Dielectric Relaxation Spectra Research Articles

Is There an Anionic Hofmeister Effect on Water Dynamics? Dielectric Spectroscopy of Aqueous Solutions of NaBr, NaI, NaNO3, NaClO4, and NaSCN

A systematic study of the dielectric relaxation spectra of aqueous solutions of NaBr, NaI, NaNO(3), NaClO(4), and NaSCN has been made over a wide range of frequencies (0.2 < or = nu/GHz < or = 89) and solute concentrations (0.05 < or = c/M < or = 1.5) at 25 degrees C. The spectra could be adequately described by a single Cole-Cole (CC) process, symmetrically broadened relative to that of pure water. However, similar quality fits were also obtained with a three-Debye-process (3D) model consisting of a small ion-pair contribution at lower frequencies and two solvent relaxations at higher frequencies. Assuming the ions to be solvent separated, the 3D model provided estimates of their association constants and their rate constants for formation and dissociation. The bulk water relaxation times obtained from both models showed almost no dependence on the nature of the anion. Nevertheless, there were subtle differences in the concentration dependences of the relaxation times which correlated with some, but not all, of the anion properties that are believed to be relevant for explaining the anionic Hofmeister series.

Dielectric spectroscopy and micellization of aqueous solutions p-isononylphenoloxyethyleneglycolether

Dielectric relaxation spectra of optically isotropic aqueous solutions of p-isononylphenoldecaglycolether (NOP-10) were measured at 1.1 MHz, 9.376 GHz, 37.5 GHz from 275 to 313 K. The data were described assuming three Debye dispersion regions. Hydration numbers of NOP-10 molecules were calculated from an amplitude of the second dispersion region. Static permittivity values of the solutions were analyzed using theories for heterogeneous systems, and it was concluded that spheroidal micelles formed in the solutions at all investigated conditions. The shape of the micelles changed from prolate spheroids to spheres and then to oblate spheroids in the solutions with 9.97, 20, 30 wt% of NOP-10 in the temperature range from 275 to 313 K. A study of solutions with lower content of NOP-10 (1.14 and 4.97 wt%) have been made from 275 to 351 K, and it was deduced that in this case spherical micelles transformed to oblate spheroids and then to discs.

Characterisation of Blends Based on Hydroxyethylcellulose and Maleic Acid‐alt‐Methyl Vinyl Ether

AbstractSummary: Hydrophilic polymeric films based on blends of hydroxyethylcellulose and maleic acid‐co‐methyl vinyl ether were produced by casting from aqueous solutions. The physicochemical properties of the blends have been assessed using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, dielectric spectroscopy, etc. The pristine films exhibit complete miscibility due to the formation of intermacromolecular hydrogen bonding. The thermal treatment of the blend films leads to cross‐linking via intermacromolecular esterification and anhydride formation. The cross‐linked materials are able to swell in water and their swelling degree can be easily controlled by temperature and thermal treatment time. The formation of the crosslinks is apparent in the dynamic properties of the blends as observed through the mechanical relaxation and dielectric relaxation spectra. The dielectric characteristics of the material are influenced by the effects of change in the local structure of the blend on the ionic conduction processes and the rate of dipolar relaxation. Separation of these processes is attempted using the dielectric modulus method. Significant deviations from a simple additive rule of mixing on the activation energy are observed consistent with hydrogen bonding and crosslinking of the matrix. This paper indicates a method for the creation of films with good mechanical and physical characteristics by exposing the blends to a relatively mild thermal treatment.Scheme of hydrogen bonding between hydroxyethylcellulose and maleic acid‐co‐methyl vinyl ether.magnified imageScheme of hydrogen bonding between hydroxyethylcellulose and maleic acid‐co‐methyl vinyl ether.

Low Frequency Dielectric Response of Antiferroelectric Liquid Crystal CS-4001*

An Antiferroelectric liquid crystal (AFLC) CS-4001 was studied to find details of the field-induced ferroelectric phase transition by various measurements including the electro-optical hysteresis loops, switching current responses, and dielectric relaxation spectra. Contributions from two low frequency dielectric modes to the phase transition anomalies are discussed on the basis of the phenomenological Landau theory further extended by Orihara and Ishibashi.

Modeling the Segmental Relaxation Time Distribution of Miscible Polymer Blends: Polyisoprene/Poly(vinylethylene)

In considering the relaxation of segments in a blend whose components have reasonably disparate glass transition temperatures, local concentration fluctuations and density fluctuations each play a role. The result is a distribution of environments around a given segment in the blend, which translates into a distribution of segmental relaxation times. In this work we focus on concentration fluctuations, making use of a simple lattice model to generate a distribution of environments, which we then translate into a dielectric relaxation spectrum. We analyze experimental data for several polyisoprene/poly(vinylethylene) (PI/PVE) blends and show that, by accounting for the relatively strong composition dependence of the blend glass transition temperature, it is possible to model the dielectric relaxation spectrum by considering concentration fluctuations at the scale of the Kuhn length, which is both composition and temperature independent.

Changes in the dielectric relaxations of water in epoxy resin as a function of the extent of water ingress in carbon fibre composites

Dielectric relaxation measurements are reported over a frequency range from 10 −1 to 10 9 Hz as a function of exposure time for an epoxy resin–carbon fibre composite, ageing at 60 °C in water. Investigation of the nature of the dipole relaxation of the water molecules, indicates the nature of their interaction with the polymer matrix. Analysis of the dielectric relaxation spectra allow identification of processes that can be attributed to ‘free’ and ‘bonded’ water, water in micro-cracking, located in carbon fibre disbonds and plasticizing the polymer matrix. Identification of the various types of location in which water exists was aided by use of the N g factor from the Kirkwood–Frölich equation, which describes the constraints on free dipole ration nature imposed by the environment in which it is located. These data indicate the power of the dielectric technique for quantitative analysis of water ingress into epoxy composites.

Dielectric relaxation spectra of chemically treated woods

AbstractThe changes in the dielectric properties of absolutely dried Sitka spruce (Picea sitchensis Carr.) wood caused by chemical treatments were investigated. Eight kinds of chemical treatments with various levels of weight percentage gain (WPG) were performed. Through the application of the Cole–Cole circular arc law to the results of the dielectric measurements in the frequency range of 1 kHz to 1 MHz at −60°C, the relaxation spectrum was calculated. The relaxation magnitude (ε0 − ε∞) was reduced by formalization, acetylation, propylene oxide, and phenol–formaldehyde resin treatments, in which chemical reactions occurred between the OH groups in the cell wall and the added reagents. On the other hand, the generalized relaxation time (τm) decreased with increasing WPG, except for acetylation, for which τm decreased up to a WPG level of 20% and then increased. In poly(ethylene glycol) impregnation, (ε0 − ε∞) decreased with increasing WPG up to about 50% and then increased, whereas τm linearly decreased with increasing WPG. No significant changes in these parameters were recognized for the wood methyl methacrylate composite and heat treatment. With the steam treatment, τm increased. The distribution of the relaxation times was broad in acetylation and narrow in propylene oxide treatment and poly(ethylene glycol) impregnation. However, it remained almost unchanged in the other treatments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 37–43, 2005

Calorimetric Study of Dynamical Heterogeneity in Blends of Polyisoprene and Poly(vinylethylene)

The specific heat capacities Cp of blends consisting of cis-polyisoprene (PI) and poly(vinylethylene) (PVE) were measured in the temperature range from 80 to 320 K by using an adiabatic calorimeter. The configurational heat capacities Cconf of blends around the glass transition temperature Tg have been determined by subtracting the vibrational heat capacities estimated with the Einstein and Debye theories. The Cconf vs temperature T curves of the blends exhibit double sigmoidal increase at two glass transition temperatures Tg1 and Tg2 and can be resolved into two empirical sigmoidal curves. For each sigmoidal curve with the index j = 1 or 2, we have also determined the magnitude of the jump ΔCj and the broadness parameter Bj of the sigmoidal curves. The dielectric relaxation spectrum for the primary process of PI/PVE blends is known to be bimodal due to dynamical heterogeneity. The relationship between the bimodal dielectric segmental relaxation and the double glass transition processes has been analyzed.

Boundary-element calculations for dielectric behavior of doublet-shaped cells

In order to simulate dielectric relaxation spectra (DRS) of budding yeast cells (Saccharomyces cerevisiae) in suspension, the complex polarization factor (Clausius-Mossotti factor) beta for a single cell and the complex permittivity of a cell suspension epsilon(sus)* were calculated with a doublet-shaped model (model RD), in which two spheres were connected with a part of a ring torus, using the boundary element method. The beta values were represented by a diagonal tensor consisting of components beta(z) parallel to the rotation axis (z axis) and beta(h) in a plane (h plane) perpendicular to the axis. The epsilon(sus)* values were calculated from the complex permittivity of the suspending medium epsilon(a)* and the components of beta. The calculation was compared with that of a conventional prolate spheroid model (model CP). It was found that model CP could be used as a first approximation to model RD. However, differences existed in beta(z) between models RD and CP; beta(z) showed three relaxation terms in the case of model RD in contrast with two terms in model CP. Narrowing the junction between the two spheres in model RD markedly decreased the characteristic frequency of one of the relaxation terms in beta(z). This suggests that the structure of the junction can be estimated from DRS. Effects of the shape change from model RD to a two-sphere model (model RD without the junction) were also examined. The behavior of beta(z) in the two-sphere model, the relaxation intensity of which was much lower than model RD, was quite similar to that in a single-sphere model. These simulations were consistent with the experimental observations of the dielectric behavior of the yeast cells during cell cycle progression.

Dielectric Polarization and the Stages of a Macromolecule's Growth

To investigate the change in the orientation polarization, particularly during the growth of a macromolecule by addition reactions in a liquid, dielectric relaxation spectra of diglycidyl ether of bisphenol A have been studied in real time. It is found that in the plot of the dielectric permittivity, ∈', measured at a fixed frequency against the polymerization time, the first step of the (inverted) sigmoid-shape part of the spectrum resembling a relaxational decrease is a dc conduction effect. After this effect vanishes, the equilibrium permittivity, ∈ s , of the liquid increases with time as covalently bonded molecular clusters form at random sites in the bulk liquid, and the dipole orientational correlation increases as a result of hydrogen bonding between the newly formed OH groups. Thereafter, the macromolecule's continuous growth in the liquid decreases the net dipole moment of the covalently bonded network, which decrease ∈ s . Thus, after the conductance effect has become negligible, a plot of ∈ s against the polymerization time shows a maximum. Both the dc conductivity, σ 0 , and the distribution parameter for dielectric relaxation decrease with time, and σ 0 follows a scaling equation for gelation. The irreversible increase in relaxation time during a macromolecule's growth is explained in terms of a decrease in the configurational entropy, and a relation between the two is provided.

Ion Pairing and Solvent Relaxation Processes in Aqueous Solutions of Sodium Malonate and Sodium Succinate

Dielectric relaxation spectra have been measured for aqueous solutions of sodium malonate and sodium succinate over a wide range of frequencies (0.2 ≤ v/GHz ≤ 89) and solute concentrations (0.025 ≤ c/M ≤ 1.0). In addition to the usual processes associated with bulk water, two further relaxation processes were detected. The faster of these, with a relaxation time of ∼16 ps, is unusual and was attributed to the presence of slow water in the hydration shells of the anions. The extent of this hydration shell is rather fragile (concentration-dependent) for malonate but not for succinate. The second, slower, process was attributed to the presence of ion pairs NaX-(aq). Unambiguous determination of the structure of the ion pair was not possible because of the internal flexibility of the anions, but the data were most consistent with a chelated solvent-shared ion pair. The kinetics of formation and dissociation of the ion pairs were evaluated from the effects of solute concentration on their relaxation times.

Spontaneous transformation of water's high-density amorph and a two-stage crystallization to ice VI at 1 GPa: a dielectric study.

Dielectric relaxation spectra of a metastable crystal phase formed on implosive and exothermic transformation of pressure-amorphized hexagonal ice have been measured in situ at 0.97 GPa pressure over a range of temperature. The metastable phase showed no relaxation peak at 130 K and 0.97 GPa. When heated at a fixed pressure of 0.97 GPa, it began to transform at approximately 145 K exothermally to a phase whose relaxation rate and equilibrium dielectric permittivity increased. A second, but slower exothermic transformation also occurred at approximately 175 K. After keeping at 213 K, the relaxation rate and equilibrium permittivity reached the known values of these two quantities for ice VI. Thus the metastable phase transformed to ice VI in two stages. It is conjectured that the intermediate phase in this transformation could be ice XII. The rate of transformation is not determined by the reorientational relaxation rate of water molecules in the ices.

Origin of the complex dielectric relaxation spectra of molecular glass formers

The origin of the three broad bands appearing in the dielectric spectra of molecular glass formers is tracked down to microscopic scales by means of neutron-scattering and molecular-dynamics simulations. Three distinct regimes are also seen in the neutron quasielastic spectrum and are shown to arise from well-separated time regions appearing in the single-particle dipole autocorrelation function derived from simulations.

Johari-Goldstein relaxation and crystallization of sorbitol to ordered and disordered phases.

The equilibrium permittivity epsilon(s) and the dielectric relaxation spectra of supercooled liquid D-sorbitol were measured during its crystallization to orientationally disordered or ordered phases depending on the sample preparation procedure at several fixed temperatures up to a period of 6 days. The epsilon(s) measurements showed that when the sample was contaminated by a minute amount of crystals, it crystallized to an ordered phase. When the liquid was not contaminated, the sample crystallized to an orientationally disordered phase. When supercooled D-sorbitol was kept close to its T(g), its dielectric spectra did not change over a period of 138.5 h. It was found that the Johari-Goldstein (JG) relaxation rate of the orientationally disordered crystalline phase is higher in comparison with that of the supercooled liquid, the spectrum broader, and the relaxation strength lower. Its glasslike transition temperature is higher than T(g) of the liquid. The results on crystallization showed that the structural changes occurring at a temperature where the alpha relaxation emerges from the JG relaxation affects the crystallization kinetics of the liquid.

Dielectric and Optical Studies of FLC Sample with Helix Inversion

Dielectric relaxation and electro-optical study in terms of tilt angle, spontaneous polarisation, birefringence, helical pitch and optical rotatory power have been carried out for 4-(1-methyloctyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (MOPOBC) sample in the temperature range of SmA and tilted SmC* and SmI A * phases. Two collective modes have been observed in the dielectric relaxation spectra. The low frequency mode is assigned to the azimuthal fluctuations of the director following the helix distortion (Goldstone mode) while the high frequency one is the optical phason like mode. The other two peaks in the spectra are also being reported. The low frequency one arise from the molecular rotation around the short axis (near 1 MHz) and another at low frequency (1–10 Hz) result from the coupling between ion movement and spontaneous polarization. The dielectric strength of the Goldstone mode has a sharp maximum about 2 K below T C . This has been explained by the helical inversion of the pitch. Results have been analysed using the Landau phenomenological model for the ferroelectric phase. Almost all expansion coefficients of the free energy density have been determined in the SmC* phase together with the viscosity coefficients describing the dynamics of the collective modes of the director.

Investigation of Relaxor Behavior in Pb(Mgg1/3Nb2/3)O3-PbTiO3 Thin Films

Relaxor properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) thin films have been analyzed in terms of large frequency dispersion of dielectric response at temperatures below that of the peak permittivity. A wide spectrum of dielectric relaxation was observed in the frequency dependent response of imaginary part of dielectric permittivity. A cumulative response of Debye relaxators was experimentally observed at lower temperatures. The Cole-Cole plots (ϵ′ vs. ϵ″) showed a broad distribution in dielectric relaxation at lower temperatures. The temperature dependence of dielectric dispersion has been analyzed using Vogel-Fulcher relation. A little modification in the Vogel-Fulcher (V-F) relation was incorporated to avoid the singularity at the V-F temperature (T f ). The activation energy (E) and the freezing temperature in PMN-PT thin films were 40 mV and 400 K, respectively. Investigation of ferroelectric properties in terms of polarization hysteresis behavior confirmed presence of interaction among nanopolar clusters.

Studies on Dynamic Heterogeneity in Miscible Polymer Blends and Dynamics of Flexible Polymers

This paper presents our three studies: (1) dynamic heterogeneity in miscible polymer blends, (2) dielectric study on the dynamics of flexible polymer chains in melts and solutions, and (3) stress relaxation of entangled polymer systems in biaxial extension. In the study of (1), we investigated the segmental and global dynamics mainly in miscible polyisoprene (PI) / poly(vinyl ethylene) (PVE) blends. Specifically, we estimated the characteristic sizes of the segmental motion. Furthermore, in order to see the effect of the concentration fluctuation (CF) on the segmental dynamics, we compared the dielectric relaxation spectra of the segmental motion between PI/PVE blend and PI-PVE diblock copolymer based on the fact that the CF amplitude is suppressed in the diblock copolymer system. In the second study, dipole inverted type-A polymers are used to investigate the detailed chain dynamics. In the third study, we determined the damping function in biaxial extensional deformation for polystyrene melts and compared with Doi-Edwards theory.

Classification of secondary relaxation in glass-formers based on dynamic properties.

Dynamic properties, derived from dielectric relaxation spectra of glass-formers at variable temperature and pressure, are used to characterize and classify any resolved or unresolved secondary relaxation based on their different behaviors. The dynamic properties of the secondary relaxation used include: (1) the pressure and temperature dependences; (2) the separation between its relaxation time taubeta and the primary relaxation time taualpha at any chosen taualpha; (3) whether taubeta is approximately equal to the independent (primitive) relaxation time tau0 of the coupling model; (4) whether both taubeta and tau0 have the same pressure and temperature dependences; (5) whether it is responsible for the "excess wing" of the primary relaxation observed in some glass-formers; (6) how the excess wing changes on aging, blending with another miscible glass-former, or increasing the molecular weight of the glass-former; (7) the change of temperature dependence of its dielectric strength Deltaepsilonbeta and taubeta across the glass transition temperature Tg; (8) the changes of Deltaepsilonbeta and taubeta with aging below Tg; (9) whether it arises in a glass-former composed of totally rigid molecules without any internal degree of freedom; (10) whether only a part of the molecule is involved; and (11) whether it tends to merge with the alpha-relaxation at temperatures above Tg. After the secondary relaxations in many glass-formers have been characterized and classified, we identify the class of secondary relaxations that bears a strong connection or correlation to the primary relaxation in all the dynamic properties. Secondary relaxations found in rigid molecular glass-formers belong to this class. The secondary relaxations in this class play the important role as a precursor or local step of the primary relaxation, and we propose that only they should be called the Johari-Goldstein beta-relaxation.

α−β Splitting Region in the Dielectric Relaxation Spectrum of PEA-PEMA Sequential IPNs

The dielectric relaxation spectra of poly(ethyl acrylate)-i-poly(ethyl methacrylate) sequential interpenetrating polymer networks, IPNs, are presented. In addition, dynamic-mechanical data were used to study the compatibility of the networks as the main relaxation predominates on the secondary relaxation in mechanical spectroscopy. When the IPNs are highly cross-linked, both networks are forced to mix at the molecular level, and as a consequence, a single main dynamic mechanical relaxation appears. By contrast, when the cross-linking density is small, the individual relaxation behavior of the component networks can be observed. The poly(ethyl methacrylate) networks with low cross-linking density show the merging of the secondary β dielectric relaxation and the main α relaxation with the same characteristics as the poly(ethyl methacrylate) chain polymer. This behavior changes, however, in the highly cross-linked network in which the influence of the main relaxation on the overall behavior is smaller, and it was not possible to separate the α and β components in the merging region. The incorporation of the poly(ethyl acrylate) chains to the cooperative motions of the poly(ethyl methacrylate) network shifts the α and β relaxations to a different extent, which induces changes in the shape of the spectrum in the merging zone.

Structure and Dynamics of Polymer−Surfactant Complexes: Dielectric Relaxation Studies

The isothermal phase diagram of the system composed of water, sodium dodecyl sulfate, and hexadecyltrimethylammonium polyacrylate, PACTA, at 25 °C, was investigated by dielectric relaxation, ionic conductivity, and viscosity. The polymer is not water-soluble and dissolves only in the presence of surfactant in micellar form. Dielectric relaxation spectra indicate the occurrence of one relaxation in the surfactant solutions, above the critical micellar concentration, and of two relaxation processes in the presence of PACTA and sodium dodecyl sulfate, C12SO4Na, in micellar form. They are ascribed to free and polymer-bound micelles, respectively. Data have been interpreted in terms of a chemical equilibrium of micelles partitioned between polymerbound and free states. The dielectric results indicate that the distance between micelles adsorbed on the polymer backbone is close to 40 nm and slightly changes, depending on the surfactant content. These results support the hypothesis of a necklace structure for the polymer-micelle complex. According to viscosity findings, in fact, the stiffness of the PACTA-C12SO4Na complex decreases on increasing the amount of bound micelles.