Dependence Of Relaxation Time Research Articles

Dielectric relaxations and the phenomena of glass transition in supercooled D-xylose aqueous mixtures

D-xylose aqueous solutions at various concentrations of water (0 ≤ x ≤ 40 %) were investigated using broadband dielectric spectroscopy and differential scanning calorimeter in the wide temperature range (150–300 K). Two resolvable relaxations were observed in all studied D-xylose aqueous solutions. The slower relaxation process (process-I) observed above the glass transition temperature (Tg), usually referred to as the structural relaxation process, is responsible for the collective movement of the D-xylose and water mixture. The faster one (process-II) observed below Tg is mainly related to the water molecular relaxation inside the D-xylose matrix. The temperature dependence of the average dielectric relaxation time and dielectric strength of both observed processes (I & II) were analyzed for all concentrations of water (x) in D-xylose. It was observed that the dielectric strength of process-II in the D-xylose water mixture increased sharply above critical concentration, x = 25 % shows moderate characteristics as compared to its isomers viz. D-ribose, D-arabinose and D-lyxose. Also the activation energies were found to be almost water content independent above critical concentration, x = 25 %. This suggests that this dynamic process was dominated by water-water interaction. Moreover, the Tg of bulk water was estimated at 133 ± 1 K and 138 ± 1.2 K from the extrapolation of DSC Tg and dielectric Tg, respectively of the D-xylose aqueous mixture using the Gordon-Taylor equation. This gives further support to the commonly accepted Tg value of bulk water.

How to Make the Stress Relaxation Experiment for Polymers More Informative.

Different viscoelastic models and characteristics are commonly used to describe, analyze, compare and improve the mechanical properties of polymers. A time-dependent linear relaxation modulus next to frequency-domain storage and loss moduli are the basic rheological material functions of polymers. The exponential Maxwell model and the exponential stretched Kohlrausch-Williams-Watts model are, probably, the most known linear rheological models of polymers. There are different identification methods for such models, some of which are dedicated to specific models, while others are general in nature. However, the identification result, i.e., the best model, always depends on the specific experimental data on the basis of which it was determined. When the rheological stress relaxation test is performed, the data are composed of the sampling instants used in the test and on the measurements of the relaxation modulus of the real material. To build a relaxation modulus model that does not depend on sampling instants is a fundamental concern. The problem of weighted least-squares approximation of the real relaxation modulus is discussed when only the noise-corrupted time-measurements of the relaxation modulus are accessible for identification. A wide class of models, that are continuous, differentiable and Lipschitz with respect to parameters, is considered for the relaxation modulus approximation. The main results concern the models that are selected asymptotically as the number of measurements tends to infinity. It is shown that even when the true relaxation modulus description is completely unknown, the approximate optimal model parameters can be derived from the measurement data that are obtained for sampling instants that are selected randomly due to the appropriate randomization introduced whenever certain conditions regarding the adopted class of models are satisfied. It is shown that the most commonly used stress relaxation models, the Maxwell and Kohlrausch-Williams-Watts models, satisfy these conditions. Since the practical problems of the identification of relaxation modulus models are usually ill posed, Tikhonov regularization is applied to guarantee the stability of the regularized solutions. The approximate optimal model is a strongly consistent estimate of the regularized model that is optimal in the sense of the deterministic integral weighted square error. An identification algorithm leading to the best regularized model is presented. The stochastic-type convergence analysis is conducted for noise-corrupted relaxation modulus measurements, and the exponential convergence rate is proved. Numerical studies for different models of the relaxation modulus used in the polymer rheology are presented for the material described by a bimodal Gauss-like relaxation spectrum. Numerical studies have shown that if appropriate randomization is introduced in the selection of sampling instants, then optimal regularized models of the relaxation modulus being asymptotically independent of these time instants can be recovered from the stress relaxation experiment data. The robustness of the identification algorithm to measurement noises was demonstrated both by analytical and numerical analyses.

A trivalent ferrite ferrofluid compound’s rheological response to angular frequency, magnetic induction and shear induction of chain clusters

At low and high temperatures in the presence and absence of magnetic fields, the effects of shear rate, angular frequency, and shear strain on the rheological characteristics of zinc ferrite ferrofluid is investigated. Chemical co-precipitation was used to create a zinc ferrite ferrofluid that was then coated with oleic acid to improve the stability of the fluid’s particles and avoid particle agglomeration. We looked at the rheological characteristics caused by the induced magnetic field, such as the shear stress, complex viscosity, storage modulus, loss modulus, relaxation modulus, viscous torque, damping factor, and figure of merit. From the analysis of time dependent relaxation modulus, a steady-state rheological system is formed at time interval beyond 50 s. As the shear and complex viscosities increase with an increase in magnetic field and a decrease in temperature, obstruction to fluid flow is produced. When a rheological system operates at low angular frequency and high shear rate, high shear stress is loaded; when it operates at high angular frequency and low shear rate, low shear stress is loaded. In the absence of magnetic field, a low viscosity 0.425 Pa.s and shear force 46 Pa were formed, while high viscosity 8.140 Pas and shear stress 168 Pa were formed when magnetic field 1.000 Tesla was applied. The oscillatory mode test demonstrates a change in structure from solid to liquid due to the establishment of a crossover point between shear strain 55 and 64%, supporting the solid–liquid phase transition behavior. The damping analysis demonstrates that the system is in fact excessively dampened, and it may now be utilized to reduce vibrations in a system. The system is really overdamped showing a maximum damping factor 2.08, according to the damping study, and can therefore be used to reduce vibrations in other systems. The fluid exhibits non-Newtonian shear-thinning behavior as shear rates increase. A high viscous torque is created at low shear strain and high angular frequency, which leads to the creation of a strong rotating magnetic field.

Time, momentum, and energy resolved pump-probe tunneling spectroscopy of two-dimensional electron systems

Real-time probing of electrons can uncover intricate relaxation mechanisms and many-body interactions in strongly correlated materials. Here, we introduce time, momentum, and energy resolved pump-probe tunneling spectroscopy (Tr-MERTS). The method allows the injection of electrons at a particular energy and observation of their subsequent decay in energy-momentum space. Using Tr-MERTS, we visualize electronic decay processes, with lifetimes from tens of nanoseconds to tens of microseconds, in Landau levels formed in a GaAs quantum well. Although most observed features agree with simple energy-relaxation, we discovered a splitting in the nonequilibrium energy spectrum in the vicinity of a ferromagnetic state. An exact diagonalization study suggests that the splitting arises from a maximally spin-polarized state with higher energy than a conventional equilibrium skyrmion. Furthermore, we observe time-dependent relaxation of the splitting, which we attribute to single-flipped spins forming skyrmions. These results establish Tr-MERTS as a powerful tool for studying the properties of a 2DES beyond equilibrium.

Table-like magnetocaloric effect due to field-induced inter-cluster interactions in Eu0.5Sr0.5MnO3–EuMnO3 composites

The table-like behavior of the magnetic entropy change is generally observed in rare-earth-based alloys (e.g. La(Fe,Si)13, Gd50Co45Fe5, Gd56Ni15Al27Zr2, GdCo x Al y etc). Here, we report similar table-like behavior in a bulk perovskite Eu0.5Sr0.5MnO3–EuMnO3 composite system with a working temperature span of ∼80 K for a field change of ∼70 kOe. AC susceptibility and time-dependent DC magnetization relaxation measurements confirm the presence of interacting ferromagnetic clusters with a Vogel–Fulcher freezing temperature of 42.7 K. The Langevin function fittings of the isothermal magnetization curves show a non-monotonous variation of cluster size with temperature. We propose a model for the high-field dependency of the ferromagnetic cluster coupling in the composite system. This widens the transition temperature region of long-range order formation and hence gives rise to the table-like magnetocaloric effect in Eu0.5Sr0.5MnO3–EuMnO3 composite systems.

Experimental study on the mechanical properties of the reinforced transparent building membrane material STFE

STFE is a new type of reinforced polymer building membrane material that combines excellent mechanical properties and transparency by using high-strength fibre mesh, which eliminates the limitations of poor transparency in coated fabric membranes and low strength in polymer membranes. In this study, in order to investigate its strength indicators and mechanical properties, material mechanical tests such as uniaxial, biaxial, and picture frame tests were conducted, obtaining the basic mechanical parameters of the material, including warp and weft direction tensile strength, tear strength, welding seam strength, elastic modulus and Poisson's ratio, shear modulus, and creep elongation rate, among others. Additionally, linear and nonlinear stress–strain mechanical models for uniaxial and biaxial loading were proposed for this material, as well as time-dependent creep and stress relaxation models. These mechanical models were validated and found suitable for numerical simulations of the material. The research results lay the preliminary foundation for the application of this material in large-span tensile transparent membrane structures.

Temperature Dependence of Nuclear Quadrupole Resonance and the Observation of Metal-Ligand Covalency in Actinide Complexes: 35Cl in Cs2UO2Cl4.

We report a study of the temperature dependence of 35Cl nuclear quadrupole resonance (NQR) transition energies and spin-lattice relaxation times (T1) for 235U-depleted dicesium uranyl tetrachloride (Cs2UO2Cl4) aimed at elucidating electronic interactions between the uranium center and atoms in the equatorial plane of the UO22+ ion. The transition frequency decreases slowly with temperature below 75 K and with a more rapid linear dependence above this temperature. The spin-lattice relaxation time becomes shorter with temperature, and as temperatures increase, the T1 decrease becomes nearly quadratic. The observed trends are reproduced by a model that assumes phonon-induced fluctuations of the electric field gradient tensor and partial electron delocalization from Cl to U. The fit of the theoretical model to experimental data allows a Debye temperature of 96 K to be estimated. The generalization of this approach to investigations of covalency in actinide-ligand bonding is examined.

Effect of sintering temperature on impedance and EMI shielding of carbon modified CoFe2O4 nanofibers via electrospinning

The electrospinning technique is employed for the synthesized cobalt ferrite/carbon nanofibers, utilizing iso-propanol as the solvent. The nanofibers prepared are subjected to sintering at three different temperatures. A comprehensive analysis is carried out on the structural, morphological, dielectric, impedance, and electromagnetic shielding effectiveness within the X-band frequency range (8.2–12.4 GHz). The application of the Debye-Scherer formula yielded an estimated crystallite size of 22 nm. The electrical response of cobalt ferrite/carbon nanofibers pellet is characterized by employing impedance spectroscopy. Variations in impedance plane plots are discussed based on frequency dependent relaxation time modulations. The impact of sintering temperature is observed in terms of increased impedance values and modifications in the conduction mechanism. These changes are contributed to distinct hopping carriers’ linkages between Fe3+-Fe2+ and Co3+-Co2+ ions. Dielectric studies are elucidated considering cation polarizability, colossal resistivity, and tangent loss. This study revealed notable characteristics of CoFe2O4/C nanofibers, including colossal resistivity (8.45 × 108 Ωcm), a dielectric constant of 22, and colossal tangent loss. The CoFe2O4/C nanofibers exhibit a characteristic electromagnetic interference (EMI) shielding performance of 30–35 dB. This remarkable shielding performance is observed in nanofibers with a 3 mm thickness, specifically in sample S1 that underwent sintering at a low temperature. The shielding effectiveness is demonstrated within the X-band frequency range.

Structural reversible adhesives based on thiol-epoxy vitrimers

This work presents a family of functional adhesives based on covalent adaptable networks (CANs). Low-cost and commercially available monomers, including diglycidyl ether of bisphenol A, pentaerythritol tetrakis (3-mercapto propionate) and dipentaerythritol hexakis (3-mercapto propionate), were cured using a base catalyst to produce highly cross-linked materials. The catalyst selection and the study of the curing reaction were performed using differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The catalyst was chosen for better feasibility of industrial production, characterized by short curing times and relatively low temperatures. Thermal stability and thermomechanical properties of the final materials were evaluated through thermogravimetry (TGA) and dynamic mechanical thermal analysis (DMTA), respectively, revealing glass transition temperatures (Tg) higher than 50 °C. Stress relaxation tests were conducted to investigate the vitrimeric behaviour of the polymers, which exhibited an Arrhenius-type dependence of relaxation times on temperature. Importantly, both materials demonstrated impressive creep resistance up to 70 °C, indicating their suitability for use at elevated service temperatures. Tensile and lap-shear tests were also performed, revealing high lap-shear strength values (up to 16 MPa) comparable to those of commercial adhesives. Furthermore, these vitrimers displayed remarkable properties such as shape memory, shape reconfiguration, and self-welding capabilities, underscoring their excellent potential for a wide range of highly demanding applications in industrial production.

Multi‐Subband Polar Optical Phonon Scattering in InAlN/AlN/GaN Heterostructures

The high density of two‐dimensional electron gas (2DEG) in InAlN/AlN/GaN heterostructures results in significant occupation of higher subbands, it is thus imperative to consider multi‐subband occupation and inter‐subband scattering in the calculations of polar optical phonon (POP) scattering. The physical parameters, such as subband energies, wave functions of the four lowest subbands, and Fermi level of InAlN/AlN/GaN heterostructures, are calculated by solving the Schrödinger–Poisson equations and applied to the multi‐subband POP scattering model. The dependence of mobility, which is limited by multi‐subband POP scattering, on temperature and 2DEG density is studied. The results show that multi‐subband occupation and inter‐subband scattering play important roles in electron transport. The higher subbands contribute 26% to room‐temperature electron mobility. Two simplified POP scattering models, which either ignore multi‐subband occupation or simplify the in‐scattering processes are evaluated. The results show that both simplified models introduce significant deviations in the mobilities that are limited by POP scattering. The relative magnitudes of mobility in each subband depend on the energy dependence of momentum relaxation time and the energy distribution of each subband.

Optoelectronic and thermoelectric properties of LiCuM (M=S, Se and Te) half-Heuslers: insights first principle calculations

The work is performed to study the structural stability and optoelectronic properties as well as thermoelectric properties of LiCuM (M=S, Se and Te) half-Heusler semiconductors using density functional theory (DFT) and semi-classical Boltzmann transport. The ground state results show that the compounds exhibit semiconducting behavior with a direct band-gap. The elastic parameters indicate that the present compounds are mechanically, dynamically stable and brittle. The calculated optical properties in GGA and GGA+U approaches show that the dominant response in the low ultraviolet and visible energy regions. The thermoelectric properties are evaluated using the Slack model and temperature dependent relaxation time in the temperature range of 100 K to 1000 K. The response of thermoelectric properties to temperature is evaluated and discussed in detail. The figure of merit with relaxation time is found to increase with temperature and reaches the optimal values in GGA and GGA+U at 1000 K are 0.69(0.01), 0.66(0.665) and 0.67(0.778) for LiCuS, LiCuSe and LiCuTe, respectively. The lattice thermal conductivity decreases with increasing temperature. These properties make these compounds promising candidates for optoelectronic and thermoelectric devices.

Nuclear Magnetic Resonance Study on Relationship between Phase Behavior and Rotational and Translational Dynamics of an Ionic Liquid with a Plastic Crystal Phase: N-Butyl-N-methylpiperidinium Hexafluorophosphate

Abstract N-butyl-N-methylpiperidinium hexafluorophosphate, [C1C4pip]PF6, is an ionic liquid with a plastic crystal (PC) phase. To investigate the dynamics of the phase transition between crystalline, plastic crystalline, and liquid phases of [C1C4pip]PF6, we measured the temperature dependences of longitudinal and transverse relaxation times (T1 and T2, respectively) for 1H and 19F using low-frequency pulse nuclear magnetic resonance (NMR) methods. T1 and T2 changes are sensitive to the rotational and translational dynamics of ions, respectively. Since H and F atoms are only present in the cation and anion, respectively, the dynamic behaviors of each ionic molecule can be investigated separately. In the phase transition between the PC and liquid phase, the temperature-dependent curves of 1H-T1 were smoothly connected, indicating the same rotational motion for the cation occurred in both phases. The curves of 19F-T1 yielded the same conclusion for the rotational motion of the anion in both phases. The temperature-dependent curves of 1H-T2 and 19F-T2 jumped abruptly from phase to phase, indicating different modes of translational motion in each phase. We observed the appearance of a translationally mobile component in both the PC phase and the crystalline phase. This was concluded to be surface or interfacial melting.

Self-Association of the Anion of 7-Oxodeoxycholic Acid (Bile Salt): How Secondary Micelles Are Formed.

Bile acid anions are steroidal biosurfactants that form primary micelles due to the hydrophobic effect. At higher concentrations of some bile acid anions, secondary micelles are formed; hydrogen bonds connect primary micelles. Monoketo derivatives of cholic acid, which have reduced membrane toxicity, are important for biopharmaceutical examinations. The main goal is to explain why the processes of formation of primary and secondary micelles are separated from each other, i.e., why secondary micelles do not form parallel to primary micelles. The association of the anion of 7-oxodeoxycholic acid (a monoketo derivative of cholic acid) is observed through the dependence of the spin-lattice relaxation time on total surfactant concentration T1 = f(CT). On the function T1 = f(CT), two sharp jumps of the spin-lattice relaxation time are obtained, i.e., two critical micellar concentrations (CMC). The aggregation number of the micelle at 50 mM total concentration of 7-oxodeoxycholic acid anions in the aqueous solution is 4.2 ± 0.3, while at the total concentration of 100 mM the aggregation number is 9.0 ± 0.9. The aggregation number of the micelle changes abruptly in the concentration interval of 80-90 mM (the aggregation number determined using fluorescence measurements). By applying Le Chatelier's principle, the new mechanism of formation of secondary micelles is given, and the decoupling of the process of formation of primary and secondary micelles at lower concentrations of monomers (around the first critical micellar concentration) and the coupling of the same processes at higher equilibrium concentrations of monomers (around the second critical micellar concentration) is explained. Stereochemically and thermodynamically, a direct mutual association of primary micelles is less likely, but monomeric units are more likely to be attached to primary micelles, i.e., 7-oxodeoxycholic acid anions.

Low-frequency electrical response related to oxygen vacancies in Al3+ substituted M-type hexaferrite

The presence of oxygen vacancies is unavoidable in many complex metal oxide materials such as hexaferrites. This article investigates the role of crystal defects, such as oxygen vacancies, and different oxidation states of Fe ions, on the electrical conduction behaviors of Al3+ substituted Ba0.4La0.1Sr0.5Al x Fe12−x O19 hexaferrites by analyzing the temperature dependent AC impedance and AC conductivity. The optimal substitution of La3+ ions and high-temperature sintering is responsible for forming oxygen vacancies while reducing Fe from Fe3+ to Fe2+ cations, as observed in structural and XPS analysis, which affects electrical conduction behaviors. The departure from ideal Debye-type relaxation behavior is also one of the effects of crystal defects. Temperature variation of relaxation time shows a sharp change at around 403 K. This may be due to different electrical entities influencing the mode of electron hopping with temperature. The activation energy calculated from the temperature dependent relaxation time confirmed the presence of electron hopping through the bridging effects of the first ionization of oxygen vacancies Fe2+––Fe3+ below a temperature of 403 K. Above 403 K, electron hopping through different oxidation states of Fe3+ + e− → Fe2+ and migration of oxygen vacancies toward the bulk surface are responsible for the conduction mechanism. The DC resistivity and AC conductivity show that the bridging effects of oxygen defects can also induce Coulomb interaction between the defect sites resulting in Efros–Shklovskii variable range hopping and correlation barrier hopping below 403 K. Above 403 K, polaron-assisted electron hopping is more desirable, as confirmed by the non-overlapping small polaron tunneling model.

Molecular Structure Related to an S = 5/2 High-Spin S2 State Manganese Cluster of Photosystem II Investigated by Q-Band Pulse EPR Spectroscopy.

The high-spin S2 state of the photosynthetic oxygen-evolving cluster Mn4CaO5, corresponding to the g = 4.1 signal for X-band electron paramagnetic resonance (EPR), was investigated using Q-band pulsed EPR, which detected a main peak at g = 3.10 and satellite peaks at 5.25, 4.55, and 2.80. We evaluated the spin state as the zero-field splitting of D = 0.465 cm-1 and E/D = 0.245 with S = 5/2. The temperature dependence of the T1 relaxation time revealed that the excited-state energy was 28.7 cm-1 higher than that of the S = 5/2 ground state. By comparing present quantum mechanical (QM) calculation models, a closed-cubane structure with the protonation state of two oxygens, W1 (= OH-) and W2 (= H2O), was the most probable structure for the S = 5/2 state. The three-pulse electron spin-echo envelope modulation (ESEEM) detected the nuclear signal, which was assigned to nitrogen as His332 ligated to the Mn1 ion. The obtained hyperfine constant for the nitrogen signal was significantly reduced from that in the S = 1/2 low-spin state. These results indicate that the S = 5/2 spin state arises from the closed-cubane structure.

Automated model discovery for muscle using constitutive recurrent neural networks

The stiffness of soft biological tissues not only depends on the applied deformation, but also on the deformation rate. To model this type of behavior, traditional approaches select a specific time-dependent constitutive model and fit its parameters to experimental data. Instead, a new trend now suggests a machine-learning based approach that simultaneously discovers both the best model and best parameters to explain given data. Recent studies have shown that feed-forward constitutive neural networks can robustly discover constitutive models and parameters for hyperelastic materials. However, feed-forward architectures fail to capture the history dependence of viscoelastic soft tissues. Here we combine a feed-forward constitutive neural network for the hyperelastic response and a recurrent neural network for the viscous response inspired by the theory of quasi-linear viscoelasticity. Our novel rheologically-informed network architecture discovers the time-independent initial stress using the feed-forward network and the time-dependent relaxation using the recurrent network. We train and test our combined network using unconfined compression relaxation experiments of passive skeletal muscle and compare our discovered model to a neo Hookean standard linear solid, to an advanced mechanics-based model, and to a vanilla recurrent neural network with no mechanics knowledge. We demonstrate that, for limited experimental data, our new constitutive recurrent neural network discovers models and parameters that satisfy basic physical principles and generalize well to unseen data. We discover a Mooney–Rivlin type two-term initial stored energy function that is linear in the first invariant I1 and quadratic in the second invariant I2 with stiffness parameters of 0.60 kPa and 0.55 kPa. We also discover a Prony-series type relaxation function with time constants of 0.362s, 2.54s, and 52.0s with coefficients of 0.89, 0.05, and 0.03. Our newly discovered model outperforms both the neo Hookean standard linear solid and the vanilla recurrent neural network in terms of prediction accuracy on unseen data. Our results suggest that constitutive recurrent neural networks can autonomously discover both model and parameters that best explain experimental data of soft viscoelastic tissues. Our source code, data, and examples are available at https://github.com/LivingMatterLab.

Spin-phonon decoherence in solid-state paramagnetic defects from first principles

Paramagnetic defects in diamond and hexagonal boron nitride possess a combination of spin and optical properties that make them prototypical solid-state qubits. Despite the coherence of these spin qubits being critically limited by spin-phonon relaxation, a full understanding of this process is not yet available. Here we apply ab initio spin dynamics simulations to this problem and quantitatively reproduce the experimental temperature dependence of spin relaxation time and spin coherence time. We demonstrate that low-frequency two-phonon modulations of the zero-field splitting are responsible for spin relaxation and decoherence, and point to the nature of vibrations in 2-dimensional materials as the culprit for their shorter coherence time. These results provide an interpretation to spin-phonon decoherence in solid-state paramagnetic defects, offer a strategy to correctly interpret experimental results, and pave the way for the accelerated design of spin qubits.

Ultrafast Charge Dynamics in Bulk Zinc Oxide under Intense Photoexcitation

The photo-induced charge dynamics of textbook wide-bandgap semiconductor ZnO have been investigated on the picosecond time-scale. We performed optical Pump-THz Probe experiments in order to measure the dielectric constant of the material after high-fluence photo-excitation of charge carriers. The technique allows access to both carrier lifetime and scattering rates, and it provides direct access to the intrinsic dielectric function changes upon excitation. A complex dynamic is unveiled in the high-fluence pumping regime, where the relaxation time is in the hundreds of picoseconds range and increases with increasing Pump fluence, while the onset of photoconductivity takes place in a few picoseconds. The plasma frequency and the relaxation time dependence on the Pump fluence are discussed.

Ionic transport and segmental dynamics in poly(ethylene oxide) based polymer electrolytes: Dependence on molecular weight of host polymer matrix

We have investigated the ion transport and segmental dynamics in poly(ethylene oxide) (PEO) and sodium tetrafluoroborate (NaBF4) salt based solid polymer electrolytes as a function of molecular weight of PEO polymer matrix at a fixed salt concentration (EO/Na = 18) using broadband dielectric spectroscopy. The molecular weight (Mv) of PEO polymer matrix was varied from 1 × 105 to 6 × 105 g/mol. The ionic conductivity of the PEO based electrolytes obtained from the complex impedance plot showed a correlation with the glass transition temperature, crystallinity and ion diffusion coefficient. The AC conductivity spectra were analyzed by using the universal power law model, except the low frequency region, where the electrode polarization contribution was dominant. The temperature dependence of ionic conductivity and the hopping frequency followed the Vogel-Tammann-Fulcher (VTF) relation, indicating a coupling between the ion transport and the segmental dynamics of polymer chains. The segmental dynamics was investigated using the derivative dielectric constant spectra. The modulus spectra were well described by the Havriliak-Nigami and the Kohlrausch-Williams-Watts functions. The temperature dependence of the conductivity relaxation time also followed the VTF relation. The ion transport in PEO based polymer electrolytes with higher molecular weight was found more cooperative than that of the other polymer electrolytes.

Observation of magnetic structural universality and jamming transition with NMR

Nuclear magnetic resonance (NMR) has been instrumental in deciphering the structure of proteins. Here we show that transverse NMR relaxation, through its time-dependent relaxation rate, is distinctly sensitive to the structure of complex materials or biological tissues at the mesoscopic scale, from micrometers to tens of micrometers. Based on the ideas of universality, we show analytically and numerically that the time-dependent transverse relaxation rate approaches its long-time limit in a power-law fashion, with the dynamical exponent reflecting the universality class of mesoscopic magnetic structure. The spectral line shape acquires the corresponding non-analytic power law singularity at zero frequency. We experimentally detect the change in the dynamical exponent as a result of the transition into maximally random jammed state characterized by hyperuniform correlations. The relation between relaxational dynamics and magnetic structure opens the way for noninvasive characterization of porous media, complex materials and biological tissues