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This study investigates the sintering optimization and characterization of (K 0.5 ,Na 0.5)NbO 3 (KNN) ceramics using spark plasma sintering (SPS) at low temperatures. The influence of sintering temperature on crystal structure, microstructure, and dielectric properties is explored. KNN ceramics were sintered as low as 400 °C and exhibit a relative permittivity (ε r) of 740 and a low dissipation factor (tan(δ)) of 0.02 at room temperature. These findings highlight the potential of SPS-sintered KNN ceramics at low temperatures for applications requiring high permittivity and low dielectric losses. • First time sintering highly dense KNN ceramics by SPS at 400 °C with a transient flux. • Highly dense KNN ceramics were sintered by SPS at 750 °C without additive. • Sintered KNN ceramics were obtained at 700 °C by SPS without post-annealing. • Grain size effect was shown to affect the permittivity at the Curie temperature but not at room temperature. [ABSTRACT FROM AUTHOR]

Dielectric properties of a ferroelectric liquid crystal 2-methylbutyl 4-decyloxybenzylidene-4'-n-aminocinnamate (DOBAMBC) confined in untreated and treated porous Anopore membrane were investigated depending on the frequency and temperature. The confinement of a ferroelectric liquid crystal in an untreated Anopore membrane leads to the disappearance of the Goldstone mode. Moreover, despite the modification of the pore surface with various surfactants, no the Goldstone mode or other additional relaxation processes were observed. The relaxation rate of the molecular δ-process is slightly shifted for untreated and treated Anopore membrane in comparison to the bulk. Generally, the relaxation rate temperature dependence shows the Arrhenius-type course, while for lecithin-treated Anopore, it is similar to the Vogel–Fulcher–Tammann-type dependence. Dielectric spectra are dominated at low frequencies by conductivity and electrode polarization effects and are modified in geometric constraints. [ABSTRACT FROM AUTHOR]

A nonterminal liquid crystal epoxy monomer is used to create an epoxy–amine network with a typical diamine 4,4′diaminodiphenylmethane. The plain matrix is compared to matrices modified with inorganic fillers: TiO2 or SiO2. Conditions of the curing reaction and glass transition temperatures in the cured products are determined through differential scanning calorimetry and broadband dielectric spectroscopy. The curing process is also followed through optical and electrical observations. The dielectric response of all investigated networks reveals a segmental α-process related to structural reorientation (connected to the glass transition). In all products, a similar process associated with molecular motions of polar groups also appears. The matrix modified with TiO2 exhibits two secondary relaxation processes (β and γ). Similar processes were observed in the pure monomer. An advantage of the network with the TiO2 filler is a shorter time or lower temperature required for optimal curing conditions. The physical properties of cured matrices depend on the presence of a nematic phase in the monomer and nonterminal functional groups in the aliphatic chains. In effect, such cured matrices can have more flexibility and internal order than classical resins. Additional modifiers used in this work shift the glass transition above room temperature and influence the fragility index in both cases. [ABSTRACT FROM AUTHOR]

The macroscopic properties of polymer nanocomposites (PNC) rely largely on the interphase between the polymer chains and the filler particles. One significant difficulty to solve this issue is to quantitatively model the structure‐property correlations due to the interfacial region in these complex materials. While dielectric spectroscopy (DS) measurements are routinely used to characterize the effective permittivity of filled polymers, fitting standard effective medium models and mixing equations to these data remains notoriously difficult to interpret. This is due to the absence of explicit reference to internal length scales characterizing the interfaces in the PNC. As an illustrative example, a two‐level homogenization framework is proposed which enables the extraction of useful information on the impact of a thin interphase confined on a nanometer length scale based on broadband DS data. This model leads to new ways of tuning the interphase so as to optimize the material's response to electric field, a situation relevant for electromagnetic shielding. This approach provides guidance on how to observe directly and experimentally the actual properties of the interface between the phases (as opposed to model‐based inference). Aside from its secure physical foundation in the theory of effective medium, a significant advantage of this approach is that a genetic algorithm (GA) technique applied to this physics‐based model enables the uniqueness of the fit parameters to be considered, as the GA method is robust in terms of finding globally optimum solutions, therefore placing confidence in non‐universal values of the percolation exponents. Recent work in physics‐informed machine learning indicates that the effective dielectric properties of PNC with many degrees of freedom due to their complex morphology can be described by considering only a few degrees of freedom describing the interface features between the phases in these composites. [ABSTRACT FROM AUTHOR]

Epoxy nano-magnetic composites exhibit remarkable and promising properties by synergistically combining the properties of epoxy resin and magnetic nanofillers. The current study deals with the synthesis of Fe3O4, NiFe2O4, and CoFe2O4 nanoparticles and their respective nanoparticles-doped epoxy composites, as well as the structural, optical, and dielectric characterization of the resultant nano-composites. To investigate the surface morphology of the synthesized nanoparticles, field emission electron microscopy (FESEM) analysis was employed. By measuring electron diffraction spectroscopy (EDS), the presence of various chemicals was verified. X-ray diffraction (XRD) was used to determine the structural details of the synthesized nanoparticles and nanoparticles-doped epoxy composites. The structural chemistry and surface functionality of the nano-epoxy composites were investigated using Fourier transform infrared spectroscopy (FTIR). The magnetic properties of the synthesized nanoparticles and nanoparticles loaded epoxy composites were also studied using a vibrating sample magnetometer (VSM). UV–visible reflection spectroscopy was also carried out to find the optical properties of the synthesized nanoparticles, neat (undoped) epoxy, and nanoparticles-doped epoxy composites. Dielectric spectroscopy measurements of nanoparticles-doped epoxy composites were performed using an Agilent E4980A precision LCR (Inductance Capacitance Resistance) meter with an Agilent 16451B-test fixture LCR and vector network analyzer (VNA) in the frequency span of 10 kHz to 2 MHz and 200 MHz to 20 GHz, respectively. The influence of the synthesized nanoparticles on the neat (undoped) epoxy composites and the results in view of future applications are fully discussed. [ABSTRACT FROM AUTHOR]

Nickel copper ferrite nanoparticles (NPs) in the form Ni0.65Cu0.35Fe2O4 were synthesized by the sol–gel method while PVA-CMC blend films were manufactured by cast method. The prepared films of PVA-CMC/(Ni0.65Cu0.35Fe2O4)x, where x = 2,4,6, and 8 wt%, were characterized using X-ray diffractometer (XRD) and Raman spectroscopy. The transmission and absorption spectra were investigated for PVA-CMC/Ni0.65Cu0.35Fe2O4 films using UV–visible spectrophotometer. The assessment of dielectric characteristics of the prepared PVA-CMC blend films was done by using broadband dielectric spectroscopy (BDS). XRD verified the production of face-centered cubic spinel structure of space group Fd3m with the lattice parameters a = 8.3310 Å for Ni0.65Cu0.35Fe2O4 NPs and the amorphous characteristics of blend films. Furthermore, XRD verified that Ni0.65Cu0.35Fe2O4 NPs were included in the blend matrix. The Raman spectra of the PVA-CMC blend films showed several strong characteristic scattering peaks. The optical bandgaps were evaluated via the Tauc's model. The optical bandgap decreases from 5.50 to 5.05 eV and the Urbach energy increases from 1.35 to 2.99 eV, gradually, with increasing NPs' concentrations. Moreover, the index of refraction rises from 1.776 (pure PVA-CMC) to 2.881 (PVA-CMC/8%Ni0.65Cu0.35Fe2O4). Also, it was discovered that as Ni0.65Cu0.35Fe2O4 NPs were added to the PVA-CMC blend matrix, optical conductivity increased as well. The results showed that the PVA/CMC blend films can be tailored by Ni0.65Cu0.35Fe2O4 additives which nominate it for optical devices applications. Three remarkable trends were investigated on the dielectric spectra of the investigated samples. The low frequency range shows a linear increase with decreasing frequency indicating the transport of the free charge carriers. Nano-confinement phenomenon affected in reducing the conductivity of the blend, even the conductivity of the nano-ferrite is higher in conductivity than the blend. [ABSTRACT FROM AUTHOR]

Interfacial characteristics of nanocomposites are critical limiting factors in the design of polymer nanocomposites. The nanocomposites have complex structures and play a pivotal role in controlling functional properties. Analysis of interfacial layers in polymer nanocomposites, existing between the polymer matrix and the nanoparticles plays a major role in determining their characteristics. High-frequency analysis of electrical conductivity and dielectric properties of carbon nanofillers which are embedded in an epoxy matrix were analysed using alternating current dielectric spectra. This article provides a correlation between the electrical transport properties and dielectric behaviour of epoxy carbon nanocomposites at different temperatures are investigated with variations in frequency. Electrical transport properties of nanocomposites are primarily dictated by electron tunnelling and matrix, nanofillers conductivity. Dielectric spectroscopy in the frequency range 10 Hz–8 MHz has been performed on epoxy nanocomposites with and without hybrid carbon nanofillers at one weight percentage (2:3 ratio). Dominant dielectric relaxation mode is observed in the base composite at a low-frequency region (≥10 Hz), whereas nanocomposite with hybrid carbon nanofillers is observed to induce two dielectric relaxations in the kHz region. Increase in non-monotonic variations in dielectric spectra makes the nanocomposite suitable for high temperature low sag conductor core, aerospace and cryogenic engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of the dielectric constant of solutions of a polar liquid in a nonpolar solvent: chlorobenzene–benzene, chlorobenzene–hexane. The measurements were carried out at a wavelength λ = 1 2. 8 0 cm in the temperature range from − 8 0 ∘ C to 2 0 ∘ C. The studies were carried out using the dielectric spectroscopy method. This method allows a more detailed study of the dielectric properties of the objects of study due to the large equilibrium ("static") dielectric constant of the object. The temperature dependence of the dielectric relaxation time of molecules in the liquid and solid states of the studied solutions is determined. It has been established that with increasing concentration (0.300, 0.562, 0.794, 1.000 for a chlorobenzene–hexane solution and 0.179, 0.368, 0.567, 0.778, 1.000 for a chlorobenzene–benzene solution) of the halogen substituent, the relaxation time increases. The measurement results of dielectric constant ε ′ and absorption coefficient ε ′ ′ obtained for concentrated solutions chlorobenzene–benzene, chlorobenzene–n–hexane at wavelengths λ = 1 2 , 80 and λ = 3 , 2 6 cm at temperature 2 0 ∘ C are given in the paper. The static dielectric constant is obtained at a frequency of 1 MHz. The obtained experimental values ε ′ , ε ′ ′ and ε 0 of investigated systems in ( ε ′ , ε ′ ′ ) plane locate on the semi-circle the center of which is on ε ′ axis. In this case, the high-frequency limit value of ε ∞ dielectric coefficient exceeds the corresponding n2 refraction index square. The macroscopic and molecular relaxation times are calculated on the base of experimental data. The thermodynamic quantities characterizing the process of dielectric relaxation are calculated for solutions of chlorobenzene–benzene, chlorobenzene–hexane. It has been determined that the height of the potential barrier separating the two equilibrium positions of a polar molecule is greatest in the state of a pure polar liquid and decreases with dilution in a nonpolar solvent. [ABSTRACT FROM AUTHOR]

A new copper(II) complex with 2-amino-6-methylpyrimidin-4-(1H)-one, [Cu(C5H7N3O)4](NO3)2·H2O (Cupyrim), has been synthesized and studied by X-ray diffraction, elemental analysis and FT-IR spectroscopy. The Cu(II) is four-coordinate in a square planar geometry by four nitrogen atoms of the four organic ligands. Hirshfeld Surface Analysis was conducted to understand crystalline packing. Overall, the structure is maintained by metal coordination as well as strong and weak (C,N)–H···O hydrogen bonds and C–H...π interactions. The IR spectrum primary peaks have been assigned to the vibration modes of the ligand functional groups. An investigation of the inhibitory properties of Cupyrim toward "Cyclin-dependent Kinase 2" (CdK2) and "inducible nitric oxide synthase" (iNOS) proteins was aided by molecular docking research. According to molecular docking, Cupyrim exhibits promising inhibitory efficacy against Parkinson's, schizophrenia, and Alzheimer's disorders. The temperature dependence of the real and imaginary part of the dielectric permittivity was analyzed with the Cole-Cole formalism as well as DSC diagrams from 45-147 °C. [ABSTRACT FROM AUTHOR]

We have designed new chiral smectic mesogens with the -CH2O group near the chiral center. We synthesized two unique rod-like compounds. We determined the mesomorphic properties of these mesogens and confirmed the phase identification using dielectric spectroscopy. Depending on the length of the oligomethylene spacer (i.e., the number of methylene groups) in the achiral part of the molecules, the studied materials show different phase sequences. Moreover, the temperature ranges of the observed smectic phases are different. It can be seen that as the length of the alkyl chain increases, the liquid crystalline material shows more mesophases. Additionally, its clearing (isotropization) temperature increases. The studied compounds are compared with the structurally similar smectogens previously synthesized. The helical pitch measurements were performed using the selective reflection method. These materials can be useful and effective as chiral components and dopants in smectic mixtures targeted for optoelectronics and photonics. [ABSTRACT FROM AUTHOR]

High-tilt angle ferroelectric liquid crystal material in surface stabilised geometry (SSFLC) is investigated for the smectic layer reorientation and its molecular dynamics by electro-optical and dielectric spectroscopy techniques. Smectic layer reorientation (5 $^o$ o to 45 $^o$ o ) is obtained by controlled cooling rate and applying electric field in the vicinity of transition temperature from chiral nematic (${N^*}$ N ∗ ) to chiral smectic C ($Sm{C^*}$ Sm C ∗ ) phase. After slow cooling down to room temperature, the stripe domain textures along the rubbing are observed with quasi-bistable states. Dielectric spectroscopy has revealed the unusual increment in the dielectric permittivity. A dielectric relaxation process at lower frequency than Goldstone mode with the increase in DC bias up to 2 $V$ V is observed in the sample cooled without any bias. This increment is found to be originated by the heliconical structure within the stripes which is seen in the optical textures recorded at the time of dielectric scan. However, this increment is not observed in the sample cooled under DC bias. Thus, there exist different phenomena in the high tilt angle SSFLC sample cooled in different conditions of DC bias; stripe domains, smectic layers reorientation, heliconical stricture and twisted structure within stripes which are significant to explore deeply in high-tilt angle ferroelectric liquid crystals. [ABSTRACT FROM AUTHOR]

Dependences of the components of the complex dielectric permittivity and specific electrical conductivity in the frequency range 10−2–107 Hz at temperatures of 213–433 K of guaiacol, a model compound of lignin, one of the most common biopolymers, are analyzed. Three groups of relaxation oscillators are identified. Their characteristics (relaxation time and activation energy) are determined. The activation energy is shown to change depending on the aggregate state. The results indicate that the dielectric relaxation and conductivity of lignin polymer and its model compounds are similar in an alternating electric field. [ABSTRACT FROM AUTHOR]

This article presents the synthesis and molecular dynamics investigation of three novel cyclic thioethers: 2,3-(4′-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2-ene (compound 1), 2,3,14,15-bis(4′,4″(5″)-methylbenzo)-1,4,7,10,13,16,19,22,25-octathiacyclotetracosa-2,14-diene (compound 2), and 2,3,8,9-bis(4′,4″(5″)-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2,8-diene (compound 3). The compounds exhibit relatively high glass transition temperatures (Tg), which range between 254 and 283 K. This characteristic positions them within the so-far limited category of crown-like glass-formers. We demonstrate that cyclic thioethers may span both the realms of ordinary and sizeable molecular glass-formers, each featuring distinct physical properties. Furthermore, we show that the Tg follows a sublinear power law as a function of the molar mass within this class of compounds. We also reveal multiple dielectric relaxation processes of the novel cyclic thioethers. Above the Tg, their dielectric loss spectra are dominated by a structural relaxation, which originates from the cooperative reorientation of entire molecules and exhibits an excess wing on its high-frequency slope. This feature has been attributed to the Johari–Goldstein (JG) process. Each investigated compound exhibits also at least one intramolecular secondary non-JG relaxation stemming from conformational changes. Their activation energies range from approximately 19 kJ/mol to roughly 40 kJ/mol. Finally, we analyze the high-pressure molecular dynamics of compound 1, revealing a pressure-induced increase in its Tg with a dTg/dp coefficient equal to 197 ± 8 K/GPa. [ABSTRACT FROM AUTHOR]

The problem of field induced phase transition into the ferroelectric phase in relaxor ceramics and in particular in PMN ceramics was studied for many years, but the results are still controversial. The temperature and field dependences of PMN polycrystalline ceramics dielectric spectra have been studied. The transitions from the glass-like into the ferroelectric phase were found both in field cooling and zero field heating after field cooling regimes under the fields above 3 kV/cm. Electric field scans near the diffuse maximum of the dielectric permittivity demonstrated the shift of the loss maximum to the high frequency at increasing of applied electric field. The experimentally observed frequency-dependent sign of the C–V effect (the decrease (negative effect) or the increase (positive effect) of dielectric permittivity at increasing field) is due to spectra hardening. In contrast to single crystal, where the application of the electric field higher than 1.6 kV/cm in <111> direction induces phase transition into ferroelectric state, in polycrystalline ceramics no clear evidence of the phase transition from the paraelectric into the ferroelectric state up to 6 kV/cm neither at 242 K nor at 246 K was found. This difference between the single crystal and polycrystalline ceramics can be explained by very strong dependence of the threshold field from the field orientation at this transition. The influence of external field on low frequency relaxation process parameters for PMN single crystal and ceramics is compared. [ABSTRACT FROM AUTHOR]

The formation of the nematic to twist-bend nematic (NTB) phase has emerged as a fascinating phenomenon in the field of supramolecular chemistry, based on complex intermolecular interactions. Through a careful analysis of molecular structures and dynamics, we elucidate how these intermolecular interactions drive the complex twist-bend modulation observed in the NTB. The study employs broadband dielectric spectroscopy spanning frequencies from 10 to 2 × 109 Hz to investigate the molecular orientational dynamics within the glass-forming thioether-linked cyanobiphenyl liquid crystal dimers, namely, CBSC7SCB and CBSC7OCB. The experimental findings align with theoretical expectations, revealing the presence of two distinct relaxation processes contributing to the dielectric permittivity of these dimers. The low-frequency relaxation mode is attributed to an "end-over-end rotation" of the dipolar groups parallel to the director. The high-frequency relaxation mode is associated with precessional motions of the dipolar groups about the director. Various models are employed to describe the temperature-dependent behavior of the relaxation times for both modes. Particularly, the critical-like description via the dynamic scaling model seems to give not only quite good numerical fittings, but also provides a consistent physical picture of the orientational dynamics in accordance with findings from infrared (IR) spectroscopy. Here, as the longitudinal correlations of dipoles intensify, the m1 mode experiences a sudden upsurge in enthalpy, while the m2 mode undergoes continuous changes, displaying critical mode coupling behavior. Interestingly, both types of molecular motion exhibit a strong cooperative interplay within the lower temperature range of the NTB phase, evolving in tandem as the material's temperature approaches the glass transition point. Consequently, both molecular motions converge to determine the glassy dynamics, characterized by a shared glass transition temperature, Tg. [ABSTRACT FROM AUTHOR]

The biological control agent Bacillus thuringiensis (Bt) coordinates metabolic and gene regulation functions to enter to the differentiation process for the synthesis of spores and Cry toxin proteins. The master regulator for sporulation initiation is Spo0A, while AbrB regulator coordinate cellular functions during vegetative and transition growth. To understand how differentiation is modified during fed-batch cultures (FBC) of Bt under variable nutrient conditions, we conducted fermentations with two different nutrient concentration and feeding times using an industrial medium. Since sporulation efficiency has been lower in FBCs than in batch cultures, AbrB was monitored by Western blot during these cultures. Kinetic parameters were used to stablish timing of cell differentiation process, and fermentations were monitored on-line using impedance spectroscopy. AbrB was accumulated during the entire fed-batch culture, when a medium with the highest concentration of carbon and nitrogen sources (FBC1) were fed. Under these conditions, sporulation efficiency and cry1Ac expression were negatively affected, compared to the wild-type strain. Conversely, when the feeding concentration was only half of FBC1, AbrB accumulates in minor proportion, and sporulation efficiency and cry1Ac expression increased (FBC2). These results suggest that variable nutrient conditions can cause an imbalance in the accumulation of transition state regulators such as AbrB during FBCs, which can be detrimental to produce spores and Cry proteins, that are the main Bt products for biological control of agricultural pests. [ABSTRACT FROM AUTHOR]

Second harmonic generation (SHG) and high-frequency dielectric properties of Li-doped KTaO 3 (K 1- x Li x TaO 3 , KLT100 x) ceramics, KLT5 and KLT10, are studied in the 15–300 K temperature range. Using the resonant microwave spectroscopy at 5.8 GHz, time-domain THz spectroscopy (∼10–40 cm−1) and far-infrared reflectivity (∼30–650 cm−1) in conjunction with the dielectric properties earlier published in the 100 Hz – 100 MHz frequency range, a broad-band dielectric response of ceramics in the whole 100 Hz – 20 THz range is obtained and compared with that recently published for KLT4.3 and KLT8 crystals. According to SHG, unlike in crystals, the ferroelectric phase transition temperature in both ceramics appears near 100 K. The dielectric soft mode softening is less pronounced, and the low-frequency permittivity increases less on cooling, when compared with crystals. The relaxational behavior below the microwave range is very similar and the main relaxations follow the same Arrhenius law as in the crystals. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy (frequency range f = 100...107 Hz and temperatures T = 293...403 K (accuracy 0.5 K), measuring voltage applied to the sample was 1.0 V) was used to study composite materials based on perfluorosulfonic membranes with inclusions of rare-earth elements, in particular, europium (III) and terbium (III) chlorides. The dispersion of the permittivity and the presence of maxima, corresponding to losses, were revealed, which indicates that relaxation processes of various natures were present. The membrane layers under investigation are characterized by relaxation parameters that correspond to a symmetrical distribution of relaxers over relaxation times. The spectrum of relaxers changed when terbium and europium metal impurities were introduced into the polymer matrix. The investigation of these polymer systems demonstrated a power-law dependence of the specific conductivity on frequency. A decrease in the exponent with increasing temperature indicates the existence of a traditional hopping mechanism for charge transfer. The observed changes in the dielectric permittivity and specific conductivity are due to a change in the nature of polarization processes because of the strong interaction of metal (terbium and europium) ions with the polymer matrix of Nafion. [ABSTRACT FROM AUTHOR]

The present work was undertaken to examine the evolution of interfacial properties of Kevlar/epoxy laminated composites hybridized by naturally woven Coco Nucifera sheath (CNS). Hand lay-up method followed by hot pressing was performed to fabricate our laminated composites. Broadband Dielectric Spectroscopy (BDS) was adopted to investigate the effect of varying CNS fractions (0%, 25%, 50%, 75% and 100%) on the molecular dynamics and the interfacial adhesion between Kevlar/epoxy and CNS/epoxy. The surface and cross-section morphology of the samples were studied in order to analyze the weaving structures of Kevlar and CNS and the interfaces between epoxy matrix and reinforcements. Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) were carried out to control the characteristic temperatures and the interactions between the two kinds of fibers (Kevlar and CNS) and the epoxy resin. The BDS results revealed different relaxations: the conduction phenomenon, the primary α -process and the interfacial polarization, called also MWS polarization, whose dielectric strength ∆ ε M W S was calculated using the WinFit software. Hence, Kevlar fibers can be successfully replaced by 25% of CNS natural fibers for advanced structural applications where interfacial adhesion is prime requirement. Graphical Abstract [ABSTRACT FROM AUTHOR]

Simple Summary: Meningiomas are the most common primary central nervous system tumors, and surgery is their primary treatment of choice. The surgical intervention aims for the maximum extent of tumor resection whilst preserving the brain's neurological functions. The effectiveness of such intervention thus depends on the capability to intraoperatively discriminate between the meningioma tissue and the surrounding brain white matter and gray matter. This study investigated dielectric contrast as a potential physical biomarker for meningioma discrimination. Dielectric contrast is based on the difference in complex permittivity, a physical property of tissues, measurable by dielectric spectroscopy. This study shows that the dielectric contrast is relevant as a potential physical biomarker to discriminate the meningioma tissue from the surrounding brain tissues. Such a biomarker has a meaningful potential to make a positive impact on the management of neurooncological patients in terms of intraoperative tumor discrimination, as well as future diagnostic or therapeutic applications. The effectiveness of surgical resection of meningioma, the most common primary CNS tumor, depends on the capability to intraoperatively discriminate between the meningioma tissue and the surrounding brain white and gray matter tissues. Aiming to find a potential biomarker based on tissue permittivity, dielectric spectroscopy of meningioma, white matter, and gray matter ex vivo tissues was performed using the open-ended coaxial probe method in the microwave frequency range from 0.5 to 18 GHz. The averages and the 95% confidence intervals of the measured permittivity for each tissue were compared. The results showed the absence of overlap between the 95% confidence intervals for meningioma tissue and for brain white and gray matter, indicating a significant difference in average permittivity (p ≤ 0.05) throughout almost the entire measured frequency range, with the most pronounced contrast found between 2 GHz and 5 GHz. The discovered contrast is relevant as a potential physical biomarker to discriminate meningioma tissue from the surrounding brain tissues by means of permittivity measurement, e.g., for intraoperative meningioma margin assessment. The permittivity models for each tissue, developed in this study as its byproducts, will allow more accurate electromagnetic modeling of brain tumor and healthy tissues, facilitating the development of new microwave-based medical devices and tools. [ABSTRACT FROM AUTHOR]

Biodiesel is widely used pure or mixed with diesel fossil fuel in diesel engines. Standards for determining biodiesel quality establish limits for the values of several physicochemical properties. However, the procedures to determine many properties are time‐consuming and demand specialized personnel and expensive equipment. Other methods to characterize biodiesel, such as electrical methods, are particularly interesting. Measurements of electrical properties (permittivity and conductivity) give valuable information about biodiesel, its feedstocks, and its blends with fossil fuel diesel, and solve the usual cost and time drawbacks. This work aims to present a thorough and systematic review of the literature on applications of electrical properties measurements of biodiesel, its feedstocks, and mixtures with other fuels. An overview of the experimental data, typical ranges of values, prediction models, and applications is presented and analyzed in detail, emphasizing blends of biodiesel with fossil fuel diesel. Correlations with important properties (kinematic viscosity, methanol content) are reviewed. Applications include transesterification monitoring, biodiesel aging, the detection of contaminants and electromagnetic heating. This research aimed to determine whether electrical properties are a valuable tool for the biodiesel industry, and what applications may be realized in light of current scientific development. It was determined that, in the current state of research, permittivity measurements could be used to accurately determine the amount of diesel and biodiesel in mixtures. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Ethaline, the 1:2 molar ratio mixture of ethylene glycol (EG) and choline chloride (ChCl), is generally regarded as a typical type III deep eutectic solvent (DES). However, careful differential scanning calorimetry (DSC) of EG + ChCl mixtures surprisingly revealed that the liquidus lines of the phase diagram apparently follow the predictions for an ideal binary non-electrolyte mixture. Applying broad-band dielectric relaxation spectroscopy to room-temperature solutions of ChCl, and of the related salts choline iodide and chlorocholine chloride, in EG up to saturation, we explored the possible reasons for this conundrum. It appears that in these solutions free ions are rather scarce. Instead, contact ion pairs and larger aggregates predominate. [ABSTRACT FROM AUTHOR]

In spite of the significance from both scientific and technological viewpoints, systematical studies on the dielectric spectra of (K,Na)NbO 3 -based lead-free ceramics particularly in the poled state had been scarcely performed so far. In this study, the compositional series of (1- x)(K 0.48 Na 0.52)(Nb 0.96 Sb 0.04)O 3 − x (Bi 0.50 Na 0.50)ZrO 3 ceramics were chosen representatively to shed more light on the characters of dielectric properties. All the ceramics in the unpoled state show dielectric spectra of large dispersion with the relaxational characteristic frequency higher than the measured upper limit of 60 MHz at room temperature. Additional resonance peaks due to the electromechanical coupling of piezoelectric effect appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra after poling. An abnormal phenomenon that poling induces the increase of low-frequency ε′ occurs in those ceramics with x ≥ 0.04 at room temperature, and is confirmed to associate closely with the orthorhombic-tetragonal and rhombohedral-orthorhombic polymorphic phase transitions. Further study of domain structure indicates that the origin of this abnormal phenomenon should be ascribed to the enhancement of domain-wall mobility because of the large reduction of domain-wall density due to the poling. [ABSTRACT FROM AUTHOR]

Viable cell concentration (VCC) is an essential parameter that is required to support the efficient cultivation of mammalian cells. Although commonly determined using at‐line or off‐line analytics, in‐line capacitance measurements represent a suitable alternative method for the determination of VCC. In addition, these latter efforts are complimentary with the Food and Drug Administration's initiative for process analytical technologies (PATs). However, current applications for online determination of the VCC often rely on single frequency measurements and corresponding linear regression models. It has been reported that this may be insufficient for application at all stages of a mammalian cell culture processes due to changes in multiple cell parameters over time. Alternatively, dielectric spectroscopy, measuring capacitance at multiple frequencies, in combination with multivariate mathematical models, has proven to be more robust. However, this has only been applied for retrospective data analysis. Here, we present the implementation of an O‐PLS model for the online processing of multifrequency capacitance signals and the on‐the‐fly integration of the models' VCC results into a supervisory control and data acquisition (SCADA) system commonly used for cultivation observation and control. This system was evaluated using a Chinese hamster ovary (CHO) cell perfusion process. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectroscopy in the frequency range from 10−2 Hz to 107 Hz was used to study the effect of hydrophobic aerosil nanoparticles on the dynamics of the Goldstone mode in a ferroelectric liquid crystal near the point of spontaneous polarisation sign reversal. The obtained results show that an important role in the modification of the dynamics of the Goldstone mode and the phenomena at the point of spontaneous polarisation sign reversal is played not only by the presence of the nanoparticles themselves in the ferroelectric liquid crystal structure, but also the state of the surface of these nanoparticles. Similarly to the hydrophilic aerosil, the polarisation sign reversal temperature slightly decreases with the increase of the hydrophobic aerosil concentration. For small concentrations of hydrophobic aerosil, only slight changes in the dynamics of the Goldstone mode over the entire temperature range are detected. The observed deviations are due to the different influence of aerosil nanoparticles on the structure and dielectric properties of the tested composite caused by the specific surface treatment. The presence of the Goldstone mode above and below the point of polarisation sign reversal seems to confirm the model of two conformers with different structure and opposite dipole moments. [ABSTRACT FROM AUTHOR]

Two neutral copper(I) halide complexes ([Cu(BTU)2X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N′-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very interesting combination of 2D supramolecular structures, liquid crystalline, emission, and 1D ionic conduction properties. Their chemical structure was ascribed based on ESI–MS, elemental analysis, IR, and NMR spectroscopies (1H and 13C), while the mesomorphic behavior was analyzed through a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (XRD). These new copper(I) complexes have mesomorphic properties and exhibit a hexagonal columnar mesophase over a large temperature range, more than 100 K, as evidenced by DSC studies and POM observations. The thermogravimetric analysis (TG) indicated a very good thermal stability of these samples up to the isotropization temperatures and over the whole temperature range of the liquid crystalline phase existence. Both complexes displayed a solid-state emission with quantum yields up to 8% at ambient temperature. The electrical properties of the new metallomesogens were investigated by variable temperature dielectric spectroscopy over the entire temperature range of the liquid crystalline phase. It was found that the liquid crystal phases favoured anhydrous proton conduction provided by the hydrogen-bonding networks formed by the NH...X moieties (X = halide or oxygen) of the benzoylthiourea ligand in the copper(I) complexes. A proton conductivity of 2.97 × 10−7 S·cm−1 was achieved at 430 K for the chloro-complex and 1.37 × 10−6 S·cm−1 at 440K for the related bromo-complex. [ABSTRACT FROM AUTHOR]

We studied the dielectric properties of a polar nematic phase (NF) sandwiched between two gold or ITO electrodes, serving as a cell surface. In bulk, NF is expected to exhibit a Goldstone mode (phason), because polarisation can uniformly rotate with no energy cost. However, because the coupling between the direction of nematic director and polarisation is finite, and the confinement, even in the absence of the aligning surface layer, induces some energy cost for a reorientation of polarisation, the relaxation frequency of the phason mode is measured in a kHz regime. The phason mode is easily quenched by a bias electric field, which enables fluctuations in the magnitude of polarisation to be followed in both the ferroelectric and paraelectric nematic phases. This amplitude (soft) mode is also influenced by boundary conditions. A theory describing the phase and amplitude fluctuations in the NF phase shows that the free energy of the system and, consequently, the dielectric response are dominated by polarisation-related terms with the flexoelectricity being relevant only at a very weak surface anchoring. Contributions due to the nematic elastic terms are always negligible. The model relates the observed low-frequency mode to the director fluctuations weakly coupled to polarisation fluctuations. [ABSTRACT FROM AUTHOR]

Microwave ablation is a technique used to treat tumorous tissue. Its clinical use has been greatly expanding in the last few years. Because the design of the ablation antenna and the success of the treatment greatly depend on the accurate knowledge of the dielectric properties of the tissue being treated, it is highly valuable to have a microwave ablation antenna that is also able to perform in-situ dielectric spectroscopy. In this work, an open-ended coaxial slot ablation antenna design operating at 5.8 GHz is adopted from previous work, and its sensing abilities and limitations are investigated in respect of the dimensions of the material under test. Numerical simulations were performed to investigate the functionality of the floating sleeve of the antenna and to find the optimal de-embedding model and calibration option for obtaining accurate dielectric properties of the area of interest. Results show that, as in the case of the open-ended coaxial probe, the accuracy of the measurement greatly depends on the likeness between the calibration standards' dielectric properties and the material under test. Finally, the results of this paper clarify to which extent the antenna can be used to measure dielectric properties and paves the way to future improvements and the introduction of this functionality into microwave thermal ablation treatments. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy (DS) is the primary technique to observe the dielectric properties of biomaterials. DS extracts complex permittivity spectra from measured frequency responses such as the scattering parameters or impedances of materials over the frequency band of interest. In this study, an open-ended coaxial probe and vector network analyzer were used to characterize the complex permittivity spectra of protein suspensions of human mesenchymal stem cells (hMSCs) and human osteogenic sarcoma (Saos-2) cells in distilled water at frequencies ranging from 10 MHz to 43.5 GHz. The complex permittivity spectra of the protein suspensions of hMSCs and Saos-2 cells revealed two major dielectric dispersions, β and γ , offering three distinctive features for detecting the differentiation of stem cells: the distinctive values in the real and imaginary parts of the complex permittivity spectra as well as the relaxation frequency in the β -dispersion. The protein suspensions were analyzed using a single-shell model, and a dielectrophoresis (DEP) study was performed to determine the relationship between DS and DEP. In immunohistochemistry, antigen–antibody reactions and staining are required to identify the cell type; in contrast, DS eliminates the use of biological processes, while also providing numerical values of the dielectric permittivity of the material-under-test to detect differences. This study suggests that the application of DS can be expanded to detect stem cell differentiation. [ABSTRACT FROM AUTHOR]

Quasistatic dielectric permittivity of D2O type I molecules (electric dipole moment perpendicular to the crystallographic c‐axis) within hydrothermally grown beryl crystals characterized by different internal pressure and content of D2O type II molecules (dipole moment parallel to the c‐axis) is measured at temperatures 4–300 K. All crystals are found to display quantum paraelectric behavior of the D2O‐I molecular subsystem permittivity, that is, permittivity growth while cooling from room temperature followed by saturation below 15–40 K. Processing the data with the Barrett expression shows that excess internal pressure and excess content of D2O‐II molecules lead to an increase in quantum temperature T1 and a decrease in the Curie constant C, with the Curie temperature TC remaining unchanged. The discovered strengthening of quantum effects (growth of T1) within an ensemble of dipole–dipole‐coupled D2O‐I molecules is associated with an enhanced azimuthal tunneling of these molecules within the hexagonal localizing potential. The data indicate the possibility of using crystal growth conditions to "tune" the strength of quantum effects in the network of polar water molecules, which provides a workbench for further studies of exotic phases of a lattice of coupled "point" electric dipoles. [ABSTRACT FROM AUTHOR]

An explicit relation between half‐width at half‐maximum ΔT in a dissipation factor of dipolar molecular rotors in a solid phase and rotational barrier height Ub was derived within the Debye relaxation model. The formula for Ub is simply expressed as Ub≈1.317kT*2ΔT. Here, T* is the temperature at the peak position in the dissipation factor, and k is the Boltzmann constant. The formula is an alternative to the familiar Arrhenius equation, from which Ub has so far been estimated in various dielectric experiments. The distinction of the proposed formula is the determination of Ub from a single peak in a dissipation factor induced by an electric field, while the Arrhenius equation needs data for the magnitudes of the dissipation factor and temperatures at several peaks. By applying the proposed formula to dipole molecular rotors (ROT‐2F) in a single crystalline and polycrystalline, for which Ub values were reported (Horansky et al., Phys. Rev. B 74, 054306 [2006]), the calculated values of Ub were quantitatively reproduced. This indicates the validity of the proposed formula, and the formula is expected to be applied to the analysis of dielectric spectra of 2D dipolar molecular rotor systems. [ABSTRACT FROM AUTHOR]

Solid solutions of (1-x)Pb(Ti0.5Zr0.5)O3–xCdNb2O6 system with x = 0.0125 ÷ 0.0500, Δx = 0.0125 were obtained by two-stage solid phase synthesis followed by sintering using conventional ceramic technology and experimental studies of crystal structure, dielectric, piezoelectric, and ferroelastic properties. At 0.0250 ≤ x the studied samples belonged to the region with a tetragonal unit cell, at 0.0250 < x ≤ 0.0375 they consisted of tetragonal phases with close cell parameters, and at x > 0.0375 a heterogeneous region was formed with clusters of phases with non-tetragonal symmetry. A twofold increase in the piezoelectric parameters was achieved compared to the PZT-Pb(W,Cd)O3 composition. [ABSTRACT FROM AUTHOR]

Single crystals of Pb1−3x▯xNd2x(MoO4)1−3x(WO4)3x (PNMWO) with scheelite-type structure, where ▯ denotes cationic vacancies, have been successfully grown by the Czochralski method in air and under 1 MPa. This paper presents the results of structural, optical, magnetic and electrical, as well as the broadband dielectric spectroscopy measurements of PNMWO single crystals. Research has shown that replacing diamagnetic Pb2+ ions with paramagnetic Nd3+ ones, with a content not exceeding 0.01 and possessing a screened 4f-shell, revealed a significant effect of orbital diamagnetism and Van Vleck's paramagnetism, n-type electrical conductivity with an activation energy of 0.7 eV in the intrinsic area, a strong increase of the power factor above room temperature for a crystal with x = 0.005, constant dielectric value (~30) and loss tangent (~0.01) up to room temperature. The Fermi energy (~0.04 eV) and the Fermi temperature (~500 K) determined from the diffusion component of thermopower showed shallow donor levels. [ABSTRACT FROM AUTHOR]

The formation of coamorphous mixtures of pharmaceuticals is an interesting strategy to improve the solubility and bioavailability of drugs, while at the same time enhancing the kinetic stability of the resulting binary glass and allowing the simultaneous administration of two active principles. In this contribution, we describe kinetically stable amorphous binary mixtures of two commercial active pharmaceutical ingredients, diazepam and nordazepam, of which the latter, besides being administered as a drug on its own, is also the main active metabolite of the other in the human body. We report the eutectic equilibrium-phase diagram of the binary mixture, which is found to be characterized by an experimental eutectic composition of 0.18 molar fraction of nordazepam, with a eutectic melting point of Te = 395.4 ± 1.2 K. The two compounds are barely miscible in the crystalline phase. The mechanically obtained mixtures were melted and supercooled to study the glass-transition and molecular-relaxation dynamics of amorphous mixtures at the corresponding concentration. The glass-transition temperature was always higher than room temperature and varied linearly with composition. The Te was lower than the onset of thermal decomposition of either compound (pure nordazepam decomposes upon melting and pure diazepam well above its melting point), thus implying that the eutectic liquid and glass can be obtained without any degradation of the drugs. The eutectic glass was kinetically stable against crystallization for at least a few months. The relaxation processes of the amorphous mixtures were studied by dielectric spectroscopy, which provided evidence for a single structural (α) relaxation, a single Johari–Goldstein (β) relaxation, and a ring-inversion conformational relaxation of the diazepinic ring, occurring on the same timescale in both drugs. We further characterized both the binary mixtures and pure compounds by FTIR spectroscopy and first-principles density functional theory (DFT) simulations to analyze intermolecular interactions. The DFT calculations confirm the presence of strong attractive forces within the heteromolecular dimer, leading to large dimer interaction energies of the order of −0.1 eV. [ABSTRACT FROM AUTHOR]

This work aims to provide a detailed understanding of the challenges related to the computation of the relative static permittivity and electrolytic conductivity of a sample medium from its impedance response recorded with interdigitated electrode (IDE) geometries. Within the scope of the study, impedance data has been measured and evaluated for a total of nine sample media using two distinct IDE geometries. Particular emphasis is laid upon the compensation of parasitic influences affecting the impedance response. With the raw data supporting this study fully disclosed, the reader is offered the opportunity to comprehensively retrace the evaluation procedure proposed in the text. [ABSTRACT FROM AUTHOR]

Ca 1-3x-y Mn y [] x Nd 2x (MoO 4) 1-3x (WO 4) 3x molybdato-tungstates (▯ denotes vacant sites) were successfully synthesized by high-temperature solid-state reaction. New materials crystallize in scheelite-type structure within whole homogeneity range of solid solution (x ≤ 0.2000 and y = 0.0200). Morphological features and particle size distribution were investigated by SEM and laser diffraction methods, respectively. Spectroscopic measurements in the UV–vis range was carried out to determine optical direct band gap (E g), Urbach energy (E U) and confirmation of structural disorder. Refractive index (n) was calculated using four different models. Magnetic studies revealed paramagnetic behavior with long-range ferrimagnetic and short-range antiferromagnetic interactions. New materials showed weak n -type electrical conductivity and thermoelectric power factor (S2σ) that strongly depends on Nd3+ ions content. Dielectric parameters, i.e. relative permittivity (ε r) and energy loss (tanδ) are insignificantly dependent on Nd3+ ions concentration. These effects were considered in terms of structural defects, thermal activation of charge carriers, and the Maxwell–Wagner polarization. [ABSTRACT FROM AUTHOR]

A new series of hydrogen-bonded liquid crystals was prepared by mixing 4-n-alkoxy-2.3-difluorobenzoic acid and 4-pentyl-4-biphenylcarbonitrile (5CB). Thermal and liquid crystal behaviour was established using differential scanning calorimetry and polarizing optical microscopy. The influence of terminal acid donors on mesogenic behaviour was discussed in detail. It was found that all complexes with a (1:1) molar ratio exhibit the smectic B phase. In addition, the binary phase diagram that has been established revealed that the mixtures with lower concentration exhibit a nematic phase at room temperature with large stability. Dielectric, electro-optic and viscoelastic properties of 5CB/9OBAFF with molar fraction x = 0.1 were discussed. [ABSTRACT FROM AUTHOR]

The search for non-invasive, fast, and low-cost diagnostic tools has gained significant traction among many researchers worldwide. Dielectric properties calculated from microwave signals offer unique insights into biological tissue. Material properties, such as relative permittivity ( ε r ) and conductivity (σ), can vary significantly between healthy and unhealthy tissue types at a given frequency. Understanding this difference in properties is key for identifying the disease state. The frequency-dependent nature of the dielectric measurements results in large datasets, which can be postprocessed using artificial intelligence (AI) methods. In this work, the dielectric properties of liver tissues in three mouse models of liver disease are characterized using dielectric spectroscopy. The measurements are grouped into four categories based on the diets or disease state of the mice, i.e., healthy mice, mice with non-alcoholic steatohepatitis (NASH) induced by choline-deficient high-fat diet, mice with NASH induced by western diet, and mice with liver fibrosis. Multi-class classification machine learning (ML) models are then explored to differentiate the liver tissue groups based on dielectric measurements. The results show that the support vector machine (SVM) model was able to differentiate the tissue groups with an accuracy up to 90%. This technology pipeline, thus, shows great potential for developing the next generation non-invasive diagnostic tools. [ABSTRACT FROM AUTHOR]

BACKGROUND: The rapid and accurate identification of colostrum, a strong non‐homogeneous food, remains a challenge. In the present study, the dielectric spectra including the dielectric constant (ε′) and loss factor (ε″) of 154 colostrum samples adulterated with 0–50% mature milk were measured from 20 to 4500 MHz. RESULTS: The results showed that the noise‐reducing spectral preprocessing, including Savitzky–Golay (S‐G), second derivative (SD), and S‐G + SD, was significantly better than scattering‐eliminating, including standard normal variate (SNV), multiplicative scatter correction (MSC), and SNV + MSC. The combination of S‐G and SD was the best. Principal component analysis results demonstrated that dielectric spectroscopy is less susceptible to the inhomogeneity of colostrum and can be used to identify doped colostrum. The identification performance of linear models was better than that of non‐linear models. The established linear discriminant analysis model based on full spectra had the best accuracy rates of 99.14% and 97.37% in the calibration and validation sets, respectively. Confirmatory tests on samples from different sources confirmed the satisfactory robustness of the proposed model. CONCLUSION: We found that the main unfavorable effect on the identification based on dielectric spectroscopy was noise interference, rather than scattering effect caused by inhomogeneity of colostrum. The satisfactory results undoubtedly cast light on rapid detection of strongly non‐homogeneous foods based on dielectric spectroscopy. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Magnetic nanostructures of CoFe2O4 were synthesized via a microwave-assisted hydrothermal route. The prepared nanostructures were investigated using X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), selective area electron diffraction (SAED) pattern, DC magnetization, and dielectric spectroscopy measurements. The crystal structure studied using HR-TEM, SAED, and XRD patterns revealed that the synthesized nanostructures had a single-phase nature and ruled out the possibility of any secondary phase. The lattice parameters and unit cell volume determined from the XRD data were found to be 8.4821 Å and 583.88 Å3. The average crystallite size (~7.0 nm) was determined using Scherrer's equation. The FE-SEM and TEM micrographs revealed that the prepared nanostructures had a spherical shape morphology. The EDX results showed that the major elements present in the samples were Co, Fe, and O. The magnetization (M) versus temperature (T) measurements specified that the CoFe2O4 nanostructures showed ferromagnetic ordering at room temperature. The blocking temperature (TB) determined using the M-T curve was found to be 315 K. The magnetic hysteresis (M-H) loop of the CoFe2O4 nanostructures recorded at different temperatures showed the ferromagnetic behavior of the CoFe2O4 nanostructures at temperatures of 200 K and 300 K, and a superparamagnetic behavior at 350 K. The dielectric spectroscopy studies revealed a dielectric constant (ε′) and loss tangent (tanδ) decrease with the increase in the frequency, as well as demonstrating a normal dispersion behavior, which is due to the Maxwell–Wagner type of interfacial polarization. The values of ε′ and tanδ were observed to increase with the increase in the temperature. [ABSTRACT FROM AUTHOR]

The freshness of anchovies (Engraulis Encrasicolus) was estimated by radio-frequency and optical techniques in order to propose non-destructive and objective methods for rapid screening. Measurements were conducted until 7 days at 0 °C, storing the fish under ice. Image analysis, dielectric spectroscopy and hyperspectral images were conducted on fish eyes whilst mechanical properties were measured on the fish body. Evaluation of images by RGB scale highlighted differences due to ageing. Maximum force decreased as a function of degradation process time. Cluster analysis on dielectric spectra and 3D-principal component analysis on hyperspectral images of fish eyes revealed a good ability to characterise ageing modification demonstrating suitable methods for the development of a non-destructive, and rapid system for evaluation of fish freshness. [Display omitted] • Anchovies freshness was measured by dielectric spectroscopy & hyperspectral imaging. • Dehydration of anchovy eyes was exploited for ageing estimation. • Multivariate approaches allowed to group the samples according to storage days. • Both techniques are rapid and contactless being promising for practical application. [ABSTRACT FROM AUTHOR]

Hydrogen-bonded liquid crystals (HBLC) formed by mixing 4-alcyloxy-2-fluorobenzoic acid (nOBAF) and the 4-pentyl-4-biphenylcarbonitrile (5CB) at (1:1), (1:3) and (3:1) (mol/mol) ratios have been investigated. Four HBLC series are prepared by changing the carbon chain length from 7 to 10 designated 5CB/nOBAF. The fluorobenzoic acids (nOBAF) are the proton donors while the pyridine unit (5CB) is the proton acceptors. Thermal behaviour and phase diagrams of the individual series have been established using differential scanning Calorimetry (DSC) and polarising optical microscopy (POM). It was found that all complexes exhibit nematic (N) and smectic G (SmG) phases. For the nematic phase, the dielectric anisotropy was increased while the thresholds voltage was decreased. This can be explained by the strong longitudinal dipole moment of the nematic phase compared to the nOBAF compounds. Furthermore, as the alkoxy chain length increases, the birefringence, response time, rotational viscosity, and splay elastic constant all decrease by the way of the reduction of the order parameter for the longer chains. In addition, hydrogen-bonded proton transfer between cyano and carboxylic acid groups have been explored by Fourier transform infrared spectroscopy (FTIR) for the first time. [ABSTRACT FROM AUTHOR]

In this paper, new results on the degradation of losartan potassium (LP, (1)), in the absence and presence of excipients, which was induced by UV light, the acid character of phosphate buffer solution (PBS) and alkaline medium, respectively, are reported through correlated studies of FTIR spectroscopy, photoluminescence and dielectric spectroscopy. The photoluminescence (PL) spectra of LP and the drug marked under the name Lorista (LO) are characterized by intense emission bands, peaking at 378 nm and 380 nm, respectively, accompanied by low intensity bands with a maximum at ~450–460 nm. Photodegradation of LO in a solid state is evidenced by a decrease in the intensity of the PL band at 380 nm, a variation that originates both in the adsorption of water vapors from the air and in the interaction of LP with excipients such as cornstarch, silicon dioxide and cellulose. The LP-water interaction is described, taking into account the main electrical parameters, i.e., complex dielectric permittivity and electrical conductivity. Photodegradation of LP and LO also induces an increase in the intensity of the emission band, at ~450–460 nm. The influence of acid and alkaline medium on the LO degradation is analyzed using phosphate buffer (PBS) and NaOH solutions, respectively. In both cases, a decrease in the intensity of the PL band, at 380 nm, is reported. The intensity diminution of the PL spectra of NaOH-reacted LP and LO is the result of the formation of the photodegradation product N-methanolamide-{[2′-(1H-tetrazol-5-yl)(1,1′-biphenyl)-4-yl]methyl} (2). This compound was proven by the studies of FTIR spectroscopy achieved on LP and NaOH-reacted LP. The appearance of the IR band at 1740 cm−1 and the increase in the absorbance in the IR band at 1423 cm−1 indicate that the photodegradation product (2) contains the C=O and C-OH functional groups. [ABSTRACT FROM AUTHOR]

Electrical measurements were carried out on nanocrystals Yb2-xVxO3+x (YbVO) (where x=0.10, 0.15, 0.20, 0.30, and 0.40) obtained in the high-energy ball milling process, which crystallite size increased from 23.3 to 42.4 nm with increasing vanadium content. Electrical conductivity and thermoelectric power studies showed insulating properties in the extrinsic region (77-300 K) and n-type semiconductivity in the intrinsic one (350-400 K) with an activation energy of 1.3 eV. Broadband dielectric spectroscopy studies showed a low relative dielectric permittivity (εr<16) and loss tangent (tan(δ)<0.05) weakly dependent on temperature and frequency with the exception of a wide maximum between 200 and 300 K, suggesting an antiferroelectric-paraelectric phase transition. The most interesting result is the observation of a strong increase in the thermoelectric power factor with an increase in unit cell volume and nanograin size in a highly thermally activated Arrhenius region. [ABSTRACT FROM AUTHOR]

The structure–property relationship of dielectric elastomers, as well as the methods of improving the control of this relationship, has been widely studied over the last few years, including in some of our previous works. In this paper, we study the control, improvement, and correlation, for a significant range of temperatures, of the mechanical and dielectric properties of polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) and maleic-anhydride-grafted SEBS (SEBS-MA) by using graphite (G) as filler in various concentrations. The aim is to analyze the suitability of these composites for converting electrical energy into mechanical energy or vice versa. The dielectric spectroscopy analysis performed in the frequency range of 10 to 1 MHz and at temperatures between 27 and 77 °C emphasized an exponential increase in real permittivity with G concentration, a low level of dielectric losses (≈10−3), as well as the stability of dielectric losses with temperature for high G content. These results correlate well with the increase in mechanical stiffness with an increase in G content for both SEBS/G and SEBS-MA/G composites. The activation energies for the dielectric relaxation processes detected in SEBS/G and SEBS-MA/G composites were also determined and discussed in connection with the mechanical, thermal, and structural properties resulting from thermogravimetric analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. [ABSTRACT FROM AUTHOR]

The nonhomogeneity of bovine colostrum leads to strong scattering effects for electromagnetic waves, which affects the application of electromagnetic spectroscopy in detecting colostrum. This work aimed to compare the performance of near-infrared spectroscopy (NIRS) and dielectric spectroscopy (DS) in quantitatively predicting the content of mature milk as an adulterant in colostrum. The near-infrared spectra in the range of 833 to 2,500 nm and the dielectric spectra in the range of 20 to 4,500 MHz of 150 adulterated colostrum samples containing 0 to 50% mature milk were analyzed. The different proportions of mature milk in colostrum significantly changed near-infrared and dielectric spectra. The principal component analysis score plot showed that both NIRS and DS could identify the proportion of mature milk in colostrum, but the 2 methods had different characteristics. Linear partial least squares regression and nonlinear least squares support vector machine (LSSVM) models based on near-infrared and dielectric spectra were established to identify doping proportions. The results showed that DS had better identification performance with a root-mean-square error of prediction of 4.9% and a residual prediction deviation of 3.441 by successive projection algorithm LSSVM, whereas NIRS was relatively weak with a root-mean-square error of prediction of 7.3% and a residual prediction deviation of 2.301 by full-spectra LSSVM. This work provides important insights for the quantitative prediction of nonhomogeneous liquid food by DS. [Display omitted] [ABSTRACT FROM AUTHOR]

Both the polyester resin matrix-based polymer ZnO nano composites and pure polyester sheet were synthesised using the solution casting method. The crystalline structure of the nano-particles was examined inside using X-ray diffraction (XRD). The fundamental polymer composition, additives, organic contaminants, and purity were all assessed by FTIR. A minor alteration in the absorption bands was seen in the polyester system with ZnO added. The thermal properties were examined using differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA), and the results unmistakably demonstrated the creation of a highly cross-linked polyester molecular structure or improved free volume fractions in polymer nano composites. A mechanical analyzer’s tensile and flexural strength tests revealed the potential for nanoparticle aggregation due to a strong interaction with resin. To calculate the relative permittivity and the loss of tangents (tan), dielectric studies had been used. Analysis of the hydrophobic properties of the pure and ZnO polyester nano composite. [ABSTRACT FROM AUTHOR]

Ferrites are usually used in accelerators for tuning radiofrequency (RF) cavities and in nonreciprocal devices controlling the power flow in RF accelerating systems. The conventional parallel-biased Ni Zn ferrites employed for varying the frequency of accelerating cavities have the disadvantage of high saturation magnetization (4pMs). Application of the transversely biased yttrium iron garnet (YIG) material in RF tuners promises a significant reduction of power loss compared with systems that use the longitudinal bias. To inject the beam and extract the beam out of the CERN accelerator rings the fast kicker magnets made from ferrite materials must be used. Power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. Investigation of the ferrite electromagnetic properties of materials up to the GHz frequency range is essential for a correct impedance evaluation. This report summarizes an approach for deriving electromagnetic properties as a function of both frequency and temperature of the AL-800 garnet material. This information will be useful for simulating ferrite behaviour under realistic operating conditions. [ABSTRACT FROM AUTHOR]

A defining property of ferroelectricity is the switching between different states by the application of an electric field. Hysteresis loops serve like a fingerprint of ferroelectric materials giving some useful information. Sometimes the interpretation of information extracted from hysteresis measurements can be challenging due to the non-ferroelectric factors such as electrical conductivity, defect dipole presence and/or dielectric properties. In this paper, the ferroelectric and non-ferroelectric factors on P-E hysteresis loops were investigated in a CuInP2S6-type single crystal. The analysis of data obtained for this single crystal allowed extracting the reliable values in the materials with a low polarization and a high conductivity. [ABSTRACT FROM AUTHOR]

In this paper, we present the dielectric and piezoelectric properties of tetragonal 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with NaNbO3 ((1-x)[0.8Na0.5Bi0.5TiO3-0.2BaTiO3]-xNaNbO3). Our experimental study has revealed that the ferroelectric phase in these compositions is suppressed with the increase of sodium niobate concentration. A broad anomaly, resembling relaxor ferroelectrics, appears in the 325-450 K temperature interval. The investigation of the electric field dependence of polarization has indicated that the double hysteresis loop behaviour is characteristic of the modified compositions, which is associated with the 1st order phase transition under the applied electric field. The experiments below room temperature have revealed that the range of stability of the ferroelectric phase is shifted to lower temperatures upon the increase of sodium niobate concentration. The electromechanical displacement in the modified compositions shows a similar maximum displacement in the whole concentration range. The electromechanical response in 0.8Na0.5B0.5TiO3-0.2BaTiO3 solid solutions is due to the piezoelectric effect, while, in the mixed compositions, it is related to the jump-like change of the lattice constants in the vicinity of electric fieldinduced 1st order phase transition. [ABSTRACT FROM AUTHOR]