Potential Decay Research Articles

Organic Charge Transfer Cocrystals as Additives for Dissipation of Contact Charges on Polymers.

Common polymers can accumulate surface charges through contact, a phenomenon known since ancient times. This charge accumulation can have detrimental consequences in industry. It causes accidents and yields enormous economic losses. Many empirical methods have been developed to prevent the problems caused by charge accumulation. However, a general chemical approach is still missing in the literature since the charge accumulation and discharging mechanisms have not been completely clarified. The current practice to achieve charge mitigation is to increase materials conductivity by high doping of conductive additives. A recent study showed that using photoexcitation of some organic dyes, charge decay can be started remotely, and the minute amount of additive does not change the material's conductivity. Here, we show the contact charging and charge decay behavior of polydimethylsiloxane doped with a series of organic charge transfer cocrystals (CTC) of TCNQ acceptor and substituted pyrene donors (CTC-PDMS). The results show that the CTC-PDMS are antistatic, and the discharging propensity of the composites follows the calculated charge transfer degree of the complexes. On the other hand, the CTC-PDMS are still insulators, as shown by their high surface resistivities. Kelvin probe force microscopy images of the contact-charged and discharged samples show a quick potential decay in CTC domains upon illumination. Combined with the fast overall decay observed, the antistatic behavior in these insulators can be attributed to an electron transfer between the mechanoions in the polymer and the CTC frontier orbitals. We believe our results will help with the general understanding of the molecular mechanism of contact charging and discharging and help develop insulator antistatics.

Effects of Ion Beam Treatment on DC Flashover Characteristics of Epoxy

The effect of ion beam treatment on surface flashover characteristics of epoxy is evaluated and explored. Epoxy samples are prepared and ion beam treatment is carried out for 10-, 15-, 20-, 25-, and 30-min durations using an end-Hall ion source. Flashover test of both pristine and treated samples is conducted at negative dc voltage in air. The results indicate the effectiveness of ion beam treatment to enhance the flashover properties of epoxy. The flashover voltage of the epoxy resin increased to 21.35% after ion beam treatment for a duration of 20 min. Optical microscopic images, scanning electron microscopy (SEM) images, and results from Fourier transform infrared spectroscopy reveal the change in physicochemical characteristics of epoxy resin after treatment. The obtained surface potential from the surface potential decay (SPD) test shows a faster decay rate of surface charges for treated samples than the pristine epoxy. Moreover, from the trap distribution characteristics, it is found that ion beam treatment reduces the surface trap depth, which increases the surface conductivity of the epoxy insulator and helps to promote the charge migration and transport along the insulator surface.

Surface trap characteristics of polyimide and effect of surface charge accumulation on surface flashover

Charge accumulation on the surface of insulation dielectric used in high voltage DC equipment is one of the important causes of surface flashover. Surface charge accumulation is closely related to surface trap characteristics. In this paper, the surface trap energy level distribution of polyimide (PI) was calculated and analyzed by the corona charging method and surface potential decay method. Besides, electron and hole trap characteristics were studied by changing the polarity and amplitude of the charging voltage. Furthermore, the influence of surface charge polarity and quantity on the flashover voltage was researched. Experimental results indicate that the energy level of traps corresponding to the maximum trapped charge density ranges around 0.94 eV. In addition, the energy level of the hole trap is slightly higher than that of the electron trap. The maximum charge density captured by the electron trap and hole trap is about 1.17 × 1021 and 1.03 × 1021 eV−1 m−3, respectively. The polarity of the surface charge can influence the conductivity characteristics of PI, the surface heterocharge reduces the volume conductivity by about 80% while the surface homocharge improves the volume conductivity of PI by about 6.4 times. Besides, both negative and positive surface charges can improve surface conductivity. The polarity of surface charge influences the flashover characteristics of PI, the flashover voltage increases by about 37.8% with the increase of homocharge density and decreases by about 23.8% with the increase of heterocharge density, which is related to the change of electric field near the cathode caused by surface charge accumulation.

Enhancement of surface electrical performances of epoxy film by blending with fluorinated and crosslinking monomer

• Fluorinated monomers were synthesized through a facile method to prepare fluorinated epoxy films. • Effects of introducing –CF 3 groups on physicochemical characters of the films are studied. • Electrical strength of the fluorinated film was evidently enhanced. In order to introduce fluorine-containing functional groups into epoxy resins to stably enhance the surface electrical properties of thin films, the trifluoromethyl group containing diglycidyl ethers bisphenol A (F-DGEBA) monomer was prepared by a simple and environmentally friendly method. Further, the film was obtained by blending the prepared monomers with DGEBA in different proportions and curing at high temperature with methyl tetrahydrophthalic anhydride (MTHPA). The prepared films not only have improved hydrophobic properties, but also exhibit better surface electrical properties. With the increase of the content of F-DGEBA, the epoxy resin films have higher surface insulation strength and better potential decay performance, which is due to the existence of –CF 3 groups changing the distribution of deep and shallow traps. Compared with the non-fluorinated film, the flashover voltage of the fluorinated film with the best electrical properties is increased by 32.2%, and the potential decay rate is also much faster.

Interfacial 2D Montmorillonite Nanocoatings Enable Sandwiched Polymer Nanocomposites to Exhibit Ultrahigh Capacitive Energy Storage Performance at Elevated Temperatures.

Polymer dielectrics are essential for advanced electrical and electronic power systems due to their ultrafast charge-discharge rate. However, a long-standing challenge is to maintain their dielectric performance at high temperatures. Here, a layered barium titanate/polyamideimide nanocomposite reinforced with rationally designed interfaces is reported for high-temperature high-energy-density dielectrics. Nanocoatings composed of 2D montmorillonite nanosheets with anisotropic conductivities are interposed at two kinds of macroscopic interfaces: 1) the interfaces between adjacent layers in the nanocomposites (inside) and 2) the interfaces between the surface of the nanocomposite and the electrode (outside). By revealing the charge transport behavior with Kelvin probe force microscope, surface potential decay, and finite element simulation, it is demonstrated that the outside nanocoatings are observed to diminish charge injection from the electrode, while the inside nanocoatings can suppress the kinetic energy of hot carriers by redirecting their transport. In this interface-reinforced nanocomposite, an ultrahigh energy density of 2.48 J cm-3 , as well as a remarkable charge-discharge efficiency >80%, is achieved at 200°C, six times higher than that of the nanocomposite without interfacial nanocoatings. This research unveils a novel approach for the structural design of polymer nanocomposites based on engineered interfaces to achieve high-efficient and high-temperature capacitive energy storage.

Nature of Cations Critically Affects Water at the Negatively Charged Silica Interface.

Understanding the collective behavior of ions at charged surfaces is of paramount importance for geological and electrochemical processes. Ions screen the surface charge, and interfacial fields break the centro-symmetry near the surface, which can be probed using second-order nonlinear spectroscopies. The effect of electrolyte concentration on the nonlinear optical response has been semi-quantitatively explained by mean-field models based on the Poisson-Boltzmann equation. Yet, to explain previously reported ion-specific effects on the spectroscopic response, drastic ion-specific changes in the interfacial properties, including surface acidities and dielectric permittivities, or strong ion adsorption/desorption had to be invoked. Here, we use sum-frequency generation (SFG) spectroscopy to probe the symmetry-breaking of water molecules at a charged silica surface in contact with alkaline metal chloride solutions (LiCl, NaCl, KCl, and CsCl) at various concentrations. We find that the water response varies with the cation: the SFG response is markedly enhanced for LiCl compared to CsCl. We show that within mean-field models, neither specific ion-surface interactions nor a reduced dielectric constant of water near the interface can account for the variation of spectral intensities with cation nature. Molecular dynamics simulations confirm that the decay of the electrochemical potential only weakly depends on the salt type. Instead, the effect of different salts on the optical response is indirect, through the reorganization of the interfacial water: the salt-type-dependent alignment of water directly at the interface can explain the observations.

Improvement of partial discharge resistance of polypropylene under AC voltage by blending elastomer

This paper reports on the partial discharge (PD) erosion characteristics of polypropylene (PP)/elastomer blends where ethylene-octene copolymer elastomer (EOC) and propylene-based elastomer are involved. The PD erosion is performed through a pair of needle-to-plane electrodes by applying 5 kV AC voltage for 2 h. A high-frequency current transformer, optical recorder, and ozone sensor are used to capture the information released during the PD erosion process. In addition, a 3D optical profilometer is employed to record the erosion profile, from which the erosion depth and the surface roughness can be extracted. Carrier trap distribution is derived from the isothermal surface potential decay measurement. The influences of elastomer type and content on the PD resistance are analyzed. The results show that the resistance is improved with the addition of elastomer, and the blend containing EOC of 20 wt% has the best PD resistance among all samples, which is 61.9% higher than that of the pure PP. It is proposed that the carrier trap characteristics, the property of elastomer, and the free volume in the material play important roles in the improvement of the PD resistance. This work provides a potential method to enhance the PD resistance of PP by blending elastomer with proper type and content.

Effects of nanofiller and voltage stabilizer on partial discharge resistance of polypropylene/elastomer blends: A comparison study

AbstractThis paper reports on the individual and synergistic influence mechanisms of nano‐silica (SiO2) and voltage stabilizers on partial discharge (PD) resistance of polypropylene blended with ethylene‐octene copolymer elastomer. The SiO2 nanoparticles and three types of voltage stabilizers, that is, benzoin, 4,4′‐dimethoxybenzil, and 3‐aminobenzoic acid are selected as fillers to prepare samples. PD is initiated in a rod‐to‐plane electrode system with an alternating current voltage of 5 kVrms. PD characteristics are captured with multi‐sensors, and the erosion profile of the test sample is measured using a three‐dimensional (3D) optical profilometer. Carrier trap distribution is extracted with isothermal surface potential decay measurement to assist the analysis of PD eroding material. Fourier transform infrared spectrum, scanning electron microscopy, X‐ray diffraction spectrum, and differential scanning calorimetry analysis are performed to reveal the change in material structures caused by the fillers. Test results indicate that the PD resistance of the blend can be improved by the addition of nano‐SiO2 and voltage stabilizers individually and synergistically. The PD resistance of PO is increased by 71.2% at most in the sample with 3 wt% nano‐SiO2 addition. The sample filled with SiO2 exhibits better PD resistance than that with the voltage stabilizer or co‐added, which should be ascribed to the introduction of deep traps, the formation of the packaged layer, the suppression of oxygen diffusion of the nanofillers, and the good compatibility between additives and the polymer matrix.

A Study of the Higgs Mass with the Effective Potential and Higgs Decays in the U(1)XSSM

As the U(1) extension of the minimal supersymmetric standard model, the U(1)XSSM has new superfields, such as right-handed neutrinos, and three Higgs singlets. In the U(1)XSSM, the lightest CP-even Higgs mass mh0 is studied by using the Higgs effective potential with one-loop corrections. We also calculate the Higgs decays h0→γγ, h0→VV(V=W,Z), h0→ll¯Z, and h0→νν¯Z. The obtained results are reasonable, and they are in favor of the study of the Higgs characteristic and the phenomenology of the U(1)XSSM.

Potential Decay Simulation on Insulating Films

Abstract Surface potential decay (SPD) of a corona charged polymeric material is a powerful tool to characterise electrical properties such as charge transport, trapping/detrapping and recombination. Over the years, various predictive simulation techniques have been proposed to describe charge transport within the material. Despite recent progress, it appears that there have been a few attempts to theoretically interpret the nature of the charge migration on the insulation surface. The aim of the present paper is to introduce a new technique with differential evolution algorithm (DEA) to reveal the steady state surface potential decay experimental results. Experimental measurement was carried on a thin film of polyethylene terephthalate (thickness: 0.5 mm; surface: 50 mm × 50 mm). The domains of variation of the factors used were respectively: 1000 V to 1800 V; 25 to 55 °C; 50 % to 80 %. The simulation results show that computational modelling and optimization approaches may improve the effectiveness to characterise electrical properties of polymers. More importantly, these studies demonstrate that DEA is effective and performs better than the experimental design method.

The effective Higgs potential and vacuum decay in Starobinsky inflation

Based on the current experimental data, the Standard Model predicts that the current vacuum state of the Universe is metastable, leading to a non-zero rate of vacuum decay through nucleation of bubbles of true vacuum. Our existence implies that there cannot have been any such bubble nucleation events anywhere in our whole past lightcone. We consider a minimal scenario of the Standard Model together with Starobinsky inflation, using three-loop renormalization group improved Higgs effective potential with one-loop curvature corrections. We show that the survival of the vacuum state through inflation places a lower bound ξ ≳ 0.1 on the non-minimal Higgs curvature coupling, the last unknown parameter of the Standard Model. This bound is significantly stronger than in single field inflation models with no Higgs-inflaton coupling. It is also sensitive to the details of the dynamics at the end of inflation, and therefore it can be improved with a more detailed study of that period.

The First Direct Measurement of Gravitational Potential Decay Rate at Cosmological Scales and Improved Dark Energy Constraint

The integrated Sachs–Wolfe (ISW) effect probes the decay rate (DR) of large-scale gravitational potential and therefore provides a unique constraint on dark energy (DE). However, its constraining power is degraded by the ISW measurement, which relies on cross-correlating with the large-scale structure (LSS) and suffers from uncertainties in galaxy bias and matter clustering. In combination with lensing-LSS cross correlation, DR can be isolated in a way free of uncertainties in galaxy bias and matter clustering. We applied this proposal to the combination of the Data Release 8 galaxy catalog of DESI imaging surveys and Planck cosmic microwave background maps. We achieved the first DR measurement, with a total significance of 3.2σ. We verified the measurements at three redshift bins ([0.2, 0.4), [0.4, 0.6), [0.6, 0.8]), with two LSS tracers (the “low-density points” and the conventional galaxy positions). Despite its relatively low signal-to-noise ratio, the addition of DR significantly improves dark energy constraints, over Sloan Digital Sky Survey baryon acoustic oscillation (BAO) data alone or Pantheon supernovae (SNe) compilation alone. For flat wCDM cosmology, the improvement in the precision of Ω m is a factor of 1.8 over BAO and 1.5 over SNe. For the DE equation of state w, the improvement factor is 1.3 over BAO and 1.4 over SNe. These improvements demonstrate DR as a useful cosmological probe, and therefore we advocate its usage in future cosmological analysis.

On the injected charge distribution and discharge currents in the dielectric films for MEMS capacitive switches

The present work attempts to provide a different approach to understand the distribution of injected charge in Si-rich SiN films that find application in MEMS capacitive switches. The study employs Thermally-Stimulated-Depolarization-Current measurements to calculate the collected charge dependence on film thickness and show that the injected charge distribution is different from simulated ones. Moreover, employing Kelvin Probe surface potential decay measurements calculates the discharge current towards the film surfaces and bulk as well as their dependence on material stoichiometry.

Boosting electrochemical nitrogen reduction performance through water-in-salt electrolyte

While electrochemical nitrogen reduction reaction (NRR) stands as a promising technique for sustainable NH3 fabrication due to its mild operation conditions, it has long been suffered from low efficiency and poor selectivity owing to the inertness of N2 and competition hydrogen evolution reaction (HER). Herein, we report the use of oxygen vacancy rich TiO2 loaded with Au nanoparticles as NRR catalyst in super concentrated lithium bis(trifluoromethane sulfonyl) imide (Li TFSI) “water-in-salt” system (20 M electrolyte) and obtain the Faradaic efficiency of 37.2 % with an NH3 yield rate of 20.3 μg h−1 cm−2 at − 0.4 V vs RHE, accompanied by the significant decay of both current density and onset potential of hydrogen evolution reaction. Electrochemical experimental and theoretical calculation results indicate that the HER process can be greatly hindered both kinetically and energetically. The unique effect of this “water-in-salt” electrolyte would offer a new idea to improve the NRR selectivity via HER suppression.

Effect of Trap Regulation on Vacuum DC Surface Flashover Characteristics of Nano-ZnO/PI Film.

The operating safety of spacecraft in space environments is closely related to the surface discharging phenomenon of dielectrics such as polyimide (PI) film in solar arrays; moreover, carrier traps in the dielectric can affect its insulation performance. Therefore, to improve the vacuum surface flashover characteristics of PI film by nano modification and reveal the effect of trap distribution on the flashover of PI composite film, first, the original PI and nano-ZnO/PI composite films with different additive amounts (0.5, 1, 2, and 3 wt.%) were prepared by in situ polymerization and their performance was evaluated by the physicochemical properties characterized by methods such as thermogravimetric analysis; second, the surface traps of the original and nanocomposite films were measured and calculated by surface potential decay method, and the carrier mobility was also obtained; finally, the vacuum direct current (DC) surface flashover characteristics and bulk resistivity of all the film samples were measured and analyzed. The experiment results showed that with the increase in the amount of nano-ZnO, both the shallow and deep trap density increased significantly, while the trap energy varied slightly, and the surface flashover voltage also increased obviously. Based on the multi-core model, the increases in the shallow and deep trap density after the introduction of nano-ZnO into the PI matrix was analyzed from the microscopic perspective of the interface. Based on the comparative analysis of the trap distribution and surface flashover voltage characteristics, a bilayer model of vacuum DC surface flashover development was proposed. In the bilayer model, deep traps and shallow traps play a dominant role in the vacuum–solid interface and the inner surface of the dielectric, respectively, and increasing the trap density could effectively inhibit secondary electron multiplication on the surface and accelerate charge dissipation inside the film. Consequently, nano-ZnO can purposefully control the trap distribution, and then improve the flashover characteristics of nano-ZnO/PI composite films, which provides a new approach for improving the spacecraft material safety.

The effects of stage house coupling on multipurpose auditorium acoustics

The current scientific research on coupled spaces has augmented the design applications of reverberation chambers and stage house-coupling in music venues in the last couple of decades, and vice-versa the halls that incorporate room acoustics coupling has attracted attention of researchers in the field. Most of the cases, depict the room acoustics coupling from a positive perspective, as the non-exponential energy decay aids clarity and reverberance, which are two simultaneous requirements to satisfy in a music hall. However, not many studies discuss the negative effects of a potential non-exponential energy decay in an auditorium, or a multi-function hall, if not intentionally and carefully utilized. This study aims to highlight the importance of stage tower design in an auditorium, which is aimed to be used dominantly for speech-oriented activities and occasionally to host recitals. The paper initially introduces the acoustical design phases of the auditorium that is within the Ted Ankara Foundation College Performance Art Center. Acoustical simulations are utilized during design phase. The selected auditorium has multiple construction phases, including pre and post acoustical treatment within the stage. Accordingly, field tests are held before and after stage tower acoustical interventions. Collected impulse responses are analyzed by Bayesian decay parameter estimations, in both stages of construction. The discomfort caused by the surplus sound energy within the stage tower, specifically the excessive late coming low frequency sound energy -boomy sound-, are validated by the double-slope sound energy decay within the hall. The desired acoustical comfort could only be provided when the multi-slope sound energy decays are overcome by sound absorptive treatment applications in stage tower and its auxiliary side and back spaces.

Synergistic Hybrid Electrocatalysts of Platinum Alloy and Single-Atom Platinum for an Efficient and Durable Oxygen Reduction Reaction.

Pt single-atom materials possess an ideal atom economy but suffer from limited intrinsic activity and side reaction of producing H2O2 in catalyzing the oxygen reduction reaction (ORR); platinum alloys have higher intrinsic activity but weak stability. Here, we demonstrate that anchoring platinum alloys on single-atom Pt-decorated carbon (Pt-SAC) surmounts their inherent deficiencies, thereby enabling a complete four-electron ORR pathway catalysis with high efficiency and durability. Pt3Co@Pt-SAC demonstrates an exceptional mass and specific activities 1 order of magnitude higher than those of commercial Pt/C. They are durable throughout 50000 cycles, showing only a 10 mV decay in half-wave potential. An in situ Raman analysis and theoretical calculations reveal that Pt3Co core nanocrystals modulate electron structures of the adjacent Pt single atoms to facilitate the intermediate absorption for fast kinetics. The superior durability is attributed to the shielding effect of the Pt-SAC coating, which significantly mitigates the dissolution of Pt3Co cores. The hybridizing strategy might promote the development of highly active and durable ORR catalysts.

Ternary NiMoCo alloys and fluffy carbon nanotubes grown on ZIF-67-derived polyhedral carbon frameworks as bifunctional electrocatalyst for efficient and stable overall water splitting

The synthesis of efficient and stable non-precious metal electrocatalytic materials is one of the main challenges in current overall water splitting research. Herein, this paper puts forward a facile pyrolysis synthesis strategy for the construction of ZIF-67DC/NiMoCo/CNT ternary alloy catalyst with three-dimensional nanostructure and abundant fluffy carbon nanotubes. Benefiting from the synergistic effect between NiMoCo ternary alloy and carbon nanotubes, the ZIF-67DC/NiMoCo/CNT bifunctional catalyst can yield current density of 10 mA cm−2 at overpotentials of 85 mV and 306 mV over HER and OER in alkaline medium, respectively. The overall water splitting device can deliver current densities of 10 mA cm−2 for long periods of time at drive voltages as low as 1.64 V with nearly negligible decay in potential. This study provides a novel and operable method for the design of non-precious metal electrocatalysts.

Influence of SiC/Epoxy Coating on Surface Charging Phenomenon at DC Voltage—Part I: Charge Accumulation

Surface charge accumulation on silicon carbide (SiC)/epoxy coatings with different contents of SiC filler, 3, 5, 7, and 10 wt%, is investigated using flat samples of epoxy substrate. In the experiments, a pair of finger-shaped electrodes was attached to the sample’s surface using direct pressing and conductive adhesive providing two different types of contacts and, respectively, surface charging methods. The electrodes were energized by applying dc voltage for various time intervals and resulted surface charge distributions between the electrodes were measured. It was found that depending on the contact type, charging duration, and filler content, different patterns of homocharge or heterocharge appeared on the material surface. Physical reasons for the observed effects are analyzed based on the calculated electric field distributions in the experimental setup, results of the auxiliary tests on material charging in a limited air volume, and surface trap energy distributions measured by utilizing the isothermal surface potential decay (ISPD) method. Application of SiC/epoxy coating for controlling surface charge accumulation is discussed.

Space Charge and Trap Distributions and Charge Dynamic Migration Characteristics in Polypropylene under Strong Electric Field

Space charge accumulation in the polypropylene will accelerate the aging of the material and lead to the degradation of its insulation performance. In the work, space charge distribution, current conduction characteristics, thermally stimulated depolarization current (TSDC) and surface potential decay (SPD) characteristics of polypropylene (PP) under strong electric field are measured and analyzed, and the bulk trap and surface trap parameters are extracted. Further, the charge transport model of PP is established to study the charge dynamic transport physical processes and characteristics under strong electric field. The experimental results show that the charge accumulation amount in PP under the action of negative polarity electric field is higher than that of positive polarity electric field, about one order of magnitude. and the corresponding trap energy levels are 0.84 eV and 0.81 eV, which both belong to deep traps. There are two obvious charge density peaks on the PP surface, which are 2.60 × 1020·eV−1·m−3 and 3.66 × 1020·eV−1·m−3, respectively, and the corresponding surface trap energy levels are 0.86 eV and 0.97 eV. The simulation results show that with the extension of the applied voltage time, the injected charges by the electrode gradually migrate to the bulk of the material and eventually the positive and negative charges are offset at the middle position. The local electric field caused by the accumulation of interfacial charges will weaken the original electric field, while the local electric field caused by the accumulation of the bulk charges will strengthen the original electric field, resulting in the distortion of the internal electric field.