Dynamic Dielectric Properties Research Articles

Critical Model Insight into Broadband Dielectric Properties of Neopentyl Glycol (NPG).

This report presents the low-frequency (LF), static, and dynamic dielectric properties of neopentyl glycol (NPG), an orientationally disordered crystal (ODIC)-forming material important for the barocaloric effect applications. High-resolution tests were carried out for 173K<T<440K, in liquid, ODIC, and solid crystal phases. The support of the innovative distortion-sensitive analysis revealed a set of novel characterizations important for NPG and any ODIC-forming material. First, the dielectric constant in the liquid and ODIC phase follows the Mossotti Catastrophe-like pattern, linked to the Clausius-Mossotti local field. It challenges the heuristic paradigm forbidding such behavior for dipolar liquid dielectrics. For DC electric conductivity, the prevalence of the 'critical and activated' scaling relation is evidenced. It indicates that commonly applied VFT scaling might have only an effective parameterization meaning. The discussion of dielectric behavior in the low-frequency (LF) domain is worth stressing. It is significant for applications but hardly discussed due to the cognitive gap, making an analysis puzzling. For the contribution to the real part of dielectric permittivity in the LF domain, associated with translational processes, exponential changes in the liquid phase and hyperbolic changes in the ODIC phase are evidenced. The novelty also constitutes tgδ temperature dependence, related to energy dissipation. The results presented also reveal the strong postfreezing/pre-melting-type effects on the solid crystal side of the strongly discontinuous ODIC-solid crystal transition. So far, such a phenomenon has been observed only for the liquid-solid crystal melting transition. The discussion of a possible universal picture of the behavior in the liquid phase of liquid crystalline materials and in the liquid and ODIC phases of NPG is particularly worth stressing.

The Dominance of Pretransitional Effects in Liquid Crystal-Based Nanocolloids: Nematogenic 4-methoxybenzylidene-4'-butylaniline with Transverse Permanent Dipole Moment and BaTiO3 Nanoparticles.

The report presents static, low-frequency, and dynamic dielectric properties in the isotropic liquid, nematic, and solid phases of MBBA and related nanocolloids with paraelectric BaTiO3 nanoparticles (spherical, d = 50 nm). MBBA (4-methoxybenzylidene-4'-butylaniline) is a liquid crystalline compound with a permanent dipole moment transverse to the long molecular axis. The distortions-sensitive analysis of the dielectric constant revealed its hidden pretransitional anomaly, strongly influenced by the addition of nanoparticles. The evolution of the dielectric constant in the nematic phase shows the split into two regions, with the crossover coinciding with the standard melting temperature. The 'universal' exponential-type behavior of the low-frequency contribution to the real part of the dielectric permittivity is found. The critical-like pretransitional behavior in the solid phase is also evidenced. This is explained by linking the Lipovsky model to the Mossotti catastrophe concept under quasi-negative pressure conditions. The explicit preference for the 'critical-like' evolution of the apparent activation enthalpy is worth stressing for dynamics. Finally, the long-range, 'critical-like' behavior of the dissipation factor (D = tgδ), covering the isotropic liquid and nematic phases, is shown.

Solid state solvation: a fresh view.

The design of efficient organic electronic devices, including OLEDs, OPVs, luminescent solar concentrators, etc., relies on the optimization of relevant materials, often constituted by an active (functional) dye embedded in a matrix. Understanding solid state solvation (SSS), i.e. how the properties of the active dye are affected by the matrix, is therefore an issue of fundamental and technological relevance. Here an extensive experimental and theoretical investigation is presented shedding light on this, somewhat controversial, topic. The spectral properties of the dye at equilibrium, i.e. absorption and Raman spectra, are not affected by the matrix dynamics. Reliable estimates of the matrix polarity are then obtained from an analysis of the micro-Raman spectra of polar dyes. Specifically, to establish a reliable polarity scale, the spectra of DCM or NR dispersed in amorphous matrices are compared with the spectra of the same dyes in liquid solvents with known polarity. On the other hand, steady-state emission spectra obtained in solid matrices depend in a highly non-trivial way on the matrix polarity and its dynamics. An extensive experimental and theoretical analysis of the time-resolved emission spectra of NR in a very large time window (15 fs-15 ns) allows us to validate this dye as a good probe of the dielectric dynamics of the surrounding medium. We provide a first assessment of the relaxation dynamics of two matrices (mCBPCN and DPEPO) of interest for OLED application, unambiguously demonstrating that the matrix readjusts for at least 15 ns after the dye photoexcitation.

The effect of ZnO particle size on the dynamic mechanical, thermal, and dielectric properties of ZnO varistor-Epoxy composites

The effect of ZnO particle size on the dynamic mechanical, thermal, and dielectric properties of ZnO varistor-Epoxy composites

Research on triazine reaction, heat resistant and dielectric properties of cyanate ester resin catalyzed by bisphenol AF

Cyanate ester (CE) resins possess a wide variety of attractive features that make them suitable for both electronic and aerospace composite applications. However, high curing temperature and long curing time limit the application range of CE resins. In this study, curing reaction, heat resistant and dielectric properties of bisphenol A-based cyanate ester (BACY) resin catalyzed by bisphenol AF (BPAF) were investigated by means of differential scanning calorimetry, Fourier transform infrared, dynamic mechanical analyser and dielectric properties analyser. The incorporation of the BPAF decreased the curing temperature and showed a strong catalytic effect in cyclotrimerization reaction of BACY. BACY resin catalyzed by 4 phr BPAF at 180 °C post-cured for 5 h presented high curing degree of 92.8% and glass transition temperature of 247.4 °C. Moreover, BACY resin catalyzed by 4 phr BPAF at 180 °C post-cured for 5 h exhibited excellent dielectric properties (ε and tan δ equal to 2.87 and 0.0084) comparable to commercial modified cyanate ester resin post-cured at 200 °C for 10 h. These results suggest that catalyst BPAF possesses promising potential application in meeting low-temperature short-term curing of high-performance cyanate ester resin based wave-transparent composites.

Microwave absorption performance of M-type hexagonal ferrite and MXene composite in Ka and V bands (5G mmWave frequency bands)

Lightweight and thin electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) have been investigated over the last decade to address the unreliability issue in all electronic technologies caused by EMI. Herein, we report the SE of the novel Ti3C2Tx MXene/doped-hexaferrite (hexagonal ferrite: BaCo0.3Ti0.3Fe11.4O19) composite. This composite suppresses electromagnetic (EM) waves dominantly via absorption over the frequency range from 30 to 50 GHz for millimeter-wave (mmWave) applications. Two-dimensional inorganic compound Ti3C2Tx MXene was synthesized using the LiF-HCl etching process, and doped-hexaferrite particles were prepared using a conventional solid-state reaction. Then, the MXene/doped-hexaferrite composite was fabricated by mixing MXene/polyvinyl-pyrrolidone (PVP) containing solution with the hexaferrite particles. The composites were characterized by a vibrating sample magnetometer for static magnetic properties and a vector network analyzer for dynamic magnetic and dielectric properties and microwave absorbing performance.A high magnetocrystalline anisotropy of hexaferrite shifted the microwave absorption peak to mmWave bands such as Ka- and V-bands, unlike spinel ferrite. The 1.5 mm thick MXene/45 wt% doped-hexaferrite composite shows a broad effective bandwidth (reflection loss (RL) less than 10 dB) of 7 GHz in the frequency range from 38 to 45 GHz. This excellent absorbing performance is mainly attributed to improved impedance matching and enhanced dielectric and magnetic losses of the composite. It was found that the SE was dominated by absorption instead of reflection.The experimental results demonstrate that the MXene/BaCo0.3Ti0.3Fe11.4O19 hexaferrite composite can be a promising and effective EM wave absorber material for millimeter-wave applications such as the fifth-generation (5G) network and opens up new opportunities for THz (6G network) EMI materials development.

Dynamic dielectric properties of an antiferroelectric/ferroelectric mixed-spin (5/2, 3/2) Ising system under a time-dependent oscillating electric field

A mixed-spin (5/2, 3/2) Ising model was proposed to investigate the antiferroelectric/ferroelectric (AFE/FE) bilayer under a time-dependent oscillating electric field. Based on Monte Carlo simulation, the effects of exchange interaction, anisotropy, and external electric field on the electric properties of the system, including dynamic order parameter, electrical susceptibility, internal energy were studied in detail. We found the phenomenon of multi-saturation values of the dynamic order parameter. We plotted the phase diagrams of the critical temperature of the system under the influence of different parameters as well. Moreover, the hysteresis behavior of the system was studied and the rich multi-loop electric hysteresis behavior was found.

Dynamic dielectric properties of isotactic polypropylene-g-maleic anhydride crosslinked by capped-end polyether diamine and filled with native or functionalized nano-graphite particles

Dynamic dielectric properties of an isotactic polypropylene matrix grafted with maleic anhydride (CA 100) and then crosslinked by polyether amine molecules and reinforced with different weight percentages of graphite nanoplatelets (GNPs), KNG180, were studied for the first time and compared to those obtained by DMA (Dynamic Mechanical Analysis). The main objective of this work was to investigate the reinforcement effect of GNPs focusing on the GNPs/matrix interfacial adhesion using dynamic dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 1 MHz and temperature range from 20 to 140 °C. The obtained interfacial polarization increments \({\Delta \varepsilon }_{\mathrm{MWS}}\) from MWS (Maxwell Wagners Sillars) relaxation showed a threshold value of 3% in weight of KNG180. This analysis suggests that interfacial compatibility between matrix and fillers in the case of nanocomposite KNG180 3 wt% is higher than those of other nanocomposites. A new plasma treatment was used to modify graphite nano-fillers to produce different types of nanocomposites. The 5 wt% plasma treated graphite nanocomposite shows a good dispersion of the nano-fillers but also a high value of \({\Delta \varepsilon }_{\mathrm{MWS}}\), which is an indication of high graphite/graphite interaction. This evolution could show that this material can be close to the formation of an electrical percolation network.

Sintering behavior, structure, and microwave properties of novel Li2xCu1-xMoO4 ceramics

In this study, we prepared a novel series of Li2xCu1-xMoO4 (x = 0.02, 0.04, 0.06, 0.08, and 0.10) microwave ceramics. The dynamic sintering behavior, crystal phases, micro-morphologies, and dielectric properties of the samples were studied. The substitution of Li+ contributed to refining the crystal grain size, promoting the densification of microstructure, and enhancing the quality factor. Due to different valence substitutions, Cu+ ions were created, which were verified by X-ray photoelectron spectroscopy (XPS) and Raman experiments. In addition, the Raman shift, full width at half maximum (FWHM) value of the A1g peak, and crystal microstrains were analyzed to gain a mechanistic understanding of the influence of structure on the dielectric properties. When x = 0.08, the Li2xCu1-xMoO4 ceramic sintered at 675 °C exhibited optimal comprehensive properties with εr = 8.17, Qf = 68 476 GHz, and τf = −25 ppm/°C, and good chemical stability between the ceramic and Al electrode was also achieved. These promising properties make Li2xCu1-xMoO4 (x = 0.08) more suitable for ultra-low temperature co-fired ceramic (ULTCC) applications.

Enhancement of the Dynamic Mechanical and Dielectric Properties of Prosopis juliflora Fiber-Reinforced Composites by Fiber Modification

ABSTRACT The utilization of the plant-based fiber-reinforced composites is being increased in recent days. The plant-based fiber used in the present study was extracted from the Prosopis juliflora plant. Alkali treatment effects of the fiber-reinforced composites on the static and dynamic mechanical and dielectric properties were investigated and compared with the untreated fiber-reinforced composites in the current work. Tests like static and dynamic mechanical, dielectrical, scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were carried out on both treated and untreated composite specimens. The temperature was varied from 25°C to a maximum temperature of 180°C to investigate the dynamic mechanical properties at a constant frequency of 2 Hz. Dielectric properties were also analyzed using impedance analyzer and compared the results of both treated and untreated composites. Characterization techniques like SEM, TGA, and XRD were carried out on both the treated and untreated composite specimens to probe the bonding and crystallinity among the composites. The results of SEM and XRD showed that the bonding and crystallinity improved with the fiber treatment such that the thermal stability also improved. The improved properties of the composite samples extend the applications in the field of automotive, packaging, construction, etc.

Low Power Contactless Bioimpedance Sensor for Monitoring Breathing Activity.

An electronic circuit for contactless detection of impedance changes in a tissue is presented. It operates on the principle of resonant frequency change of the resonator having the observed tissue as a dielectric. The operating frequency reflects the tissue dielectric properties (i.e., the tissue composition and on the tissue physiological changes). The sensor operation was tested within a medical application by measuring the breathing of a patient, which was an easy detectable physiological process. The advantage over conventional contact bioimpedance measurement methods is that no direct contact between the resonator and the body is required. Furthermore, the sensor’s wide operating range, ability to adapt to a broad range of measured materials, fast response, low power consumption, and small outline dimensions enables applications not only in the medical sector, but also in other domains. This can be extended, for example, to food industry or production maintenance, where the observed phenomena are reflected in dynamic dielectric properties of the observed object or material.

Dynamic Mechanical and Dielectric Properties of Fly Ash/(Polystyrene/Low-Density Polyethylene) Composites

Abstract By using the melt mixing method, polystyrene (PS), low-density polyethylene (LDPE), and a PS/LDPE blend have been prepared. Fly ash was used as filler embedded in the PS/LDPE blend to form composites. The dynamic mechanical analysis (DMA) showed that the storage modulus (E′) decreases as the temperature increases. E′ increases clearly with fly ash loading, and the maximum E′ value was found for the composite loaded with 30 % fly ash content. The mean-field theory developed by Kerner was used to predict the dynamic mechanical properties of the composites from their pure components. A good agreement was investigated between the deduced theoretical values via iteration method and the experimental results. The dielectric constant (ε′), dielectric loss, and dielectric loss tangent (tan δ) have been measured at different constant frequencies. The ε′ and tan δ commence to decrease by increasing the applied frequency.

Nonrotational Mechanism of Polarization in Alcohols.

Chemical polarity governs various mechanical, chemical, and thermodynamic properties of dielectrics. Polar liquids have been amply studied, yet the basic mechanisms underpinning their dielectric properties remain not fully understood, as standard models following Debye's phenomenological approach do not account for quantum effects and cannot aptly reproduce the full dc-up-to-THz spectral range. Here, using the illustrative case of monohydric alcohols, we show that deep tunneling and the consequent intermolecular separation of excess protons and "proton-holes" in the polar liquids govern their static and dynamic dielectric properties on the same footing. We performed systematic ultrabroadband (0-10 THz) spectroscopy experiments with monohydric alcohols of different (0.4-1.6 nm) molecular lengths and show that the finite lifetime of molecular species and the proton-hole correlation length are the two principle parameters responsible for the dielectric response of all the studied alcohols across the entire frequency range. Our results demonstrate that a quantum nonrotational intermolecular mechanism drives the polarization in alcohols while the rotational mechanism of molecular polarization plays a secondary role, manifesting itself in the sub-terahertz region only.

Effect of electrode on dielectric susceptibility and pyroelectric properties of a ferroelectric thin film capacitor using landau-khalatnikov theory

The influence of electrodes on the dielectric susceptibility and pyroelectric properties of a ferroelectric thin film with surface transition layers has been investigated within the framework of Landau-Khalatnikov dynamic theory. The contribution of the electrodes is reflected by the depolarization field in the free-energy function. The large electrode effect implies the strong depolarization field in ferroelectric thin films. The results show that the electrode materials can greatly impact the dynamic dielectric and pyroelectric properties of a ferroelectric thin film.

Dynamic dielectric properties characterization of tapered dielectrophoresis microelectrodes for selective detection and rapid manipulation of cells

PurposeThis paper aims to present the dielectrophoresis (DEP) force (FDEP), defined as microelectrofluidics mechanism capabilities in performing selective detection and rapid manipulation of blood components such as red blood cells (RBC) and platelets. The purpose of this investigation is to understand FDEP correlation to the variation of dynamic dielectric properties of cells under an applied voltage bias.Design/methodology/approachIn this paper, tapered design DEP microelectrodes are used and explained. To perform the characterization and optimization by analysing the DEP polarization factor, the change in dynamic dielectric properties of blood components are observed according to the crossover frequency (fxo) and adjustment frequency (fadj) variation for selective detection and rapid manipulation.FindingsExperimental observation of dynamic dielectric properties change shows clear correlation to DEP polarization factor when performing selective detection and rapid manipulation. These tapered DEP microelectrodes demonstrate an in situ DEP patterning efficiency more than 95%.Research limitations/implicationsThe capabilities of tapered DEP microelectrode devices are introduced in this paper. However, they are not yet mature in medical research studies for various purposes such as identifying cells and bio-molecules for detection, isolation and manipulation application. This is because of biological property variations that require further DEP characterization and optimization.Practical implicationsThe introduction of microelectrofluidics using DEP microelectrodes operate by selective detecting and rapid manipulating via lateral and vertical forces. This can be implemented on precision health-care development for lab-on-a-chip application in microfluidic diagnostic and prognostic devices.Originality/valueThis study introduces a new concept to understand the dynamic dielectric properties change. This is useful for rapid, label free and precise methods to conduct selective detection and rapid manipulation of mixtures of RBC and platelets. Further, potential applications that can be considered are for protein, toxin, cancer cell and bacteria detections and manipulation. Implementation of tapered DEP microelectrodes can be used based on the understanding of dynamic dielectric properties of polarization factor analysis.

Relaxation dynamics of Ni/epoxy composites studied by dielectric relaxation spectroscopy

Dynamic dielectric properties of nickel (Ni)/epoxy composites are investigated by broadband dielectric spectroscopy over a wide frequency range (approximately 1–107 Hz) and temperature range (approximately −20 to 200°C). Multiple dielectric relaxation processes in the Ni/epoxy composites are identified, corresponding to conductivity, interfacial polarization (IP), and α-relaxation. With increasing temperature, both dielectric permittivity and loss of composites increase, arising from enhanced dipolar mobility; approaching the glass transition temperature ( T g), a clear α-relaxation appears, which can be attributed to the onset of cooperative chain movement. Further increasing temperature activates the long-range movement of space charges, as manifested by an IP superimposed on the ionic conductivity. A transition from insulator (below T g) to semiconductor (above T g) is also observed for the studied composite system.

Comparative Studies on Structure-Property Relationships of the Polyimide Films Derived from the Dianhydride containing Alicyclic cis-Ethylenic Double Bond

An ester dianhydride bearing alicyclic cis-ethylenic double bond, bicyclo [2.2.1]hept-5-ene-2, 3-diylbis(methylene)bis(1, 3-dioxo-1, 3-dihydroisobenzofuran-5-carboxylate) (BHEM) and its hydrogenated analogue bicyclo[2.2.1]heptane-2, 3-diylbis(methylene)bis(1, 3-dioxo-1, 3-dihydroisobenzofuran-5-carboxylate) (BHSM) were synthesized and polymerized with three aromatic diamines, respectively, to prepare two analogous series of polyimide (PI) films. Comparative studies were carried out to elucidate how the unsaturated bicylo[2.2.1]heptenyl structure and the saturated bicyclo[2.2.1]heptyl structure in polymer main chain influence the properties of the PI films. The structural characteristics of the two analogous alicyclic structures including reactivity, bulkiness, configuration, polarity were found to impact the solubility, hydrophobicity, surface morphology, and the thermal, optical and dynamic dielectric properties of PI films. The aggregation state of both series of PI films was analyzed by wide-angle X-ray scattering (WAXD) and computed tomography (CT) fluorescence, which reveals the structural characteristics differences between unsaturated alicyclic containing cis-ethylenic double bond with planar sp2 hybrid configuration and saturated alicyclic with wholly tetrahedral sp3 hybrid configuration. It indicates that the thermally crosslinkable alicyclic cis-ethylenic double bonds in BHEM incline to induce a closer polarized chain packing via inter-chain Π-Π complex, while the wholly tetrahedral sp3 configuration of the bulkier saturated alicyclic in BHSM inhibits the chain aggregation in the PI film and leads to greater chain mobility.

Detection of Neural Activity of Brain Functional Site Based on Microwave Scattering Principle

A method of detecting brain neural activity with the microwave transmission technology is presented in this paper. This method is based on the fact that the dielectric properties of brain functional site vary with the electrophysiological neural activity. The analysis of the uniform plane wave propagation of dynamic layered medium shows that the phase change of transmission coefficient (S-parameters) is consistent with the variation frequency of permittivity in the dynamic dielectric layer. A 3D head model was introduced to assign dynamic dielectric properties to the cerebral cortex by embedding a tissue piece in this head model. A six-element horn antenna array around the head model was designed, and two types of brain activity at various locations (visual cortex and auditory cortex) inside the head model has been discussed. The simulation results of microwave scattering in different directions show that forward scattering has better applicability. The frequency of the permittivity variation associated with the brain neuronal activity (10 Hz, 20 Hz) can be extracted from the phase variation on S-parameters. In addition, the specific absorption rate analysis ensures the safety of using the microwave in the design of human head detection systems.

Structural, magnetic, dielectric and high frequency response of synthesized rare earth doped bismuth nano garnets (BIG)

Abstract Rare earth doped bismuth (Bi) iron garnets (BIG) having composition Bi3−xRxFe5O12 for x = 1.5 (here R stands for rare earth elements like Y, Gd, Pr, Ho and Yb) have been studied in this work. The samples were prepared using sol-gel method. X-Ray diffraction (XRD), Scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR), Vibrating sample magnetometer (VSM) and Vector network analyzer (VNA) were employed on the samples to evaluate the properties of the doped Bi nanogarnets. Single-phase garnet structure was confirmed through XRD and the crystallite sizes were found to be 66–73 nm, depending upon the type of rare earth ions. SEM images helped to observe the morphology and measurement of grain size of the doped Bi nanogarnets. Vibrational bands showed the presence of garnet phase and were confirmed through FTIR analysis. Detailed dynamic magnetic and dielectric properties were measured using VNA from 1 to 6 GHz. Real and imaginary part of the permittivity, permeability, dielectric and magnetic losses, ac conductivity, electric modulus and Q factor were calculated for the rare earth doped Bi nanoferrites. Gd doped Bi nanoferrites showed higher permittivity values whereas Pr doped show higher ac conductivity as compared to other samples. Yb doped Bi nanoferrites have Q factor values at 4.8 GHz. Static magnetic properties of the doped Bi nanogarnets were investigated using magnetic loops. Magnetic remanence (Mr) Saturation magnetization (Ms) and coercivity (Hc), Bohr magneton, anisotropy constant and initial permeability were also calculated. The dielectric and magnetic studies of the rare earth doped Bi nanogarnets suggested the applications of these rare earths doped nanogarnets for microwave devices and high frequency applications in GHz regime.

Dynamic dielectric properties of the ferroelectric ceramic Pb(Zr0.95Ti0.05)O3 in shock compression under high electrical fields

Shock-induced depolarization of the ferroelectrics could generate a depoling current, which has been utilized widely in the energy conversion devices, such as explosive-driven ferroelectric generators and high pulsed power sources. Among all these ferroelectrics, the lead zirconate/titanate ferroelectric ceramic received most of the attention due to their high energy density and low depolarization pressure, especially Pb(Zr0.95Ti0.05)O3 (PZT 95/5). The dynamic permittivity of PZT 95/5 under the shock compression is critical for their applications, which determines the efficiency of the energy conversion. However, to reveal the dynamic permittivity of the ferroelectrics is challenging, the depolarization process during the shock compression is not only short (∼μs) but also coupled with a high electrical field. In this study, the dynamic permittivity of the PZT 95/5 ceramic in shock compression under high electrical fields has been investigated by using a designed oscillation circuit. The experimental results show that the relative permittivity of PZT 95/5 is about 500 at the initial shock compression, and it is only about 220 after shock transit. This decrease would be explained by the PZT 95/5 phase transition under high pressure. In addition, it is found that the permittivity of poled PZT 95/5 is more sensitive to the electrical field than depoled PZT 95/5, and the damping resistances of poled PZT 95/5 could also be influenced by electric fields.