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In this study, several experimental techniques were applied to probe thermal properties, molecular dynamics, crystallization kinetics and intermolecular interactions in binary mixtures (BMs) composed of flutamide (FL) and various poly(N-vinylpyrrolidone) (PVP) polymers, including a commercial product and, importantly, samples obtained from high-pressure syntheses, which differ in microstructure (defined by the tacticity of the macromolecule) from the commercial PVP. Differential Scanning Calorimetry (DSC) studies revealed a particularly large difference between the glass transition temperature (Tg) of FL+PVPsynth. mixtures with 10 and 30 wt% of the excipient. In the case of the FL+PVPcomm. system, this effect was significantly lower. Such unexpected findings for the former mixtures were strictly connected to the variation of the microstructure of the polymer. Moreover, combined DSC and dielectric measurements showed that the onset of FL crystallization is significantly suppressed in the BM composed of the synthesized polymers. Further non-isothermal DSC investigations carried out on various FL+10 wt% PVP mixtures revealed a slowing down of FL crystallization in all FL-based systems (the best inhibitor of this process was PVP Mn = 190 kg/mol). Our research indicated a significant contribution of the microstructure of the polymer on the physical stability of the pharmaceutical—an issue completely overlooked in the literature. [ABSTRACT FROM AUTHOR]

The theory of orientation polarization and dielectric relaxation was developed by P. Debye more than 100 years ago. It is based on approximating a molecule by a sphere having one or more dipole moments. By that the detailed intra- and intermolecular interactions are explicitly not taken into consideration. In this article, the principal limitations of the Debye approximation are discussed. Taking advantage of the molecular specificity of the infrared (IR) spectral range, measurements of the specific IR absorption of the stretching vibration υ(OH) (at 3370 cm−1) and the asymmetric υas(CH2) (at 2862.9 cm−1) are performed in dependence on the frequency and the strength of external electric fields and at varying temperature. The observed effects are interpreted as caused by orientation polarization of the OH and the adjacent CH2 moieties. [ABSTRACT FROM AUTHOR]

A theoretical model that describes the degradation of the resistive states of the memristor over time has been proposing. It has been showing that the current through the memristor cell is limiting by tunneling through the barrier at the nonstoichiometric oxide/metal interfaces. Degradation of the resistive state is generated by diffusive dissolution of the conductive channel. It leads to a change in the space charge region of the metal/dielectric interface. The impact of the filament cross-section, the width of the rupture region, and vacancy concentration in this area on the degradation of HRS and LRS states were investigated. The model explains various kinds of memristor degradation observed in the experimental works of different authors. The connection between the type of degradation and the filament parameters/environment of the dielectric has been demonstrating. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectroscopy (BDS) measurements were performed on cotton cloth samples with softener agents in natural environments, and a recent analytical technique of fractal analysis refined in dielectric spectroscopy was used for water structures. Three relaxation processes observed in the GHz, MHz, and kHz regions were attributed to the dynamic behaviors of hydrogen-bonding networks (HBNs) of water and interacting molecules, hydrated polymer chains, and ions restricted in the interfaces of large structures. Fractal analysis of the GHz region suggested that the GHz frequency process was retained, even in the dry state, revealing a broad spatial distribution of HBN fragments of various sizes. This typical tendency for heterogeneous hydration in cotton cloth was emphasized by the addition of a softener agent, as the value of Cole–Cole's relaxation time distribution parameter changed from 0.55 to 0.41. The addition of the softener agent still retained the GHz frequency process, even in the dry state. This result means that the softener inhibited the formation of hydration sites on the cellulose surface and induced the dispersion of hydration sites. Thus, HBNs are fragmented by the softener agent. On the other hand, water molecules still aggregate to retain HBNs in a restricted area. The heterogeneous dispersion of HBN fragments broadens the GHz relaxation process, and the lower-frequency tail overlaps with the lower relaxation process because of chain dynamics with interacting water molecules. The structure formed by these water molecules, which is restricted by polymer chains and related to the stiffening effect of cotton fabric, is also heterogeneously hindered by the appropriate concentration of the softening agent. These indications were also consistent with the T2 relaxation time obtained using the Carr–Purcell–Meiboom–Gill method of nuclear magnetic resonance measurements and are consequently reflected in the hydration model for macroscopic properties of cotton fabric. [ABSTRACT FROM AUTHOR]

A hybrid technique is proposed to manipulate the field distribution in a substrate integrated waveguide (SIW) H-plane horn to enhance its radiation characteristics. The technique comprises two cascaded steps to govern the guided waves in the structure. The first step is to correct the phase of fields and form a quasi-uniform distribution in the flare section so that the gain increases and side-lobe-level (SLL) decreases. This is obtained by loading the structure with a novel modulated metal-via lens. Field expansion on the radiating aperture of the SIW H-plane horn generates backward surface waves on both broad walls which increases the backlobe. In the second step, these backward surface waves are recycled and directed forward with the aid of holography theory. This is achieved by adding a couple of dielectric slabs with holographic-based patterns of metallic strips on both broad walls. With this step, the backlobe is reduced and the endfire gain is further increased. Using the proposed technique, the structure is designed and fabricated to operate at f = 30 GHz which simultaneously improves the measured values of gain to 11.65 dBi, H-plane SLL to - 17.94 dB, and front-to-back ratio to 17.02 dB. [ABSTRACT FROM AUTHOR]

The three–phase structure of Polylactic acid (PLA), cold crystallized at two different crystallization temperatures (TC), is performed by complementary electrical characterization techniques in a wide frequency range. Initially amorphous samples are crystallized from the glassy state at 80 °C / 4 h and 130 °C / 2 h in two different Dielectric Spectroscopy setups i.e., a typical Dielectric Response setup (0.1 Hz-1 MHz) for TC = 80 °C, and an RF Impedance Analyzer (1 MHz to 1 GHz) for TC = 130 °C. The implementation of both setups allows for the crystallization monitoring by continuous acquisition of the dielectric α-relaxation spectra, since the corresponding dielectric loss maxima are located at around 104 Hz for TC = 80 °C, and 5 × 107 Hz for TC = 130 °C. X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC) studies reveal the presence of only the α΄-crystal form of PLA at TC = 80 °C, transforming to the more stable α-form at elevated temperatures. Spherulite size and density is monitored by Polarizing Optical Microscopy (POM) and are strongly depended on the crystallization (cold/melt) process for samples crystallized at 130 °C. Determination of the different fractions (Crystalline, Mobile Amorphous and Rigid Amorphous) reveals that samples crystallized at 130 °C exhibit an extra amount of RAF, formed upon cooling below Tg, contrary to the case of samples crystallized at lower temperatures. Combined dielectric response studies over nine orders of magnitude (from 0.1 Hz to 1 GHz) are performed systematically, as a function of temperature, time and frequency and a complete analysis of all relaxation dynamics is presented. The implementation of high frequency dielectric response, along with other typically used techniques, is proven to be a powerful tool for the complete characterization of semicrystalline polymers. [ABSTRACT FROM AUTHOR]

Resins are important for enhancing both the processability and performance of rubber. Their efficient utilization requires knowledge about their influence on the dynamic glass transition and their miscibility behavior in the specific rubber compound. The resins investigated, poly-(α-methylstyrene) (AMS) and indene-coumarone (IC), differ in molecular rigidity but have a similar aromaticity degree and glass transition temperature. Transmission electron microscopy (TEM) investigations show an accumulation of IC around the silanized silica in styrene–butadiene rubber (SBR) at high contents, while AMS does not show this effect. This higher affinity between IC and the silica surface leads to an increased compactness of the filler network, as determined by dynamic mechanical analysis (DMA). The influence of the resin content on the glass transition of the rubber compounds is evaluated in the sense of the Gordon–Taylor equation and suggests a rigid amorphous fraction for the accumulated IC. Broadband dielectric spectroscopy (BDS) and fast differential scanning calorimetry (FDSC) are applied for the characterization of the dielectric and thermal relaxations as well as for the corresponding vitrification kinetics. The cooling rate dependence of the vitrification process is combined with the thermal and dielectric relaxation time by one single Vogel–Fulcher–Tammann–Hesse equation, showing an increased fragility of the rubber containing AMS. [ABSTRACT FROM AUTHOR]

Polymer mixtures are an important object of scientific and industrial interest and doping with salts is a common way to implement composite conductivity. The structure and properties of composites based on oligomers of different molecular weight, namely amorphous diglycidyl ether of poly(ethylene glycol) (DEG-1, Mw = 372 g/mol) and highly crystalline poly(ethylene glycol) (PEG, Mw = 10,000 g/mol), and Li+ ions have been investigated. Polymeric organic-inorganic systems have been investigated by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and broadband dielectric spectroscopy. Using DSC and WAXS methods, it has been shown that composites with PEG have an amorphous-crystalline structure. The average crystallite size is 4.0 nm according to the study of WAXS. The DSC method revealed a decrease in the degree of PEG crystallinity in the composite due to the plasticizing ability of DEG-1 and the interaction of PEG with lithium perchlorate salt. Using the SAXS method, it has been established that there are regions of heterogeneity with a size of 95-130 nm in the volume of the studied composites. Studies of the electrical characteristics of polymer systems have shown that the doping of the composite with a lithium salt leads to an increase in the conductivity of the samples by two orders of magnitude. The temperature dependences of the conductivity at direct current for the studied composites do not obey the Arrhenius dependence and are analyzed using the Vogel-Tamman-Fulcher equation. The studied composites can be attributed to fragile. [ABSTRACT FROM AUTHOR]

Direct‐ink‐writing (DIW) provides a high‐efficiency way for thermoset printing while rapid in‐situ curing has a significant role in manufacturing rate, quality, performance, and flexibility. In this review, in‐situ curing methods that can be integrated into DIW were discussed, including frontal polymerization, electromagnetic heating, photochemistry, electron beam, and resistance heating curing. The in‐situ process monitoring and curing kinetic analysis technologies such as differential scanning calorimetry (DSC), Raman spectroscopy, Fourier transform infrared spectroscopy (FT‐IR), broadband dielectric spectroscopy (BDS), ultrasonic dynamic mechanical analysis (UDMA), fluorescence spectroscopy, were briefly presented. The working mechanism and features of these characterization measurements are studied. Furthermore, machine learning and other artificial intelligence tools used for the optimization of printing materials, topology design, printing path, and defect detection sensitivity are reviewed. Finally, some future research directions for the DIW and in‐situ curing of thermosets are addressed. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The flash auto-combustion method was used to synthesize nanocrystalline spinel ferrites with the general formula Cd1−xNixFe2O4 (x = 0, 0.25, 0.50, 0.75, and 1.0). Structural characterizations of all prepared samples were carried out by the X-ray diffraction technique (XRD), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscope (SEM). Broadband dielectric spectroscopy (BDS) and vibration sample magnetometer (VSM) measurements were used to evaluate the dielectric and magnetic characteristics of the synthesized ferrite samples, respectively. The formation of the main cubic phase with space group Fd3m was confirmed by X-ray diffraction examination besides hemitate hexagonal phase α-Fe2O3. Rietweld refinement revealed that increasing Ni-doping content led to decrease the volume fraction of hemitate hexagonal phase until it vanished at x = 1 and decreasing of lattice parameters. Along with the X-ray diffraction revealed that the particle size and lattice strain were increased with increasing Ni content (x). The two distinctive absorption bands of spinel ferrites were identified using FTIR, and their dependency on Ni concentration was studied and explained. The saturation magnetization (Ms) and coercivity (Hc) increased as the Ni concentration increased, according to VSM measurements. The frequency dependence of the permittivity for the studied composition as sintered @ 950 °C in comparison with the as-prepared ones shows development of a net of micro-capacitors like behavior in the former. This is due to a thin layer of weakly conducting grain boundaries separating the effectively conducting grains. The conductivity spectra of the compositions show two distinguished trends separated by a characteristic frequency. These three phenomena will be discussed and explained in some detail. [ABSTRACT FROM AUTHOR]

The molecular dynamics of two addition type polynorbornenes, exo‐PNBSi and PTCNSi1, bearing microporosity has been investigated by broadband dielectric spectroscopy, fast scanning calorimetry, and neutron scattering. Both polymers have the same side groups but different backbones. Due to their favorable transport properties, these polymers have potential applications in separation membranes for gases. It is established in literature that molecular fluctuations are important for the diffusion of small molecules through polymers. For exo‐PNBSi, two dielectric processes are observed, which are assigned to Maxwell/Wagner/Sillars (MWS) process due to blocking of charge carriers at internal voids or pore walls. For PTCNSi1, one MWS‐polarization process is found. This points to a bimodal pore‐size distribution for exo‐PNBSi. A glass transition for exo‐PNBSi and for PTCNSi1 could be evidenced for the first time using fast scanning calorimetry. For Tg and the corresponding apparent activation energy, higher values were found for PTCNSi1 compared to exo‐PNBSi. For both polymers, the neutron scattering data reveal one relaxation process. This process is mainly assigned to methyl group rotation probably overlayed by carbon–carbon torsional fluctuations. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) heterostructures (HSs) built on 2D materials provide an ideal platform for research of energy migration at the nanoscale. However, the underlying charge transfer mechanism in type II vdW HSs is still not well understood. Here, ultrafast exciton dynamics are investigated in trilayer‐WS2‐MoS2‐WSe2 and trilayer‐MoS2‐WSe2‐WS2 HSs by broadband pump‐probe spectroscopy. A two‐step process of exciton transfer in trilayer‐WS2‐MoS2‐WSe2 is directly observed when the band edge exciton of WSe2 is excited. The electrons in WSe2 are initially transferred to the high lying electronic state of MoS2‐WS2 on a time scale of tens of femtoseconds, and then electrons eventually relax into the conduction band minimum of MoS2 within 1 ps. Furthermore, the transfer of interlayer excitons is observed for the first time in trilayer‐MoS2‐WSe2‐WS2. Both transfer processes can be better understood by the Dexter charge exchange model. Due to the nature of Dexter type transfer that the exchange rate exponentially depends on the donor−acceptor distance, the interlayer exciton transfer rate is nearly a hundred times slower than that of exciton transition in bilayer HSs. The results deepen the understanding of charge transfer in 2D vdW HSs and also indicate that the exciton effect and orbital hybridization make HS a strong coupling system. [ABSTRACT FROM AUTHOR]

Charge transport, diffusion properties, and glassy dynamics of blends of imidazolium-based ionic liquid (IL) and the corresponding polymer (polyIL) were examined by Pulsed-Field-Gradient Nuclear Magnetic Resonance (PFG-NMR) and rheology coupled with broadband dielectric spectroscopy (rheo-BDS). We found that the mechanical storage modulus (G ′) increases with an increasing amount of polyIL and G ′ is a factor of 10,000 higher for the polyIL compared to the monomer ( G I L ′ = 7.5 Pa at 100 rad s−1 and 298 K). Furthermore, the ionic conductivity (σ 0) of the IL is a factor 1000 higher than its value for the polymerized monomer with 3.4 × 10 − 4 S cm−1 at 298 K. Additionally, we found the Haven Ratio ( H R) obtained through PFG-NMR and BDS measurements to be constant around a value of 1.4 for the IL and blends with 30 wt% and 70 wt% polyIL. These results show that blending of the components does not have a strong impact on the charge transport compared to the charge transport in the pure IL at room temperature, but blending results in substantial modifications of the mechanical properties. Furthermore, it is highlighted that the increase in σ 0 might be attributed to the addition of a more mobile phase, which also possibly reduces ion-ion correlations in the polyIL. [ABSTRACT FROM AUTHOR]

An efficient use of plasticizers in rubber compounds requires an understanding of their miscibility behavior. Besides the chemical properties of both rubber and plasticizer, the rigidity of the plasticizer plays an important role for their miscibility. The miscibility is investigated here using the glass transition measured by differential scanning calorimetry and broadband dielectric spectroscopy (BDS). Additionally, the interfacial relaxation and phase separation measured by BDS are confirmed by transmission electron microscopy. While the flexible plasticizer, poly‐(α‐methylstyrene), stays miscible in a silica‐filled polybutadiene rubber compound, the more rigid plasticizer, indene‐coumarone (IC), shows a phase separation at high concentrations. The phase‐separated IC tends to accumulate at the silica surface. [ABSTRACT FROM AUTHOR]

At this time, the development of advanced elastic dielectric materials for use in organic devices, particularly in organic field-effect transistors, is of considerable interest to the scientific community. In the present work, flexible poly(dimethylsiloxane) (PDMS) specimens cross-linked by means of ZnCl2-bipyridine coordination with an addition of 0.001 wt. %, 0.0025 wt. %, 0.005 wt. %, 0.04 wt. %, 0.2 wt. %, and 0.4 wt. % of gold nanoparticles (AuNPs) were prepared in order to understand the effect of AuNPs on the electrical properties of the composite materials formed. The broadband dielectric spectroscopy measurements revealed one order of magnitude decrease in loss tangent, compared to the coordinated system, upon an introduction of 0.001 wt. % of AuNPs into the polymeric matrix. An introduction of AuNPs causes damping of conductivity within the low-temperature range investigated. These effects can be explained as a result of trapping the Cl− counter ions by the nanoparticles. The study has shown that even a very low concentration of AuNPs (0.001 wt. %) still brings about effective trapping of Cl− counter anions, therefore improving the dielectric properties of the investigated systems. The modification proposed reveals new perspectives for using AuNPs in polymers cross-linked by metal-ligand coordination systems. [ABSTRACT FROM AUTHOR]

We here demonstrate the preparation of composite polymer electrolytes (CPEs) for Li-ion batteries, applicable for 3D printing process via fused deposition modeling. The prepared composites consist of modified poly(ethylene glycol) (PEG), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and SiO2-based nanofillers. PEG was successfully end group modified yielding telechelic PEG containing either ureidopyrimidone (UPy) or barbiturate moieties, capable to form supramolecular networks via hydrogen bonds, thus introducing self-healing to the electrolyte system. Silica nanoparticles (NPs) were used as a filler for further adjustment of mechanical properties of the electrolyte to enable 3D-printability. The surface functionalization of the NPs with either ionic liquid (IL) or hydrophobic alkyl chains is expected to lead to an improved dispersion of the NPs within the polymer matrix. Composites with different content of NPs (5%, 10%, 15%) and LiTFSI salt (EO/Li+ = 5, 10, 20) were analyzed via rheology for a better understanding of 3D printability, and via Broadband Dielectric Spectroscopy (BDS) for checking their ionic conductivity. The composite electrolyte PEG 1500 UPy2/LiTFSI (EO:Li 5:1) mixed with 15% NP-IL was successfully 3D printed, revealing its suitability for application as printable composite electrolytes. [ABSTRACT FROM AUTHOR]

Silicone rubber (SiR) insulators are widely used in transmission and distribution electrical power systems. Dielectrics properties give an important efficiency to SiR insulators that can be lost after ageing. The aim of this study is to investigate the effect of temperature, immersion and ultraviolet (UV) radiation on the ageing phenomenon of SiR insulator samples. The evolution of bulk condition of the samples after the ageing cycle was diagnosed by broadband dielectric spectroscopy measurement, a correlation between dielectric properties and the surface hydrophobicity of the samples has been discussed. DC surface resistivity was measured after ageing. A comparison was made between the characteristics of the samples in the new state and the aged one. Experimental results show that the low frequency dispersion dominates the dielectric response of the studied material. The thermal ageing causes a decrease of the dielectric loss tangent (DLT) in the low frequencies which improves the FOV of the aged samples. UV radiation can cause a change in the physicochemical structure of the samples, not only at the surface but also at the bulk level. The immersion ageing results in an increase in the DLT, especially for low conductivity solutions. The water can diffuse inside the samples during the immersion. In fact, a limited amount of water can still reside inside the samples even after a long period of drying. There is a good agreement between the surface hydrophobicity and the dielectric properties of the samples, the link with these properties is dependent to the ageing stress. [ABSTRACT FROM AUTHOR]

Acrylic acid‐styrene copolymer films were deposited plasma‐chemically more gently using the pulsed plasma mode instead of the continuous mode, with linear and some slightly branched chains and marginal crosslinking. Then, the styrene unit of copolymers was wet‐chemically sulfonated by chlorosulfuric acid. On exposure to air, the formed 4‐chlorosulfonic acid groups hydrolyze to sulfonic acid groups (–SO3H). Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and broadband dielectric spectroscopy were employed to characterize the composition, structure, functional groups, and electrochemical performance of the copolymers. A high concentration of sulfonic acid‐containing groups was obtained in the sulfonated polystyrene sample. The values of the DC conductivity σDC for the sulfonated sample of the acrylic acid and styrene copolymer are ca. five orders of magnitude higher than that of the not‐sulfonated copolymer materials. [ABSTRACT FROM AUTHOR]

Dielectric response and thermal behavior of an orientationally disordered organic crystal cyclobutanol were critically investigated with differential scanning calorimetry and broadband dielectric spectroscopy (10−2 to 107 Hz) from the deep glassy crystalline state to its melting temperature. The effort was made to understand the relaxation dynamics of plastic crystals of diverse characteristics, which lack translational degrees of freedom and to explore features of different transition and to get a comprehensive understanding on glass-forming dynamics. Information about polymorphism, solid–solid phase transitions, their kinetic freezing, structural and secondary relaxation were explored. The structural relaxation showed non-Arrhenius T-dependence and non-Debye features in the frequency domain. The resolved secondary relaxation in cyclobutanol was identified to be intermolecular or Johari–Goldstein (JG) relaxation from coupling model predictions. The investigated sample was revealed as an intermediate system in Angell's criteria of strong–fragile classification. The data on cyclobutanol filled the gap for attaining a comprehensive picture on low molecular cyclic alcohols, where Tg showed a progressive increase with molecular weight, while the steepness index exhibited a smooth switch over from fragile to strong behavior. [ABSTRACT FROM AUTHOR]

Entanglement dynamics of uniaxially-oriented, disentangled ultra-high molecular weight polyethylene nanocomposites modified with gold nanoparticles are investigated, using dielectric spectroscopy, during the transition to melt state. The dc conduction is approximately calculated via the logarithmic derivative of dielectric permittivity and is observed to decrease with the formation of entanglements. As the draw ratio increases, the progressive formation of entanglements resulted in a stronger dc conductivity decrease due to the loss of orientation in the pre-melt crystalline and partially oriented amorphous chain segments. Additionally, a sharp peak is obtained in the absence of dc conductivity, attributed to the dipolar contribution of the Maxwell-Wagner-Sillars (MWS) interfacial polarization between the gold nanoparticles and the polymer chains. The relaxation time of the MWS interfacial polarization increases with the progressive formation of entanglements, as observed in a previous study. The results presented shed light on the process of entanglement formation in oriented ultrahigh molecular weight polyethylene nanocomposites.

Broadband dielectric spectroscopy of blood above 50 GHz is scarce due to hardware limitations, affordability, and complexity. This study explores the use of a rectangular waveguide as a probe for analysing human blood in the 55 to 95 GHz range, at temperatures from 23 °C to 36 °C, and Haemoglobin levels between 0 and 16 g/dL, focusing on practical aspects such as sample preparation and the setup's mechanical, thermal, and calibration requirements. The research highlights the effectiveness of the Short-Open-Load calibration method, evidenced by precise measurements of saline solutions. Furthermore, analysis of 84 human blood samples indicates that while Haemoglobin levels introduce some uncertainty in dielectric constant measurements, dielectric loss readings remain consistent across temperature and Haemoglobin variations, with a low uncertainty of under 2.65%, indicating the potential use of this parameter in future millimetre-wave techniques for non-invasive testing of blood analytes. • Open-ended waveguide allows dielectric characterisation of fluids above 50 GHz. • Time critical reducing dielectric effects caused by Erythrocyte Sedimentation Rate. • Blood's dielectric loss more sensitive to haemoglobin changes than dielectric constant. • Higher haemoglobin content dampens dielectric constant changes caused by temperature. [ABSTRACT FROM AUTHOR]

Cellulose nanofibers (CNFs) nanocomposites were prepared using poly(methylmethacrylate- co -methacrylic acid) (PMMA- co -MAA) to investigate the macromolecular mobility within the composite, with particular focus on the effect of H-bonding. Dynamic mechanical analysis (DMA) and broadband dielectric spectroscopy (BDS) were used to fully characterize the molecular mobility for which the effect of the introduction of H-bond forming moieties and the addition of CNFs (5 and 15 wt%) were assessed. Despite similar T g values (determined by Differential Scanning Calorimetry), a deeper analysis of the relaxation times associated with the α-relaxation evidenced a significant effect induced by CNFs, which is in fact slowing down the macromolecular relaxation processes. The activation energy of the β-relaxation remained unchanged despite the introduction of MAA units in the main chain and the successive addition of CNFs. However, the latter led to the appearance at low frequencies of a new β'-relaxation correlated with the interactions between the CNF surface -OH groups and the -COOH groups of the matrix. The γ-relaxation showed a 45 % increase in activation energy from PMMA to PMMA- co -MAA + CNF nanocomposites regardless of the CNF content, due to the possibility of CNFs to interact and hinder the motion of the main chain methyl groups in α position. [Display omitted] [ABSTRACT FROM AUTHOR]

We report a broadband dielectric spectroscopic (BDS) study on the clustering fragile glass-former meta-toluidine (m-TOL) from 187 K up to 289 K over a wide frequency range of 10-3-109 Hz with focus on the primary α relaxation and the secondary β relaxation above the glass temperature Tg. The broadband dielectric spectra were fitted by using the Havriliak-Negami (HN) and Cole-Cole (CC) models. The β process disappearing at Tβ,disap = 1.12Tg exhibits non-Arrhenius dependence fitted by the Vogel-Fulcher-Tamman-Hesse equation with T0βVFTH in accord with the characteristic differential scanning calorimetry (DSC) limiting temperature of the glassy state. The essential feature of the α process consists in the distinct changes of its spectral shape parameter βHN marked by the characteristic BDS temperatures TB1βHN and TB2βHN. The primary α relaxation times were fitted over the entire temperature and frequency range by several current three-parameter up to six-parameter dynamic models. This analysis reveals that the crossover temperatures of the idealized mode coupling theory model (TcMCT), the extended free volume model (T0EFV), and the two-order parameter (TOP) model (Tmc) are close to TB1βHN, which provides a consistent physical rationalization for the first change of the shape parameter. In addition, the other two characteristic TOP temperatures T0TOP and TA are coinciding with the thermodynamic Kauzmann temperature TK and the second change of the shape parameter at around TB2βHN, respectively. These can be related to the onset of the liquidlike domains in the glassy state or the disappearance of the solid-like domains in the normal liquid state. [ABSTRACT FROM AUTHOR]

In this paper, broadband dielectric spectroscopy was applied to investigate molecular dynamics of 1,2,3,4,6-penta-O-(trimethylsilyl)-D-glucopyranose (S-GLU) at ambient and elevated pressures. Our studies showed that apart from the structural relaxation, one well resolved asymmetric secondary process (initially labeled as β) is observed in the spectra measured at p = 0.1 MPa. Analysis with the use of the coupling model and criterion proposed by Ngai and Capaccioli indicated that the β-process in S-GLU is probably a Johari-Goldstein relaxation of intermolecular origin. Further high pressure experiments demonstrated that there are in fact two secondary processes contributing to the β-relaxation. Therefore, one can postulate that the coupling model is a necessary, but not sufficient criterion to identify the true nature of the given secondary relaxation process. The role of pressure experiments in better understanding of the molecular origin of local mobility seems to be much more important. Interestingly, our research also revealed that the structural relaxation in S-GLU is very sensitive to compression. It was reflected in an extremely high pressure coefficient of the glass transition temperature (dTg/dp = 412 K/GPa). According to the literature data, such a high value of dTg/dp has not been obtained so far for any H-bonded, van der Waals, or polymeric glassformers. [ABSTRACT FROM AUTHOR]

Glassy dynamics of polymethylphenylsiloxane (PMPS) is studied by broadband dielectric spectroscopy in one-dimensional (1D) and two-dimensional (2D) nanometric confinement; the former is realized in thin polymer layers having thicknesses down to 5 nm, and the latter in unidirectional (thickness 50 µm) nanopores with diameters varying between 4 and 8 nm. Based on the dielectric measurements carried out in a broad spectral range at widely varying temperatures, glassy dynamics is analyzed in detail in 1D and in 2D confinements with the following results: (i) the segmental dynamics (dynamic glass transition) of PMPS in 1D confinement down to thicknesses of 5 nm is identical to the bulk in the mean relaxation rate and the width of the relaxation time distribution function; (ii) additionally a well separated surface induced relaxation is observed, being assigned to adsorption and desorption processes of polymer segments with the solid interface; (iii) in 2D confinement with native inner pore walls, the segmental dynamics shows a confinement effect, i.e., the smaller the pores are, the faster the segmental dynamics; on silanization, this dependence on the pore diameter vanishes, but the mean relaxation rate is still faster than in 1D confinement; (iv) in a 2D confinement, a pronounced surface induced relaxation process is found, the strength of which increases with the decreasing pore diameter; it can be fully removed by silanization of the inner pore walls; (v) the surface induced relaxation depends on its spectral position only negligibly on the pore diameter; (vi) comparing 1D and 2D confinements, the segmental dynamics in the latter is by about two orders of magnitude faster. All these findings can be comprehended by considering the density of the polymer; in 1D it is assumed to be the same as in the bulk, hence the dynamic glass transition is not altered; in 2D it is reduced due to a frustration of packaging resulting in a higher free volume, as proven by ortho-positronium annihilation lifetime spectroscopy. [ABSTRACT FROM AUTHOR]

This work is devoted to the investigation of the broad band dielectric spectra of 0.83PbMg1/3Nb2/3O3-0.17PbTiO3 (PMN-17PT) single crystals which have intermediate random fields. The necessity to understand the impact of random fields for the phase transition in heterogeneous perovskite oxides is of central importance. The thorough studies of dielectric properties revealed that the structural phase transition in PMN-17PT has a very complex dynamics. The temperature dependences of dielectric permittivity show that this material has features characteristic of polar nano regions and order-disorder phase transition dynamics. We speculate that this is the fingerprint of the phase transition in such heterogeneous perovskite oxides. [ABSTRACT FROM AUTHOR]

We simulate the mixing (demixing) process of a quiescent binary liquid mixture with a composition-dependent viscosity which is instantaneously brought from the two-phase (one-phase) to the one-phase (two-phase) region of its phase diagram. Our theoretical approach follows a standard diffuse-interface model of partially miscible regular binary mixtures wherein convection and diffusion are coupled via a nonequilibrium capillary force, expressing the tendency of the phase-separating system to minimize its free energy. Based on 2D simulation results, we discuss the influence of viscosity ratio on basic statistics of the mixing (segregation) process triggered by a rapid heating (quench), assuming that the ratio of capillary to viscous forces (a.k.a. the fluidity coefficient) is large. We show that, for a phase-separating system, at a fixed value of the fluidity coefficient (with the continuous phase viscosity taken as a reference), the separation depth and the characteristic length of single-phase microdomains decrease monotonically for increasing values of the viscosity of the dispersed phase. This variation, however, is quite small, in agreement with experimental results. On the other hand, as one might expect, at a fixed viscosity of the dispersed phase both of the above statistics increase monotonically as the viscosity of the continuous phase decreases. Finally, we show that for a mixing system the attainment of a single-phase equilibrium state by coalescence and diffusion is retarded by an increase in the viscosity ratio at a fixed fluidity for the dispersed phase. In fact, for large enough values of the viscosity ratio, a thin film of the continuous phase becomes apparent when two drops of the minority phase approach each other, which further retards coalescence. [ABSTRACT FROM AUTHOR]

Al/Pt nanolaminates with a bilayer thickness (tb, width of an Al/Pt pair-layer) of 164 nm were irradiated with single laser pulses with durations of 10ms and 0.5 ms at 189 W/cm² and 1189 W/cm², respectively. The time to ignition was measured for each pulse, and shorter ignition times were observed for the higher power/shorter pulse width. Videographic images of the irradiated area shortly after ignition show a non-uniform radial brightness for the longer pulse, while the shorter pulse shows uniform brightness. A diffusion-limited single step reaction mechanism was implemented in a finite element package to model the progress from reactants to products at both pulse widths. The model captures well both the observed ignition delay and qualitative observations regarding the non-uniform radial temperature. [ABSTRACT FROM AUTHOR]

We have investigated the Debye-like relaxation in a series of monoalcohols (MAs) by broadband dielectric spectroscopy and thermally stimulated depolarization current techniques in order to get further insight on the time dispersion of this intriguing relaxation. Results indicate that the Debyelike relaxation of MAs is not always of exponential type and conforms well to a dispersion of Cole-Davidson type. Apart from the already reported non-exponentiality of the Debye-like relaxation in 2-hexyl-1-decanol and 2-butyl-1-octanol, a detailed analysis of the dielectric permittivity of 5-methyl-3-heptanol shows that this MA also presents some extent of dispersion on its Debye-like relaxation which strongly depends on the temperature. Results suggest that the nonexponential character of the Debye-like relaxation might be a general characteristic in the case of not so intense Debye-like relaxations relative to the α relaxation. Finally, we briefly discuss on the T-dependence and possible origin for the observed dispersion. [ABSTRACT FROM AUTHOR]

This study assesses the impact of Treated Distillate Aromatic Extract (TDAE) oil, at concentrations of 0–20 parts per hundred rubber (phr), on the glass transition temperature (T g) of High Vinyl/Low Styrene Styrene-Butadiene Rubber (HVLSS-SBR), polybutadiene rubber (BR), and their blends with weight ratios of 70/30 and 50/50. Using Dynamic Mechanical Analysis, Broadband Dielectric Spectroscopy, and Positron Annihilation Lifetime Spectroscopy, we found that TDAE modifies T g and fractional free volume (F v) differently across materials. In HVLSS-SBR, TDAE reduced T g by approximately 10 °C and increased F v by 0.8 %. In BR, TDAE raised T g by 5–7 °C without altering F v. The 70/30 blend showed no T g change but a 0.6 % F v increase. For the 50/50 blend, one Havriliak-Negami equation indicated a T g rise of 2–3 °C and a 0.4 % F v increase. A two-equation analysis revealed a 6 °C T g increase and 0.9 % F v boost in the BR-rich phase, versus a 2 °C rise and 0.3 % F v uptick in the HVLSS-SBR-rich phase. The sequence of compatibility, influenced by TDAE, is crystalline BR > amorphous BR > HVLSS-SBR >70/30 blend >50/50 blend. This study provides valuable insights into the behavior of TDAE oil in rubber blends and can serve as a basis for further research in this field. [Display omitted] [ABSTRACT FROM AUTHOR]

Polymers have become indispensable across fields of application, and understanding their structure–property relationships and dynamic behaviour is essential for performance optimization. Polymer membranes, particularly ion exchange membranes, play a crucial role in renewable energy conversion technologies, fuel cells, solar energy conversion, and energy storage. In this context, broadband dielectric spectroscopy (BDS) offers a powerful, non-destructive approach to investigate the electrical response and relaxation dynamics of polymers. These properties are investigated by parametrizing the system's impedance response in terms of a network of circuit elements, i.e. the electrical equivalent circuit (EEC), whose impedance resembles the one of the system under investigation. However, the determination of the EEC from BDS data is challenging due to system complexity, interdependencies of circuit elements, and researcher biases. In this work, we propose a novel approach that incorporates a convolutional neural network (CNN) model to predict the EEC topology. By reducing user bias and enhancing data analysis, this approach aims to make BDS accessible to both experienced users and those with limited expertise. We show that the combination of machine learning and BDS provides valuable insights into the dynamic behaviour of polymer membranes, thus facilitating the design and characterization of tailored polymers for various applications. We also show that our model outperforms state-of-the-art machine learning methods with a top-5 accuracy of around 80% for predicting the circuit topology and a parameter fitting error as low as 0.05%. [ABSTRACT FROM AUTHOR]

[Display omitted] • The dielectric dispersion and relaxation dynamics revealed the frequency and temperature dependent molecular interaction of amino acid complex. • The fragility index show that the L-glutamic acid is super strong than L-arginine. • Thermal parameters indicate the direction and nature of interaction among the solute and solvent. • The FT-Raman, FT-IR and Vibrational spectral findings significantly specified the strength and nature of molecular interaction. • Correlation of dielectric, thermal and spectral data confirms and validates the molecular interaction. The dielectric dispersion behavior of amino acids (L-arginine and L-glutamic acid) was studied in the aqueous state by Broadband Dielectric Spectroscopy (BDS). The complex permittivity spectra of the solutions were recorded for the frequency regime 10 MHz – 50 GHz at a temperature range of 283 K to 303 K for various mole fractions. The interaction of polarized side chains of the solute (positive in L-arginine and negative in L-glutamic acid) with hydrated polar media is the significance of the work. The hydration effect of the amino acid modifies the dielectric and physicochemical properties of the solution. The study of Differential Scanning Calorimetry (DSC) analysis and thermal parameters specifies that the L-glutamic acid has super strong nature than L-arginine. The formation of hydrogen bond, nature and strength of the interaction through side chain are confirmed by spectral analysis (FT-Raman, FT-IR and NMR). The geometrical properties were computed with DFT/B3LYP −6-31G(d,p) basis set. The obtained spectral signals were compared with experimental data. The experimental and quantum mechanical calculations are used to identify the hydrodynamic coupling of the solution. The present study correlate the dielectric, thermal parameters, spectral inferences with molecular structure, dynamics is a novel approach which confirms the nature and strength of the complex formation. [ABSTRACT FROM AUTHOR]

This work explores the potential of GQDs@PEG@Mg-ZnFe 2 O 4 nanocomposite in water splitting and energy storage applications. The synthesized hybrid showed remarkable dielectric properties indicating its potential for low-frequency telecommunications and electronics applications. The impedance spectroscopy disclosed the contribution of grains and grain boundaries in the realization of colossal permittivity (104) in GQDs@PEG@Mg-ZnFe 2 O 4. Moreover, GQDs@PEG@Mg-ZnFe 2 O 4 showed excellent energy storage performance, indicated by its specific capacitance of 100 Fg−1 and a retention ratio of 99 % over 1000 cycles at a 1 Ag−1 current density. GQDs@PEG@Mg-ZnFe 2 O 4 nanohybrid also showed remarkable electrocatalytic activity, both for hydrogen evolution reaction and oxygen evolution reaction. The determined Tafel slope value was found to be 90 mVdec−1 and 110 mVdec−1 at a 10 mA/cm2 current density, respectively. These results highlight the multifunctional nature of the GQDs@PEG@Mg-ZnFe 2 O 4 nanocomposite and its potential as a versatile material to address challenges in both energy storage and conversion technologies. [Display omitted] • A hybrid electrocatalyst GQDs@PEG@Mg-ZnFe 2 O 4 was synthesized through a facile technique. • The coexistence of graphene quantum dots (GQDs) and polyethylene glycol (PEG) resulted in enhanced dielectric constant of GQDs@PEG@Mg-ZnFe 2 O 4 ternary nanohybrid. • The remarkable capacitive behavior and high cyclic stability of GQDs@PEG@Mg-ZnFe 2 O 4 , indicates its potential as an energy storage material. • The superior OER and HER activity of the ternary nanohybrid, with a lower Tafel slope mak it promising for water electrolysis. • GQDs@PEG@Mg-ZnFe 2 O 4 ternary nanohybrid is a potential candidate for both low-frequency and water-splitting applications. [ABSTRACT FROM AUTHOR]

The effect of Pr3+-Zn2+ doping on the magnetic and dielectric properties of Co 2 Y-type barium hexaferrites with the chemical composition Ba 2 Co 2 Fe 12-x-y Pr x Zn y O 22 (x = 0.00, 0.10, 0.20, and y = 0.00, 0.15, 0.25), was investigated in this study. The prepared Pr3+-Zn2+ substituted Co 2 Y-type barium hexaferrites were calcined for 5 h at 1100 °C in a digital heating chamber. The XRD analysis confirms the presence of a crystalline phase in the undoped Co 2 Y-type barium hexaferrite samples, with a space group identified as R-3m. Characteristic absorption bands of Co 2 Y-type barium hexaferrites were observed at 540 and 422 cm−1 due to the asymmetric stretching vibration of Fe3+ and O2− at both, octahedral and as well as tetrahedral crystallographic sites. The magnetic interaction between the particles causes slight agglomeration. Dielectric and impedance spectroscopy were performed using Koop's phenomenological theory and the Maxwell-Wagner two-layer dielectric relaxation model. The ε ′ was found to decrease with an increase in applied frequency due to the space-charge polarization phenomenon. The rise in ε′ at higher frequencies enhances the material's suitability for high-frequency applications. The magnetic parameters were extracted from the M − H hysteresis loop, and it was observed that they were affected by the site preferences of Pr3+ and Zn2+. The prepared Y-type hexaferrite's optimized magnetic parameters make it a good option for magnetic memory applications. [Display omitted] • Synthesis of Pr3+–Zn2+ substituted Co 2 –Y-type barium hexagonal ferrites using sol-gel method. • Refining the crystal structure through Rietveld refinement, alongside calculations of force constants and bond lengths. • High frequency enhancement of dielectric constant with the tuning of the dielectric tangent loss and AC conductivity • Tuned magnetic parameters resulting from the attenuation of super-exchange interaction due to Pr3+–Zn2+ doping. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mn x Fe 2-x Mg 0.5 Ni 0.5 O 4 spinel ferrites were prepared utilizing a flash auto-combustion technique. • XRD confirmed formation of cubic phase spinel ferrite phase with space group Fd-3 m. • FTIR spectra validate the positions of the cations and their vibrational modes. • Optical band gaps Eg of investigated samples were found to decrease from 1.79 eV to1.24 eV. • The magnetic properties demonstrated soft ferrite nature with small hysteresis curve. Mn x Fe 2-x Mg 0.5 Ni 0.5 O 4 spinel ferrite nanoparticles (0.0 ≤ x ≤ 1) were prepared utilizing a flash auto-combustion technique. The as-prepared ferrite nanoparticles have been investigated and characterized using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and Fourier transform infrared analysis (FTIR). The dielectric, optical and magnetic characteristics of the synthesized spinel ferrite samples were investigated using broadband dielectric spectroscopy (BDS), diffuse reflectance spectroscopy (DRS) and vibration sample magnetometers (VSM). The cubic phase spinel ferrite with space group Fd-3m was identified through XRD. X-ray diffraction indicates that the lattice constant increases and the crystallite size declines with increasing Mn concentration. The positions of the cations and their vibrational modes in the crystal structure with oxygen ions are demonstrated through the FTIR spectra. The morphology was examined using HRTEM showed polycrystalline cubic spinel structure with faceted planes. The optical band gap Eg was determined using Kubelka–Munk model where, it decreased from 1.79 eV to1.24 eV as Mn content increases. The replacement of manganese significantly affects the dielectric characteristics of the synthesized spinel ferrites. The real (ε′), imaginary (ε″) parts of dielectric constant and ac conductivity exhibit an increase in their values as manganese substitution (x) increases from 0 to 0.25 mol %, and thereafter decreases. The presence of a relaxation phenomenon in all prepared samples except the undoped sample (Ni 0.5 Mg 0.5 Fe 2 O 4) is shown by the imaginary modulus's (M′′) dependence on frequency. The magnetic properties exhibited soft ferrite nature with small hysteresis curve for all spinel ferrites samples. The magnetic properties of Mn x Fe 2-x Mg 0.5 Ni 0.5 O 4 nanoparticles were measured and analysed, including saturation magnetization (Ms), remanence (Mr), coercivity (Hc), and squareness ratio. (Ms), and (Mr), exhibit an increase in their values as manganese substitution (x) increases from 0 to 0.25 mol %, and thereafter decreases while squareness ratio decreased. The magnetic parameters greatly affected by Mn substitution ratio. [ABSTRACT FROM AUTHOR]

• Verify the feasibility of a new measurement system for broadband complex dielectric permittivity with a single probe that integrates LCR meter (20 Hz–2 MHz) and time domain reflectometry (1 MHz–1 GHz). • The selected electrode materials and the conductivity of the materials under testing are critical factors regarding the electrode polarization in low-frequency measurements. • The reflection decoupled ratio (RDR) method is robust to process time domain reflectometry data and provide spectra in varying dispersion ranges within 1 MHz–1 GHz. A pragmatic approach to probe setup is desired for broadband dielectric measurement and monitoring. We propose and validate the utilization of a single probe that integrates two different convenient instruments for measuring the complex dielectric permittivity across complementary frequency ranges. The aim is to acquire a broad-spectrum complex dielectric permittivity, thereby providing more information about the tested materials. We deploy an LCR meter with a two-electrode configuration (impedance spectroscopy) to span 20 Hz–2 MHz ranges and time domain reflectometry (TDR) with the reflection decoupled ratio (RDR) method to achieve a spectrum around 1 MHz–1 GHz. The results suggest: 1) the selected electrode materials and the conductivity of the materials under testing are critical factors regarding the electrode polarization in low-frequency measurements, 2) the reflection decoupled ratio (RDR) method can provide spectra in varying dispersion ranges, 3) the feasibility of the measurement system for a broadband complex dielectric permittivity is verified. [ABSTRACT FROM AUTHOR]

The ferroelectric nematic phase (N F) has quickly become the most studied system in liquid crystal research. In this work, we investigate the origin of such polar structure by studying a compound for which the N F phase directly follows the isotropic liquid phase on cooling, making it a particularly interesting system. Our experimental results evidence the presence of polar correlations already in the high-temperature phase, in which ferroelectric order can be induced under a sufficiently strong electric field. In the N F phase, molecular dynamics and polar correlations are investigated through detailed dynamic dielectric measurements, while second harmonic generation experiments evidence a large value of the main coefficient of the second order dielectric susceptibility tensor. Lastly, experimentally determined parameters are employed for calculations based on a recently proposed theoretical model for the stability of the N F phase. The obtained results suggest that the parallel alignment of dipoles is driven by a subtle interplay between electrostatic and excluded volume interactions. • Polar correlations start to occur in the high-temperature isotropic phase. • The colossal dielectric constants of the ferroelectric nematic phase are ruled out. • The parallel alignment of dipoles stems from intricate electrostatic and excluded volume interactions. [ABSTRACT FROM AUTHOR]

Monocrystalline Germanium quantum dots (Ge QDs), grown by molecular beam epitaxy (MBE), are intricately embedded within a SiO 2 oxide layer of a metal-insulator-semiconductor (MIS) structure, catering to optoelectronic applications. These monocrystalline Ge QDs exhibit high density (D ∼ 5 x 1012 cm−2), possess a spherical morphology, and an average size of 6 nm with narrow size distribution. A comprehensive investigation into the influence of these quantum dots on the electrical transport and dielectric properties of the metal-insulator-semiconductor (MIS) structure was conducted through current-voltage (I–V) spectroscopy and impedance spectroscopy. Notably, I–V measurements demonstrate that Ge QDs enhance conduction phenomena, thereby improving electrical transport within the MIS structure. Furthermore, the capacitance-voltage (C–V) and conductance-voltage (G-V) measurements, spanning the inversion and accumulation regions, demonstrate a memory effect induced by Ge QDs within the MOS structure. Extensive analysis of dielectric parameters, including permittivity (ε′), dielectric loss (ε"), dissipation factor (tan δ ), as well as electrical modulus (M' and M"), across a broad frequency range and under varying bias voltages, reveals no anomalous electrical or dielectric behavior attributable to the presence of Ge QDs in MIS structure. Consequently, these findings affirm the viability of the novel MIS structures with Ge QDs for the development of optoelectronic devices such as photodetectors or solar cells. [ABSTRACT FROM AUTHOR]

Polyelectrolyte-based conductive hydrogels are being extensively explored for applications in energy storage and as electrode materials for batteries. We synthesized ionically crosslinked sodium carboxymethyl cellulose (NaCMC), esterified NaCMC, and Ca2+ doped esterified NaCMC hydrogels. This work aims to understand the effect of Ca2+ ions on the NaCMC and esterified NaCMC. FTIR, SEM, Rheology and EIS studies were performed to understand the structure and dynamics of hydrogels. Results confirmed that Ca2+ ions have an important role in determining the rheological and dielectric response of hydrogels. Power law behavior was observed in their rheological response with exponent (n) of 0.81 for G′ and 0.76 for G″ of ionically crosslinked NaCMC, 5.38 for G′ and 4.70 for G″ of esterified NaCMC, whereas, negative exponents −1.44 for G′ and −1.10 for G″ of Ca2+ ion doped esterified NaCMC. Ionically crosslinked NaCMC hydrogels have relaxation times (τ) in the range of 8.9 × 10−5 s–2.8 × 10−5 s may be due to the formation of temporary dipoles by electrostatic bridge formations with dc conductivity of (0.1 S/cm–5 S/cm), whereas, esterified NaCMC showed relaxation times (10−3 s–8.9 × 10−5 s) with increasing ester crosslinks and dc conductivity of (0.05 S/cm–0.8 S/cm). Interestingly, Ca2+ ion doped esterified hydrogels showed multiple dielectric relaxations on Ca2+ ion addition with different relaxation times may be due to change in ionic environment. The understanding obtained from this work may be useful for designing tuneable hydrogels with optimum electrical and mechanical properties. • Addition of Ca2+ in esterified NaCMC showed decrease in mechanical properties and multiple dielectric relaxation processes • Storage modulus increased for ionically crosslinked (Metal ligand coordination) and esterified NaCMC, however, decreasing trend was observed for Ca2+ doped esterified NaCMC hydrogels • Dielectric relaxation times decreased with Ca2+ ion addition for ionically crosslinked NaCMC hydrogels • Decrease in dielectric relaxation time observed with increasing ester crosslinks in esterified NaCMC hydrogels [ABSTRACT FROM AUTHOR]

• Complex dielectric spectra of propylene carbonate (PC) and its alcohol mixtures are characterized from 0.1 ∼ 18 GHz. • Increasing PC concentration respectively causes the dissociation and association of homogeneous and heterogeneous H-bond networks. • Parallel orientational rearrangement between heterogeneous dipoles are observed, leading to strong dielectric enhancement effect. • Molecular dynamic simulations are conducted for visualizing radial distribution functions and orientational correlations of various atoms. • In PC-rich solvent, MeOH molecules tend to form clusters surrounded by PC cages, resulting in significant change of individual volume fractions. This work investigates the dielectric properties and the relaxation behaviors of propylene carbonate (PC) and its binary mixtures with methanol and ethanol. A coaxial-circular cutoff waveguide junction was employed to characterize broadband dielectric spectra ranging from 0.1 GHz to 18 GHz, and a two-group Debye model was used to extract relaxation parameters. Excess thermodynamic parameters, Kirkwood orientational correlation factors, and Bruggeman factors for PC-alcohol mixtures were also analyzed and presented. These data provide insights into microscopic dynamic processes as the PC concentration in the mixtures gradually increases. These processes include the continuous disassociation of the alcohols' hydrogen-bond (H-bond) networks, the formation of new PC-alcohol H-bond networks, the parallel alignment of heterogeneous dipoles, and a significant enhancement of the dielectric effect. Furthermore, a series of molecular dynamics (MD) simulations using the TraPPE-UA forcefield were conducted, and the obtained thermodynamic and electromagnetic parameters demonstrated good agreement with experimental results. Based on radial distribution functions, dipole–dipole spatial orientational correlations, and H-bond life times extracted from the MD simulations, we observed the gradual formation of PC-cage and alcohol-cluster microstructures in PC-rich mixtures. The data and physical insights provided in this work are expected to have practical implications in high-energy battery applications and the pharmaceutical industry. [ABSTRACT FROM AUTHOR]

In this work we synthesized and studied a series of linear polylactides (PLA) with a fixed L/ d -lactide stereoisomer ratio, covering together the wide range of molecular weights, M n , from ∼6 to ∼80 kg/mol. The basic aims are the segmental mobility mapping, in terms of time scale and fragility, the recording of the M n dependences of the glass transition temperature and fragility, and, finally, the comparison with corresponding findings from the literature. Obviously, the direct M n effects on T g are assessed by preserving PLA at the amorphous state, i.e., via melting and relatively fast cooling. The segmental mobility is studied by conventional and temperature modulated calorimetry, whereas the molecular dynamics is assessed employing the technique of broadband dielectric spectroscopy in combination with proper critical analysis and evaluation routes. The calorimetric and dielectric T g (M n) trends were found consistent between each other as well as with previous findings in similar systems, both with respect to experimental findings and theoretic predictions for PLAs of similar L/D ratio. The M n threshold of entanglements seems to lay between 13 and 28 kg/mol. The fragility index of the α relaxation, i.e., the dielectric analogue of the glass transition, exhibits a similar dependence to that of T g (M n). When decreasing M n to very low values, the high fragility (∼150) drops down to 0 (M ñ 6 kg/mol), denoting the vanishing of the polymer chains' cooperativity. Qualitatively interesting alternations are recorded in the dielectric strength of the α relaxation and the relaxation times width. The effects are discussed in terms of the various parameters co-affecting the polymer dynamics, namely, chain lengths, free volume and dynamical heterogeneities. [Display omitted] • Preparation and molecular dynamics investigation of linear PLA with from ∼6 to ∼80 kg/mol. • Recording of the M n dependence of the calorimetric/dielectric T g and of the fragility index of α relaxation. • The M n threshold for entanglements is estimated between 13 and 28 kg/mol. • Consistent findings with previous experimental ones and theoretic predictions for PLAs of similar L/D ratio. [ABSTRACT FROM AUTHOR]

A simple composite DyFe (1-x) Mn x O 3 (x = 0, 0.1, 0.3, 0.5) powders were successfully prepared by the sol–gel method. The effect of Mn modification on the structure, thermal and phase transition behaviour of DyFeO3 orthoferrite was investigated. Mn modification didn't show any structural change and all the samples confirmed the pure orthorhombic phase with Pbnm space group. However, a contradicting trend in the variation of lattice parameters were observed due to the presence of mixed oxidation state of Dy, Fe and Mn in the sample leading to oxygen vacancies. The presence of mixed oxidation state was confirmed through X-ray photoemission spectra (XPS). Scanning electron microscopy (SEM) and Williamson Hall (WH) plot confirmed a decrease in particle sizes with increasing Mn concentration leading to an increase in the specific surface area which suggested an inhibition of grain growth with Mn modification. The defects-initiated change in physical behaviour in terms of structural, thermal, microstructural and dielectric are analyzed and discussed in detail. • Parameter optimization and synthesis of Mn modified DyFeO 3 orthoferrite at low temperature using sol-gel technique. • Observance of mixed oxidation state mediated structural parameters variation in the synthesized samples. • Confirmation of mixed oxidation state using X-ray photoemission spectra (XPS). • Exploration of variation in transition temperature through dielectric analysis in wide frequency range. • Considerable reduction in bulk resistance and relaxation time increasing Mn concentration in the sample. [ABSTRACT FROM AUTHOR]

Recently, polyurethanes (PURs) have become a very promising group of materials with considerable utilization and innovation potential. This work presents a comprehensive analysis of the changes in material properties important for PUR applications in the electrical industry due to the incorporation of magnesium oxide (MgO) nanoparticles at different weight ratios. From the results of the investigations carried out, it is evident that the incorporation of MgO improves the volume (by up to +0.5 order of magnitude) and surface (+1 order of magnitude) resistivities, reduces the dielectric losses at higher temperatures (−62%), improves the thermal stability of the material, and slows the decomposition reaction of polyurethane at specific temperatures (+30 °C). In contrast, the incorporation of MgO results in a slight decrease in the dielectric strength (−15%) and a significant decrease in the mechanical strength (−37%).

Broadband dielectric spectroscopy in a broad temperature range was employed to study ionic conductivity and dynamics in tetraalkylammonium- and tetraalkylphosphonium-based ionic liquids (ILs) having levulinate as a common anion. Combining data for ionic conductivity with data obtained for viscosity in a Walden plot, we show that ionic conductivity is controlled by viscosity while a strong association of ions takes place. Higher values for ionic conductivities in a broad temperature range were found for the tetraalkylphosphonium-based IL compared to its ammonium homolog in accordance with its lower viscosity. Levulinate used in the present study as anion was found to interact and associate stronger with the cations forming ion-pairs or other complexes compared to the NTf2 anion studied in literature. In order to analyze dielectric data, different fitting approaches were employed. The original random barrier model cannot well describe the conductivity especially at the higher frequencies region. In electric modulus representation, two overlapping mechanisms contribute to the broad low frequencies peak. The slower process is related to the conduction mechanism and the faster to the main polarization process of the complex dielectric permittivity representation. The correlation of the characteristic time scales of the previous relaxation processes was discussed in terms of ionic interactions. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectroscopy (BDS) was applied to study polarization phenomena in alkaline silicate glasses, in particular, properties and structure of subsurface (anodic) polarized layers forming in poling with deposited film electrodes of different structures. A model of poled glasses which does not contradict experimental data is proposed. In accordance with the model, a poled glass is presented as two resistor‐capacitor circuits in a series connection, one of which is the polarized layer and another is the rest of the sample. It is found that the electric properties of the layers essentially depend on the structure of the anodic electrode used in glass poling. It is also shown that the dielectric response of poled glass samples is mainly determined by the electric properties of the submicron polarized layers and this gives an opportunity to reveal specific properties of the layers rather than ones of the glass sample bulk. Revealed temperature dependence of DC conductivity of the polarized layers obeys Arrhenius's law, and determining activation energy does not depend on the electrode. Finally, it is noted that today above‐mentioned information about polarized layers can be obtained only by BDS. [ABSTRACT FROM AUTHOR]

Glass-forming ability is one of the most desired properties of organic compounds dedicated to optoelectronic applications. Therefore, finding general structure–property relationships and other rules governing vitrification and related near-glass-transition phenomena is a burning issue for numerous compound families, such as Schiff bases. Hence, we employ differential scanning calorimetry, broadband dielectric spectroscopy, X-ray diffraction and quantum density functional theory calculations to investigate near-glass-transition phenomena, as well as ambient- and high-pressure molecular dynamics for two structurally related Schiff bases belonging to the family of glycine imino esters. Firstly, the surprising great stability of the supercooled liquid phase is shown for these compounds, also under high-pressure conditions. Secondly, atypical self-organization via bifurcated hydrogen bonds into lasting centrosymmetric dimers is proven. Finally, by comparing the obtained results with the previous report, some general rules that govern ambient- and high-pressure molecular dynamics and near-glass transition phenomena are derived for the family of glycine imino esters. Particularly, we derive a mathematical formula to predict and tune their glass transition temperature (Tg) and its pressure coefficient (dTg/dp). We also show that, surprisingly, despite the presence of intra- and intermolecular hydrogen bonds, van der Waals and dipole–dipole interactions are the main forces governing molecular dynamics and dielectric properties of glycine imino esters. [ABSTRACT FROM AUTHOR]

In this article, the optical and dielectric performance of the Ge, Ge/In2Se3 and Ge/In2Se3/Ga2S3 interfaces are reported and discussed. The growth nature of the physically vacuum deposited thin film layers is investigated by means of X-ray diffraction and energy dispersive X-ray spectroscopy. Each 200 nm thick layer exhibited an amorphous type of crystallization with appropriate atomic stoichiometry. Optically, the Ge/In2Se3/Ga2S3 system is found to exhibit a conduction and a valence band offsets of values of 0.53 and 0.47 eV at the Ge/In2Se3 and of values of 0.30 and 0.70 eV at the In2Se3/Ga2S3 interfaces, respectively. The values are high enough to actualize quantum confinements in the heterojunction device. The formed double and three layers displayed higher light absorbability than single layers. On the other hand, the dielectric dispersion analysis has shown a wide tunability in the dielectric property in visible light and near IR regions. The dielectric responses at the Ge/In2Se3 and at the Ge/In2Se3/Ga2S3 interfaces are linear below 2.10 eV and 1.53 eV, respectively. The modeling of the dielectric function revealed the optical conductivity parameters presented by the drift mobility, scattering time, plasmon frequency and free electron density. It was observed that the quantum condiment at the Ge/In2Se3 interfaces improved both of the drift mobility and made the scattering time longer at femtosecond levels. The establishing of the second quantum confinement at the second interface In2Se3/Ga2S3 raised the drift mobility more and extended the scattering time further. With the estimated plasmon frequencies, the formation of the Ge/In2Se3/Ga2S3 interface appears to be promising for use in optoelectronic device production especially in photodetection issues. [ABSTRACT FROM AUTHOR]