Relaxation Intensity Research Articles

Real-time monitoring the formation of polymer double network for gel polymer electrolyte by means of dielectric spectroscopy

A non-destructive method of detecting the internal information of the system is attempted in a polymer double network for gel polymer electrolyte in lithium-ion battery. The real-time monitoring for polymerization of 1,3-dioxolane (DOL) and cross-linking of cyanoethyl poly(vinyl alcohol) (PVA-CN) is carried out in a coin cell at 0–80 ℃ by means of dielectric spectrum. A widely distributed dielectric relaxation varying with monitoring time and temperature is observed in the frequency range of 3–103 kHz, and the relaxation parameters of the three sub-relaxations are obtained by fitting the dielectric spectrum with the HN equation. It is found that the relaxation intensity Δε and relaxation time τ are obviously dependent on the monitoring time and temperature: Δε and τ change obviously near the respective gel points of DOL and PVA-CN (DOL at 25 ℃, PVA-CN at 60 ℃), suggesting gelation at two gel points respectively. The different structural changes of the system before and after gelling temperature are speculated, and the possible microstructure of the system in each temperature range is proposed after analyzing the relaxation parameters. The applicability of the real-time dielectric monitoring in the study of the structure of gel polymer electrolytes is preliminarily concluded.

The impact of the phase composition of bacterial cellulose on the low-temperature mobility of its molecules

We describe the properties of the bacterial cellulose of various origins obtained with the help of XRD, FTIR, and dielectric spectroscopy methods. The samples were produced by Gluconacetobacter bacteria (with Іα phase content of 36%) and a symbiotic culture of bacteria and yeasts present in Kombucha fermented drink (with Іα phase content of 62%). An increase in the Іα phase concentration results in a decrease in the intensity of the low-temperature dielectric relaxation and its shift toward higher temperatures. We demonstrate that this dielectric relaxation occurs primarily due to the reorientation of the methylol groups on the surfaces of the cellulose crystallites. We also report that the concentration of the activated relaxers in Іβ cellulose allomorph exceeds that of the Іα allomorph.

Multiphysics analysis of a high-intensity ultrasound system applied to a three-layer animal tissue

High-intensity ultrasound systems for medical therapy must be carefully designed, implemented, and applied to avoid tissue damage or injury considering stimulation and relaxation time, frequency, and intensity of ultrasound. Based on these concerns and considering a test three-layer animal tissue consisting of skin, muscle, and bone, we determined the frequency and intensity at which ultrasound effectively stimulates the test animal tissues. In addition, from these ultrasound frequencies and intensities, and taking care the critical temperature recommended to preserve the integrity of the human tissue and avoid any tissue injury, we determine the stimulation and relaxation times. For this purpose, we performed a multiphysics simulation that describes the spatial and temporal dynamics of the thermoacoustic effect of ultrasound applied to test animal tissues. To practically demonstrate this ultrasound behavior, we perform an experimental setup based on an electronic HITU device designed and implemented to freely adjust the ultrasound intensity and frequency, as well as the stimulation time of the test animal tissues. Finally, we conclude that, depending on the test tissue, an ultrasound therapy system should allow the selection of the intensity and frequency of applied ultrasound, as well as the stimulation time to avoid tissue injury, which can be considered by health ministries around the world.

An empirical method to compensate the NMR calibrated porosity of the tight volcanic rocks based on comprehensive laboratory studies

The nuclear magnetic resonance (NMR) response is known to deviate from the true value for the volcanic reservoirs, particularly when the pore throat size is ultralow. Consequently, the related petrophysical parameters such as porosity, permeability, and pore size distribution from NMR measurements are greatly influenced. An empirical method to correct the NMR calibrated porosity for the tight volcanic rocks is proposed after comprehensive investigations of influential factors combined with mineralogical and petrophysical analyses. The laboratory result indicates that the relative porosity deviation is negatively correlated with the geometric mean of the transversal relaxation time (T2) but positively correlated with the clay content. Moreover, both the paramagnetic materials, such as the manganese (Mn) content, and the diamagnetic materials, such as the magnesium (Mg) content, contribute to the NMR relaxation intensity reduction but with different mechanisms. The NMR calibrated porosity can be compensated through multiple regressions with these controlling factors, which can be generalized to other tight volcanic reservoirs.

Влияние электрического поля на рекомбинационную люминесценцию коллоидных квантовых точек сульфида серебра

The paper studies the effect of external electric field on the optical properties of the spherical Ag2S quantum dots. Colloidal Ag2S nanoparticles passivated with 2-mercaptopropionic acid were obtained by photoinduced synthesis in the ethylene glycol. The nanoparticles shape and characteristic size were determined using the transmission electron microscopy. To analyze the external electric field influence, a series of samples was prepared based on the optically passive polymer film, where the nanoparticles were embedded. The films were placed between two glasses coated with the transparent electrodes based on the indium tin oxide (ITO). Intensity value of the external electric field created in such structures reached 500 kV/cm. The photoluminescence signal was registered using the CCD fiber spectrometer with spectral resolution of 1.16 nm. Spectrally resolved nanoparticles photoluminescence kinetics was measured by time-corre-lated counting of the separate photons. It was found that the presence of a field led to an increase in intensity and rate of the photoluminescence relaxation due to the surface states. This fact is related to acceleration of the free holes transportation to the recombination centers in the external electric field. It is shown that under long-term exposure to laser radiation with a wavelength of 405 nm and the average power of 5 mW, the nanocrystal photoluminescent properties could degrade, as it occurs due to formation of new centers of non-radiative recombination and photoionization of the quantum dots

Experimental observation of mesoscopic fluctuations to identify origin of thermodynamic anomalies of ambient liquid water

We report a new experimental approach for observing mesoscopic fluctuations underlying the thermodynamic anomalies of ambient liquid water. In this approach, two sound velocity measurements with different frequencies, namely inelastic X-ray scattering (IXS) in THz band and ultrasonic (US) in MHz band, are required to investigate the relaxation phenomenon with the characteristic frequency between the two aforementioned frequencies. We performed IXS measurements to obtain the IXS sound velocity of liquid water from the ambient conditions to the supercritical region of liquid-gas phase transition (LGT) and compared the results with the US sound velocity in the literature. We found that the ratio of the two sound velocities, Sf, which corresponds to the relaxation intensity, exhibits a simple but significant change. Two distinct rises were observed in the high-temperature and low-temperature regions, implying that two relaxation phenomena exist: in the high-temperature region, a peak was observed near the LGT critical ridge line, which was linked with changes in the density fluctuation and isochoric and isobaric specific heat capacities; in the low-temperature region, Sf increased toward the low-temperature region, which was linked with the change in the isochoric heat capacity. We concluded that these two relaxation phenomena are originated from critical fluctuations of liquid-gas phase transition (LGT) and liquid-liquid phase transition, respectively. The linkage between Sf and isochoric heat capacity in the low-temperature region proves that the relaxation is the cause of the well-known heat capacity anomaly of ambient liquid water. In this study, both LGT and LLT critical fluctuations were observed, and the relationship between thermodynamics and the critical fluctuations was comprehensively discussed.

Effect of UV Radiation on Dissipative Processes in Polyacrylates of Different Elasticities

Dynamic mechanical relaxation spectroscopy is used to study the relaxation behavior of elastic alkyl(met) polymers. The items of interest are acrylates on metal substrates before and after UV irradiation of different durations. Analysis is based on comparing the intensity of local dissipative relaxation in irradiated and non-irradiated polymers, along with their glass transition temperatures and elastic properties.

Effect of B4C content and annealing on complex permittivity and microwave-absorption properties of B4C/Al2O3 coatings

The B4C/Al2O3 coatings were fabricated by air plasma spraying technology, and their complex permittivity and microwave absorption properties in the X-band were investigated before and after annealing (500 °C/2 h). Both the real and imaginary parts of the complex permittivity of the coatings decreased after annealing, which can be attributed to the weakening of polarization relaxation intensity and the reduction of electrical conductivity caused by the escape of carbon atoms. In addition, the density of B4C/Al2O3 coatings decreased from 3.01 to 2.16 g/cm3 with increasing B4C content. The B4C/Al2O3 coatings exhibit a minimum reflection loss (RL) value of −39.58 dB and the effective absorption bandwidth (RL＜−10 dB, EAB) covers 1.9 GHz at a thickness of 1.6 mm. After annealing, the above coatings still had an EAB of 1 GHz. Therefore, the B4C/Al2O3 coatings can be considered as a promising microwave-absorption candidate with good high-temperature microwave-absorbing performance and low density.

Achieving structural rejuvenation in metallic glass by modulating β relaxation intensity via easy-to-operate mechanical cycling

Structural rejuvenation is an effective measure to optimize the mechanical properties of metallic glasses (MGs). Sophisticated solutions to rejuvenation include thermal cycling, laser shocking, and multiaxial stress loading. Here, we propose an easy-to-operate mechanical cycling as an alternative strategy to tailor the mechanical relaxation, deformation, and structural heterogeneity of MGs. Structural rejuvenation in a La-based MG is achieved via mechanical cycling even at very few cycles (102 tension load cycles) and low frequencies (10−3 Hz). The results manifest intuitively the competition between structural relaxation and rejuvenation, which constitutes the structural evolution in MGs. A theoretical model is constructed which reveals a scenario that mechanical cycling wakes up frozen flow defect, accelerating creep and, thus, enhancing the β relaxation in MGs. Therefore, this handy anti-ageing methodology provides an alternative pathway to optimize the mechanical properties of MGs. It also contributes to a more comprehensive understanding of the structure-property relationship in amorphous materials, especially with regard to the correlation between structural rejuvenation and relaxation behavior in such topologically disordered materials.

Intra- vs Intermolecular Cross-Links in Poly(methyl methacrylate) Networks Containing Enamine Bonds

The molecular dynamics of a copolymer composed of methyl methacrylate (MMA) and (2-acetoacetoxy)ethyl methacrylate (AEMA) monomers and the influence on it of intra- to intermolecular cross-links of AEMA units with ethylenediamine (EDA) was studied by combining dielectric relaxation experiments and thermal investigations. The dielectric spectra of the non-cross-linked copolymer show three dynamical processes: a slow relaxation (α) and a faster (β), both dominated by the MMA dynamics, and an even faster secondary relaxation (γ) reflecting the AEMA dynamics. Already for low cross-linking densities, the γ process is very much affected and eventually disappears, increasing the cross-linking density. The secondary β relaxation however was nearly unaffected by cross-linking. The effect of cross-linking on the α relaxation was very pronounced with an important increasing of the glass transition temperature Tg. There was also an increase of the dynamic heterogeneity and the relaxation intensity when increasing the cross-linking density (up to the maximum explored, 9 mol % EDA). The quality of the average time scale and Tg value have similarities in behavior for intra- and intermolecular cross-linking, but clear differences in the dynamic heterogeneities where observed. These differences can be interpreted in connection with the sparse internal structure of the collapsed single chains obtained by intramolecular cross-linking.

Rheo-Dielectrics and Diffusion of Type-A Rouse Chain under Fast Shear Flow: Method of Evaluation of Non-Equilibrium Parameters for FENE, Friction-Reduction, and Brownian Force Intensity Variation

Rouse model is the basic molecular model for unentangled linear polymer chains in melts. Recent studies suggest that the Rouse parameters characterizing the unentangled melts, the spring strength κ , the segmental friction coefficient ζ, and the mean-square Brownian force intensity B, change under fast flow thereby providing significant rheological nonlinearities with those melts (Matsumiya et al., Macromolecules, 51, 9710 (2018)). This article theoretically analyzes effects of the flow-induced changes of these parameters on the dielectric and diffusion behavior of the Rouse chain having so-called type-A dipoles parallel along the chain backbone. It turned out that the dielectric behavior under steady shear is determined by non-equilibrium parameters, rκ = κ/κeq and rζ,ij = ζij/ζeq but irrelevant to rB,ij = B ij/Beq, where the subscript “eq” stands for the quantities at equilibrium and the subscripts “ij” denote the spatial direction under shear flow: i and/or j = x, y, and z for the velocity, velocity gradient, and vorticity directions, respectively. Specifically, the complex dielectric permittivity ε* is analytically expressed in terms of the parameters rκ and rζ,ij, which in turn enables us to evaluate these parameters from data of the dielectric relaxation time and intensity under steady shear (obtained in future experiments). In contrast, the advective diffusion behavior under steady shear is determined by rζ,ij and rB,ij but irrelevant to rκ. The mean-square displacement ‹Δr2CM› of the center of mass defined with respect to the known non-diffusive advection point is analytically expressed in terms of rζ,ij and rB,ij, thereby allowing us to evaluate rB,ij from the diffusion data under steady shear and the dielectrically determined rζ,ij. The method of experimental evaluation of the non-equilibrium parameters presented in this article provides us with a complementary basis for analyzing nonlinear rheological behavior of unentangled melts.

Evaluating Membrane Electrical Properties of SMMC7721 Cells with TiO₂ NPs Applications to Cytotoxicity by Dielectric Spectroscopy.

Titanium dioxide nanoparticles (TiO₂ NPs) represent one of the most frequently applied nanomaterials in numerous areas of daily life. Recent studies show that TiO₂ exposure increases the occupational risk of liver injury and inflammation, and even liver cancer to the workers of factories handling these NPs. However, the potential risks and biophysical effects of TiO₂ on hepatic cells need extensive evaluation. To this end, we explored the electrophysiological changes in the human liver cancer cell line SMMC7721 following exposure to TiO₂ NPs. TiO₂ NPs decreased the first (Δε1) and second dielectric relaxation intensity (Δε₂) of the SMMC7721 cells by 6.62% and 0.86% respectively, and significantly increased the first characteristic frequency (fc1, 4.82%) and the first Cole-Cole parameter (β1, 1.24%). The double spherical-shell model showed that TiO₂ NPs significantly lowered the permittivity of unit-membrane and capacitance, as well as the conductivity of extracellular fluid, cytoplasm, and nuclear contents compared to the untreated control. Conclusively, this study revealed that TiO₂ NPs induce cytotoxic effects by disrupting the permeability and electrical conductivity of unit membranes. Further, we report that dielectric spectrum combined with model parameter analysis can evaluate the bioelectrical effects of TiO₂ NPs on human liver cancer cells.

Aluminosilicate glass-ceramics/reduced graphene oxide composites doped with lithium ions: The microstructure evolution and tuning for target microwave absorption

Ceramic-based composites are desirable lightweight materials for electromagnetic (EM) energy absorption. However, due to the lack of an effective electromagnetic wave attenuation mode, pure ceramics still face significant challenges in absorbing electromagnetic waves. It is still challenging to obtain advanced electromagnetic wave absorption (EMA) materials with low fillings, thin thickness, super absorption capacity, and effective absorption bandwidth (EAB) through clever microstructure design and appropriate multi-component strategy. Herein, a dielectric aluminosilicate/reduced graphene oxide (RGO) nanocomposite with different lithium content was constructed via a solvothermal sintering method. The microstructure and heterogeneous dielectric interface form perfect impedance matching, multiple polarization, coupling effects, and have excellent absorption performance. The absorbers display a minimal reflection loss (RL min ) of −51.95 dB by tuning the relaxation intensity, and the broadest covers all X band. In addition, the classic RCS simulation method to evaluate microwave absorption performance has practical application value in the field of radar stealth.

Novel edible starch films incorporating papain for meat tenderization

Papain incorporated films were developed as novel edible packaging for meat tenderization. Pregelatinized high dissolution (HD) and low dissolution (LD) cassava starch with different water solubilities were incorporated with papain. The edible films produced were characterized for morphology, mechanical relaxation and mechanical and barrier properties. Papain interacted with and modified the O-H bond through hydrogen bonding and disrupted the ordered structure of starch, while increasing the intensity of mechanical relaxation. LD produced more homogeneous microstructures than HD films containing papain by preventing aggregation. Interaction between starch and papain stabilized the film structure, reducing water sensitivity and solubility. Films containing papain at 5% to 15% showed improved tenderness of beef, with reduced Warner-Bratzler shear values and hardness after incubation for 30 min. HD films gave higher tenderization due to fast dissolution and release of enzymes on the meat surface, while increased papain in films improved the degree of tenderness and protein conformation in packaged beef.

Modulation of physicochemical properties of magnetic agarose microspheres by hydrolysis-suppressive sequential crosslinking

Separation and purification of target proteins are essential for drug discovery and development. A magnetic separation has been exploited due to its high efficiency. Despite many studies on chemical crosslinking of a magnetic agarose microsphere (MAM), the study on a crosslinking reaction preventing MAM from hydrolytic degradation during the reaction and the effects of the crosslinks on the physicochemical and electrochemical properties of the crosslinked MAM (CL-MAM) has rarely been reported. In our study, CL-MAM was prepared using a sequential crosslinking by which MAM was crosslinked using epichlorohydrin (ECH) in DMSO after crosslinking the MAM by 1,3-dichloro-2-propanol (DCP) for a short time. Such a crosslinking prevented the hydrolytic degradation of DCP-crosslinked MAM ( D -CL-MAM) and DCP and ECH-crosslinked MAM (DE-CL-MAM). MAM had a mean diameter of 110 ± 57.42 µm and its morphology was not affected by the crosslinking. In FT-IR analysis, increase of peak intensity at 1037 cm −1 confirmed newly formed C-O-C bonds in the agarose of CL-MAM. Thermal stability of MAM increased by both DCP crosslinking and subsequent ECH crosslinking of the agarose. While T g of MAM was not shifted by the crosslinking, the onset temperatures of glass transition and thermal decomposition increased by DCP crosslinking and further increased by DCP and ECH-crosslinking. Stiffness (S) and elastic modulus (E) of MAM were enhanced by DCP crosslinking and subsequent ECH crosslinking, indicating a half of ECH formed crosslinks between agarose mainchains while the other half crosslinked adjacent pyranose rings in the agarose mainchain. Permittivity analysis revealed that α relaxation temperature of the agarose film corresponded to T g determined by DSC analysis and the relaxation intensity decreased with increasing crosslink density of the agarose. The higher swelling ratio of DE-CL-MAM compared to D -CL-MAM was attributed to greater S and E values of DE-CL-MAM. The hydrolysis-repressive sequential crosslinking of MAM using DCP and ECH can be a feasible approach to modulate physicochemical and electrochemical properties of MAM. • Hydrolysis-suppressive crosslinkings by DCP and ECH were effective to crosslink MAM. • DCP-crosslinked MAM had enough stability to be crosslinkable by ECH in DMSO. • The sequential crosslinkings did not induce morphological changes of the MAM. • The crosslinking improved thermal stability of MAM, not influencing T g . • Mechanical and swelling properties of crosslinked MAM depended on degree of crosslinks.

Quasielastic neutron scattering study on proton dynamics assisted by water and ammonia molecules confined in MIL-53.

Dynamics of water and other small molecules confined in nanoporous materials is one of the current topics in condensed matter physics. One popular host material is a benzenedicarboxylate-bridging metal (III) complex abbreviated to MIL-53, whose chemical formula is M(OH)[C6H2(CO2)2R2] where M = Cr, Al, Fe and R = H, OH, NH2, COOH. These materials absorb not only water but also ammonia molecules. We have measured the quasi-elastic neutron scattering of MIL-53(Fe)-(COOH)2·2H2O and MIL-53(Fe)-(COOH)2·3NH3 which have full guest occupancy and exhibit the highest proton conductivity in the MIL-53 family. In a wide relaxation time region (τ = 10−12–10−8 s), two relaxations with Arrhenius temperature dependence were found in each sample. It is of interest that their activation energies are smaller than those of bulk H2O and NH3 liquids. The momentum transfer dependence of the relaxation time and the temperature dependence of the relaxation intensity suggest that the proton conduction is due to the Grotthuss mechanism with thermally excited H2O and NH3 molecules.

Effects of different wet heating methods on the water distribution, microstructure and protein denaturation of pork steaks

AbstractThis study aimed to investigate the influence of different wet heating methods (SC: steam cooking; BC: boiling cooking) on the water distribution, microstructure and protein denaturation of pork steaks. Results showed that SC increased the proton relaxation intensity (T1 and T2) and the amount of immobilized water, but decreased the amount of free water compared with BC treatment. Proton density images showed that the red area was more in SC treatment than BC treatment. Muscle volume contraction and microstructure destruction in SC treatments were lower than that of BC treatments. Meanwhile, SC had higher protein solubility, but lower surface hydrophobicity as compared with BC. Additionally, pork steaks containing salt cooked by the same heating method had higher water mobility than those of without salt. Moreover, salting process aggravated the swelling of muscle fibre structure and protein denaturation.

Water status evolution of pork blocks at different cooking procedures: A two-dimensional LF-NMR T1-T2 relaxation study

A two-dimensional low-field nuclear magnetic resonance (LF-NMR) T1-T2 relaxation technique was developed to contrast the water status evolution during different cooking procedures (steam and boiling cooking). Meat quality, water distribution, microstructure and protein properties were determined. The results showed that steamed meats had lower cooking loss and shear force, but higher redness, proton relaxation intensity (T1 and T2) and proton density than boiled meats. The differences in water distribution between the two cooking procedures appeared at approximately 40 °C, with acceleration at 60 °C, and the most remarkable difference was shown at 80 °C. Boiling resulted in more damage to muscle structure and greater protein denaturation than steam cooking. Meanwhile, α-helixes and β-turns increased, but β-sheets and random coils decreased in steamed meats compared with boiled meats. Changes in microstructural and protein properties were closely associated with water status evolution in cooked meat during cooking.

Study on dielectric relaxation Spectra of Surfactant-free Microemulsion composed of Water / Ethanol / Triethyl Citrate

In this paper, the dielectric relaxation behavior of surfactant-free microemulsion composed of pure water / ethanol / triethyl citrate (TEC) from 40Hz to 110MHz was studied. There is an obvious relaxation phenomenon between 103 and 105Hz in the selected experimental path, which is presumed to be interfacial polarization relaxation, indicating that there is a microscopic phase region in the system. The dielectric relaxation parameters fitted by a dispersion term Cole-Cole formula, that is, relaxation intensity Δε and relaxation time t, obviously vary with the phase composition of the system, and different trends can indicate that the system is in different microemulsion phase regions. It is proved that the dielectric spectrum technique can accurately characterize the surfactant-free microemulsion.

Щодо розрахунку релаксації напружень в тонкостінних циліндричних оболонках із лінійно-в'язкопружних матеріалів

The problems of stress relaxation analysis in thin-walled cylindrical shells made of linear viscoelastic materials under uniaxial and biaxial loading have been solved. The analysis is based on a there-dimensional model of viscoelasticity starting from the hypothesis of the deviators proportionality. The viscoelastic properties of a material are given with relationships that establish the dependence between stress and strain intensities as well as between the mean stress and volumetric strain by the Bolzmann-Volterra type equation. The kernels of relaxation intensity and volumetric relaxation are given with the Rabotnov exponential-fractional functions. The parameters of relaxation kernels are determined from creep test result using the relationships between creep kernels under the complex stress state and creep kernels under the one- dimensional stress state. The problems of the analysis of normal and tangential stresses relaxation in thin-walled cylindrical shells made of high density polyethylene “ПЭВП” under uniaxial tension, pure torsion and combined tension with torsion loading have been solved and experimentally approved.