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The proliferation of urbanization and the integration of new energy sources have stimulated the development of gas-insulated transmission lines and switchgear (GIL/GIS). In particular, the compact DC GIS in offshore converter platforms will significantly reduce footprints for DC switchyards, exhibit exceptional climatic resistance, and facilitate the cost-effective connection of remote offshore wind farms and submarine links. Nevertheless, insulators used in GIS/GIL always suffer from surface charge accumulation under DC stress, which could distort and enhance the local electric field and thus trigger a flashover at the gas–solid interface if it exceeds certain magnitude levels. This susceptibility becomes a major concern affecting the reliability of DC gas-insulated systems. Beyond these engineering-related challenges lie fundamental physics problems involving mechanisms of charge accumulation and charge-induced flashover which still require exploration. To this end, this paper presents an overview of recent advancements on this topic whilst highlighting relevant issues to be addressed. Specifically, the surface charge accumulation phenomena under DC fields are reviewed, and the charging mechanisms are summarized from macroscopic to microscopic perspectives. Further, the correlation between surface charge and surface flashover is discussed. Moreover, recent developments in tailoring methods for surface charging are also presented. Finally, perspectives are given on current research progress and future needs. [ABSTRACT FROM AUTHOR]

As trapping sites for surface charges, the surface trap is an important factor affecting the insulation performance of the epoxy–SF6 interface, which is closely related to the microstructure and its evolution. However, existing studies often ignore the effect of the degradation of the epoxy surface on the surface traps and charge accumulation during the long-term service of the insulation system. In this study, the surface physicochemical evolution and its influence on surface traps of a typical epoxy–SF6 insulation structure were researched under a DC-temperature gradient condition, and an evolution mechanism of surface traps was proposed. The results show that the free radicals introduced during the material degradation process increase the density and depth of both positive and negative charge traps on the epoxy surface. The effect of free radicals formed by the cleavage of epoxy molecules on the electronic orbital and molecular electrostatic potential of epoxy molecules is the intrinsic reason for the evolution of surface trap evolution. This work may help to understand the long-term evolution mechanisms of the physicochemical characteristics of the epoxy–SF6 interface in DC field and may provide a theoretical basis for the long-term failure mechanism revealing and the insulation performance enhancement. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation is used to study the transport characteristics of NaCl solution in boron nitride nanotubes (BNNTs). It presents an interesting and well-supported MD study of the crystallization of NaCl from its water solution under the confinement of a 3 nm thick boron nitride nanotube with varied surface charging conditions. The results of the molecular dynamics simulation indicate that NaCl crystallization occurs in charged BNNTs at room temperature when the concentration of NaCl solution reaches about 1.2 M. The reason for this phenomenon is as follows: when the number of ions in the nanotubes is high, the double electric layer that forms at the nanoscale near the charged wall surface, the hydrophobicity of BNNTs, and the interaction among ions cause ions to aggregate in the nanotubes. As the concentration of NaCl solution increases, the concentration of ions when they aggregate in the nanotubes reaches the saturation concentration of the NaCl solution, resulting in the crystalline precipitation phenomenon. [ABSTRACT FROM AUTHOR]

Electrochemical biosensors based on structure‐switching aptamers offer many advantages because they can operate directly in complex samples and offer the potential to integrate with miniaturized electronics. Unfortunately, these biosensors often suffer from cross‐reactivity problems when measuring a target in samples containing other chemically similar molecules, such as precursors or metabolites. While some progress has been made in selecting highly specific aptamers, the discovery of these reagents remains slow and costly. In this work, a novel strategy is demonstrated to distinguish molecules with miniscule difference in chemical composition (such as a single hydroxyl group)—with cross reactive aptamer probes—by tuning the charge state of the surface on which the aptamer probes are immobilized. As an exemplar, it is shown that the strategy can distinguish between DOX and many structurally similar analytes, including its primary metabolite doxorubicinol (DOXol). Then the ability to accurately quantify mixtures of these two molecules based on their differential response to sensors with different surface‐charge properties is demonstrated. It is believed that this methodology is general and can be extended to a broad range of applications. [ABSTRACT FROM AUTHOR]

High-voltage direct current (HVDC) links are starting to become widely implemented thanks to their interesting advantages such as reduced operation losses, the absence of reactive power, which allows energy transport via underground cables over long distances, and improved power control. The latter advantage is very essential for renewable energy resource integration into power grids. However, a thorough understanding of the behavior of insulation systems for HVDC components is critical so as to ensure a more reliable service. Indeed, the existence of the direct current (DC) voltage in HVDC components may induce surface and space charge accumulation that can stress insulation further or even promote discharge inception and propagation. As such, this work focuses on showcasing the effect of surface charge on streamers that develop on the interface of liquid–solid insulation due to the advent of lightning impulse (LI) voltage in the HVDC link. This study was performed using finite-element-based numerical simulations that include a quasi-electrostatic model for surface charge accumulation and an electrohydrodynamic fluid model for streamer initiation and propagation. The geometry used was point–plane configuration where the high voltage is applied to the needle electrode located above the liquid–solid interface. The obtained results suggest that streamer initiation is affected by both the accumulated surface charge density and polarity. For a positive streamer, an accumulation of positive surface charge increases the discharge inception voltage as a result of a weakening in the electric field, while an accumulation of negative surface charge decreases the discharge inception voltage due to an intensification in the electric field. Moreover, streamer travel distance and velocity are also both shown to be affected by surface charge accumulation. [ABSTRACT FROM AUTHOR]

The ability to control the mobility and function of droplets is fundamental to developing open surface microfluidics. Despite notable progress in the manipulation of droplets, the existing strategies are still limited in functionalizing droplets. Herein, the coupling of droplet motion and functionalization elicited by an invisible charge wall is reported. The charged superamphiphobic surface is overlapped with a conductor to induce free charge, creating the invisible charge wall at the overlapping boundary. The charge wall can trap droplets and polarize them into Janus charged state. It is found that the trapping degree and the charge distribution in the Janus charged droplet depend on the original surface charge on the superamphiphobic surface. The invisible charge wall can also be established at diverse boundary curvatures, allowing to design pathways for droplet manipulations. Furthermore, the enrichment of protein and nanomaterial in the manipulated Janus charged droplet is demonstrated. The strategy provides a potential microfluidic platform with orthogonal functionalities. [ABSTRACT FROM AUTHOR]

In this article, the influence of polishing orientation on surface charge accumulation and flashover characteristics of the basin spacer in a downsized dc-gas insulated transmission line (GIL) are explored by experiments. Results show that the surface charge distribution of the polished spacers is different from the untreated one. Heteropolar charges can be observed in the polished area and outward expansion area under prestressing condition. The flashover voltages of all polished spacers are decreased. The radial polishing (RP) has the greatest impact on the flashover voltage, and the flashover voltage of the radially polished spacer is decreased by 11% under positive prestressing condition. The metal dust adsorptions of the spacers are also measured, which shows that the radially polished spacer is easier to absorb metal dust and the metal dust diffuses in the radial direction. SEM and energy spectrum scanning of different spacers show that there are more exposed alumina particles on the surface of the polished area. The microdischarge induced by alumina particles is the source of heteropolar charges. When the polished area of the spacers is repaired with epoxy paint, heteropolar charges disappear on the surface of the repaired spacer. It is confirmed that charge accumulation and flashover along the spacer surface are mainly affected by the change of surface morphology on the polished area. [ABSTRACT FROM AUTHOR]

Pickering emulsions stabilized by cellulose nanofibrils (CN) have sparked significant attention, however the fundamental mechanisms underpinning the stabilization process remain insufficiently elucidated. Focusing on an academic debate of surface charge's contribution to stabilization, this study first explored how the varying carboxyl group contents of TEMPO-oxidized CN (TCNs) impacted Pickering emulsions' formation and stability. TCNs with 662 μmol/g carboxyl groups exhibited distinctive attributes, including larger particle sizes (322 nm in length), improved thermal stability (maximum decomposition temperature of 317 °C), and increased viscosity (1.57 Paִִ⋅s) compared to their counterparts with 963–1011 μmol/g charge density. Notably, the former one, with a larger three-phase contact angle (51.5°), higher interfacial tension, and greater detachment energy (21.69 × 10−18 J), resulted in a homogeneous dispersion of spherical oil droplets and super-stable Pickering emulsions with a consistent emulsifying index of 100% over 30 days. These findings clearly clarified that TCNs with a lower charge density exhibit superior emulsifying properties. In addition, for the first time, a distinct oil droplet-decorated fibrillar structure was observed, probably suggesting that TCNs might be able to serve as anchoring matrixes to guide the distribution of oil droplets. These structures seemed to impeded the migration and accumulation of the oil droplets, consequently enhancing the stability of the resulting Pickering emulsions. To sum, this study clearly elucidated the role of surface charge in stabilizing cellulose-based Pickering emulsions and proposed a new model to expound the cellulose-oil interaction mechanisms, thus providing new theoretical and practical insights on utilization of CN as highly effective emulsifier for super-stable food-grade Pickering emulsions. [Display omitted] • TEMPO-oxidized nanofibrils (TCNs) are effective to stabilize Pickering emulsions. • Clarify surface charge's contribution and further understand stabilization mechanism. • Relatively low charge density instead of high charge density for better stability. • Distinct oil droplet-decorated fibrillar structures enhance emulsion's stability. [ABSTRACT FROM AUTHOR]

Surface charge polarity and density influence the immune clearance and cellular uptake of intravenously administered lipid nanoparticles (LNPs), thus determining the efficiency of their delivery to the target. Here, we modified the surface charge with ascorbyl palmitate (AsP) used as a negatively charged lipid. AsP-PC-LNPs were prepared by dispersion and ultrasonication of AsP and phosphatidylcholine (PC) composite films at various ratios. AsP inserted into the PC film with its polar head outward. The pKa for AsP was 4.34, and its ion form conferred the LNPs with negative surface charge. Zeta potentials were correlated with the amount and distribution of AsP on the LNPs surface. DSC, Raman and FTIR spectra, and molecular dynamics simulations disclosed that AsP distributed homogeneously in PC at 1–8% (w/w), and there were strong hydrogen bonds between the polar heads of AsP and PC (PO2−), which favored LNPs' stability. But at AsP:PC > 8% (w/w), the excessive AsP changed the interaction modes between AsP and PC. The AsP–PC composite films became inhomogeneous, and their phase transition behaviors and Raman and FTIR spectra were altered. Our results clarified the mechanism of surface charge modification by AsP and provided a rational use of AsP as a charged lipid to modify LNP surface properties in targeted drug delivery systems. Furthermore, AsP–PC composites were used as phospholipid-based biological membranes to prepare paclitaxel-loaded LNPs, which had stable surface negative charge, better tumor targeting and tumor inhibitory effects. [ABSTRACT FROM AUTHOR]

In this study, a downsized direct current (dc)-gas-insulated transmission line (GIL) model is applied to investigate the surface charging and discharging characteristics of the basin-type spacer in 0.1-MPa SF6 and air. Under a low electric field, the surface charge accumulation is dominated by the bulk conduction of the spacer. As the charging voltage increases, gas ionization occurs in the localized strong electric field, taking over the dominant position. In 0.1-MPa SF6 gas, flashovers typically develop along the convex surface of the spacer under both positive and negative voltages because the homo-charge accumulation induced by brush discharges on the concave surface aggravates the electric field distortion at the convex side. In air, the dc flashovers have the polarity effect. Under the negative voltage, the flashover development is similar to that in SF6 gas. But for positive polarity, the space charge region of positive polarity intensifies the electric field ahead of the corona region, thus promoting the air-gap breakdown at the concave side of the spacer. [ABSTRACT FROM AUTHOR]

Electrostatics and constant current circuits are traditionally discussed without their connection being clearly evident. The conceptual framework and analytical operational methods developed in the study of electrostatics are not used in circuit analysis. In order to bring these two fields of study closer together, a circuit consisting of a battery and conducting wires will be examined where the surface distribution of charge takes center stage in the causal relationship when investigating the emergence of electric current. This allows the use of knowledge about the interaction of electric charges to be employed in the understanding of the physical processes occurring in the circuit components as the connections are established. By examining the circuit in this fashion, the spectrum of problems that can be discussed within the same content is broadened. [ABSTRACT FROM AUTHOR]

[Display omitted] Hypothesis : The properties of the oxidized surface for common materials, such as silicon and titanium, are known to be markedly different from the reduced surface. We hypothesize that surface-oxidized aluminum gallium nitride ((oxidized-AlGaN)/GaN) surface charge behavior is different to unoxidized AlGaN (with ultrathin native oxide only), which can be validated via surfactant adsorption. Understanding these differences will explain why (oxidized-AlGaN)/GaN-based sensors are better performing than AlGaN ones, which has been previously demonstrated but not understood. Experiments : The surface of an AlGaN/GaN structure was oxidized with hot piranha solution and oxygen plasma. AFM force measurements and imaging were performed to probe the charge properties of the surface in aqueous solutions of varying pH containing only an acid or base, or with an added ionic surfactant: cationic cetyltrimethylammonium bromide (CTAB) or anionic sodium dodecylsulfate (SDS). Findings : The (oxidized-AlGaN)/GaN surface is positively charged at pH 4 and pH 5.5, although pH 5.5 should be close to the isoelectric point of the surface. The surface is negatively charged at pH 10 and pH 12, and sufficiently charged to attract cooperative adsorption of CTAB aggregates at pH 12. At pH 2, the evidence is inconclusive, but the surface is most likely positively charged. Compared to unoxidized AlGaN, the (oxidized-AlGaN)/GaN surface shows a wider range of surface charge magnitude over pH values between 2 and 12. This suggests that the (oxidized-AlGaN)/GaN surface has a higher surface hydroxyl group density than unoxidized AlGaN, which explains the higher sensitivity for pH sensors based on (oxidized-AlGaN)/GaN structures. [ABSTRACT FROM AUTHOR]

Background: Limited information is available on the changes in surface electrochemical properties of different‐sized particles of an Anthrosol, compared with the corresponding parental upland soil. Aims: Our overarching goal was to clarify the contribution of different‐sized particles to the soil surface charge. The specific objectives of this work were to examine the differences in the surface charge properties between the Anthrosol and its upland parental Gleysol and to reveal the properties of the different‐sized fractions separated from the Anthrosol, compared with those of the upland Gleysol. Materials and methods: The properties (e.g., negative surface charge, zeta potential, and particle sedimentation) of different‐sized fractions of nanoparticle (NP), coarse colloid, silt, and sand fractions separated from an upland Gleysol and its derived Anthrosol were compared. Results: NPs in both the Anthrosol and the Gleysol carried more negative charge than did the coarse colloids, with cation exchange capacities (CEC) being 186.5% and 58.8% greater, respectively. On the other hand, the presence of more positively charged Fe/Al (hydr)oxides compensated for the negative charge, resulted in a zeta potential of the NPs similar to that of the coarse colloids. More secondary minerals were observed in the coarse colloids of the Anthrosol than in the same fraction of the Gleysol, resulting in more negative charge on the surface of the Anthrosol coarse colloids. The coarse colloid fraction of the Anthrosol, therefore, had a greater CEC, despite representing a smaller mass fraction than in the Gleysol. Overall, the CEC of the Anthrosol was 21% lower than that of the parent Gleysol, which was consistent with the findings of the surface charge, using the cesium (Cs+)‐adsorption method. The sedimentation observations demonstrated that the suspension stability of the NPs was higher than that of the coarse colloids, and that they tended to disperse particularly under high pH conditions. Conclusions: Although the surface charge potential of the Anthrosol was lower than that of the upland Gleysol, the accumulation of organic matter and formation of secondary phyllosilicates resulted in maintenance of the nutrient‐ and pollutant‐binding capacity and agricultural productivity of the Anthrosol. [ABSTRACT FROM AUTHOR]

Free metal particle can affect surface charge accumulation on epoxy insulator installed in gas-insulated transmission line (GIL) or gas-insulated switchgear (GIS), which results in reduction of surface flashover voltage thus threatening the safe operation of the power equipment. This article reports on the charge accumulation behavior on a real size epoxy insulator with bouncing metal particle under DC voltage. A coaxial electrode system was designed for the test under −30 kV, a metal particle-launching system was employed to inject the bouncing linear particle to the insulator surface. The charge distribution was measured by a Kelvin-type probe, and the influence of the particle on the charge accumulation was analyzed with the help of electric field simulation. The results showed that there were mainly two moving patterns of the bouncing particle: the charges were accumulated with speckle shape and the charged particle that hit the edge of electrode had more remarkable influence on the charge accumulation than other particles. It is suggested that the charge distribution feature is dependent upon the collision point and the trajectory of the bouncing particle. [ABSTRACT FROM AUTHOR]

An engineering approach to the computational prediction of surface charging during dielectric tests of medium voltage devices is presented. It is based on a formulation of the saturation charge boundary condition applied to an iteratively estimated area on the insulation surface. The simulation procedure is explained for a simple case study including a rod electrode, shaped barrier, and grounded enclosure. Applications of this procedure to 3-D models of medium voltage devices are presented. [ABSTRACT FROM AUTHOR]

Background: Polyamidoamine (PAMAM) dendrimer applications have extended from tumor cells to multidrug-resistant tumor cells. However, their transportation in multidrug-resistant tumor cells remains unclear. Herein, we investigated the exocytosis rule and mechanism of PAMAM dendrimers in multidrug-resistant tumor cells. Results: Using a multidrug-resistant human breast cancer cell model (MCF-7/ADR), we performed systematic analyses of the cellular exocytosis dynamics, pathways and mechanisms of three PAMAM dendrimers with different surface charges: positively charged PAMAM-NH2, neutral PAMAM-OH and negatively charged PAMAM-COOH. The experimental data indicated that in MCF-7/ADR cells, the exocytosis rate was the highest for PAMAM-NH2 and the lowest for PAMAM-OH. Three intracellular transportation processes and P-glycoprotein (P-gp) participated in PAMAM-NH2 exocytosis in MCF-7/ADR cells. Two intracellular transportation processes, P-gp and multidrug resistance (MDR)-associated protein participated in PAMAM-COOH exocytosis. P-gp and MDR-associated protein participated in PAMAM-OH exocytosis. Intracellular transportation processes, rather than P-gp and MDR-associated protein, played major roles in PAMAM dendrimer exocytosis. PAMAM-NH2 could enter MCF-7/ADR cells by forming nanoscale membrane holes, but this portion of PAMAM-NH2 was eliminated by P-gp. Compared with PAMAM-OH and PAMAM-COOH, positively charged PAMAM-NH2 was preferentially attracted to the mitochondria and cell nuclei. Major vault protein (MVP) promoted exocytosis of PAMAM-NH2 from the nucleus but had no effect on the exocytosis of PAMAM-OH or PAMAM-COOH. Conclusions: Positive charges on the surface of PAMAM dendrimer promote its exocytosis in MCF-7/ADR cells. Three intracellular transportation processes, attraction to the mitochondria and cell nucleus, as well as nuclear efflux generated by MVP led to the highest exocytosis observed for PAMAM-NH2. Our findings provide theoretical guidance to design a surface-charged tumor-targeting drug delivery system with highly efficient transfection in multidrug-resistant tumor cells. Especially, to provide more DNA to the nucleus and enhance DNA transfection efficiency in multidrug-resistant tumor cells using PAMAM-NH2, siRNA-MVP or an inhibitor should be codelivered to decrease MVP-mediated nuclear efflux. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy insulator installed in gas-insulated transmission line (GIL) and gas-insulated switchgear (GIS) has been recognized as a crucial factor for electric field distortion that results in the reduction of surface flashover voltage. This article reports on the gaseous ionization dependence of the charge accumulation pattern on a real-size epoxy insulator with multiarc surface profile by using various gas atmospheres. A coaxial electrode system was designed to investigate the charging behavior under dc voltages of −10, −20, and −30 kV. The insulator and electrodes were placed in a metal-enclosed test chamber, which was filled with 0.1 MPa air or 0.4 MPa SF6/N2 mixture to estimate the influence of the gas atmosphere on the charge accumulation behavior by a Kelvin-type probe. The accumulation mechanism and the electric field distortion induced by the charges were demonstrated based on numerical simulation. The results indicated that positive charges were accumulated in the shape of speckle on insulator surface in air, whereas both positive and negative charges were accumulated in SF6/N2 mixture and positive charge speckles appeared in SF6/N2 mixture only when the voltage raised up to −30 kV. It is considered that the charge accumulation behavior is determined by the competition result among the bulk, the gas and the surface conductions. As compared with the case in air, gaseous ionization in SF6/N2 mixture is more difficult to occur, which leads to the obvious difference in the charge accumulation pattern. [ABSTRACT FROM AUTHOR]

Charges due to ionization at conductors at low electric field serves as the main source of charge carriers that is responsible for surface charge enhancement, especially for hetero-polar charges on the convex surface side of spacers inside DC gas-insulated transmission lines (GILs). In this paper, simulation results of charge generation processes from gas side, including natural ionization, micro-discharge and field emission, are presented. The results show that for the case where the electric field strength is -6.548 kV/mm and the gas pressure is 0.4 Mpa, when conductor roughness Ra is lower than 24.16 µm, natural radiation ionization is the main cause of the dark current. When Ra is between 24.16 µm and 188.59 µm, the dark current is dominated by micro-discharge. The Fowler-Nordheim (F-N) field emission occurs when Ra exceeds 188.59 µm. Considering the roughness of the conductor in the actual GIL, the increase in the dark current due to local roughness is mainly due to micro-discharge rather than F-N field emission. The results in this paper provide an important part for further determining of conductor surface conditions in high voltage direct current (HVDC) GILs and serve as an important reference for completion of the surface charging model of spacers under DC. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy insulator installed in gas insulated switchgear (GIS) or gas insulated transmission line (GIL) has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on surface charge accumulation behavior on a actual epoxy insulator for 100 kV GIL prototype with multi-arc surface profile. A coaxial electrode system is used to investigate the charging behavior under DC voltages with metal particles positioned at various positions of the surface so as to estimate its influence on the charge accumulation behavior using a Kelvin type probe. The results show that positive charges are accumulated mainly on the nonplanar region around the high voltage electrode in the shape of speckles, and the average charge distribution along the radial direction presented a double-peak feature. Moreover, the charge accumulation is enhanced by metal particles contacting to the grounded electrode. Using a numerical simulation method, it is suggested that the charge accumulation is mainly determined by gaseous ionization which is enhanced by the metal particle induced electric field distortion. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on polymer insulating material has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on the charge accumulation behavior between a pair of finger-shaped electrodes on epoxy/Al2O3 nanocomposites under dc voltage superimposed by repetitive pulses. The charge distribution was measured by means of an electrostatic voltmeter, from which the average charge density could be calculated. Effects of dc voltage, nanofiller content, and pulse voltage on charge accumulation behavior were investigated. Obtained results showed that with the increase in the filler content from 0 wt% to 5 wt%, the average charge density increased initially then appeared to decrease. The superposition of repetitive pulses on dc voltage led to a remarkable growth in charge accumulation as compared with that when only dc voltage was applied. It is suggested that the charges are originated from local gaseous ionization and/or electrode injection, which is determined by the combined voltage. The charge density is dependent upon the surface trap, which is affected by nanofiller content. The superposition of repetitive pulse is considered as a possible reason to encourage local gaseous ionization that results in enhanced accumulation of surface charge. [ABSTRACT FROM AUTHOR]

This study was designed to evaluate and compare the stability, antioxidant and anticancer activities of selenium nanoparticles (SeNPs) decorated with different molecular weight (MW) of chitosan (CS) (1500 Da, 48 kDa, 510 kDa). The size range of well‐dispersed SeNPs was effectively controlled by I− first and then coated with CS. The morphology, size and surface charge of generated SeNPs were characterised by several technologies. Fourier transform infrared spectroscopy was used to investigate the relationship between SeNPs and CS. SeNPs decorated with CS (510 kDa) can keep stable for more than 45 days. As observed from the results of a simple photometric system, the antioxidant activities of decorated SeNPs were enhanced compared to undecorated SeNPs. SeNPs coated with higher MW of CS (510 kDa) showed the strongest antioxidant activities. Moreover, the treatments of SeNPs decorated with CS inhibited the growth of HepG2 cells in a time‐ and dose‐dependent manner. The proposed results demonstrated the critical roles of the MW of CS on the stability, antioxidant and anticancer properties of CS‐coated SeNPs, which provided an important design cue for future applications of functional foods and additives. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Based on extensive experimental investigations on many different oxide nanoparticles, it is now a well-established view that the counter-ions exhibit ion specific effects due to their high charge density and strong interaction with oppositively charged surfaces. On the other hand, studies regarding co-ion effects are scarcely reported in the literature. In this study we have measured the surface charge densities and gel-times of silica nanoparticles in a number of salts which have the same counter-ions but different co-ions, i.e. anions in this case. Gel-times were measured in LiCl, NaCl, NaNO 3 , NaClO 4 , NaClO 3 and Na 2 SO 4 as well as in KCl, KNO 3 , and K 2 SO 4. We have seen clear correlations between the gel-times and the extent of ion pairing in the solutions; salts that have strong ion pairing exhibit longer gel-times than salts having highly dissociated ions. To better understand the mechanisms at work we have determined the surface charging of silica nanoparticles in these salt solutions and we have observed that the surface charging behavior of silica nanoparticles follows the trends seen in the gel-time studies. From our gel-time determinations and potentiometric measurements we can claim that there is a clear co-ion effect on the gelling and surface charging of silica nanoparticles. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on the insulator surface and the resulting flashover voltage reduction are considered the primary factors to hinder the large-scale use of HVDC system, especially the gas-insulated system. In this study, Buckminster-fullerene C60 of different loadings is introduced into epoxy resin for the purpose of restricting the mobility of charge carriers within the material and thus suppressing the charge accumulation on the insulator surface under dc voltage. Experimental results have shown that with the addition of tiny amount of fullerene C60 into epoxy, the conductivity of the composites decreases significantly with the loading and reaches its minimum around 100∼200 ppm, which can be as low as 20% that of neat epoxy. By using the Kelvin-probe method and an advanced inversion algorithm, the surface charge distribution on the fullerene-filled epoxy resin insulators with different filler loadings are obtained. It is observed that the addition of 200 ppm fullerene C60 into epoxy resin can effectively suppress the charge accumulation on the insulator surface. The interfacial polarization model is adopted to interpret the mechanism of surface charge accumulation, which shows that reducing the bulk conductivity of the insulator can effectively suppress the surface charging. This paper provides a potential solution for engineering epoxy based insulators used for the dc power system. [ABSTRACT FROM AUTHOR]

Charge generation at the interfaces of gas-insulated switchgear or gas-insulated lines is mostly studied from a macroscopic point of view. Integral current measurements are a common method to determine the average inception field strengths and intensities of micro discharges. However, because of the lack of spatial resolution and measurement sensitivity, these experiments do not provide deeper insights on the microscopic processes. By applying surface potential measurement techniques, studying the charge generation of single interface protrusions and drawing conclusions relative to their spatial distribution have become possible. This paper presents a spatially resolved analysis of charge-generation processes at rough aluminum electrodes and insulating interfaces. The results reveal a highly inhomogeneous charge generation at the interfaces even for electric fields below 6 kV/mm. Analyzing the charge generation from a macroscopic perspective has been demonstrated to possibly underestimate the local charge generation by up to three orders of magnitude. Using sulfur hexafluoride (SF6) as the insulation gas at 0.45 MPa and Al2O3-filled epoxy resin insulators, the inception field strength for charge generation at the insulating interface is measured to be 3 kV/mm. For a technical insulation system that includes both a rough aluminum electrode and an insulating interface, significant discharge intensities are observed at a 5-kV/mm electric field. From these results, micro discharges are expected to be highly relevant for dimensioning of gas-insulated devices. [ABSTRACT FROM AUTHOR]

Surface charge accumulation of polymer insulating materials is harmful to the safe operation of electrical equipment, especially under DC electric field excitation. In order to ensure the safety and stable operation of HVDC power system such as Gas-insulated transmission line, it is necessary to understand the influence of the surface charge on the flashover and improve the surface charge dynamic characteristics. In this paper, Epoxy resin (EP) is deposited by SiOx thin films with different plasma treatment conditions. The flashover voltages are measured with and without surface charges. The results show that the flashover occurs at lower voltage due to the accumulated charges on the EP surface. In particular, the surface charge with the same polarity of flashover discharge can reduce the surface flashover voltage significantly. Moreover, the charge decay rate is increased up to 90% by plasma treatment of 3 min, corresponding flashover voltage is increased. In addition, the flashover voltages of samples during the surface charge dissipation are obtained. Both static impact index I and dynamic impact index S are introduced to estimate effect of surface charge on dielectric surface flashover. [ABSTRACT FROM AUTHOR]

The design of spacers for operation under DC stress is a challenging part for gasinsulated substations (GIS) and gas-insulated transmission lines (GIL). This series of papers has proposed a novel way to develop a spacer for operation under high-voltage direct-current (HVDC) conditions. In this part, a model spacer based on adaptively controlling surface charges is briefly introduced and is verified using routine tests, including electric field strength simulations, X-ray imaging, mechanical simulation and mechanical testing. In addition, the thermal expansion coefficient and thermal conductivity of the spacer are also measured to investigate its operational stability under various thermodynamic conditions. The results show that the geometrical improvements and SiC doping are available to reduce both the normal electric field strength around the central electrode and the tangential electric field strength around the enclosure. The mechanical properties of the concave side of the spacer are slightly lower than those of the regular spacer, while the mechanical properties of the convex side demonstrate the major improvements during both simulations and water pressure-based destructive testing. It is hoped that this work will provide a new approach for the design of spacers for use in HVDC GIS or GIL. [ABSTRACT FROM AUTHOR]

The established theories behind low-field ion-drift currents assume that the charge generation from natural ionization is the main source of the charge-carriers, and that it defines the current flowing through the insulation gas in gas-insulated direct current (DC) devices. This charge generation is assumed to be independent of the applied electric field in the cases where the electric field is sufficiently below the onset of microdischarges at the interfaces. However, the results of a few previous studies have suggested the presence of a field-dependent current contribution from some conduction processes, which might significantly accelerate the decay of the surface charges distributed on the insulator surfaces. In this paper, an extensive study on low-field charge transport is presented, and the influences of the insulation volume, electric field, and gas pressure on low-field charge transport are discussed. In accordance with the common structure employed in gas-insulated devices, Al2O3-filled epoxy resin is used in the solid parts of the device and sulfur hexafluoride (SF6) is used for gaseous insulation. At electric fields of approximately 1800 V/m, a gas current that is up to 30 times higher, when compared to the conduction currents caused by the charge generation from natural ionization, is observed. This enhanced current reveals a further conduction process acting in a limited range of low electric fields and is characterized to be independent of the applied voltage polarity. With an increase in the gas pressure, the current amplitude is found to increase linearly and higher electric field is required to reach its maximum. At electric fields below 200 V/m, the conduction current reverses its pressure dependency and increases with decreasing gas pressure. The reported findings strongly indicate that the enhanced low-field charge transport in gasinsulated devices may be owing to electrophoretic conduction. [ABSTRACT FROM AUTHOR]

• Preparation of charge impregnated surface using triboelectrification is studied. • Charge density profile is estimated from drop impact on pillared surface. • Drop translation over surface with charge density gradient has been established. • Higher charge gradient accelerates drop transport. • Velocity rises faster in case of higher surface contact angle. Though different methodologies like thermal and magnetic fields have been tried to control a droplet's mobility in biochemical and medical applications, charge imprinted super-amphiphobic surface is the recent and promising development in which droplets can be transported through any predefined path over the surface. Such surfaces are electrified by impacting water droplets from varying release heights through triboelectrification. Impacting droplets on pillared surface dynamics of the same have been analyzed to understand the nature of electrostatic charge distribution generated. Further to this, droplet actuation on such surfaces with surface charge gradient has been simulated. Charge separation inside the liquid droplet and charge accumulation near the interface has been visualized to understand the phenomenon. Asymmetry in droplet shape and charge distribution has been analyzed as the reason behind the droplet actuation. The effect of different charge density gradients and surface wettability over droplet mobility has also been studied. [ABSTRACT FROM AUTHOR]

• The effects of channel shape and surface charge on the ion current rectification in asymmetric nanochannels were comprehensively investigated. • Simple increase or decrease of the spatial size will not beneficial for improving the ICR performance. • The specified asymmetric surface charge on the outer wall surface can strongly enhance the ICR performance. • The research results provide essential insights on the ion transport and useful guidelines for the design and performance optimization of biological sensors and nanofluidic devices. Ion current rectification (ICR) in nanochannels has attracted increasing attention for its great potential in the applications of ionic circuits and biological sensors. Herein, the influence of nanochannel shape and surface charge on the ion transport and ICR performance of asymmetric nanochannels was numerically investigated. Firstly, three asymmetric nanochannels with different shapes (bullet, conical, and trumpet) were constructed to investigate the spatial size effect on the ICR behavior. And then selected the best-performing one to further analyze the effect of the surface charge on the ICR. In the investigation of spatial size effect, it is found that the increases and the decreases of spatial size will not be beneficial for improving the ICR performance and the conical nanochannel exhibits the best performance. In the investigation of surface charge effect, it is found that specified asymmetric surface charge on the outer wall surface enhances the corresponding ICR performance, revealing the cooperative role with inner wall surface charge. Besides, it is found that the outer wall surface charge is dominant when the nanochannel length is small and the inner wall surface charge is dominant when the nanochannel length is large. Moreover, the finite length enhancement effect for ICR performance is illustrated by tuning the range of outer wall surface charged zone, indicating the charged zone near the entrance and exit plays the dominant role on ion transport. The obtained results provide essential insights on the ion transport and useful guidelines for the design and performance optimization of biological sensors and nanofluidic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• An experimental method for surface charge density at liquid-liquid interface based on streaming potential setup is proposed. • After validation, the setup measures the surface charge at the surfactant-free decane-KCl solution interface. • The negative surface charge at the decane-KCl solution interface is confirmed, which is found to increase when increasing the pH. Surface charging at immiscible liquid-liquid interface is essential to the emulsion stability, surfactant adsorption, and various engineering applications such as drug delivery and mineral flotation. However, droplet electrophoresis, as a widely-used electrokinetic method to measure the surface charge density, has various limitations in physical modeling and sample preparation. In this work, an alternative experimental method based on streaming potential setup is proposed. A Y-Y shaped microchannel was used to make a flat and stable liquid-liquid interface. The inner wall was coated with polymer to suppress the interference of the solid-liquid interfacial electrokinetics in the liquid-liquid one. The experimental setup was first verified by revisiting the aqueous solution-silicon surface charging, after which the surfactant-free decane-KCl solution interface charging was investigated. The negative surface charge at the decane-KCl solution interface is confirmed and found to increase when increasing the pH. This result is compatible with the probable charging mechanism that the acquired negative surface charge results from hydroxyl ion adsorption onto the interface. The proposed method enables the simplicity and flexibility for further side-by-side studies on the liquid-liquid interface charging mechanism and will inspire the quantitative macroscopic interfacial modeling for numerous scenarios, such as the droplet electrophoresis and interfacial electro-hydrodynamics. [Display omitted] [ABSTRACT FROM AUTHOR]

• The coupling effect of surface charge and boundary slip are studied. • The boundary slip tends to decrease the surface charge density. • The surface charge in turn reduces the boundary slip. • The boundary slip greatly enhances the energy conversion. • Output power deviates significantly upon the constant and coupling property. Inspired by the universal phenomena in nature and advances in nanotechnology, the ion transport in nanochannel receives increasing attention and shows great promising in energy conversion. The precedent studies generally predicted the ion transport by tuning the single physical parameter, the understanding of ion dynamics in the real multi-physical coupling systems is still scarce. Here, an ion transport model coupled with surface charge and slip effects is proposed to investigate the energy conversion behavior in nanochannel. The results show that the surface charge density increases with the increasing bulk concentration, nanochannel size and solution pH. The original boundary slip tends to decrease the surface charge density and the surface charge in turn reduces the boundary slip significantly, which manifests the strong coupling effect of diverse factors. The output power and energy conversion efficiency increases first and then decrease with the increasing bulk concentration and pH. The increase of channel size is beneficial for promoting output power, but unfavorable on energy conversion efficiency. More important, the boundary slip greatly enhances the output power and energy conversion efficiency, leading to a maximum output power and energy conversion efficiency is 2.7 pW and 30%, respectively. As a proof of concept, this work shows the distinct deviation in power generation in ion nanochannel with the constant and dependent physical property, providing the useful information to guide the design of real fluidic energy devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Laser-ablated template and fluoroalkyl silane modified composite coatings are used to prepare a micro- and nano-structure on silicone rubber surfaces. By testing the surface potential accumulation and dissipation process, we assess the suppression of surface charge on superhydrophobic silicone rubber. The surface physicochemical properties and resistivity are examined. The electron and hole trap distribution are analysed using isothermal current decay theory. Peak density of traps associated with the superhydrophobic surfaces are found to be promoted to lower energy levels relative to unmodified silicone. Surface micro-structure increases trap density and reduce trap depth; nano coatings are shown to further reduce surface trap depth. The improvements shown to suppress surface charge accumulation is beneficial to a range of electrical industries and helps mitigate surface flashover on insulation. [ABSTRACT FROM AUTHOR]

Synthesis of iron nanoparticles (INPs) with a biocompatible coating usually is a multistep process which requires harsh, special and protected reaction conditions. In the current experiment, the authors used Xanthomonas campestris cells to develop a facile method for fabrication of biocompatible INPs. Bacterial cells were supplied with ferric citrate as an iron precursor. Transmission electron microscopy micrographs exhibited that xanthan gum‐coated INPs are synthesised and deposited on the surface of X. campestris cells and produced nanoparticles were 20–80 nm in diameter with 41.7 nm mean particle size. Xanthan gum coating with about 7 nm thickness formed a clear hollow around each nanoparticle. According to thermogravimetric analysis, the coating was about 13.4% of the total INPs weight. Prepared particles had a zeta potential of −114 mv which is an ideal surface charge to make particles colloidally stable in aqueous matrixes. Xanthan gum‐coated INPs were non‐crystalline with low saturation magnetisation value of about 0.26 emu/g. [ABSTRACT FROM AUTHOR]

Charge accumulation on a solid dielectric surface is one of the critical concerns for the design and optimization of the insulation system in a high-voltage power equipment, since it will lead to the overstress of electrical insulation. Therefore, it is important to obtain the charge density distribution on a solid dielectric surface with high accuracy. The acquisition of surface charge for insulators requires multipoint potential measurements to establish the inverse calculation for the determination of an unknown charge distribution. Up to now, extensive studies have been conducted on this subject; nevertheless, the methods are either too complicated and time consuming, or only applicable for specific arrangements, or with poor accuracy. In this paper, the problem is divided into two categories, i.e., shift-variant system and shift-invariant system, and the basic principle of an improved inversion algorithm is interpreted to solve the problem. The 2-D Fourier transform and Wiener filter techniques are employed in the algorithm for shift-invariant system thus the relationship between potential and charge density can be processed in spatial frequency domain, which tremendously simplifies the conventional procedure. The accuracy and resolution of the algorithm are discussed in detail with the aid of numerical examples. In the end, experiments are conducted and the effectiveness of the algorithm is verified. [ABSTRACT FROM AUTHOR]

The Gas Insulated Switchgear (GIS) equipment observes surface charge accumulation under DC or AC voltage in real operation, which could distort the electric field and incur flashover eventually. With a 3D high-resolution surface charge measurement system established on actual 220 kV GIS basin insulator, the present research captured the surface charge distribution characteristics of the insulator under DC and AC voltage through high-precision probe scanning on the insulator surface. The test results show that: 1) Surface charge demonstrates obvious polarity effect under DC voltage. Under positive DC voltage, there accumulated mainly positive surface charges. Under negative DC voltage, the polarity of accumulated surface charges is all negative. Regardless of charge polarities, the surface charge density increases as the voltage amplitudes mounts and the voltage application duration prolongs. 2) Surface charge accumulation also takes place under AC voltage application. All charges are negative and distribute in a uniformed manner but in smaller density comparing to the DC scenario. As the voltage amplitudes increase, the surface charge density first increases, then decreases and finally reaches a near saturation state. As voltage application goes on, the surface charge accumulation becomes more obvious. Above all, the insulation issues in relation to surface charge accumulation require due attention in the application and maintenance of GIS equipment, and the present research attempts to provide useful reference for the optimal design of GIS/GIL insulators. [ABSTRACT FROM PUBLISHER]

The ability to retain localized charges at the surface or interface of dielectric materials is a universal property that applies to many different fields such as tribocharging, charge nanopatterning, nanoxerography, etc. Once the surface is charged, its stability and subsequent discharging rate will determine the potential applications of a given system. This decay rate is properly defined by the macroscopic equations which depend on dielectric constants and conductivities of the two media. Here, we derive the equations to model the decay of charge distributions localized at the surface/interface of materials and solve them avoiding additional approximations made so far. Addressing the problem in the Fourier space, we arrive to a compact generic equation which provides a useful tool to determine both the bulk and surface conductivities of a material. Furthermore, we show that Kelvin Probe Force Microscopy (KPFM) is a particularly suited method to exploit this tool. Monitoring the charge decay of previously injected charge patches on silicon dioxide (SiO 2), together with an appropriated data analysis, we verify the behavior predicted by our equations. This allows us to characterize the surface and bulk conductivities of SiO 2 layers as well as its dependence with the relative humidity. [Display omitted] • Surface charging of dielectric materials is a universal property. • The dependence of the surface charge decay rate with the system geometry is established. • Surface and bulk conductivities are obtained with Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

Charge accumulation on a solid insulator surface is one of the critical factors for the development of dc gas-insulated equipment since it will lead to the overstress of polymeric insulation due to local field distortion and enhancement. Therefore, it is important to study the charge accumulation phenomenon on spacer surface under dc field. For decades, researchers have made tremendous progress on this subject by measurement and simulation. However, measurement results are quite different by different researchers due to various electrode configurations and experimental conditions. Further, most researchers use potential to represent charge density, which is not rigorous in that many charge density distribution details are hidden behind the potential. As for pure numerical simulation, reports are rather academic and sometimes cannot accord with the real fact. In this paper, attempts are made to characterize the charge accumulation patterns on spacer surface in HVDC gas-insulated system. Surface charge distributions on a model GIL spacer in 0.1 MPa air under DC voltage are obtained by an advanced measurement method, from which the dominant uniform charging pattern and random charge speckles are separated. Mechanism responsible for the dominant uniform charging pattern is discussed with the aid of a simulation model. Results indicate that, in a well-cleaned system, the electric current through the spacer bulk is the principal factor, but gas conduction is not negligible due to some inevitable ion sources. Highly localized pockets of charge are also observed, which are referred to as speckles. They may originate from micro discharges due to tiny metal particles on the spacer surface or microscopic protrusions on the electrodes. [ABSTRACT FROM PUBLISHER]

Polyimide (PI) films have excellent electrical, mechanical and thermal properties in aspect of resisting corona, aging and radiation. However, the pulse voltage combined with dc voltage often causes concentration of local electrical field, which makes the surface charge behaviors more complex and threatens the system. As a means of surface treatment, direct fluorination has been proved as an effective way to improve the polymer properties, without compositing the bulk characteristics. Therefore, this paper intends to reveal the effects of fluorination on surface charge coupling behaviors of the PI films under dc and pulse voltage combination. The PI samples fluorinated for 0, 15, 45 and 60 min were obtained. Surface corona discharging was stressed under the combination of dc and pulse voltage. The surface charge accumulation, decay and distribution were measured coupled with an analysis of trap distribution. The results show the surface charge dynamic behaviors are strongly correlated with the fluorination time, pulse voltage amplitude and polarities of the dc and pulse voltage combination. The trap distribution results imply that the effect of fluorination and charging condition attribute to the change of trap depth and amount. Besides, surface charge behaviors are greatly improved by appropriate fluorination. [ABSTRACT FROM AUTHOR]

The abnormal stability of bulk nanobubbles has attracted substantial attention from academia and industry since classical Epstein–Plesset theory predicts that gas bubbles cannot keep stable thermodynamic equilibrium spontaneously. The dual nature of ionic surfactants, acting simultaneously as charge carriers and attenuators of surface tension at the gas–liquid interface, enables them to play a unique role in bulk nanobubble stabilization. Herein the stability of bulk nanobubbles in anionic, cationic and nonionic surfactant solutions over a wide range of concentration is studied. Experimental results show that different kinds of surfactant molecules are involved in the nucleation and stabilization of bulk nanobubbles in different ways. We demonstrate that the accumulation of net charges carried by surfactant ions at the interface is predominantly responsible for stabilizing nanobubbles, instead of the reduction of surface tension. With theoretical calculations, we further quantify the coupling action of interfacial tension and surface charge on the stable equilibrium state of bulk nanobubbles. The result illustrates that the interfacial tension and the degree of gas saturation together determine the upper limit of the bubble size that can exist stably. Our study identifies a route to explore the intrinsic mechanism of bulk nanobubble's stability. [Display omitted] • Stability of bulk nanobubbles in ionic and nonionic surfactant solutions is studied. • Surfactant molecules are involved in the nucleation and stabilization of nanobubbles. • Accumulation of net charges is predominantly responsible for stabilizing nanobubbles. • Coupling action of interfacial tension and surface charge is revealed. • Interfacial tension and gas supersaturation together determine the upper bound size. [ABSTRACT FROM AUTHOR]

Tailoring Electrode Surface Charge to Achieve Discrimination and Quantification of Chemically Similar Small Molecules with Electrochemical Aptamers (Adv. Funct. Cross-reactivity, drug discrimination, drug quantification, electrochemical aptamer biosensors, nanostructured electrodes, surface charge Keywords: cross-reactivity; drug discrimination; drug quantification; electrochemical aptamer biosensors; nanostructured electrodes; surface charge EN cross-reactivity drug discrimination drug quantification electrochemical aptamer biosensors nanostructured electrodes surface charge 1 1 1 01/05/23 20230103 NES 230103 B Electrochemical Aptamer Biosensors b In article number 2208534, Fu, Soh, and co-workers report an electrochemical biosensor to distinguish molecules with a minuscule difference in chemical composition by tuning the charge state of the surface on which the aptamer probes are immobilized. [Extracted from the article]

Perfluoroalkyl compounds (PFCs) are environmental toxicants and their widespread detection and accumulation in the environment can be detrimental to the ecosystem. In this study, surface charge of GO membranes was engineered to enhance selectivity of graphene oxide (GO) membranes and for the removal of perfluorooctanoic acid (PFOA ∼400 Da) in real concentration ranges in wastewater streams. The structure and physicochemical properties of the GO and modified GO nanosheets and their corresponding membranes were assessed using several characterization techniques. The modified GO membranes showed a water flux of 83.1 ± 1 L m−2 h−1 together with maximum rejection efficiency of 98.4% for 50 ppm PFOA at pressure of 0.45 MPa, which is the highest value reported to date. Compared to the GO membrane, the modified GO membrane exhibited higher water flux and PFOA rejection efficiency by 300% and 70%, respectively. The high surface charged and electron rich GO nanosheets reduce the interlayer spacing in the modified membrane and simultaneously enhance the surface hydrophilicity which leads to increased PFOA retention and enhanced water permeation. These results point to the potential of the modified GO membranes for wastewater treatment. [Display omitted] • Surface of graphene oxide membrane was engineered by positive and negative chargers. • PDDA and PSS were used to, respectively, create positive and negative charges. • The modified membranes showed high increase in water-flux and PFOA rejection efficiency. • The obtained rejection efficiency for PFOA molecules by PDDA-GO membranes was 98.4%. [ABSTRACT FROM AUTHOR]

Ferrihydrite is a poorly crystalline iron (hydr)oxide and highly efficient adsorbent for heavy metals. Al-substitution in ferrihydrite is ubiquitous in nature. However, the effect of Al-substitution on the surface reactivity of ferrihydrite remains unclear due to its low crystallinity. The present study aims to clarify the microstructure and interfacial reaction of Al-substituted ferrihydrite. Al-substitution had little effect on the morphology and surface site density of ferrihydrite, while the presence of ≡AlOH−0.5 sites resulted in higher proton affinity and surface positive charge of ferrihydrite. Besides, the affinity constant of Pb2+ adsorption on the surface of ferrihydrite decreased at higher Al content, which further decreased the adsorption performance of ferrihydrite for Pb2+. The modeling results revealed that bidentate complex was the dominant Pb complexation species on the surface of ferrihydrite, which was less affected by Al-substitution. The present study provides important insights into the effect of Al-substitution on the interfacial reaction at the ferrihydrite-water interface. The obtained parameters may facilitate the future advance of surface complexation model. [Display omitted] • Pb2+ adsorption on Al-substituted ferrihydrite was studied by CD-MUSIC model. • The presence of Al–O sites contributed to a higher proton affinity and surface charge. • Al-substitution decreased the adsorption performance of ferrihydrite for Pb2+. • Bidentate complexes were the dominant Pb species on the surface of ferrihydrite. [ABSTRACT FROM AUTHOR]

Electrically-insulating samples placed on the grounded sample tray in ionization detectors perturb the electric field within the detector. The resulting alpha particle emissivity of the samples is reduced depending on the magnitude and polarity of the surface voltage. Data are shown for samples with positive and negative surface charge, as well as methods to both measure and eliminate the effects of the surface charge. [ABSTRACT FROM PUBLISHER]

As one kind of the basic insulating materials, polyimide has been widely used in turn to turn insulation and turn to ground insulation in inverter-fed motors. However, the pulse voltage from the converter often causes overvoltage and localized high electrical field in the insulation system. During applying the pulse voltage, charges accumulate on the surface of the insulator, which could affect the dielectric property and cause the breakdown of insulation. Direct fluorination is a method to modify the surface layer of the polymers without changing the bulk properties. As a result of the fluorination, hydrogen atoms are replaced by the fluorine atoms and the component of the polymer surface is changed, which can influence the surface charge accumulation and affect the electrical properties. The experiment in this paper was focused on the effect of pulse duration and pulse number on surface charge of the polyimide films. The polyimide films with the fluorination time of 0, 15, 45 and 60 min were prepared. Surface charging was performed by corona discharging using repetitive pulse power at the temperature of 20 °C with the relative humidity of ~15%. The repetition frequency was 1 kHz and the pulse duration was 50, 110 and 210 μs, respectively. The surface charge decay was measured using a specific probe coupled with an electrostatic voltmeter. The results showed that the surface charge increases with increasing the pulse number and the duration of the microsecond pulse. [ABSTRACT FROM AUTHOR]

In this study, the Escherichia coli ( E. coli ) strain ATCC 11775 was studied to determine its surface charging properties in a range of different aqueous salt solutions, with the aim of evaluating its potential as a monitor organism for water treatment. Zeta potential measurements were carried out in various solutions containing: NaCl, CaCl 2 , MgSO 4 , ZnSO 4 and C 14 TAB, at different pH values and concentrations. Interestingly, it was found that the zeta potential of this strain of E. coli remained fairly constant at pH values over about 6, in 1 mM NaCl solutions. In order to explain the cell surface charging properties, a simple, mass action surface ionization model was developed. This model indicates that the surface charging of these E. coli cells can be modeled simply using the ionization behavior of the acid groups in the common anionic membrane lipid phosphatidylserine (PS). There appeared to be no specific, strong adsorption of either divalent anions or cations, until high salt concentrations, above about 0.1 M. The results suggest that at high concentrations both Ca 2+ and SO 4 2− ions are strongly adsorbed at the cell surface. However reduction of the magnitude of the surface electrostatic potential, due to Ca 2+ ion adsorption, did not appear to cause any cellular binding. In comparison, cationic surfactant was strongly adsorbed by the cell membrane surface, even at concentrations of 0.1 mM, and light scattering studies indicated that the adsorption of the surfactant appeared to lyse the cell membrane and release internal cellular materials leading to a significant reduction in cell size. [ABSTRACT FROM AUTHOR]

As one of the basic insulating materials, polyimide films have been widely used in turn to turn insulation and turn to ground insulation in wind turbine generators. However, the pulse voltage from the converter often causes overvoltage and localized high electrical field in the insulation system. Surface charge could affect the dielectric property and cause the breakdown of insulation. Direct fluorination is a method to modify the surface layer of the polymers without changing the bulk properties. As a result of the fluorination, hydrogen atoms are replaced by the fluorine atoms and the component of the polymer surface is changed, which can influence the surface charge accumulation and affect the electrical properties. The experiment in this paper was focused on the effect of direct fluorination on surface charge of polyimide films under pulse voltage. The polyimide films with the fluorination time of 15, 30, 45 and 60 min were prepared, together with the unfluorinated one as a comparison. Surface charging was performed by corona discharging using repetitive pulse power at the temperature of 25 °C with the relative humidity of ~45%. The rising time of the pulse was 25 μs and the frequency was set at 200, 400, 600 and 1000 Hz, respectively. The surface charge decay was measured using a specific probe coupled with an electrostatic voltmeter. The results showed that the surface charge behavior was affected by the fluorination, corona discharging time, pulse voltage amplitude and frequency. [ABSTRACT FROM PUBLISHER]

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. The prominent characteristics of the SiR coating are the hydrophobicity and the hydrophobicity recovery, which can suppress the development of leakage currents and dry-band discharges, and prevent the flashover incidents. Fluorination is a method to change the chemical component of the surface layer of polymers, which could induce the corresponding change in hydrophobicity and some electrical properties, thus influencing the dc surface flashover characteristics. Room temperature vulcanized (RTV) SiR samples were fluorinated in a stainless reaction vessel at about 298K (25°C) using a F2/N2 mixture with 12% F2 by volume and 0.05 MPa (500 mbar) for respectively 5, 10, 15 and 20 minutes. The hydrophobicity of samples with different fluorination time was measured by the static contact angle tests after corona aging. The variation of hydrophobicity with the lapse of time was recorded. Dc flashover tests in different conditions were carried out between two plane electrodes on top of the material sample. The flashover voltage was found to be associated with the surface hydrophobicity status of samples. Obtained results showed the effects of the fluorination on the surface charge, hydrophobicity performance and dc flashover voltage. It is suggested that the appropriate fluorination can improve surface hydrophobicity and suppress surface charge accumulation, thus raising the dc flashover voltage. [ABSTRACT FROM AUTHOR]

Epoxy is widely used in electronic and electrical devices because of its excellent insulation properties. The addition of nanoparticles to epoxy could change the material structure and then charge behaviors are altered as a consequence. The accumulation of surface charge may cause electric field distortion, which would lead to surface flashover. In this paper, the samples were made by dispersing nano-scale boron nitride (BN) particles in Epoxy with the weight ratios of 5, 10, 20, 30, 40 wt%. The samples were charged by a dc corona triode system using needle-plate electrodes. The distribution of charges was measured with an electrostatic voltmeter and the effect of nanoparticles on charge accumulation and decay behavior was studied. A flashover test was carried out under a dc stress between two finger-type electrodes. The effect of nanoparticles on flashover characteristics and the relation between surface charging and surface flashover were also investigated. The results showed that the traps between nanoparticles and the polymer, which were introduced by the added nanoparticles, could cause surface charge accumulation. In addition, the flashover occurred at a lower voltage because of the accumulated charge on the sample surface. [ABSTRACT FROM AUTHOR]

Stationary DC electric fields are determined by the resistivity distribution of the insulation materials. In the presence of interfaces between different insulation materials, charge accumulation at these boundary layers may have a significant influence on the electric field distribution and with it on the breakdown strength of the arrangement. In many previous works, surface charging of model spacers was investigated. However, the ion flow problem to properly account for the electric conduction in the gas has not yet been solved. The role of different ion sources and the behavior of the resulting ion currents in the gas phase on the charge accumulation process have to be investigated in more detail. In this paper, the transient charge accumulation process on a PTFE spacer surface with a focus on charges originating from the gas phase is investigated experimentally and by simulations. These charges are produced by natural radiation. The transition of the ohmic conduction regime in the gas to a saturated ion current with increasing voltage is analyzed. Furthermore, the importance of additional charge sources like partial discharges and field emission from the electrodes is highlighted. The experimental results indicate that additional charges are generated already at voltage levels significantly below the measured PD inception voltage. These charges originate from micro discharges on the electrodes and have to be taken into account when designing HVDC GIS applications. [ABSTRACT FROM AUTHOR]

Polyimide film, as a special type of engineering plastic film, is a basic insulating material and is widely applied in the electrical and electronic industry. Addition of nanoparticles into polyimide can improve the insulating properties compared with undoped material. However, due to the change of the material structure, the trap characteristics and charge behavior are altered as a consequence. The existence of surface charge has a great effect on the breakdown characteristic and is the main reason leading to dielectric breakdown. Fluorination as change the chemical component in surface layer of polymers should give rise to the corresponding change in electrical properties of the surface layer thus influence the charge injection from electrodes when they are used as an insulator. This paper presents a study aimed at clarifying the effect of fluorination and nanoparticles on the surface charge accumulation and decay behaviors of fluorinated polyimide nanocomposite film. Samples were prepared by dispersing nano-scale Al2O3 into polyimides with weight percentages of 0, 1, 3, 5 and 7 respectively. Then the samples were surface fluorinated in a laboratory vessel at about 328 K (55 °) using a F2/N2> mixture with 20% F2 by volume and 0.05 MPa (500 mbar) for 30 minutes. Corona charging tests were performed at room temperature with a relative humidity of ˜ 40%. The charge distribution was measured by means of an electrostatic voltmeter. The results show the dependence of the charge density as well as the charge decay rate upon the fluorination and nanoparticle concentration, varying as a function of the charge polarity and charging time. It is suggested that the fluorination can significantly improve the decay rate of the surface charge in polyimide films. [ABSTRACT FROM AUTHOR]