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Utilization of electro‐responsive biomaterials with antibacterial properties is advantageous for facilitating septic wound healing and tissue regeneration. However, the dose‐response effects of electrical stimuli from these materials against bacteria are not rigorously characterized, and achieving synergy of bactericidal and pro‐regenerative effects of biomaterials remains a major challenge. Here, a graded series of flexible BaTiO3/P(VDF‐TrFE) electroactive nanocomposite membranes (EMs) are developed with varying surface charge intensities, to serve as antibacterial dressing for septic wound healing. EMs display broad‐spectrum antibacterial effects against both Gram‐positive and Gram‐negative bacteria in a dose‐dependent manner, depending on the magnitude of their surface electrical potential. Mechanistically, the surface charge of EMs increase intracellular levels of reactive oxygen species within bacteria cells, which in turn caused oxidative damage to the bacterial membrane, thereby suppressing bacterial activity and biofilm formation. Moreover, in vivo studies demonstrated that EMs effectively inhibited S. aureus infection and accelerated wound healing in a mouse skin defect model, as well as ameliorated P. gingivalis‐mediated periodontal inflammation in a mouse periodontitis model. Hence, this study optimizes the antibacterial properties of electroactive materials and characterizes the dose‐response effects of surface electrical charge against bacteria, thus validating the therapeutic applications of electroactive biomaterials in combating bacterial infection. [ABSTRACT FROM AUTHOR]

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

Surface complexation models (SCMs) based on Gouy-Chapman theory are often used to describe adsorption of ions onto mineral surfaces. To compensate for the buildup of charge at a solid surface, the composition of the electric diffuse layer next to the surface must balance the surface charge. To calculate the diffuse layer composition, several nonlinear equations and integrals must be solved, usually with an iterative approach. Before convergence, charge balance is typically not fulfilled. One numerical difficulty is that, because of these charge balance errors, the iterative solver may attempt to take the square root of a negative number. Herein, we show that for electrolytes containing only monovalent or divalent ions (i.e., most electrolytes encountered in practice), we can greatly simplify the integrals and eliminate the appearance of complex-valued integrands; it is even possible to derive explicit analytical formulas. Furthermore, using the new method prevents converging to non-physical roots of the Grahame equation, which links surface potential to surface charge. To the best of our knowledge, the presented formulation has not been implemented in geochemical modelling software before, although similar mathematical expressions have been presented in the literature. In Gouy-Chapman theory, ions can only be distinguished by their charges, but this is not consistent with all experimental findings. We present a model that allows for the preferential accumulation of ions in the diffuse layer. The model, which is implemented mathematically by including ion exchange sites with a variable exchange capacity, is flexible and more numerically tractable than the standard models for the diffuse layer. [ABSTRACT FROM AUTHOR]

Poly(lactic) acid (PLA) is a bio-compatible polymer widely used in additive manufacturing, and in the form of cellular foam it shows excellent mechanical and piezoelectric properties. This type of structure can be easily 3D-printed by Fusion Deposition Modelling (FDM) with commercially available composite filaments. In this work, we present mechanical and electrical investigations on 3D-printed low-cost and eco-friendly foamed PLA. The cellular microstructure and the foaming degree were tuned by varying extrusion temperature and flowrate. The maximum surface potential and charge stability of disk samples were found in correspondence of extrusion temperature between 230 and 240 °C with a flowrate of 53–44% when charging on a heated bed at 85 °C. The cells' morphology and correlated mechanical properties were analyzed and the measured piezoelectric d 33 coefficient was found to be 212 pC/N. These findings show the importance of printing parameters and thermal treatment during the charging process in order to obtain the highest charge storage, stability and material flexibility. These results suggest that 3D-printed cellular PLA is a promising sustainable material for sensing and energy-harvesting applications. [ABSTRACT FROM AUTHOR]

Electric double layers are ubiquitous in science and engineering and are of current interest, owing to their applications in the stabilization of colloidal suspensions and as supercapacitors. While the structure and properties of electric double layers in electrolyte solutions near a charged surface are well characterized, there are subtleties in calculating thermodynamic properties from the free energy of a system with charged surfaces. These subtleties arise from the difference in the free energy between systems with constant surface charge and constant surface potential. In this work, we present a systematic, pedagogical framework to properly account for the different specifications on charged bodies in electrolyte solutions. Our approach is fully variational—that is, all free energies, boundary conditions, relevant electrostatic equations, and thermodynamic quantities are systematically derived using variational principles of thermodynamics. We illustrate our approach by considering a simple electrolyte solution between two charged surfaces using the Poisson–Boltzmann theory. Our results highlight the importance of using the proper thermodynamic potential and provide a general framework for calculating thermodynamic properties of electrolyte solutions near charged surfaces. Specifically, we present the calculation of the pressure and the surface tension between two charged surfaces for different boundary conditions, including mixed boundary conditions. [ABSTRACT FROM AUTHOR]

The spontaneous polarization in ferroelectrics provides an effective way to engineer interfacial charge distribution at the ferroelectric heterojunctions, thereby depletion width in p-n junction and energy band structures. Here, we integrated p-type multiferroic 7% neodymium-doped bismuth ferrite Bi 0.93 Nd 0.07 FeO 3 (BFO7Nd) polycrystalline ceramic bulk with n-type transparent conductive indium tin oxide (ITO) to demonstrate the influence of ferroelectric polarization on surface potential and its effect on photoelectrochemical (PEC) water reduction. Kelvin probe force microscopy (KPFM) results reveal the surface potential change during ferroelectric polarization switching, suggesting that the polarization bound charges may have an effect on space charge region between ITO-BFO7Nd, thus dominating surface potential at the electrode/electrolyte interface. This implies that the interface barrier between ITO and BFO7Nd can be easily modulated by polarization bound charges. The electron lifetime of upward-polarization (P-up) ITO-BFO7Nd is estimated 29.30 ms, about 15 times longer than unpoled ITO-BFO7Nd. The photocurrent density of P-up ITO-BFO7Nd is ∼1.2 × 10−6 A/cm2 (at 0 V vs RHE), which is one-order higher compared to that of the unpoled and P-down states under illumination with an intensity of 100 mWcm−2. This work shows that ferroelectric polarization combined with photogenerated carriers is an effective approach for effective charge transfer in multiferroic ceramic to boost PEC solar water splitting. [ABSTRACT FROM AUTHOR]

Redox reactions have been observed when an electrostatically charged insulator is placed in contact with a solution, and this phenomenon is referred to as single-electrode electrochemistry. In this study we explore how important is the chemical reactivity of the charge carriers on the surface compared to the voltage caused by the density of charges on the surface which set up an electric double layer. We address complications arising from the surface potential's dependence upon the electrolyte concentration caused by the fixed surface charge density of the electrode. We present an analytical solution for the effective potential in single-electrode electrochemistry at a planar surface and show that it is not the same as the potential at the insulating surface. We reach two major conclusions: (1) the voltage applied to the reaction from discharging the electrode approaches a limiting value, and (2) the majority of single-electrode reactions are caused primarily by the chemical reactivity of the charge carrier on the electrode surface and not from discharging the static charge on the electrode. [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]

In this study, the temporal variation of an electric potential distribution was measured in a surface dielectric barrier discharge experiment using the Pockels effect. A branching pattern and homogeneous distribution were respectively observed when positive and negative voltages were applied. When continuous alternating current was applied to the electrode, the spatial distributions of the electric potential significantly changed between the first and subsequent discharge cycles. The results indicate that the electrostatic repulsive forces caused by the residual charges on the dielectric surface affect the dynamic patterns of the discharge morphology. [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]

The accumulation of surface charges is a crucial challenge, especially for HVDC components. Accumulated surface charges can change the electric field distribution and generate weak points, especially in case of superimposed transient voltages and, therefore lower the performance e.g. of insulators. Hence, an accurate measurement of the surface potential and so the surface charges is necessary to optimize these components. Commonly, the surface potential is measured with an electrostatic voltmeter. In this study a procedure for determining the spatial impulse response of a compensating electrostatic voltmeter depending on only the surface to probe distance is presented. Based on the performed measurements a mathematical model is developed to describe the capacitive influence and significance of the local surface potential on the measurement result. The actual measurement value is a weighted and averaged value given by the actual position and its surrounding, which is also confirmed by numerical simulations. The performed procedure enables high accuracy of the measurement of surface potentials and so of surface charges using different types of electrostatic voltmeters and shows the limitation of the measurement procedure. This knowledge increases the possibility to design optimized components for HVDC systems. [ABSTRACT FROM AUTHOR]

When designing spacecraft with electric propulsion (EP) devices, it is important to assess spacecraft integration to ensure that the important components are not subject to significant sputtering by high-energy ions. In addition to the EP device and its plume, surface charging of spacecraft has to be modeled properly, as surface potential can directly affect the sputtering rate. Three surface charging models are incorporated into the spacecraft module of the numerical simulation framework–Thermophysics Universal Research Framework (TURF), and these include: 1) dielectric; 2) conductive; and 3) charge propagation models. The charge propagation model has been upgraded to solve the surface charge distribution implicitly, allowing a wide range of electrical conductivity values without causing the simulation to become unstable. Each of the charging models is verified against a simple problem where an analytical solution can be determined. Then, the coupling of the surface charging model and a hybrid particle/fluid model is tested in a more complex problem, where the floating potential on a sphere immersed in plasma is to be obtained. Finally, the surface charging model in an EP plume simulation is demonstrated. These problems are multiscale in that the charging model has to resolve an electron timescale (i.e., plasma oscillation) while the particle time step has to be orders of magnitude larger than the electron timescale in order to maintain a long enough sampling window for the ion current to effectively reduce the statistical noise. Therefore, two separate time steps are introduced for a stable convergence of the coupled models. [ABSTRACT FROM AUTHOR]

High-level surface-charging events are frequently observed on spacecrafts in aurora region. Besides the sunlit condition, two major factors causing charging events are the ambient plasma density and the precipitating electron flux. For the first factor, when the ambient plasma density is relatively low due to weak solar UV output during solar minimum, more surface-charging events are reported to occur for polar satellite. Moreover, the increased energetic electron precipitation during high geomagnetic activities in solar cycle decent years, may also contribute to the charging events. To evaluate these two factors comprehensively, we present a statistical survey of over 2000 surface charging events recorded by Defense Meteorological Satellite Program (DMSP) satellites over one solar cycle. The relationship between charging events and Kp index, F10.7 index, and monthly average sunspot number is investigated. It is shown that the occurrence frequency of charging events is larger at descending years of solar cycle. In addition, the conditional probabilities of the charging events increase as Kp increase. There is a threshold for Kp index, under which most of the charging events cannot occur, and this threshold grows as F10.7 increases. Finally, it is demonstrated that the surface charging potential is strongly correlated with the Kp index. Although there is no obvious correlation between the surface charging potential and F10.7 index, we still observe a decreasing trend of the surface potential range as F10.7 increases. [ABSTRACT FROM AUTHOR]

Superconducting magnet is one of the core components of international thermonuclear experimental reactor (ITER). Due to the harsh operating environment, for the sake of ensuring the stable operation of the superconducting magnet, the superconducting magnet insulation is required to have excellent electrical and irradiation resistance. However, pure epoxy resin is difficult to adapt to the harsh environment in the ITER, so it needs to be modified to improve its insulation performance. In this paper, the epoxy/AlN nanocomposites with 1 wt% filler content of AlN nanoparticles were prepared, and the dispersion of nanoparticles was observed. High-energy electron beam was used to treat nanocomposites with the dose of 300, 500, and 700 kGy. The relative permittivity and conductivity of the nanocomposites after irradiation were tested. In addition, the data of surface potential were measured after surface charging for analyzing the dynamic behavior of surface charge and calculating the trap distribution of the nanocomposites with various irradiation doses. The flashover voltage of the nanocomposites influenced by irradiation in LN2 was also analyzed. The results show that irradiation can cause the change of trap distribution and flashover voltage, and the change trend is not monotonous. [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]

Epoxy resin is widely used in disc-type spacers of gas insulated switchgear (GIS). Surface flashover related to the existence of surface charge often occurs on the spacer, which is a great threat to the application of GIS and the safety of entire grid. Moreover, the influences on surface charge under pulse voltage produced by switch overvoltage, accompanying with the AC voltage, are still unclear. In order to research the comprehensive effect of AC and pulse voltage on surface charge, in this paper, epoxy resin sample was charged by a corona discharge system and the charge distribution was measured by an electrostatic voltmeter. The results are obtained from the research of different pulse amplitudes, pulse numbers and pulse polarities. The surface potential is a negative value after AC voltage applied for a period of time. When AC and negative pulse voltage are applied, smaller pulse voltage would push the original negative charges away. As a result, initial negative surface potential decreases. But bigger pulse voltage could increase the charge accumulation. When the pulse polarity becomes positive, surface potential at the sample center will be positive value at the beginning and then it gradually changes from positive to negative potential. In addition, the influence on surface charge decay rate will be enhanced with the increase of pulse number under the same pulse voltage. Trap energy distributions were used to analyze charge decay process in the last section. [ABSTRACT FROM AUTHOR]

The surface potential decay time is related to the number of collisions neutral gas particles with the polymer surface per unit area per time. [Display omitted] • We measured surface potential of an insulating sample using Kelvin probe system to investigate the neutral gas effect on charge compensation. • Gas cluster ion beam was used to accumulate charges and to minimize damage to the sample surface. • Neutral gas effect on surface charge of insulating sample depends on the type of injection gas. • Surface potential curves were fitted by exponential decay function to obtain decay time. Surface charging of an insulating sample has been a significant issue in surface analysis. In time-of-flight secondary ion mass spectrometry, the charge also accumulates on the surface of an insulating sample by the primary ion beam, such as an argon gas cluster ion beam. Such charging can lead to not only degraded mass resolution but also low image resolution, and thus it is necessary to compensate for surface charging of insulating sample. Therefore, several efficient methods have been proposed for charge compensation, such as using a low-energy electron flood gun, applying a bias voltage to the sample stage, and using a gas flooding system. Here, we measured the surface potential of a polymer film to investigate the gas effect on the charge compensation using a Kelvin probe. During the measurements, the chamber pressure was gradually increased by injecting gases, such as He, Ne, Ar, N 2 , and O 2. We found that the injection gas may reduce the surface charging of the sample, depending on the type of gas. [ABSTRACT FROM AUTHOR]

We theoretically investigate electrostatic properties between two charged surfaces with a grafted polyelectrolyte layer in an aqueous electrolyte solution by using the Poisson-Boltzmann approach accounting for ion partitioning. In order to consider the ion partitioning effect, we focus on changes of electrostatic properties due to the difference in dielectric permittivity of the polyelectrolyte layer and the aqueous electrolyte solution. We find that ion partitioning enhances electrostatic potential in the region between two charged soft surfaces and hence increases the electrostatic interaction between two charged soft surfaces. Ion partitioning effect on osmotic pressure is enhanced not only by an increase in the thickness of polyelectrolyte layer and Debye length but also by a decrease in ion radius. [Display omitted] • Ion partitioning effect involves an increase of electrostatic potential and osmotic pressure. • An increase in surface charge density amplifies the ion partitioning. • A higher thickness of polyelectrolyte layer results in a stronger ion partitioning. • A small radius of ions enhances ion partitioning. [ABSTRACT FROM AUTHOR]

Perm-selectivity consisting of water flux J w and solute flux J s or in form of J s /J w ratio is an important parameter of designing Forward Osmosis (FO) membrane as it indicates the membrane performance and how much solute replenishment over the extracted pure water from the feed solution. Parameter J s /J w ratio is dependent on hydrodynamic condition i.e cross-flow velocity (CFV), solute type i.e. diffusivity, trans -membrane surface potential. This study employed Cellulose Triacetate (CTA) membrane for representing low-charge membrane and Polyamide-Thin Film Composite (PA-TFC) for the membrane of highly negative surface charge. Six (6) different models were used to quantify the effect of external mass transfer, the ideal solution, non-ideal solution, trans -membrane surface potential on the transport of solute across the membrane. Our new model was proven to improve the prediction of perm-selectivity. The improvement was attributed to the application of trans -membrane potential-dependent solute partitioning for solute permeability correction and the application of experimentally obtained mass transfer coefficient. By the incorporation of the Donnan effect in determining the transmembrane potential, it was found that in the low charge membrane namely CTA, the dominant transport mechanism was diffusion, while in a highly negative surface charged membrane namely TFC, the partition of solute to be the dominant mechanism. Operation at a low CFV posed less impact of the membrane charge. The newly developed model provided a good foundation for FO process design under different CFVs and modified surface charges. [Display omitted] • The solute transport is affected by the membrane surface charge which is incorporated in our developed model. • The incorporation of surface charge dependent-solute partitioning was noticed. • The implementation of experimental mass transfer coefficient was proven to improve the prediction of perm-selectivity. • Optimally high negative charge of the membrane or optimally low CFV operation was suggested for implementation. [ABSTRACT FROM AUTHOR]

Most studies on corona-charged nonwoven filters have used grounded electrodes during charging and surface potential measurements but not during filtration experiments. This study was focused on the investigation of a grounded metal grid effect on the filtration efficiency. The results showed that the filtration outcome strongly depends on the filter–grid distance. Moreover, the electric charge was maintained for a considerably long duration when the ground electrode was used, which led to an increase in the filtration efficiency. The efficiency exceeded 90% at a voltage of 10 kV with the grid and was <70% at 30 kV without the grid. • Potential decay and filtration performance of corona charged filters were investigated. • The effect of a grounded metal grid on the filtration efficiency was investigated. • The "filter–grid" distance affects both potential decay and filtration efficiency. • Electric charges are kept longer on the filter surface with the grid electrode. • The filtration performance was significantly improved with the grid electrode. [ABSTRACT FROM AUTHOR]

To clarify the importance of the surface charge for the formation of polyelectrolyte multilayers, layer-by-layer (LbL) assemblies of polydiallyldimethylammonium chloride (pDADMAC) and polystyrenesulfonate (PSS) have been investigated on cellulose films with different carboxylic acid contents (20, 350, 870, and 1200 μmol/g) regenerated from oxidized cellulose. The wet cellulose films were thoroughly characterized prior to multilayer deposition using quantitative nanomechanical mapping (QNM), which showed that the mechanical properties were greatly affected by the degree of oxidation of the cellulose. Atomic force microscopy (AFM) force measurements were used to determine the surface potential of the cellulose films by fitting the force data to the DLVO theory. With the exception of the 1200 μmol/g film, the force measurements showed a second-order polynomial increase in surface potential with increasing degree of oxidation. The low surface potential for the 1200 μmol/g film was attributed to the low degree of regenerationof the cellulose film in aqueous media due to increasing solubility with increasing charge. The multilayer formation was characterized using a quartz crystal microbalance with dissipation (QCM-D) and stagnation-point adsorption reflectometry (SPAR). Extensive deswelling was observed for the charged films when pDADMAC was adsorbed due to the reduced osmotic pressure when ions inside the film were released, and the 1:1 charge compensation showed that all the charges in the films were reached by the pDADMAC. The multilayer formation was not significantly affected by the charge density above 350 μmol/g due to interlayer repulsions, but it was strongly affected by the salt concentration during the layer build-up. [ABSTRACT FROM AUTHOR]