Characteristic Relaxation Time Research Articles

Exploring the role of lignin structure in molecular dynamics of lignin/bio-derived thermoplastic elastomer polyurethane blends

The relaxation behavior of two lignins (Alcell organosolv, OSL, and hydroxypropyl modified Kraft, ML) and bio-based thermoplastic polyurethane (TPU) blends have been studied by Differential scanning calorimetry (DSC), Dynamic-mechanical analysis (DMA) and Dielectric relaxation spectroscopy (DRS). The effect of blending on the glass and local relaxation processes as a function of composition, frequency, and temperature has been assessed. The dielectric spectra were resolved into dipolar relaxations as well as conductive processes for differing blend compositions. Characteristic relaxation times, activation energies and dielectric relaxation strengths of lignin/xTPU blends were also investigated. It was found that blending suppresses the α-relaxation process of the blends compared to virgin TPU. On the other hand, while the position of the β-relaxation was not influenced by blending, a reduction of the activation energies, Ea, of this process was observed in the lignin/xTPU blends. Finally, changes are observed in the conductivity behavior of both blends, with conductivity processes more favorable for the OSL/xTPU blends.

Bottom-up Construction of Dynamic Density Functional Theories for Inhomogeneous Polymer Systems from Microscopic Simulations

We propose and compare different strategies to construct dynamic density functional theories (DDFTs) for inhomogeneous polymer systems close to equilibrium from microscopic simulation trajectories. We focus on the systematic construction of the mobility coefficient, $\Lambda(r,r')$, which relates the thermodynamic driving force on monomers at position $r'$ to the motion of monomers at position $r$. A first approach based on the Green-Kubo formalism turns out to be impractical because of a severe plateau problem. Instead, we propose to extract the mobility coefficient from an effective characteristic relaxation time of the single chain dynamic structure factor. To test our approach, we study the kinetics of ordering and disordering in diblock copolymer melts. The DDFT results are in very good agreement with the data from corresponding fine-grained simulations.

Dynamic Heterogeneity in Ring-Linear Polymer Blends.

We present results from a direct statistical analysis of long molecular dynamics (MD) trajectories for the orientational relaxation of individual ring molecules in blends with equivalent linear chains. Our analysis reveals a very broad distribution of ring relaxation times whose width increases with increasing ring/linear molecular length and increasing concentration of the blend in linear chains. Dynamic heterogeneity is also observed in the pure ring melts but to a lesser extent. The enhanced degree of dynamic heterogeneity in the blends arises from the substantial increase in the intrinsic timescales of a large subpopulation of ring molecules due to their involvement in strong threading events with a certain population of the linear chains present in the blend. Our analysis suggests that the relaxation dynamics of the rings are controlled by the different states of their threading by linear chains. Unthreaded or singly-threaded rings exhibit terminal relaxation very similar to that in their own melt, but multiply-threaded rings relax much slower due to the long lifetimes of the corresponding topological interactions. By further analyzing the MD data for ring molecule terminal relaxation in terms of the sum of simple exponential functions we have been able to quantify the characteristic relaxation times of the corresponding mechanisms contributing to ring relaxation both in their pure melts and in the blends, and their relative importance. The extra contribution due to ring-linear threadings in the blends becomes immediately apparent through such an analysis.

Magnetic nanoparticle-based biomolecule imaging with a scanning magnetic particle spectrometer

This study reports on a wash-free, inexpensive and sensitive approach of biomolecule imaging with magnetic nanoparticles (MNPs) via a custom-built scanning magnetic particle spectrometer (SMPS). Streptavidin-coated MNPs are used as magnetic biomarkers for the detection of Immunoglobulin G (IgG) conjugated with biotin (IgG-Biotin) while five samples with different-concentration IgG-Biotin are prepared for experiments. The measurements of the ac susceptibility indicate that the conjugation of the IgG-Biotin onto the surface of the MNPs forms cross-linking between the MNPs, thus increasing the characteristic Brownian relaxation time from 0.627 to 1.448 ms. The ratio of the 3rd to the 1st harmonics is measured on the samples with different-concentration IgG-Biotin in ac magnetic fields with a frequency ranging from about 300 Hz to 2 kHz. It shows that the measurement sensitivity of the IgG-Biotin concentration decreases from 4.62 × 10–3 to 0.39 × 10–3 nM−1 with increasing excitation frequency. Phantom images of the harmonic ratio, measured with the SMPS, indicate that unbound and bound MNPs can be easily distinguished. Furthermore, the excitation frequency dependence of the contrast-to-noise ratio of the images is discussed based on the measurement sensitivity and the standard deviation of the measured image intensity. This study demonstrates the feasibility of the SMPS for imaging biomolecules bound onto the MNPs, which is of great interest to disease diagnostics and therapy.

T2-FLAIR Mismatch Sign Is Caused by Long T1 and T2 of IDH-mutant, 1p19q Non-codeleted Astrocytoma.

T2-fluid-attenuated inversion recovery images (FLAIR) mismatch sign is now known to be a specific yet insensitive image feature for IDH-mutant, 1p19q non-codeleted astrocytoma. The current study revealed that lesion presenting T2-FLAIR mismatch exhibited extremely long T1- and T2-relaxation time while T2-FLAIR matched lesions showed low to moderate values. On the other hand, IDH-wildtype tumors presented noticeably short T1- and T2-relaxation time. These different relaxation time characteristics seemed to render T2-FLAIR mismatch sign of becoming such a unique and specific image feature for IDH-mutant, 1p19q non-codeleted astrocytoma.

Well-Posedness of the Fractional Zener Wave Equation for Heterogeneous Viscoelastic Materials

AbstractZener’s model for viscoelastic solids replaces Hooke’s law σ = 2με(u) + λ tr(ε(u)) I, relating the stress tensor σ to the strain tensor ε(u), where u is the displacement vector, μ > 0 is the shear modulus, and λ ≥ 0 is the first Lamé coefficient, with the constitutive law (1 + τDt) σ = (1 + ρDt)[2με(u) + λ tr(ε(u)) I], where τ > 0 is the characteristic relaxation time and ρ ≥ τ is the characteristic retardation time. It is the simplest model that predicts creep/recovery and stress relaxation phenomena. We explore the well-posedness of the fractional version of the model, where the first-order time-derivative Dt in the constitutive law is replaced by the Caputo time-derivative $\begin{array}{} D_t^\alpha \end{array} $ with α ∈ (0, 1), μ, λ belong to L∞(Ω), μ is bounded below by a positive constant and λ is nonnegative. We show that, when coupled with the equation of motion ϱü = Div σ + f, considered in a bounded open Lipschitz domain Ω in ℝ3 and over a time interval (0, T], where ϱ ∈ L∞(Ω) is the density of the material, assumed to be bounded below by a positive constant, and f is a specified load vector, the resulting model is well-posed in the sense that the associated initial-boundary-value problem, with initial conditions u(0, x) = g(x), u̇(0, x) = h(x), σ(0, x) = S(x), for x ∈ Ω, and a homogeneous Dirichlet boundary condition, possesses a unique weak solution for any choice of g ∈ [$\begin{array}{} \mathrm{H}^1_0 \end{array} $(Ω)]3, h ∈ [L2(Ω)]3, and S = ST ∈ [L2(Ω)]3×3, and any load vector f ∈ L2(0, T; [L2(Ω)]3), and that this unique weak solution depends continuously on the initial data and the load vector.

Energy Consumption, Conversion, and Transfer in Nanometric Field-Effect Transistors (FET) Used in Readout Electronics at Cryogenic Temperatures

The energy consumed by electron devices such as field-effect-transistors (FET) in an integrated circuit is mostly used to process different electrical signals. However, a fraction of that energy is also converted into heat that gets transferred throughout the integrated circuit and modifies the local temperature. The modification of the local temperature, which is interpreted as a self-heating mechanism, is a function of different charge carrier scattering mechanisms, the characteristic energy relaxation times for charge carriers, the heat carrier mechanisms, the geometry of the FET, the volume of the integrated circuit, and the composed thermal properties of the integrated circuit and the system package. Besides all those dependencies, the charge and heat transport properties are temperature dependent. All these features make the electrothermodynamic analysis and modeling of low-power cryogenic electron devices a compulsory need. In this work, we introduce an analysis based on experimental results obtained from characterizing FET test structures in the temperature range between 300 K and down to 3.1 K.

Monitoring real‐time curing of epoxies in situ using single‐sided NMR

AbstractAdhesively bonded joints using epoxy are widely used in aircraft and aerospace structures. Quality control and defect detection during epoxy curing in such applications is critical. We used single‐sided nuclear magnetic resonance (NMR) to nondestructively probe and spatially resolve the change in the characteristic NMR relaxation time (T2) of epoxies during curing on a substrate. Time‐dependent T2 values were fit to a Weibull function to model temporal changes in the NMR measurables. Our results demonstrate that the reduction in molecular mobility of various epoxy/curing agent mixtures occurs more rapidly at the interface than in the bulk. Further use of single‐sided NMR to acquire spatially resolved T2 data will provide a route for elucidatory epoxy curing studies. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 616–623

Multivariable non-invasive association of isocitrate dehydrogenase mutational status in World Health Organization grade II and III gliomas with advanced magnetic resonance imaging T2 mapping techniques.

To investigate multivariable analyses for noninvasive association of the isocitrate dehydrogenase (IDH) mutational status in grade II and III gliomas including evaluation of T2 mapping-sequences. Magnetic resonance imaging (MRI) examinations with histopathologically proven World Health Organization grade II and III gliomas were retrospectively enrolled. Multivariate receiver operating characteristics (ROC) analyses to associate IDH mutational status were performed containing quantitative T2 mapping analyses and qualitative characteristics (sex, age, localization, heterogeneity, oedema, necrosis and diameter). Relaxation times were calculated pixelwise by means of standardized ROI analyses. Interobserver variability also was tested. Out of 32 patients (mean age: 50.7 years; range: 32-83), nine had grade II gliomas and 24 grade III, while 59.5% showed a positive IDH mutated state (IDHm) and 40.5% were wildtype (IDHw). Multivariable ROC analyses were calculated for relaxation time and range, localization and age with a cumulative 0.955 area under the curve (AUC) (p < 0.001), while central T2-relaxation time had by far the highest single variable sensitivity (AUC: 0.873; range: 0.762; age: 0.809; localization: 0.713). Age (cut off: 49 years; p = 0.031) and localization (p = 0.014) were the only qualitative parameters found to be significant as IDHw gliomas were older and IDHm gliomas were preferentially located fronto-temporal. This is the first study evaluating quantitative T2 mapping sequences for association of the IDH mutational status in grade II and III gliomas demonstrating an association between relaxation time and mutational status. Analyses of T2 mapping relaxation times may even be suitable for predicting the correct IDH mutational state. Prognostic accuracy increases significantly in predicting the correct mutational state when combing T2 relaxation time characteristics and the qualitative MRI features age and localization.

The effect of aggregation of cured rubber particles on rheology of thermoplastic vulcanizates

AbstractIn this work, we study the effect of microstructure of rubber particle aggregates on linear and nonlinear viscoelastic properties of olefinic thermoplastic vulcanizates (TPVs) based on ethylene‐propylene‐diene rubber (EPDM) and polypropylene (PP). TPVs samples with identical rubber content and different extent of rubber particle aggregation are prepared through dynamic vulcanization of PP/EPDM blends (conventional method) with different compositions as well as dilution of PP/EPDM 40/60 TPVs. Morphological observations show larger aggregates of cured rubber particles in the diluted samples (D) compared to the ones prepared by conventional method (B). The difference between the microstructures of the two series of samples decreases with increasing rubber content. Linear viscoelastic measurements demonstrate higher elastic modulus and dynamic viscosity at low frequency for D samples compared to B ones, representing the effect of aggregation of the dispersed rubber phase. The higher extent of aggregation in D samples also leads to a lower percolation threshold and smaller linear viscoelastic region. From fitting of a structure‐dependent model on the stress growth results, longer characteristic relaxation times are obtained for D samples due to the presence of rubber aggregates. Additionally, A higher degree of orientation and less contribution of rubber aggregate destruction are found under shear flow in D samples.

Effect of Zinc Chloride Activation on D-Glucose Derived Carbons Based Capacitors Performance in Ionic Liquid

Various carbon materials have been synthesized applying hydrothermal carbonization process and subsequent ZnCl2 activation step using different mass ratios of activating reagent. The resulting powder materials were characterized physically and electrochemically in a two-electrode cell configuration using 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid. Activated materials porosity was highly dependent on the activation conditions i.e. on the ratio of ZnCl2 used in the activation process. The best material having Brunauer–Emmett–Teller specific surface area SBET = 2320 m2 g−1, micropore surface area Smicro = 1510 m2 g−1 and total pore volume Vtot = 1.01 cm3 g−1 where the highest amount of ZnCl2 was used for the synthesis of carbon material. High specific parallel capacitance (140 F g−1), a wide region of ideal polarizability (ΔV ≤ 3.0 V), short characteristic relaxation time (2.12 s), and high energy density (48 W h kg−1) values have been established for material with the highest porosity showing great potential for these supercapacitor systems to be used in practical application as energy storage devices.

Crystal structures and rotational dynamics of a two-dimensional metal halide perovskite (OA)2PbI4.

The extended charge carrier lifetime in metal halide perovskites is responsible for their excellent optoelectronic properties. Recent studies indicate that the superb device performance in these materials is intimately related to the organic cation dynamics. Here, we focus on the investigation of the two-dimensional hybrid perovskite, (C8H17NH3)2PbI4 (henceforth, OA+ = C8H17NH3 +). Using elastic and quasielastic neutron scattering techniques and group theoretical analysis, we studied the structural phase transitions and rotational modes of the C8H17NH3 + cation in (OA)2PbI4. Our results show that, in the high-temperature orthorhombic (T > 310 K) phase, the OA+ cation exhibits a combination of a twofold rotation of the NH3-CH2 head group about the crystal c-axis with a characteristic relaxation time of ∼6.2 ps, threefold rotations (C3) of NH3 and CH3 terminal groups, and slow librations of the other atoms. Contrastingly, only the C3 rotation is present in the intermediate-temperature orthorhombic (238 K < T < 310 K) and low-temperature monoclinic (T < 238 K) phases.

Spin accumulation dynamics in spin valves in the terahertz regime

The notion of spin accumulation and spin relaxation in the diffusive regime was introduced by Valet and Fert in 1993 to describe the current-perpendicular-to-plane (CPP) diffusive transport in metallic magnetic multilayers. This theory has been quite successful in explaining the giant magnetoresistance of magnetic multilayers in CPP geometry in the frequency range from DC to a few gigahertz. In this paper, we investigate the dynamic aspect of spin accumulation from the theoretical point of view when reaching the terahertz (THz) frequency range. The characteristic relaxation time of electron elastic scattering is typically in the femtosecond range. However, since spin accumulation results from a diffusion process involving a very large number of individual scattering events, the characteristic time of spin accumulation variation when the current and/or the magnetic configuration are varied can be significantly longer than that of the input signal, eventually reaching the picosecond range. In spintronic devices operating in the THz range such as those based on ferrimagnetic or antiferromagnetic materials, the spin accumulation amplitude and, correlatively, the device magnetoresistance can therefore depend on the actual device operating frequency. We investigate this question by extending the Valet and Fert theory in the time domain.

Концентрационные и диффузионные характеристики атомов внедрения (C, O, N) и модули упругости в ванадии и сплавах V – 4 Cr – 4 Ti, V – W – Cr, V – Ta – Cr – Zr

The elastic (Young’s) modulus and relaxation properties (amplitude-independent internal friction) of bcc metals and alloys (vanadium, V–4Cr–4Ti, V–W–Cr, and V–Ta–Cr—Zr alloys) have been studied in the temperature range of 25–400°С by means of dynamic mechanical spectroscopy within a low-frequency range (0.5–30.0 Hz). No carbon in vanadium and V–W–Cr alloy in solid-solution state is revealed. In the case of vanadium and V–W–Cr alloy, the solid-solution concentrations of oxygen and nitrogen and the diffusion characteristics thereof (diffusion activation energy, characteristic relaxation time, and the preexponential factor in the diffusion equation) have been determined. In the case of V–4Cr–4Ti alloy, carbon, oxygen, and nitrogen solid solutions have not been observed. In V–Ta–Cr–Zr alloy, the solid-solution concentrations of interstitial atoms (C, O, N) are substantially lower than those in vanadium and V–W–Cr alloy. The values of elastic modulus in vanadium alloys can be either higher or lower than the elastic modulus inherent in vanadium depending on type of alloy (alloying) and on temperature. The V–4Ti–4Cr alloy exhibits the smallest value of the elastic modulus among all the materials under study. The temperature curves of the elastic (Young’s) modulus for the studied materials exhibit no features, except for a slight local relaxation of the Young’s modulus in the case of vanadium and V–W–Cr alloy in the temperature range of the relaxation peaks.

Microscopic theory of the influence of dipole superparamagnetics (type &lt;beta-CD&lt;FeSO_4&gt;&gt;) on current flow in semiconductor layered structures (type GaSe, InSe)

A statistical approach to description of the charge carrier transfer processes in hybrid nanostructures taking into account electromagnetic fields is proposed using the method of the nonequilibrium statistical operator Zubarev. Generalized transfer equations are obtained, which describe non-Markov processes of charge transfer in the system taking into account magnetic and polarization processes under the influence of external and induced internal electromagnetic fields. Weakly nonequilibrium charge transfer processes in nanostructures are considered, and a nonequilibrium statistical operator is obtained, by means of which the magneto-diffusion transfer equations for electrons in layered nanostructures are obtained. A generalized Cattaneo-type diffusion equation in time fractional derivatives is obtained for electrons with a characteristic relaxation time and a generalized model is proposed that takes into account the complexity of relaxation electro-magnetic diffusion processes for electrons in layered nanostructures.

Фотоиндуцированное поглощение и импульсна запись динамических голограмм в кристаллах силиката висмута

Dynamics of the photoinduced absorption and holographic-grating recording in photorefractive bismuth silicate crystal has been studied. It has been shown that, with the use of nanosecond laser pulses and at the intensity above 1 МW/cm2, the induced absorption takes place due to population of the short-lived trapping levels having the characteristic relaxation times from milliseconds to a few tens of milliseconds. Recording of dynamic holograms in bismuth silicate has been realized in these conditions. Two mechanisms of holographic grating recording have been established, with the lifetimes differing by three orders of magnitude. Though the intensities are relatively low, below or on the order of 1 MW/cm2, the medium response is determined by a photorefractive nonlinearity mechanism with relaxation times at a level of several seconds. The intensities above 5 MW/cm2 are associated with fast components (ms relaxation times) appearing due to population of short-lived traps. It has been demonstrated that a contribution of each mechanism is dependent on the intensity of laser radiation and that, for the intensities above 10-15 MW/cm2, the decisive part is played by the short-lived traps with lifetimes on the order of milliseconds.

Key factors influencing the low-field NMR characterisation of gas- and oil-bearing shales: a case study of the shales from the southern Sichuan Basin and Dongying sag, China

The response characteristics of transverse relaxation time (T2) of key experimental parameters [waiting time (TW), number of scans (NS) and echo number (NECH)], sample size and probe fluid, are analysed systematically based on NMR experiments of oil- and gas-bearing shales from the Shahejie Formation in Dongying sag and the Wufeng and Longmaxi Formations in the southern Sichuan Basin. The results indicate that: 1) the optimised NMR parameters for TW, NS and NECH are 1,500 ms, 64 and 6,000, respectively, which will ensure higher accuracy and signal-to-noise ratio (SNR); 2) the total signal amplitude of the T2 spectrum increases with decreasing grain size. The T2 spectra of shale which grain size bigger than 10 mesh can characterize the shale PSD; 3) water porosity clearly decreases with increasing brittle minerals but decreasing clay content than n-dodecane-saturated porosity, which indicates the hydration of clay and brittle minerals together controls the reconstruction of PSD. [Received: May 30, 2018; Accepted: October 24, 2018]

Effects of particle diameter and magnetocrystalline anisotropy on magnetic relaxation and magnetic particle imaging performance of magnetic nanoparticles

The dynamic magnetization of immobilized spherical single-domain magnetic nanoparticles (MNPs) with uniaxial or cubic magnetocrystalline anisotropy was studied computationally by executing simulations based on the Landau–Lifshitz–Gilbert (LLG) equation. For situations when a static magnetic field was suddenly applied and then removed, the effects of particle diameter and anisotropy (considering both type of symmetry and characteristic energy) on the characteristic magnetic relaxation time were studied parametrically. The results, for both anisotropy symmetries, show that when a static magnetic field is suddenly turned on or off the MNPs undergo a successive two-step or combined one-step relaxation. Whether a MNP relaxes with one or two steps when the field is turned on is determined by the competition between the energy of the applied magnetic field, the magnetic anisotropy energy, and thermal energy. When the applied magnetic field is suddenly turned off, our results show good agreement with theoretical predictions for the cases of and , where represents the magnetic anisotropy energy barrier, is the Boltzmann constant and represents the absolute temperature. For the case of an applied alternating magnetic field (AMF) that is typical of magnetic particle imaging (MPI) applications, the effects of particle diameter and anisotropy symmetry were studied in terms of time-domain magnetization dynamics, dynamic hysteresis loops, harmonic spectra, and x-space point spread functions (PSFs). Results illustrate that the type of magnetocrystalline anisotropy (uniaxial versus cubic) has a significant effect on the MPI performance of the nanoparticles. These computational studies provide insight into the role of particle diameter and magnetic anisotropy on the performance of MNPs for applications in magnetorelaxometry and MPI.

Dynamic relaxation process of a 3D super crystal structure in a Cu:KTN crystal

In this Letter, we report the existence and relaxation properties of a critical phenomenon on called a 3D super crystal that emerges at T = TC − 3.5°C, that is, in the proximity of the Curie temperature of a Cu:KTN sample. The dynamics processes of a 3D super crystal manifest in its formation containing polarized nanometric regions and/or polarized clusters. However, with strong coupling and interaction of microcomponents, the characteristic relaxation time measured by dynamic light scattering demonstrates a fully new relaxation mechanism with a much longer relaxation time. As the relaxation mechanism of a relaxator is so-far undetermined, this research provides a novel perspective. These results can help structure a fundamental theory of ferroelectric relaxation.

Влияние естественной влажности на характерное время десорбции метана из углей различной степени метаморфизма

Goal. To study the effect of natural internal moisture content on the kinetics of methane desorption from coals of varying degrees of metamorphization. Methodology. For the research, coal was used after a long (more than 100 days) preliminary exposure in a dry, closed indoors. The measurements were carried out on several samples of Donbass coals with different volatile content. Two groups of coal samples were used - dry, with natural internal humidity and one sample with artificial humidity of 1.5%. The volumetric method was used for measurements. The method includes three stages: 1st  saturation of coal with compressed methane, 2nd  preliminary discharge of compressed gas from a container with coal after its saturation, and 3rd  collection of methane released by coal into a storage vessel. Before registration of desorption, pressurized gas was discharged from the free volume of containers into the atmosphere. The desorption unit contains a low-temperature trap (78°C) for water vapor and a warming radiator for methane entering the storage vessel. To determine the numerical values of the characteristic time of desorption of methane from coal, we used information on the change in gas pressure in the storage vessel during desorption. To analyze the results, a method based on the concept of a change in the characteristic relaxation time of desorption during methane emission was used. Results. Experimental results show that in wet coals the ratio between the amount of methane in coal and the intensity of its outflow at any desorption site is less than in dry coals. It was found that in coals of the metamorphic series the presence of natural moisture leads to a decrease in the intensity of methane emission, a decrease in the characteristic desorption time and a decrease in the activation energy of methane desorption by 0.4 - 2.5 kJ / mol. The features of the kinetics of desorption indicates competition energetics of interactions between methane and water with the surface of the pores of coal. Scientific novelty. It was found that even without artificial humidification, but in the presence of natural internal moisture in coal, the degassing time during desorption is reduced (in comparison with dry coal). Practical significance. The research results can be used to optimize the duration of hydraulic saturation of the coal seam and the water consumption during coal degassing.