Charge Distribution Characteristics Research Articles

THEORETICAL PREDICTION AND COMPREHENSIVE CHARACTERIZATION OF AN ALL-NITROGENATOMIC RING, CYCLO[18]NITROGEN (N18).

The cyclic molecule cyclo[18]carbon composed of 18 carbon atoms has been observed in condensed phase experiment in recent years and has attracted great attention. Through state-of-art quantum chemistry calculation, this study found that 18 nitrogen atoms can also form a macrocyclic system, cyclo[18]nitrogen (N18), though its lifetime is very short at room temperature and can only exist for a relatively long time at very low temperatures. We comprehensively theoretically studied properties of N18, including geometric configurations, thermal decomposition mechanism and rate, molecular dynamics behavior, energetic properties, vibrational and electronic spectra. We also discussed in depth the electronic structure of N18, including nature of the N-N bonds, lone-pairs, charge distribution characteristics, electronic delocalization, and aromaticity. This work is not only the first exploration of the macrocyclic N18 molecule, but also the first time to systematically examine a very long-chain substance fully composed of nitrogen atoms in isolated state.

Improving ion rejection by optimizing the structure and charge distribution of the Janus membrane

Due to the asymmetry of charge distribution and geometric structure, the Janus membrane can simultaneously intercept counter-ions and co-ions. This work constructed four Janus membrane configurations using numerical simulation methods. Due to the different potential within the membrane and the selectivity level, there is a significant deviation in the interception performance. The results found that the change in the height of the Janus membrane affects the distribution of anion and cation concentration inside the nanochannel, and the asymmetry of the nanochannel height is more conducive to interception than a uniform nanochannel. The effect of the nanochannel length of the first section on the rejection rate is higher than that of the second section. Considering the design of the membrane, we recommend that the pore length of the first section be set to about 50 nm. Since the flow potential balances the electroviscous force, the optimization of the flow rate for ion transport is often opposite to the interception effect. The Janus membrane has asymmetric pore size and charge distribution characteristics and has excellent retention ability for divalent salts under low-pressure intensity and high-concentration conditions.

Blending Modification Technology of Insulation Materials for Deep Sea Optoelectronic Composite Cables

The insulation layer of deep-sea optoelectronic composite cables in direct contact with high-pressure and highly corrosive seawater is required for excellent water resistance, environmental stress cracking resistance (ESCR), and the ability to withstand high DC voltage. Although high-density polyethylene (HDPE) displays remarkable water resistance, it lacks sufficient resistance to environmental stress cracking (ESCR). This article is based on a blend modification approach to mixing HDPE with different vinyl copolymer materials (cPE-A and cPE-B). The processing performance and mechanical properties of the materials are evaluated through rheological and mechanical testing. The materials’ durability in working environments is assessed through ESCR tests and water resistance experiments. Ultimately, the direct current electrical performance of the materials is evaluated through tests measuring space charge distribution, direct current resistivity, and direct current breakdown strength. The results indicate that, in the polyethylene blend system, the rheological properties and ESCR characteristics of HDPE/cPE-A composite materials did not show significant improvement. Further incorporation of high melt index linear low-density polyethylene (LLDPE) material not only meets the requirements of extrusion processing but also exhibits a notable enhancement in ESCR performance. Meanwhile, copolymerized polyethylene cPE-B, with a more complex structure, proves effective in toughening HDPE materials. The material’s hardness significantly decreases, and when incorporating cPE-B at a level exceeding 20 phr, the composite materials achieve excellent ESCR performance. In a simulated seawater environment at 50 MPa, the water permeability of all co-modified composite materials remained below 0.16% after 120 h. The spatial charge distribution and direct current resistivity characteristics of the HDPE, cPE-A, and LLDPE composite systems surpassed those of the HDPE/cPE-B materials. However, the HDPE/cPE-B composite system exhibited superior dielectric strength. The application of composite materials in deep-sea electro–optical composite cables is highly promising.

Facile strategy for intrinsic low-κ dielectric polymers: molecular design based on space charge conservation.

The growing need for high-power and compact-size microelectronic integrated circuits (ICs) in modern microelectronic industries and 5G communication systems demands low dielectric constant (κ) polymer dielectrics with excellent temperature capability, mechanical property and processability. However, conventional molecular design strategies often face difficulties of a trade-off between optimizing the dielectric performance of polymers and maintaining the aforementioned properties. Herein, we present an innovative and facile strategy that utilizes the space charge distribution characteristics of the target co-monomer to solve this trade-off. Based on this design strategy, a novel polyaryl ether ketone (PAEK) with two different charge distribution units (BAF and SBI) was designed and synthesized. Both the experimental results and computational simulations confirm that these two components serve to weaken the polarization of molecular chains in the electric field, induce higher molecular chain packing density and fewer weaknesses, and synchronously regulate the κ, dielectric loss (tan δ), thermal and mechanical properties and processability by generating a strong inter-chain electrostatic interaction. The resultant copolymer, PAEK-4F6S, exhibits exceptional low κ and tan δ values of 1.98 and 0.0024 at 1 MHz, respectively, and these values remain stable over a broad frequency (1-106 Hz, 8.2-12.4 GHz) and temperature range (30-150 °C). Furthermore, the resultant copolymer demonstrates excellent thermal stability and mechanical properties, with a glass transition temperature (Tg) of 195 °C, 5 wt% decomposition temperature (Td5%) of 498 °C under N2, tensile strength of 63.5 MPa and tensile modulus of 1011.2 MPa, respectively. The synthesis procedure of these resultant copolymers is facile, and they are found to have favorable solution and melt processing properties, making them suitable for processing and scalable production. More importantly, this design strategy is beneficial for lowering the κ and tan δ values, and simultaneously enhancing the comprehensive performances of the objective polymers, which provides a completely novel and facile approach for the design and fabrication of high performance low-κ polymers suitable for the needs of microelectronics and communication fields.

A Self-Capacitance Proximity E-Skin With Long-Range Sensibility for Robotic Arm Environment Perception

Proximity sensing is a major requirement for intelligent robots and robotic arms to ensure safety and closed-loop control in human–robot interactions. E-skins have received increasing attention because of their ease of arraying and installation. However, problems, such as insufficient sensing distance and inaccurate distance prediction, still exist. To solve these problems, we propose a self-capacitance-based long-range proximity sensing e-skin. First, two electrode shape classifications, external edge and internal holes, were analyzed and optimized in COMSOL to explore the variation trends of charge distribution and capacitance proximity characteristics. Then, based on the self-capacitance proximity theory, the parameters of the fitting function for the actual capacitance–distance curves for the four electrodes were solved using the planning solution method. The results show that the sensor has a good dynamic response, a long proximity sensing range (10.9 cm), high distance estimation accuracy (σ = 0.45), and good repeatability (>2 h). Finally, we integrate the sensor array with the end joint of the robotic arm to complete a sorting task. A closed-loop control demonstration of safe obstacle avoidance and deceleration was achieved, thereby demonstrating the great potential of e-skin for future human–machine collaboration scenarios.

Space Charge Characteristics of Electrothermally Aged Oil-Paper Insulation Under Slightly Nonuniform Electric Field

To study the change characteristics of space charge in oil paper insulation under a slightly non-uniform electric field and a uniform electric field, the existing space charge measuring device was improved, and sphere–plate and column–plate electrode models were prepared. Oil paper insulation samples at different aging stages were obtained via electrothermal aging. The real-time waveforms of the space charge distribution in the samples at different aging stages were measured in the process of polarization with a direct-current (DC) voltage and depolarization with a DC voltage, and the effects of different electric-field types on the charge distribution and motion characteristics of oil paper insulation samples at different aging stages were examined. The results indicated that the existence of a slightly non-uniform electric field accelerated the change in the charge-density peak at the interface and increased the fluctuation range of the charge-density curve in the process of applying a DC voltage. With the aggravation of electrothermal aging, the amount of charge injected into the sample increased, and the slightly non-uniform electric field intensified this process, affecting the accumulation and dissipation of space charge in the sample. Electrothermal aging increased the trap distribution density and energy-level depth. However, for an oil paper insulation sample at the same aging stage, compared with the uniform electric field, the slightly non-uniform electric field had no obvious effect on the trap energy-level depth, but it increased the amount of trapped charge and changed the trap density distribution in the sample. The results of this study provide a theoretical basis for examining the influence of slightly non-uniform electric fields on the space charge distribution characteristics of oil paper insulation subjected to AC/DC combined electrothermal aging.

Discharge Characteristics and Numerical Simulation of the Oil–Gas Surface under DC Voltage

Low insulation strength at the oil–gas surface due to oil leakage and partial discharge of oil-immersed power equipment is a major threat to the safe and reliable operation of power systems. This paper investigates the initiation and development of the oil–gas surface discharge. The oil–gas surface discharge test platform was established, and discharge tests were carried out at different gap distances (1–2.5 mm). By coupling the electric field and flow field, the multi-layer dielectric discharge streamer model was built, and the characteristics of charge and electric field distribution at different gap distances were studied. The test results show that the liquid surface between the electrodes rises during the discharge process. Furthermore, the surface discharge voltage exceeds the air gap discharge voltage. With the simulation analysis, the oil–gas surface discharge is a typical streamer development process. Under 50 kV applied voltage and 2.5 mm gap distance, the average development speed of the streamer is 12.5 km/s. The larger the gap distance is, the greater the average streamer development speed is. The recording and numerical simulation of the discharge process are of great significance for exploring the mechanism of oil–gas surface discharge, optimizing the discharge process, and diagnosing partial discharges.

Numerical Simulation of Trap Modulated Multi-Mobility Charge Transport Under AC Field

Based on the characteristics of charge distribution under AC electric field with a wide frequency range, this paper focuses on the applicability of the traditional bipolar charge transport model under AC field in oil-impregnated paper (OP) insulation by simulation. Three physical processes of charge injection, migration and trapping/detrapping are discussed. In reaction to the influence of amplitude variation of AC field on injection rate, the charge injection process is described by a concatenation of the Ohmic mechanism and the Schottky mechanism. On account of the correspondence between the frequency and carrier mobility, the single mobility mode is modified to the multi-mobility mode, which exhibits the effect of localized state differences in materials on charge migration. The charge hysteresis under AC field is to do with the trapped charges, so the multi-energy trap distribution model is adopted to reveal the matching relationship between the period of electric field and charge residence time in deep traps. By comparing the simulation results and experimental phenomena, the modified model achieves space charge accumulation under a wide frequency range, and the shape of charge distribution is similar to the experiments, which proves the validity of the model. Further, the simulation results demonstrate that the net charge accumulation decreases with the increase of the electric field frequency, while the total charge accumulation shows an inverse trend with frequency, which is related to the coexistence of positive and negative charges.

Surface Charging and Flashover Characteristics of DC-GIS Epoxy Insulators Under AC–DC Composite Voltage

In this article, the surface charge distribution and flashover characteristics of epoxy basin insulators under ac–dc composite voltage with specific proportions in a down-sized dc-gas-insulated switchgear (GIS) are investigated by experiments. Results show that more heteropolar charges are observed on the insulator surface and tend to diffuse toward the central high-voltage electrode with increasing the composite voltage amplitude. Higher prestressing would result in a decline of the ac component but lifting of the absolute amplitude of the flashover voltage. With direct ramp voltage stressing, the insulators present higher flashover voltage than that with prestressing. Besides, the higher the component of ac voltage, the easier the surface flashover. The surface modification of the insulators is performed by direct fluorination. The surface charge distribution and flashover voltage of the fluorinated insulator are improved due to the increase in surface conductivity. It is confirmed that ac/dc superimposed voltage would have significant effects on the insulation performance of dc-GIS and direct fluorination is an effective method to improve the flashover voltage.

Efficient removal of lead(II) ions in water using functionalized poly(styrene) oligomers

In this research, chemically functionalized polystyrene oligomers with acrylamide monomers were applied as alternative adsorbent towards Pb(II) from aqueous solutions. Adsorption process of Pb(II) was optimized using the 2*' fractional factorial design with replicates at the central point supplemented with the central composite design where the percentage adsorption was chosen as the response variable. This variable was simultancously optimized using the desirability functions approach to select the best conditions for the adsorption process. The experimental data reveal that after the optimization, the maximal response was exhibited at 38 °C, pH 5.80, initial adsorbate concentration (36.40 mg L™, and adsorbent dosage (10.77 mg) with the desirability function of 0.9260. Theoretical values and experimental data determined by the central composite design showed a high correlation with a R? value of 0.9810. Under these optimal conditions, the theoretical value for the removal of Pb(II) was 93.12%, while that experimental assay gives a maximum value of 91.23%. Likewise, the analysis of surface charge distribution, the structural and morphological characteristics confirmed the successful chemical modification of poly(styrene) oligomers.

Surface charge distribution characteristics on insulating materials under negative corona in sphere-plane gaps

The accumulation of space charge on the insulation surface can affects the distribution of the total electric field. The surface charge distribution characteristics of dielectrics under negative corona have been studied using spherical plate gaps in this paper. In order to measure the surface potential of three insulating materials under the influence of a DC corona by vibrating electrostatic probe. The experiment tested the surface potential of silicone rubber circular specimen and two umbrella-type disks with different curvatures under negative corona in a spherical gap. Afterwards, a new inversion algorithm was proposed in order to convert the surface potential to a surface charge density. Potential spots were found on the surface of silicone rubber, and the degree of charge clustering of umbrella-type disks was positively correlated with curvature. This experiment will serve as a foundation for future research on the surface charge distribution characteristics of insulation in HVDC corona equipment. Meanwhile, it can also be applied to optimize the insulation design.

Surface Flashover Induced by Metal Contaminants Adhered to Tri-Post Epoxy Insulators under Superimposed Direct and Lightning Impulse Voltages

Metal contaminants can distort the surface electric field of the tri-post epoxy insulator and cause serious surface charge accumulation, significantly reducing the insulation performance of the insulator under the superimposed DC and lightning impulse voltage. In this paper, an experimental platform for charge accumulation and surface flashover of tri-post epoxy insulators under the superimposed DC and lightning impulse voltage was built, by surface point measurement and charge inversion calculation, the surface charge distribution characteristics of tri-post insulators with attached particles was experimentally explored and the influence law of attached metal particles on the charge accumulation was discussed. The results show that metal particles can cause a surge in the surface charge density of the tri-post epoxy insulator, forming bipolar charge spots whose polarity is opposite to that of the adjacent electrodes. The adsorbed metal dust can cause the polarity reversal of adjacent surface charges, forming a large-area unipolar charge spot. Moreover, the flashover voltage of a tri-post insulator under DC superimposed lightning impulse voltage with a clean surface and attached metal particle was measured, and the synergistic induction mechanism of charge spot accumulation and metal particle discharge on the flashover along the face of the tri-post insulator is thereby revealed. Compared with the clean insulators, the surface flashover voltages of tri-post epoxy insulators with metal contaminants adhered decrease under the superimposed voltages of different polarities, but the decline amplitude is greater under the heteropolar composite voltage. When adhered to the middle of the insulator leg, the distribution range of bipolar charge spots is the widest, and the surface flashover voltage decreases sharply, which can drop by 32% compared with the absence of particles. In addition, when the metal dust adsorbed by the tri-post epoxy insulator has a wide distribution range, the impact of metal dust on the flashover voltage is greater than that of the attached metal particles, and its hazard cannot be ignored. The research results can provide a reference for the insulation test method and optimal design of the DC tri-post epoxy insulator.

Investigating the mechanism of fluorescence probe of quinoline derivatives for detecting phosgene in gas and liquid phases

Based on density functional theory and time-dependent density functional theory, the excited state charge distribution characteristics and fluorescence mechanism of fluorescence probe Q-1 and Q-CN have been discussed. The twisting potential energy curve proves that the diethylamine group in Q-CN will be twisted in S1 state. The frontier molecular orbitals proves that Q-CN has a small degree of charge coupling and the oscillator intensity is close to zero, so it is not conducive to luminescence. The results of “hole-electron” analysis prove that the quenching of Q-CN fluorescence is caused by the delocalization of the charge in S1 state.

Co-crystals of ethenzamide with 2-nitrobenzoic acid - Conformational analysis, MD simulations and DFT investigations

In crystal engineering and pharmaceutical chemistry, co-crystals have a wide range of applications. Ethenzamide (EA) is found to form co-crystal with 2-nitrobenzoic acid (NBA). Geometry properties like stability energy, charge distribution, bond length, electronic properties and thermodynamic characteristics have been analyzed. The C–H⋯O hydrogen bond involves C–H of EA and oxygen of NBA. Configuration with the angle, N3–C4–C5–C6 gives the lowest energy conformation. Partition coefficient value suggests that EA-NBA has pharmaceutics behavior. RMSD values show the simulation's relative stability and the complexes, remained stable throughout.

Size and charge distribution characteristics of fine and ultrafine particles in simulated lunar dust: Relevance to lunar missions and exploration

Astronaut anecdotal data, biologic studies, and multi-perspective reports indicate that lunar dust will be a significant hindrance to exploring the Moon, both robotically and by humans. Hence, important characteristics of the lunar dust must be established. Critically needed are detailed particulate matter size, dust cloud concentration, and charge distribution analyses to determine the viability of methods for real-time measurement on the lunar surface. In this study, we applied various state-of-the-art aerosol measurement techniques to characterize fine (0.1–2.5 ​μm) and ultrafine (<0.1 ​μm) JSC-1A lunar simulant particles. The different techniques were assessed at 1 ​atm and evaluated for viability on the lunar surface (i.e., hard vacuum). To represent suspended dust, the simulant was dispersed as an aerosol and size distributions were measured in real-time using multiple aerosol instruments. Results show a unimodal distribution centered at approximately 0.2 ​μm, in fair agreement with previously reported measurements. To demonstrate portability and networkability, two low-cost particulate matter sensors were evaluated for measurement of suspended dust concentration. Strong correlations with an industry standard instrument support the potential candidacy of these sensors for future in-situ measurements on the Moon. Evaluating the capability of compact, low-cost instruments and larger, more robust instruments to precisely and accurately measure particle size distributions is a critical step to determine the prospect of measuring particulate matter with lightweight sensors in multiple lunar environments. In addition, assessing the compact instrument mass, power, portability, complexity, and measurement speed will provide key guidance into mitigating dust-related challenges to future lunar missions.

Characterization of Polycrystalline Cathode Materials in Five Dimensions (5D)

Thermal stability is one of the most desired features for large-scale energy applications, such as batteries used in electronics and electric vehicles. Thermal runaway, heat generation, and gas release are likely to happen for batteries under thermal abuse conditions, leading to severe performance degradation and safety risks. Although the decomposition of electrolytes at high temperatures has been widely studied in the community, a systematic and in situ study of the intrinsic instability of the cathodes in Li ion batteries is lacking. Polycrystalline nickel-rich Li layered oxides (LiNi x Mn y Co1-x-y O2, NMC) were chosen as the platform materials considering the recent improvements in specific capacity but also the rising safety concerns in Ni-rich cathodes.Here we used one of state-of-the-art techniques in microscopy: the full-field transmission X-ray microscope (TXM) to capture the 3D tomography of charged NMC particles, together with the X-ray absorption near edge structure (XANES) spectroscopic capability for Ni oxidation state. Moreover, we performed the XANES-3DTXM measurements during the whole process of heating the NMC cathodes from room temperature up to 250°C, which enables us to monitor the full evolution of NMC secondary particles in real time in 5 dimensions (3D spatial + tunable X-ray energy + temperature).This in situ XANES-3DTXM approach allows us to observe the real-time morphological and chemical evolution at elevated temperatures. The large field of view and reasonably high spatial resolution offer the capability to analyze NMC cathodes at different length scales, ranging from voids of tens of nanometers, to cracks of hundreds of nanometers, to secondary particles of tens of micrometers.With quantification of morphological (e.g., relative volume change, porosity, crack propagation) and chemical (e.g., the oxidation state of Ni, local charge distribution) characteristics as a function of temperature and time, the fundamental degradation mechanisms in polycrystalline nickel-rich Li layered oxides under thermally abuse conditions are thereupon unveiled. Based on these analyses and discoveries, we proposed to alter the primary particle arrangement as an effective solution to alleviate the thermal issues in nickel-rich Li layered oxides.Figure: Schematic of the in situ heating setup, 3D rendering of a NMC secondary particle, and selected morphology section and Ni oxidation state mapping at different temperatures. Figure 1

Exploring the relationship between the “ON-OFF” mechanism of fluorescent probes and intramolecular charge transfer properties

In this study, the excited state charge distribution characteristics and fluorescence mechanism of HClO detection probes HN-ClO (weak fluorescence) and HN-ClO-F (strong fluorescence) probes were investigated based on density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results of electrostatic potential (ESP) map and hole-electron analysis show that the HN-ClO and HN-ClO-F probes have obvious charge separation characteristics in the excited state. The excited state energy decomposition and Merz-Kollman charge analysis demonstrate the existence of distinct planar intramolecular charge transfer (PICT) features in HN-ClO and HN-ClO-F. Due to the strong charge coupling caused by the planar structure, the fluorescence of HN-ClO-F could occur. Furthermore, the weak fluorescence of HN-ClO is caused by inter-system crossing (ISC) between S1 and T1 state. Our result proves that the ICT process could exist in HN-ClO-F, but the PICT process does not cause fluorescence quenching, which have provided an excellent supplement to the mechanism of fluorescent probes. The conclusion is consistent with the fluorescence phenomenon observed in the experiment.

Investigation on the thermal properties, space charge and charge trap characteristics of silicone rubber nano–micro composites

The micro-aluminium trihydrate (ATH) and nano-alumina fillers in the silicone rubber (SR) significantly improve the electrical, thermal and mechanical properties. ATH fillers improved the resistance to the corona ageing and water droplet-initiated erosion. Scanning electron microscopy (SEM) analysis was carried out to understand degradation condition caused due to corona ageing and damage caused due to water droplet-initiated discharges. The inclusion of these fillers significantly altered the surface and bulk charge distribution characteristics of the polymer. A right shift is observed in the trap distribution characteristics. The reduced electric field threshold limit for space charge formation is observed with composites, due to increment in impurities/agglomerations with respect to increment in filler concentration. Performance of composites subjected to polarity reversal is improved on inclusion of nano-filler in addition to micro-filler. The inclusion of fillers enhanced the thermal conductivity and improved significantly thermal stability of the SR composite.

Surface charge measurement under AC voltage using active electrostatic probe and controllable phase truncation scheme

This paper proposes a method for controlling and extracting the truncated phase of AC voltage. Combined with surface potential measurement based on the active electrostatic probe and the inversion algorithm, charge accumulation on the insulator surface is obtained under various electrode configurations and AC voltage. Simulation and experimental results show that the active electrostatic probe method not only provides high measurement accuracy but also has an insignificant effect on the measured electric field. By combining the characteristics of surface charge distribution with the truncated phase of AC voltage, the off-line charge measurement results can be integrated with the microscopic discharge process, to overcome the drawbacks of the traditional off-line measurement method. Thus, we can gain a better understanding of the dynamic process of charge distribution under AC voltage. In addition, the accuracy and reliability of the inversion algorithm are verified using the dust figure method.

Charge accumulation characteristic on polymer insulator surface under AC voltage in air and C 4 F 7 N/CO 2 mixtures

Charge accumulation has always been a problem for the safe operation of gas insulated switchgear (GIS)/gas insulated transmission line (GIL) both under AC and DC. It is of great significance to investigate the behaviour of surface charge under high voltage. In this study, the charge distribution characteristics and accumulation mechanism on insulator surface in air and heptafluorobutyronitrile/carbon dioxide (C4F7N/CO2) mixtures under AC voltage are studied via the means of surface potential measurement and inversion algorithm, combined with the improved method of controlling the truncated phase of AC voltage. The results show that under the needle–plate electrode structure, charge distribution on the insulator surface presents a three-tier concentric circle structure both in air and C4F7N/CO2 gas mixtures, and the charge composition of the innermost circle is closely related to the truncated phase of AC voltage. Under the same amplitude of voltage, the range of charge distribution on insulator surface in C4F7N/CO2 mixtures is smaller than that in air, with the negative charges domination. It is suggested that the characteristic of charge distribution in C4F7N/CO2 mixtures is related to the larger electron attachment cross-section of C4F7N gas in a wide range of electron energy distribution.