Moderate Field Research Articles

Polyetherimide nanocomposites filled with in‐situ synthesised bismaleimide‐DDE@CCTO hybrid nanofibers enabling improved dielectric and interfacial performance

AbstractMost current research of nanocomposite dielectrics for modern electronic devices and electric equipment usually focuses more on dielectric properties while in some extent ignoring the interfacial adhesion characteristics. However, the poor interfacial adhesion frequently results in serious dielectric field distortion, which would in return impair the dielectric performance enhancement. As such, how to simultaneously achieve the excellent dielectric properties and interfacial adhesion performance in organic‐inorganic nanocomposite system is worth in‐depth investigation. To realise this aim, novel hybrid nanofibers are neatly fabricated using in situ copolymerisation reaction of bismaleimide and diamino‐diphenyl ether monomers on the CCTO nanofiller surface via covalent bond connections. The resulting nanocomposites achieve high dielectric constant (9.3) and low dielectric loss (0.0185) at 1 kHz. The BMI‐DDE@CCTO/PEI yields a high discharge energy density (3.09 J/cm3) at moderate electric field (200 MV/m). Noticeably, the nanocomposites enable stable dielectric performance over a wide temperature range from room temperature to 150°C. Moreover, the binding energy for BMI‐DDE and PEI is 1052 kJ/mol according to DFT calculation. As such, the authors speculate this interesting study would inspire the broad researchers devoting to investigating bismaleimide‐coated high‐aspect‐ratio nanofillers and their dielectric materials for collaboratively improved dielectric and interfacial performance.

Numerical analysis of electro-thermo-convection in a differentially heated square cavity with electric conduction

Natural convection with an electric field in the classic differentially heated square cavity is numerically studied. The electric conduction model for the generation of free space charges, which applies to weak and moderate electric field with weakly conducting liquids, is specially considered. The whole set of governing equations is implemented in the open-source finite-volume framework of OpenFOAM. Thorough investigation has been undertaken to analyze the thermal and flow characteristics of electro-thermo convection. The results reveal that the introduction of an electric field leads to a suppressive influence on flow motion across all considered Rayleigh numbers (Ra), aligning with recent experimental findings. This effect becomes more pronounced with increasing conduction number (C 0), resulting in the reduction of flow intensity and a thicker thermal boundary layer. Consequently, heat transfer is subdued due to the electric field, causing a decrease in the Nusselt number (Nu) as C 0 increases. To elucidate the mechanism how the electric field impacts natural convection, the torques induced by the electric and buoyancy forces are computed. Higher C 0 will lead to a lower buoyancy torque and stronger electric torque, where the electric torque is opposite to the buoyancy torque, thus the weaker flow strength is shown at higher C 0. Finally, to quantify the reduction in heat loss, the relative Nusselt number (Rnu) is introduced. It is found that there is a critical Ra corresponding to minimal Rnu, and for the parameters considered in this study, the minimum Rnu of 0.563 is observed at C 0 = 0.2 and Ra = 1.2 × 104. For large Ra, the Rnu almost keeps constant with increasing Ra.

Novel high-entropy relaxors with ultrahigh energy-storage efficiency and density

One of the major problems in ceramic capacitors is that their limited energy storage density (Wrec) and efficiency restrict the development in cutting-edge energy storage applications. In this paper, the non-equimolar ratio high-entropy ceramics are designed using the “entropy” strategy based on the traditional ferroelectric BaTiO3. Ultimately, the superparaelectric region of BaTiO3 is extended successfully, forming the local polymorphic distortion structure and realizing the transformation of ferroelectrics-relaxor ferroelectrics. Here, the outstanding Wrec of 7.3 J/cm3, the excellent ξ of 214.71 J/kV·m2, and the highest energy storage efficiency (η = 94.3 %) in high-entropy ceramics are obtained under moderate electric fields, indicating a breakthrough progress in energy storage applications of high-entropy relaxor ferroelectrics. Additionally, our work compared performance across multiple dimensions using measurement parameters, giving readers a more comprehensive reference.

A novel low-loss and high-stability (1-x)Na0.98NbO3–xBi(Al0.5Y0.5)O3 lead-free composite ceramics for dielectric energy storage capacitors

Environmentally friendly, high-performance, lead-free dielectric ceramic capacitors are urgently required for efficient and clean energy storage devices. However, most ferroelectric capacitors require excessively high electric fields to achieve large energy storage densities. In this study, we designed and fabricated a (1-x)Na0.98NbO3–xBi(Al0.5Y0.5)O3 (abbreviated as (1-x)NN-xBAY) composite system with different BAY doping levels using a traditional solid-state reaction method. By introducing 12 mol% BAY into nonstoichiometric NN, the polarization–electric field loop of the 0.88NN–0.12BAY ceramic became significantly slender and showed a superior relaxor behavior. Consequently, a remarkably low dielectric loss of tanδ < 0.005, high energy storage density of ∼ 4.64 J/cm3, and high efficiency of ∼ 85.98 % were simultaneously obtained in the 0.88NN–0.12BAY ceramic under a moderate electric field of 223.47 kV/cm. Furthermore, it exhibited ultrahigh stability in the temperature range of 25–200 °C and wide frequency range of 1–200 Hz, even after 108 electrical cycles. This study demonstrated a promising candidate material for energy storage devices operating under low or medium electric fields.

The early evolution of magnetar rotation – II. Rapidly rotating magnetars: implications for gamma-ray bursts and superluminous supernovae

ABSTRACT Rapidly rotating magnetars have been associated with gamma-ray bursts (GRBs) and superluminous supernovae (SLSNe). Using a suite of two-dimensional magnetohydrodynamic simulations at fixed neutrino luminosity and a couple of evolutionary models with evolving neutrino luminosity and magnetar spin period, we show that magnetars are viable central engines for powering GRBs and SLSNe. We also present analytical estimates of the energy outflow rate from the proto-neutron star (PNS) as a function of polar magnetic field strength B0, PNS angular velocity Ω⋆, PNS radius R⋆, and mass outflow rate $\dot{M}$. We show that rapidly rotating magnetars with spin periods P⋆ ≲ 4 ms and polar magnetic field strength B0 ≳ 1015 G can release 1050 to 5 × 1051 erg of energy during the first ∼2 s of the cooling phase. Based on this result, it is plausible that sustained energy injection by magnetars through the relativistic wind phase can power GRBs. We also show that magnetars with moderate field strengths of B0 ≲ 5 × 1014 G do not release a large fraction of their rotational kinetic energy during the cooling phase and, hence, are not likely to power GRBs. Although we cannot simulate to times greater than ∼3–5 s after a supernova, we can hypothesize that moderate field strength magnetars can brighten the supernova light curves by releasing their rotational kinetic energy via magnetic dipole radiation on time-scales of days to weeks, since these do not expend most of their rotational kinetic energy during the early cooling phase.

The giant flexoelectric effect in a luffa plant-based sponge for green devices and energy harvesters

Soft materials that can produce electrical energy under mechanical stimulus or deform significantly via moderate electrical fields are important for applications ranging from soft robotics to biomedical science. Piezoelectricity, the property that would ostensibly promise such a realization, is notably absent from typical soft matter. Flexoelectricity is an alternative form of electromechanical coupling that universally exists in all dielectrics and can generate electricity under nonuniform deformation such as flexure and conversely, a deformation under inhomogeneous electrical fields. The flexoelectric coupling effect is, however, rather modest for most materials and thus remains a critical bottleneck. In this work, we argue that a significant emergent flexoelectric response can be obtained by leveraging a hierarchical porous structure found in biological materials. We experimentally illustrate our thesis for a natural dry luffa vegetable-based sponge and demonstrate an extraordinarily large mass- and deformability-specific electromechanical response with the highest-density-specific equivalent piezoelectric coefficient known for any material (50 times that of polyvinylidene fluoride and more than 10 times that of lead zirconate titanate). Finally, we demonstrate the application of the fabricated natural sponge as green, biodegradable flexible smart devices in the context of sensing (e.g., for speech, touch pressure) and electrical energy harvesting.

Effect of Moderate Electric Fields on the Physical and Chemical Characteristics of Cheese Emulsions.

Cheese powder is a multifunctional ingredient that is produced by spray drying a hot cheese emulsion called cheese feed. Feed stability is achieved by manipulating calcium equilibrium using emulsifying salts. However, the increased demand for 'green' products created a need for alternative production methods. Therefore, this study investigated the impact of ohmic heating (OH) on Cheddar cheese, mineral balance, and the resulting cheese feed characteristics compared with a conventional method. A full factorial design was implemented to determine the optimal OH parameters for calcium solubilization. Electric field exposure and temperature had a positive correlation with mineral solubilization, where temperature had the greatest impact. Structural differences in pre-treated cheeses (TC) were analyzed using thermorheological and microscopic techniques. Obtained feeds were analyzed for particle size, stability, and viscosity. OH-treatment caused a weaker cheese structure, indicating the potential removal of calcium phosphate complexes. Lower component retention of OH_TC was attributed to the electroporation effect of OH treatment. Microscopic images revealed structural changes, with OH_TC displaying a more porous structure. Depending on the pre-treatment method, component recovery, viscosity, particle size distribution, and colloidal stability of the obtained feeds showed differences. Our findings show the potential of OH in mineral solubilization; however, further improvements are needed for industrial application.

Production of iron-enriched kale leaves (Brassica oleracea L. var. acephala) utilizing combinations of novel food processing technologies

Despite its rich content, iron bioavailability from leafy greens is low relative to protoporphyrin-bound (e.g. heme) iron, richest in red meat. We hypothesized that combinations of novel food processing techniques, i.e., vacuum impregnation (VI), water-bath (WB), overnight immersion (IM) in an iron sulfate solution, and moderate electric field (MEF) could improve kale leaf iron content and produce protoporphyrin-bound iron derivatives in situ. Combination MEF treatments increased leaf iron concentrations ∼160x greater than control. A ferroprotoporphyrin IX isomer was detected in MEF and IM-treated kale, providing up to 0.75 mg protoporphyrin-bound iron/100 g kale leaf fresh weight (FW). IM and MEF treatments also significantly increased leaf total chlorophyll concentrations ∼3x greater than the control. The novel food processing techniques employed herein produced kale with significantly higher concentrations of free + heme-bound iron, as well as total chlorophyll, relative to other plant-based sources. Future testing will determine if this “iron-enhanced” kale delivers more iron, as compared to other iron-rich food sources.

Caloric effects in liquid crystal-based soft materials

With the increased environmental awareness, the search for environmentally friendlier heat-management techniques has been the topic of many scientific studies. The caloric materials with large caloric effects, such as the electrocaloric (EC) and elastocaloric (eC) effects, have increased interest due to their potential to realize new solid-state refrigeration devices. Recently, caloric properties of soft materials, such as liquid crystals (LCs) and LC elastomers (LCEs), are getting more in the focus of caloric materials investigations, stimulated by large caloric effects observed in these materials. Here, an overview of recent direct measurements of large caloric effects in smectic LC 14CB and main-chain LCEs is given. Specifically, high-resolution thermometric measurements revealed a large EC response in 14CB LC exceeding 8 K. Such a large effect was obtained at a relatively moderate electric field of 30 kV cm−1 compared to solid EC materials. We demonstrate that such a small field can induce the isotropic to smectic A phase transition in 14CB, releasing or absorbing relatively large latent heat that enhances the EC response. Furthermore, it is demonstrated that in main-chain LCEs, the character of the nematic to isotropic transition can be tuned from the supercritical towards the first-order regime by decreasing the crosslinkers’ density. Such tuning results in a sharper phase transition and latent heat that enhance the eC response, exceeding 2 K and with the eC responsivity of 24 K MPa−1, about three orders of magnitude larger than the average eC responsivity found in the best shape memory alloys. Significant caloric effects in soft LC-based materials, observed at much smaller fields than in solid caloric materials, demonstrate their ability to play an important role as new cooling elements, thermal diodes, and caloric-active regeneration material in new heat-management devices.

Electrically Tunable Nonlinearity at 3.2 Terahertz in Single-Layer Graphene.

Graphene is a nonlinear material in the terahertz (THz) frequency range, with χ(3) ∼ 10-9 m2/V2 ∼ 15 orders of magnitude higher than that of other materials used in the THz range, such as GaAs or lithium niobate. This nonlinear behavior, combined with ultrafast dynamic for excited carriers, proved to be essential for third harmonic generation in the sub-THz and low (<2.5 THz) THz range, using moderate (60 kV/cm) fields and at room temperature. Here, we show that, for monochromatic high peak power (1.8 W) input THz signals, emitted by a quantum cascade laser, the nonlinearity can be controlled using an ionic liquid gate that tunes the graphene Fermi energy up to >1.2 eV. Pump and probe experiments reveal an intense absorption nonlinearity at 3.2 THz, with a dominant 3rd-order contribution at EF > 0.7 eV, hence opening intriguing perspectives per engineering novel architectures for light generation at frequencies > 9 THz.

Outstanding Energy Storage Performance of NBT-Based Ceramics under Moderate Electric Field Achieved via Antiferroelectric Engineering.

Ultrahigh energy-storage performance of dielectric ceramic capacitors is generally achieved under high electric fields (HEFs). However, the HEFs strongly limit the miniaturization, integration, and lifetime of the dielectric energy-storage capacitors. Thus, it is necessary to develop new energy-storage materials with excellent energy-storage densities under moderate electric fields (MEFs). Herein, the antiferroelectric material Ag0.9Ca0.05NbO3 (ACN) was used to modify the relaxor ferroelectric material 0.6Na0.5Bi0.5TiO3-0.4Sr0.7Bi0.2TiO3 (NBT-SBT). The introduction of ACN results in high polarization strength, regulated composition of rhombohedral (R3c) and tetragonal (P4bm), nanodomains, and refined grain size. An outstanding recoverable energy density (Wrec = 4.6 J/cm3) and high efficiency (η = 82%) were realized under an MEF of 260 kV/cm in 4 mol % ACN-modified NBT-SBT ceramic. The first-principles calculation reveals that the interaction between Bi and O is the intrinsic mechanism of the increased polarization. A new parameter ΔP/Eb was proposed to be used as the figure of merit to measure the energy-storage performance under MEFs (∼200-300 kV/cm). This work paves a new way to explore energy-storage materials with excellent-performance MEFs.

Effect of moderate electric field on rheological properties, cell wall components, and microstructure of apple tissue

Effect of moderate electric field on rheological properties, cell wall components, and microstructure of apple tissue

Oriented External Electric-Field Effects on the Activation of Aryl CO Bond in Anisole using Rh(PEP) (E=Al, B, Ga) Catalysts.

The present work reports a DFT-based mechanistic investigation of aryl C-O bond activation in anisole catalysed by a Rh-Al pincer-type complex at room temperature. The study is extended to analogues Rh-E complexes based on Group 13 elements (E=B/Ga). Our results show a preference for the heterolytic cleavage pathway over oxidative addition in the C-O bond activation. The calculated barriers range from 16 to 36 kcal/mol, following the order: E=Al<E=Ga<E=B. A strong correlation between the activation barriers and the local electric field (LEF) at the Rh metal centre for the studied Rh-E complexes was observed. Additionally, the ability of Oriented External Electric Field (OEEF) to lower the reaction barrier by applying the OEEF along the direction of electron reorganization, that is, "the reaction axis", was examined. Our results demonstrate the significant effect of applied OEEF on the aryl C-O bond activation in Rh-E systems. Furthermore, the effect of OEEF on the C-O bond activation using modified Rh-E (E=B, Al, or Ga) complexes, in which electronic structure modifications enable a more efficient barrier control by the OEEF, was showcased. Notably, applying a moderate field strength reduces the high reaction barrier for the Rh-B system by approximately 13 kcal/mol.

Non-thermal pasteurization of milk by an innovative energy-saving moderate electrical field equipped with elongated electrodes and process optimization

Environmental concerns and consumer demand necessitate alternative pasteurization techniques that sustainably produce safe and high-quality milk. To this end, a new non-thermal (<42 °C) moderate electric field (MEF) system was developed with elongated electrodes and a reduced electrode gap. Response surface methodology optimized technical and thermo-physical attributes, including viscosity, density, freezing point, solid non-fat (SNF), temperature, power usage, and specific energy consumption (SEC), by altering electrical field intensities (EFI) and mass flow rates (ṁ) from 25 to 30 V/cm and from 0.017 to 0.033 kg/s, respectively. The results were then compared with the conventional thermal pasteurization (CP, 63 °C for 30 min). Besides, process cost analysis in terms of electricity consumption was performed to identify cost reduction opportunity for the industry, and milk samples were analyzed by scanning electron microscopy to elaborate on the mechanisms involved. MEF optimal processing conditions were 29.8 V/cm EFI and 0.018 kg/s ṁ, which reduced 98.58% of energy consumption, 98.51% of SEC, and 99.09% of processing time in comparison with CP. Also, MEF possessed higher productivity than CP. D-value for total count bacteria (TCB) in MEF was significantly lower than CP (0.06 vs. 14.80 min), and MEF and CP reduced TCB by 99% and 88.61%, respectively. Compared with the previously reported MEF milk pasteurizer, the MEF system developed in this study saved energy, cost, and time by 99.2%, 99.0%, and 78.4%; therefore, this emerging technology could further contribute to sustainable manufacturing of foods.

Simulations of magnetization reversal in FM/AFM bilayers with THz frequency pulses

It is widely known that antiferromagnets (AFMs) display a high frequency response in the terahertz (THz) range, which opens up the possibility for ultrafast control of their magnetization for next generation data storage and processing applications. However, because the magnetization of the different sublattices cancel, their state is notoriously difficult to read. One way to overcome this is to couple AFMs to ferromagnets—whose state is trivially read via magneto-resistance sensors. Here we present conditions, using theoretical modelling, that it is possible to switch the magnetization of an AFM/FM bilayer using THz frequency pulses with moderate field amplitude and short durations, achievable in experiments. Consistent switching is observed in the phase diagrams for an order of magnitude increase in the interface coupling and a tripling in the thickness of the FM layer. We demonstrate a range of reversal paths that arise due to the combination of precession in the materials and the THz-induced fields. Our analysis demonstrates that the AFM drives the switching and results in a much higher frequency dynamics in the FM due to the exchange coupling at the interface. The switching is shown to be robust over a broad range of temperatures relevant for device applications.

A comparison between pulsed electric field and moderate electric field for their effectiveness in improving the freezing tolerance of rocket leaves

Two electrotechnologies: pulsed electric fields (PEF) and moderate electric field (MEF) in combination with vacuum impregnation of glycerol as cryoprotectant were used to increase the freezing tolerance of rocket leaves. Rocket leaves were treated with PEF using a nominal field strength of 1200 V/cm or MEF at different combinations of voltage and frequency. Leaves were then immersed in a glycerol solution at 32, 36 and 40% (w/v) under vacuum for 26 min. After this treatment, the leaves were allowed to rest for 3 days before they were frozen and thawed. Leaf survival was assessed at different time points after thawing with microscopic observations and wilting tests. When the viability of the leaves was assessed 5 min after thawing, 60–68% of the leaves in the batch survived. There was no difference in the levels of surviving leaves when PEF and the lowest-tested voltage used in MEF were tested. However, from the leaves surviving 5 min after thawing, approximately half of them die over a 24 h period after thawing.

Effects of electric field intensity regulation on protein aggregation behaviour and foaming property of soybean 7S globulin

In this study, the aggregation behaviour of soybean 7S globulin after moderate electric field (MEF) treatment was investigated, and the influence of the electric field and temperature field on the structure and foaming property of the aggregates were analysed and compared with conventional water bath (COV). The results showed that MEF treatment enhanced the properties of the aggregates. The properties of the treated aggregates were significantly better than those of native 7S globulin. At an electric field strength of 8 V/cm, the solubility, turbidity, and particle size increased from 95.81 % to 99.37 %, 0.097 to 0.189 and 61.97 nm to 113.21 nm, respectively, and the absolute value of potential decreased from 23.56 mV to 22.12 mV. The SDS-PAGE and size exclusion chromatography (SEC) results showed that the electric field had a positive effect on the aggregate formation of the Fourier-transform infrared spectroscopy (FTIR), fluorescence spectroscopy, surface hydrophobicity (H0) and total sulfhydryl (SHT) results indicated that the spatial structure of the protein was changed by MEF treatment. The protein β-sheet content was reduced, and the Try that was originally buried inside the molecule was exposed, resulting in an increase in H0 and a decrease in SHT. The foaming property of the 7S globulin aggregates was improved by MEF treatment.

Optimizing energy storage properties under moderate electric fields in Na0.5Bi0.5TiO3-based ceramics via configuration entropy modulation

Lead-free ceramic capacitors with large energy storage density and efficiency synchronously under moderate electric fields is a challenging. In this work, a pathway of configuration entropy modulation (ΔSconfig) overcomes this challenge. The (1-x)(Na0.5Bi0.47La0.03)0.94Ba0.06TiO3-xSr(Sn0.2Ti0.2Al0.2Ta0.2Hf0.2)O3 ceramics were successfully synthesized. With the system ΔSconfig increases from 0.98 R to 1.79 R. The 0.85 NBLBT-0.15 SSTATH ceramic obtains a large recoverable energy density (Wrec = 4.28J/cm3) and ultra-high efficiency (η = 92.6%) under 260 kV/cm. The implementation of prominent energy storage performance can be attributed to the refinement of grain and domain size, and the increase of band gap and activation energy, which caused by the increase in ΔSconfig. More critically, the same composition also possesses great frequency (1–100 Hz) and thermal (20–140 °C) stability of energy storage performance as well as the high power density of PD ∼ 36.19 MW/cm3 and transient discharge rate of t0.9–44 ns at 120 kV/cm. This work shows that the regulation of ΔSconfig is an effective strategy to achieve outstanding energy storage properties under moderate electric fields.

Improved energy storage performance in rare-earth modified lead-free BNT-based relaxor ferroelectric ceramics

Dielectric ceramic capacitors with high energy storage performance are indispensable components in high-power pulse electronic systems. Herein, a collaborative optimization design is employed to achieve excellent energy storage performance in rare-earth oxides modified 0.76(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.24Sr0.7Bi0.2TiO3 (BNBT-SBT) ceramics by simultaneously enhancing the breakdown field strength (Eb) and relaxor behavior. To this end, ferroelectric domains are partially transformed into polar nanoregions by introducing relaxor ferroelectric SBT, while a smaller grain size is produced by doping rare-earth elements to improve the Eb and further disrupt the long-range order of ferroelectric polarization. It is found that the La-doped BNBT-SBT ceramic simultaneously exhibits a superior energy storage density of 4.4 J cm−3 and an ultrahigh efficiency of ∼91% under a moderate electric field of 300 kV/cm. The good temperature stability (30–120 °C), frequency endurance (1–100 Hz), electric fatigue resistance (1–106 cycles), and excellent power density (108 MW cm−3) are also obtained in the lead-free Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics. These prominent properties indicate that the La-doped BNBT-SBT ceramic is a promising candidate for applications of high-energy storage capacitors.

Combining high pressure and electric fields towards Nannochloropsis oculata eicosapentaenoic acid-rich extracts

Nannochloropsis oculata is naturally rich in eicosapentaenoic acid (EPA). To turn this microalga into an economically viable source for commercial applications, extraction efficiency must be achieved. Pursuing this goal, emerging technologies such as high hydrostatic pressure (HHP) and moderate electric fields (MEF) were tested, aiming to increase EPA accessibility and subsequent extraction yields. The innovative approach used in this study combined these technologies and associated tailored, less hazardous different solvent mixtures (SM) with distinct polarity indexes. Although the classical Folch SM with chloroform: methanol (PI 4.4) provided the highest yield concerning total lipids (166.4 mglipid/gbiomass), diethyl ether: ethanol (PI 3.6) presented statistically higher values in terms of EPA per biomass, corresponding to 1.3-fold increase. When SM were used in HHP and MEF, neither technology independently improved EPA extraction yields, although the sequential combination of technologies did result in 62% increment in EPA extraction. Overall, the SM and extraction methodologies tested (HHP—200 MPa, 21 °C, 15 min, followed by MEF processing at 40 °C, 15 min) enabled increased EPA extraction yields from wet N. oculata biomass. These findings are of high relevance for the food and pharmaceutical industries, providing viable alternatives to the “classical” extraction methodologies and solvents, with increased yields and lower environmental impact.Key points• Et2O: EtOH is a less toxic and more efficient alternative to Folch solvent mixture• HHP or MEF per se was not able to significantly increase EPA extraction yield• Combinations of HHP and MEF technologies increased both lipids and EPA yieldsGraphical abstract