively. Also, a comparison of our theoretical model with experimental data of the first harmonic component of the electric permittivity (non-linear dielectric increment) for a solution of 5 CB in squalane leads to a satisfactory enough agreement.

A molecular dynamics study of the dielectric properties of aqueous solutions of alanine and alanine dipeptide.

Molecular dynamics simulations were used to compute the frequency-dependent dielectric susceptibility of aqueous solutions of alanine and alanine dipeptide. We studied four alanine solutions, ranging in concentration from 0.13-0.55 mol/liter, and two solutions of alanine dipeptide (0.13 and 0.27 mol/liter). In accord with experiment we find a strong dielectric increment for both solutes, whose molecular origin is shown to be the zwitterionic nature of the solutes. The dynamic properties were analyzed based on a dielectric component analysis into solute, a first hydration shell, and all remaining (bulk) waters. The results of this three component decomposition were interpreted directly, as well as by uniting the solute and hydration shell component to a "suprasolute" component. In both approaches three contributions to the frequency-dependent dielectric properties can be discerned. The quantitatively largest and fastest component arises from bulk water [i.e., water not influenced by the solute(s)]. The interaction between waters surrounding the solute(s) (the hydration shell) and bulk water molecules leads to a relaxation process occurring on an intermediate time scale. The slowest relaxation process originates from the solute(s) and the interaction of the solute(s) with the first hydration shell and bulk water. The primary importance of the hydration shell is the exchange of shell and bulk waters; the self-contribution from bound water molecules is comparatively small. While in the alanine solutions the solute-water cross-terms are more important than the solute self-term, the solute contribution is larger in the dipeptide solutions. In the latter systems a much clearer separation of time scales between water and alanine dipeptide related properties is observed. The similarities and differences of the dielectric properties of the amino acid/peptide solutions studied in this work and of solutions of mono- and disaccharides and of the protein ubiquitin are discussed.

Alpha sub-phase in a new ferroelectric fluorinated compound

Dielectric and DSC methods were used to study a new fluorinated liquid crystalline compound exhibiting ferroelectric and paraelectric phases as well as an intermediate alpha sub-phase. Two dielectric relaxation processes were revealed in the SmC* phase: a typical Goldstone mode over the whole temperature range and a soft mode in the pre-transition region on both sides of the SmC*–SmA* transition. From the temperature dependencies of the dielectric increments and critical frequencies for the dielectric relaxation processes observed in all the liquid crystalline phases, as well as from texture observations, it was shown that there is a SmC*α sub-phase between the ferroelectric SmC* and paraelectric SmA* phases.

Water Absorption Effect on the Dynamic Properties of Nylon-6 by Dielectric Spectroscopy

New results of dielectric spectroscopy in semicrystalline nylon-6 samples with different moisture contents are presented by using a wide frequency (10-2−3 × 106 Hz) and temperature range (133−433 K). The dielectric absorption spectra in frequency domain are decomposed in Cole−Cole distributions corresponding to the local γ and β modes, two segmental α modes, and a high-intensity Maxwell−Wagner−Sillars relaxation. The presence of two segmental relaxations in the isothermal runs, attributed to the plasticized and the unplasticized α mode, is interpreted as the manifestation of two different length and time scales of cooperative motions. A quantitative comparison between the results obtained for the wet and dry samples, such as relaxation times variation, activation energies, Vogel−Tammann−Fulcher parameters, dielectric increments, and distribution widths, is presented for each mode and shows how the progressive drying of the sample during the experiment affects all these quantities.

Dielectric spectroscopy and electrophoretic mobility measurements interpreted with the standard electrokinetic model

We report results from complementary electrokinetic measurements—dielectric relaxation and electrophoretic mobility—undertaken to test the applicability of the standard electrokinetic theory with a model system. Dielectric spectra were obtained at frequencies between 1 kHz and 40 MHz with a new, two-electrode cell design [Hollingsworth and Saville, J. Colloid Interface Sci. 257 (2003) 65–76]; mobility data were acquired with an electrophoretic light scattering instrument. Data from the two-electrode cell were collected at different electrode separations and interpreted with newly developed procedures to remove the influence of electrode polarization. Methodology A employs extrapolation to infinite electrode separation to compute the dielectric constant and conductivity as functions of frequency. The contributions from suspended particles are reported in terms of dielectric constant and conductivity increments. Methodology B uses a theoretical model of electrode polarization and the standard electrokinetic model in a nonlinear regression scheme. Results are presented in several forms: frequency-dependent dielectric constant and conductivity increments, frequency-dependent dielectric constants and conductivities, and the complex dipole coefficient. It is shown that the standard model provides a consistent methodology for interpreting particle behavior; ζ-potentials inferred from mobility and dielectric relaxation agree to within experimental error. Moreover, the cell design and interpretation are straightforward and provide relatively simple ways to obtain complementary measurements over a wide frequency range. The results unambiguously show that electrokinetic character of this dispersion follows the standard model.