Polymer electrolytes—relaxation and transport properties

Relaxations in polymer electrolytes were studied in poly(ethylene oxide) and epoxidized natural rubbers both filled with lithium perchlorate. Impedance relaxation was investigated over a wide range of salt concentration at room temperature. Imaginary part of impedance as a function of frequency exhibits generally one maximum and one minimum. These two extreme values rule properties in the DC limit. They can be related to transport properties and degree of dissociation. It turns out that DC conductivity is dominantly ruled by transport coefficient.     

Dielectric relaxation in polyvinylidenefluoride–polysulfone blends

Dielectric properties of polymer blend of polyvinylidenefluoride (PVDF) and polysulfone (PSF) of different wt. % have been studied to understand the molecular motion and their relaxation behavior in the frequency range of 100 Hz to 10 kHz at different temperatures between 30 and 190 °C. The dielectric constant of the blend decreased with frequency and increased with the increasing temperature and PSF content in the blend. The magnitude of dielectric loss also increased with increase in temperature and PSF content. The observed characteristic has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending of PSF with PVDF. At constant frequency and temperature, the blend follows a linear relationship between logarithm of their dielectric constant and different ratios of blend. The appearance of a peak for each concentration in dielectric loss suggests the presence of relaxing dipoles in the blend. In addition of PSF with PVDF, the peak shifts toward higher frequency side suggesting the speed up the relaxation process. AC dielectric data is also combined with thermally stimulated depolarization current (TSDC) data which is generally studied for low-frequency dielectric properties of polymers blends so as to produce the results in a wide frequency range. The glass transition temperature (T_g) of the blend was studied by differential scanning calorimetric technique (DSC), the T_g was compared and correlated with TSDC peak. The blend samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to study the formation of blend and micro structural properties of the materials. The shifting of peak toward lower diffraction angle side confirms the reduction in particle size with increasing amorphous content in the blend.     

Asymmetric fluctuation–relaxation paths in FPU models

A recent theory by Bertini, De Sole, Gabrielli, Jona-Lasinio and Landim predicts a temporal asymmetry in the fluctuation–relaxation paths of certain observables of nonequilibrium systems in local thermodynamic equilibrium. We find temporal asymmetries in the fluctuation–relaxation paths of a form of local heat flow, in the nonequilibrium FPU-$\beta$ model of Lepri, Livi and Politi.     

Nonlinear order-parameter relaxation in the nonlinearσ-model

An equation of motion for the order parameter of a relaxational nonlinear-model is derived by renormalization-group considerations ind=2+ dimensions. The result is then used to describe the nonlinear relaxation of the order parameter after switching off an initial symmetry-breaking field below the critical temperature.     

Ghost lines in Mössbauer relaxation spectra

The appearance in Mössbauer relaxation spectra of ghost lines, which are narrow lines that do not correspond to transitions between real hyperfine energy levels of the resonant system, is examined. It is shown that in many cases of interest, the appearance of these ghost lines can be interpreted in terms of the relaxational averaging of one or more of the static interactions of the ion.     

Dielectric relaxation in NBT–ST ceramic composite materials

Lead-free piezoelectric ceramic composites (1-x) Na_0.5Bi_0.5TiO₃-xSrTiO₃, where x?=?0.05, 0.10, 0.15 and 0.2, are prepared by mixing independently-prepared individual phases through sol–gel method. X-ray diffraction revealed the coexistence of rhombohedral and cubic phases. Surface morphology of the composites is observed using SEM, and both the phases are observed in the samples. Spectroscopic studies of the composites are characterized based on Fourier transform infrared, and vibration bands are analyzed at room temperature in the wave number region 500–3,000 cm^?1. Dielectric properties of these composites are measured from room temperature to 400 °C in the frequency range 1–10 kHz, and these studies indicate the presence of defect clusters within the composite materials. P–E hysteresis loops of these samples were measured as a function of temperature and observed large anomalies in the behavior compared to pure sodium bismuth titanate (NBT) (the host material). Unlike NBT, all the composites exhibited excellent P–E loops. In addition, decrease in remanence polarization is observed, with increase of SrTiO₃ at room temperature. Piezoelectric parameter d₃₃ is measured on poled composites.     

Thermal relaxation for the Relativistic Ornstein–Uhlenbeck Process

The thermal relaxation of a relativistic particle diffusing in a fluid at equilibrium is investigated through a numerical study of the Relativistic Ornstein–Uhlenbeck Process. The spectrum of the relaxation operator has both a discrete and a continuous component. Both components are fully characterized and the limit between them is given a simple interpretation. Short-time relaxation is addressed separately, and a global effective relaxation time is also computed. The general conclusion is that relativistic effects slow down thermalization.     

Grain boundary segregation and relaxation in nano-grained polycrystalline alloys

The present study carries out systematic thermodynamics analysis of Grain Boundary(GB)segregation and relaxation in NanoGrained(NG)polycrystalline alloys.GB segregation and relaxation is an internal process towards thermodynamic equilibrium,which occurs naturally in NG alloys without any applied loads,causes deformation and generates internal stresses.The analysis comprehensively investigates the multiple coupling effects among chemical concentrations and mechanical stresses in GBs and grains.A hybrid approach of eigenstress and eigenstrain is developed herein to solve the multiple coupling problem.The analysis results indicate that the GB stress and grain stress induced by GB segregation and relaxation can be extremely high in NG alloys,reaching the GPa level,which play an important role in the thermal stability of NG alloys,especially via the coupling terms between stress and concentration.The present theoretic analysis proposes a novel criterion of thermal stability for NG alloys,which is determined by the difference in molar free energy between a NG alloy and its reference single crystal with the same nominal chemical composition.If the difference at a temperature is negative or zero,the NG alloy is thermal stable at that temperature,otherwise unstable.     

“Constant-loss” relaxation response in crystals and glasses

Nowick and his associates have stated that many ionic crystals and glasses exhibit a loss per cycle which is independent of frequency over an appreciable range and have suggested that such behavior constitutes a new universality. Furthermore, much such data seem to approach an asymptotic, nearly temperature-independent ac loss at sufficiently low temperatures. In order to further evaluate these conclusions, small-signal ac relaxation data for a CaTiO₃:30% Al³⁺ ceramic material are analyzed in detail and the results compared to those published by Nowick and associates for the same material. It is found that a plausible conducting-system dispersion model based on the effective-medium approximation for hopping charges yields results globally similar to, but somewhat different in detail from, those of Nowick et al. But a response model which includes both such conducting-system response and dielectric-system dispersion well fits the data over a wide temperature range. To do so, it requires the presence of a non-zero high-frequency-limiting resistivity probably arising from localized charge motion. No constant-loss individual dispersions appear in the model, but it nevertheless yields approximately constant loss over a limited frequency range at low temperatures. It suggests that asymptotic behavior is associated with the nearly temperature-independent dielectric-dispersion contribution to the response at low temperatures, and it does not verify the Nowick conclusion that the slope of the ac conductivity approaches a constant value near 0.6 at high temperatures.     

β relaxation theory for simple systems: some addenda

The evolution of the tagged particle probability density for a hard sphere system is evaluated within the -relaxation window. Relaxation curves obtained by molecular dynamics studies by Barrat, Hansen and Roux for a binary mixture are analyzed quantitatively with -relaxation scaling formulae. The dynamical light scattering data obtained by Pusey and van Megen for colloidal suspensions are described by the combined - and -relaxation scaling results. The range of validity of asymptotic expressions near a glass transition singularity is discussed for the Debye-Waller factor as a function of packing fraction. The applied theoretical formulae are those of the mode coupling theory for the liquid to glass transition.     

Are methyl groups relaxation sinks in small proteins?

The longitudinal relaxation of well-resolved protons in the N-terminal domain of lambda repressor has been studied in the native protein and in a sample in which all of the leucine methyls have been selectively deuterated. The relaxation rates in these two samples have been compared in order to study the contribution of the leucine methyls to the relaxation behavior of aromatic protons in the protein.     

Zero- and low-field μ+ spin relaxation behavior in MnSi

Conclusion As is demonstrated in the present work, the zero-field technique is a powerful method in studying diffusion/trapping of the ⁺, especially for the case of slow hopping. In the case of MnSi, the hopping time _c has been determined to be longer than 20 sec, with the width of the nuclear random fields / = 3.80 ± 0.4 Oe. The role of the ⁺ in low-field relaxation studies is unique, since it provides information inaccessible to NMR techniques.Work supported by Japan Society for the Promotion of Science, the Toray Science Foundation, the Grant-in-Aid of the Japanese Ministry of Education, Culture and Science, and the Atomic Energy Control Board and National Research Council of Canada.     

Rotational stretched exponential relaxation in random trap–barrier model

The relaxation behavior of complex-disordered systems, such as spin glasses, polymers, colloidal suspensions, structural glasses,and granular media, has not been clarified. Theoretical studies show that relaxation in these systems has a topological origin. In this paper, we focus on the rotational stretched exponential relaxation behavior in complex-disordered systems and introduce a simple phase space model to understand the mechanism of the non-exponential relaxation of these systems. By employing the Monte Carlo simulation method to the model, we obtain the rotational relaxation function as a function of temperature. We show that the relaxation function has a stretched exponential form under the critical temperature while it obeys the Debye law above the critical temperature.     

Long-time relaxation processes in the nonlinear Schrödinger equation

The nonlinear Schrödinger equation, known in low-temperature physics as the Gross-Pitaevskii equation, has a large family of excitations of different kinds. They include sound excitations, vortices, and solitons. The dynamics of vortices strictly depends on the separation between them. For large separations, some kind of adiabatic approximation can be used. We consider the case where an adiabatic approximation can be used (large separation between vortices) and the opposite case of a decay of the initial state, which is close to the double vortex solution. In the last problem, no adiabatic parameter exists (the interaction is strong). Nevertheless, a small numerical parameter arises in the problem of the decay rate, connected with an existence of a large centrifugal potential, which leads to a small value of the increment. The properties of the nonlinear wave equation are briefly considered in the Appendix A.     

Anisotropic relaxation time T′2 of solid 3He

This paper investigates an anisotropy of the adiabatic relaxation time T ₂′ for single crystalline bcc ³He. No difference in the calculation of T ₁(0) was revealed between the nearest-neighbor anti-ferromagnetic Heisenberg model and the multiple exchange model. However, we may distinguish these two models by the anisotropy of the adiabatic relaxation time T ₂′. The results presented in this paper are compared with experimental observations.     

Dielectric relaxation and ion transport in silver–boro-tellurite glasses

Glass systems of composition xAg₂SO₄–20Ag₂O–(80?x) [0.50 B₂O₃–0.50 TeO₂], where x = 5, 10, 15, 20, 25 and 30 mol% have been prepared by melt-quenching technique. Frequency- and temperature-dependent conductivity measurements have been carried out in the frequency range 10 Hz to 10 MHz and at a temperature range of 303–353 K, respectively. DC conductivities exhibit Arrhenius behavior over the entire temperature range with a single activation barrier. Addition of Ag₂SO₄ expands the glass network and, consequently, conductivity increases. This suggests that the structure and network expansion are the key parameters for enhancing conductivity. Impedance spectra of these glasses show a single semicircle, indicating one type of conduction. AC conductivity behavior of the glasses was analyzed using both single power law and Kolhrauh–William–Watts (KWW) stretched exponential relaxation function. The power law exponent (s) is temperature-dependent, while the stretched exponent (β) is insensitive to temperature. Scaling behavior has also been carried out using reduced plots of conductivity with frequency, which suggests the ion transport mechanism remains unaffected by temperature and composition.     

Studies of dielectric relaxation in natural fiber–polymer composites

Polymer composites of a polyester resin matrix filled with short palm tree lignocellulosic fibers were studies by means of dielectric spectroscopy in the frequency range 0, 1–100 kHz and temperature interval from 40 °C to 200 °C. Three relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in Palm fiber, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and the interfacial relaxation that is attributable to the accumulation of charges at the Palm fibers/polyester interfaces.     

Energy relaxation in aϕ 4 with long range interactions

We investigate the influence of long range interactions on the relaxation behaviour of a lattice model with an on-site potential of ⁴-type and infinite range harmonic interactions. For finite number of particlesN, it is shown that the autocorrelation functions <E _n(t)E _n > of the fluctuations of the one-particle energiesE _n(t) decays exponentially. The corresponding relaxation time is proportional toN and is given by (T, N) =N₀(T). The temperature dependent time scale ₀ can explicitly be related to the dynamics of a one-particle correlator of the noninteracting system. The results are derived using Mori-Zwanzig projection formalism. The corresponding memory kernel is calculated within a mode coupling approximation and by a perturbative approach. Both results agree in leading order in 1/N. It is speculated that any interaction of range generates a timescale .     

A new method for multi-exponential inversion of NMR relaxation measurements

The NMR technique has been widely applied to petroleum well logging and rock core analysis since the 1990s when NUMAR introduced a reliable NMR logging tool to the oil industry. It has been playing an important role for prospecting and exploiting resource of oil and gas for the last ten years. In an oil well, NMR can provide parameters of reservoir and fluid properties, such as porosity, pore size distribution, bound water volume, bulk volume of free water, permeability, in-situ fluid dif…