Secondary electron emission(SEE)induced by the positive ion is an essential physical process to influence the dynamics of gas discharge which relies on the specific surface material.Surface charging has a significant ...Secondary electron emission(SEE)induced by the positive ion is an essential physical process to influence the dynamics of gas discharge which relies on the specific surface material.Surface charging has a significant impact on the material properties,thereby affecting the SEE in the plasma-surface interactions.However,it does not attract enough attention in the previous studies.In this paper,SEE dependent on the charged surface of specific materials is described with the computational method combining a density functional theory(DFT)model from the first-principle theory and the theory of Auger neutralization.The effect ofκ-Al2O3 surface charge,as an example,on the ion-induced secondary electron emission coefficient(SEEC)is investigated by analyzing the defect energy level and band structure on the charged surface.Simulation results indicate that,with the surface charge from negative to positive,the SEEC of a part of low ionization energy ions(such as Ei=12.6 eV)increases first and then decreases,exhibiting a nonlinear changing trend.This is quite different from the monotonic decreasing tendency observed in the previous model which simplifies the electronic structure.This irregular increase of the SEEC can be attributed to the lower escaped probability of orbital energy.The results further illustrate that the excessive charge could cause the bottom of the conduction band close to the valence band,thus leading to the decrease of the orbital energy occupied by the excited electrons.The nonlinear change of SEEC demonstrates a more realistic situation of how the electronic structure of material surface influences the SEE process.This work provides an accurate method of calculating SEEC from specific materials,which is urgent in widespread physical scenarios sensitive to surface materials,such as increasingly growing practical applications concerning plasma-surface interactions.展开更多
Electrocatalytic and plasma-activated processes receive increasing attention in catalysis. Density functional theory(DFT) calculations are state-of-the-art tools for the fundamental study of reaction mechanisms and pr...Electrocatalytic and plasma-activated processes receive increasing attention in catalysis. Density functional theory(DFT) calculations are state-of-the-art tools for the fundamental study of reaction mechanisms and predicting the performance of catalytic materials. Proper application of DFT-based methods is crucial when investigating charge-doped electrode surfaces during electrocatalytic and plasma-activated reactions. Here, as a model electrode for plasma-activated CO2 splitting, we studied the interactions of O, CO, and CO2 with the neutral and progressively charged Ag(111) metal surfaces. We show that the application of correction procedures is necessary to obtain accurate adsorption energy profiles of O atoms,CO and CO2 molecules on Ag surfaces that are under the influence of additional electrons. Interestingly,the oxidation of CO is found to shift from a Langmuir–Hinshelwood mechanism on a neutral electrode to an Eley–Rideal mechanism on charged electrodes. Furthermore, we show that the surface charging of Ag(111) electrodes increase their CO2 reduction performance by enhancing the adsorption of O atoms and desorption of CO molecules. A further increase in the absolute charge-state of the electrode surface is expected to waive the thermodynamic barriers for the CO2 splitting reaction.展开更多
The surface charge characteristics in a three-electrode surface dielectric barrier discharge(SDBD)are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the...The surface charge characteristics in a three-electrode surface dielectric barrier discharge(SDBD)are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the most commonly used SDBD structure for airflow control, with an exposed electrode supplied with sinusoidal AC high voltage, a grounded encapsulated electrode and an additional exposed electrode downstream supplied with DC voltage. The ionic wind velocity and thrust can be significantly improved by increasing DC voltage although the plasma discharge characteristics are virtually unaffected. It is found that the negative charges generated by the discharge of the three-electrode structure accumulate on the dielectric surface significantly further downstream in an AC period compared to the actuator with a two-electrode structure. The negative charges in the downstream region increase as the DC voltage increases.In addition, the DC voltage affects the time required for the positive charge filaments to decay.The positive DC voltage expands the ionic acceleration zone downstream to produce a greater EHD force. The amplitude of the DC voltage affects the electric field on the dielectric surface and is therefore a key factor in the formation of the EHD force. Further research on the surface charge characteristics of a three-electrode structure has been conducted using a pulse power to drive the discharge, and the same conclusions are drawn. This work demonstrates a link between surface charge characteristics and EHD performance of a three-electrode SDBD actuator.展开更多
Surface charges greatly affect the discharge/flashover development process across an insulator. The relationship between surface charge distribution on insulating materials and measurement data based on Pockels techni...Surface charges greatly affect the discharge/flashover development process across an insulator. The relationship between surface charge distribution on insulating materials and measurement data based on Pockels technique is discussed, and an improved algorithm is built to calculate the real surface charge density from original data. In this algorithm, two-dimensional Fourier transform technique and Wiener filter are employed to reduce the amount of numerical calculation and improve the stability of computation, Moreover, this algorithm considers not only the influence of sample＇s thickness and permittivity, but also the impact of charges at different positions. The achievement of this calibration algorithm is demonstrated in details. Compared with traditional algorithms, the improved one supplies a better solution in the calibration of surface charge distribution on different samples with different thickness.展开更多
In this paper,plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface.The physicochemical characteristics of samples are investigated and the elec...In this paper,plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface.The physicochemical characteristics of samples are investigated and the electrical performances measured.The obtained results show that compared with untreated and single treated samples,the samples treated by step gradient modification significantly improve the flashover performance.According to experiment and simulation,the mechanism explanations are summarized as follows.First,it is found that the step gradient conductivity can effectively optimize the electric field distribution of a needle-needle electrode.Then,step gradient modification suppresses the accumulation of surface charge at the triple junction and makes the charge distribution more uniform.Furthermore,it can accelerate the surface dissipation on a high electrical field region and control the dissipation rate on a low electrical field region.All these results can restrain surface discharge and increase the flashover voltage.The step gradient modification method proposed in this paper provides a new idea for improving the surface insulation performance.展开更多
Non-thermal plasma surface modification for epoxy resin（EP）to improve the insulation properties has wide application prospects in gas insulated switchgear and gas insulatedtransmission line.In this paper,a pulsed Ar...Non-thermal plasma surface modification for epoxy resin（EP）to improve the insulation properties has wide application prospects in gas insulated switchgear and gas insulatedtransmission line.In this paper,a pulsed Ar dual dielectrics atmospheric-pressure plasma jet（APPJ）was used for Si CxHyOzthin film deposition on EP samples.The film deposition was optimized by varying the treatment time while other parameters were kept at constants（treatment distance：10 mm,precursor flow rate：0.6 l min-（-1）,maximum instantaneous power：3.08 k W and single pulse energy：0.18 m J）.It was found that the maximum value of flashover voltages for negative and positive voltage were improved by 18%and 13%when the deposition time was3 min,respectively.The flashover voltage reduced as treatment time increased.Moreover,all the surface conductivity,surface charge dissipation rate and surface trap level distribution reached an optimal value when thin film deposition time was 3 min.Other measurements,such as atomic force microscopy and scanning electron microscope for EP surface morphology,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy for EP surface compositions,optical emission spectra for APPJ deposition process were carried out to better understand the deposition processes and mechanisms.The results indicated that the original organic groups（C–H,C–C,C=O,C=C）were gradually replaced by the Si containing inorganic groups（Si–O–Si and Si–OH）.The reduction of C=O in ester group and C=C in p-substituted benzene of the EP samples might be responsible for shallowing the trap level and then enhancing the flashover voltage.However,when the plasma treatment time was longer than 3 min,the significant increase of the surface roughness might increase the trap level depth and then deteriorate the flashover performance.展开更多
The ion flow field on the ground is one of the significant parameters used to evaluate the electromagnetic environment of high voltage direct current（HVDC） power lines.HVDC lines may cross the greenhouses due to the...The ion flow field on the ground is one of the significant parameters used to evaluate the electromagnetic environment of high voltage direct current（HVDC） power lines.HVDC lines may cross the greenhouses due to the restricted transmission corridors.Under the condition of ion flow field,the dielectric films on the greenhouses will be charged,and the electric fields in the greenhouses may exceed the limit value.Field mills are widely used to measure the groundlevel direct current electric fields under the HVDC power lines.In this paper,the charge inversion method is applied to calculate the surface charges on the dielectric film according to the measured ground-level electric fields.The advantages of hiding the field mill probes in the ground are studied.The charge inversion algorithm is optimized in order to decrease the impact of measurement errors.Based on the experimental results,the surface charge distribution on a piece of quadrate dielectric film under a HVDC corona wire is studied.The enhanced effect of dielectric film on ground-level electric field is obviously weakened with the increase of film height.Compared with the total electric field strengths,the normal components of film-free electric fields at the corresponding film-placed positions have a higher effect on surface charge accumulation.展开更多
In an insulating system including solid and gas dielectrics, discharge type has a strong impact on charge accumulation at the interface between two dielectrics, and hence charge decay. In order to clarify the influenc...In an insulating system including solid and gas dielectrics, discharge type has a strong impact on charge accumulation at the interface between two dielectrics, and hence charge decay. In order to clarify the influence, a surface charge measurement system was constructed, and three types of discharge, i.e. surface discharge, and low intensity and high intensity coronas, were introduced to cause surface charge accumulation. The decay behavior of surface charges after different types of discharge was obtained at various temperatures. It was found that total surface charges monotonically decreased with time, and the decay rate became larger as temperature increased. However, after a surface discharge or a high intensity corona, surface charge density in the local area appeared to fluctuate during the decay process. Compared with this, the fluctuation of surface charge density was not observed after a low intensity corona. The mechanisms of surface charge accumulation and decay were analysed. Moreover, a microscopic physical model involving charge production, accumulation, and decay was proposed so that the experimental results could be explained.展开更多
The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes(CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around ...The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes(CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid–liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results,we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work.展开更多
Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DN...Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows： i） when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii）for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii） when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.展开更多
The surface charge accumulation on polymers often leads to surface flashover.Current solutions are mainly based on the introduction of inorganic fillers.The high-cost process and low compatibility remain formidable ch...The surface charge accumulation on polymers often leads to surface flashover.Current solutions are mainly based on the introduction of inorganic fillers.The high-cost process and low compatibility remain formidable challenges.Moreover,existing researches on all-organic insulation focus on capturing electrons,contrary to alleviating charge accumulation.Here,an all-organic modification coating was prepared on polystyrene(PS)with the large-scale atmospheric-pressure plasma,which exhibits outperformed function in mitigating surface charge accumulation.The surface charge dissipation rate and surface conductivity are promoted by about 1.37 and 9.45 times,respectively.Simulation and experimental results show that this all-organic modification coating has a smaller electron affinity potential compared with PS.The decrease of electron affinity potential may result in accelerated surface charge decay of PS,which has never been involved in previous works.Moreover,this coating also has good reliability in a repeated surface flashover.This facile and large-scale approach brings up a novel idea for surface charge regulation and the manufacture of advanced dielectric polymers.展开更多
This work treats the Al_(2)O_(3)-ER sample surface using dielectric barrier discharge fluorination(DBDF),DBD silicon deposition(DBD-Si),atmospheric-pressure plasma jet fluorination(APPJ-F)and APPJ silicon deposition(A...This work treats the Al_(2)O_(3)-ER sample surface using dielectric barrier discharge fluorination(DBDF),DBD silicon deposition(DBD-Si),atmospheric-pressure plasma jet fluorination(APPJ-F)and APPJ silicon deposition(APPJ-Si).By comparing the surface morphology,chemical components and electrical parameters,the diverse mechanisms of different plasma modification methods used to improve flashover performance are revealed.The results show that the flashover voltage of the DBDF samples is the largest(increased by 21.2%at most),while the APPJ-F method has the worst promotion effect.The flashover voltage of the APPJ-Si samples decreases sharply when treatment time exceeds 180 s,but the promotion effect outperforms the DBD-Si method during a short modified time.For the mechanism explanation,firstly,plasma fluorination improves the surface roughness and introduces shallow traps by etching the surface and grafting fluorine-containing groups,while plasma silicon deposition reduces the surface roughness and introduces a large number of shallow traps by coating Si Oxfilm.Furthermore,the reaction of the DBD method is more violent,while the homogeneity of the APPJ modification is better.These characteristics influence the effects of fluorination and silicon deposition.Finally,increasing the surface roughness and introducing shallow traps accelerates surface charge dissipation and inhibits flashover,but too many shallow traps greatly increase the dissipated rate and facilitate surface flashover instead.展开更多
We present the variations of electrical parameters of dielectric barrier discharge(DBD)when the DBD generator is used for the material modification,whereas the relevant physical mechanism is also elaborated.An equival...We present the variations of electrical parameters of dielectric barrier discharge(DBD)when the DBD generator is used for the material modification,whereas the relevant physical mechanism is also elaborated.An equivalent circuit model is applied for a DBD generator working in a filament discharging mode,considering the addition of epoxy resin(EP)as the plasma modified material.The electrical parameters are calculated through the circuit model.The surface conductivity,surface potential decay,trap distributions and surface charge distributions on the EP surface before and after plasma treatments were measured and calculated.It is found that the coverage area of micro-discharge channels on the EP surface is increased with the discharging time under the same applied AC voltage.The results indicate that the plasma modified material could influence the ignition of new filaments in return during the modification process.Moreover,the surface conductivity and density of shallow traps with low trap energy of the EP samples increase after the plasma treatment.The surface charge distributions indicate that the improved surface properties accelerate the movement and redistribution of charge carriers on the EP surface.The variable electrical parameters of discharge are attributed to the redistribution of deposited surface charge on the plasma modified EP sample surface.展开更多
Up to now,the DNA molecule adsorbed on a surface was believed to always preserve its native structure.This belief implies a negligible contribution of lateral surface forces during and after DNA adsorption although th...Up to now,the DNA molecule adsorbed on a surface was believed to always preserve its native structure.This belief implies a negligible contribution of lateral surface forces during and after DNA adsorption although their impact has never been elucidated.High-resolution atomic force microscopy was used to observe that stiff DNA molecules kinetically trapped on monomolecular films comprising one-dimensional periodically charged lamellar templates as a single layer or as a sublayer are oversaturated by sharp discontinuous kinks and can also be locally melted and supercoiled.We argue that kink/anti-kink pairs are induced by an overcritical lateral bending stress(>30 pNnm)inevitable for the highly anisotropic 1D-1D electrostatic interaction of DNA and underlying rows of positive surface charges.In addition,the unexpected kink-inducing mechanical instability in the shape of the template-directed DNA confined between the positively charged lamellar sides is observed indicating the strong impact of helicity.The previously reported anomalously low values of the persistence length of the surface-adsorbed DNA are explained by the impact of the surface-induced low-scale bending.The sites of the local melting and supercoiling are convincingly introduced as other lateral stress-induced structural DNA anomalies by establishing a link with DNA high-force mechanics.The results open up the study in the completely unexplored area of the principally anomalous kinetically trapped DNA surface conformations in which the DNA local mechanical response to the surface-induced spatially modulated lateral electrostatic stress is essentially nonlinear.The underlying rich and complex in-plane nonlinear physics acts at the nanoscale beyond the scope of applicability of the worm-like chain approximation.展开更多
Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry.Electric control is widely used to modify interfacial water,where the influence of surface char...Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry.Electric control is widely used to modify interfacial water,where the influence of surface charges is inevitable.Here we obtain positively and negatively charged surfaces using Li Ta O_(3) crystals and observe that a large net surface charge up to 0.1 C/m;can nominally change the contact angles of pure water droplets comparing to the same uncharged surface.However,even a small amount of surface charge can efficiently increase the water contact angle in the presence of aerosols.Our results indicate that such surface charges can hardly affect the structure of interfacial water molecular layers and the morphology of the macroscopic droplet,while adsorption of a small amount of organic contaminants from aerosols with the help of Coulomb attraction can notably decrease the wettability of solid surface.Our results not only provide a fundamental understanding of the interactions between charged surfaces and water,but also help to develop new techniques on electric control of wettability and microfluidics in real aerosol environments.展开更多
A surface charge measuring system using the capacitive probe method is analysed. The present study shows that the measuring system cannot have a steady-state output and that the error resulting from the finite leakage...A surface charge measuring system using the capacitive probe method is analysed. The present study shows that the measuring system cannot have a steady-state output and that the error resulting from the finite leakage resistance of the measuring system will be accumulated during the measuring process. Based on the theoretical analysis a new type probe with a low charge leakage and high resolution is designed. The surface charge accumulated on the Teflon insulator under a DC voltage is measured using this new probe and some phenomena of the surface charging are reported.展开更多
Foam stability tests were performed using sodium dodecyl sulfate(SDS)surfactant and SiO2 nanoparticles as foaming system at different asphaltene concentrations,and the half-life of CO_(2) foam was measured.The mechani...Foam stability tests were performed using sodium dodecyl sulfate(SDS)surfactant and SiO2 nanoparticles as foaming system at different asphaltene concentrations,and the half-life of CO_(2) foam was measured.The mechanism of foam stability reduction in the presence of asphaltene was analyzed by scanning electron microscope(SEM),UV adsorption spectrophotometric concentration measurement and Zeta potential measurement.When the mass ratio of synthetic oil to foam-formation suspension was 1:9 and the asphaltene mass fraction increased from 0 to 15%,the half-life of SDS-stabilized foams decreased from 751 s to 239 s,and the half-life of SDS/silica-stabilized foams decreased from 912 s to 298 s.When the mass ratio of synthetic oil to foam-formation suspension was 2:8 and the asphaltene mass fraction increased from 0 to 15%,the half-life of SDS-stabilized foams decreased from 526 s to 171 s,and the half-life of SDS/silica-stabilized foams decreased from 660 s to 205 s.In addition,due to asphaltene-SDS/silica interaction in the aqueous phase,the absolute value of Zeta potential decreases,and the surface charges of particles reduce,leading to the reduction of repulsive forces between two interfaces of thin liquid film,which in turn,damages the foam stability.展开更多
Drilling is a most important and crucial operation in the excavation industries.With the objective of looking into the enhancement of diamond drilling performance detailed laboratory investigations were carried out on...Drilling is a most important and crucial operation in the excavation industries.With the objective of looking into the enhancement of diamond drilling performance detailed laboratory investigations were carried out on phosphate rock.The effect of Poly（Ethylene Oxide）（PEO） added to the drilling water was studied by varying machine parameters and PEO concentration.The responses were rate of penetration and torque at the bit rock interface.Slake durability tests were also performed to understand the slaking behavior of phosphate rock in PEO solutions.展开更多
This paper investigated the dependence of out-of-plane electret-based vibration energy harvesters’output power,frequency bandwidth,and resonance frequency on surface charge density and load resistance.As the external...This paper investigated the dependence of out-of-plane electret-based vibration energy harvesters’output power,frequency bandwidth,and resonance frequency on surface charge density and load resistance.As the external acceleration amplitude and electret size were held constant,the following results are predicted by the numerical investigation：（1）An optimum value exists in the surface charge density to maximize the output power.As the surface charge density is increasing,electrostatic forces are enhanced,which emphasizes that the soft spring effect widens the frequency bandwidth and lowers the resonance frequency.（2）Different surface charge densities correspond to different optimum initial air gaps,resonance frequency,and optimum load resistance.（3）With the attenuation of the surface potential,the output power,frequency drift,and frequency bandwidth decreased.（4）An optimum value exists in the load resistance to maximize the output power.As the load resistance is decreasing,electrostatic force is enhanced,which lowers the resonance frequency.（5）A maximum frequency bandwidth exists with further load resistance increasing,and the initial air gap is smaller,the greater the frequency bandwidth.展开更多
To investigate the effect of the rib structure on the discharge characteristics of the plasma display panel, the potential distribution, particles density distribution and ions incident angle distribution were examine...To investigate the effect of the rib structure on the discharge characteristics of the plasma display panel, the potential distribution, particles density distribution and ions incident angle distribution were examined by simulation of a two-dimensional particle-in-cell/Monte Carlo collision, with two kinds of rib structure： the stripe rib structure and the Waffle rib structure. The results showed that the distribution of electric potential at the corner of the discharge cell was almost the same for these two rib structures while in the centre there was a difference between these two rib structures. The striation phenomenon could be observed in both cases. The distribution of density also indicated that the striation phenomenon was accompanied by the firing of discharge, and the Waffle rib structure might reduce the density humps. In the cell with a stripe rib structure, the profiles of the surface charge density along the sustained dielectric layer presented a better fluctuating distribution than that in the cell with a Waffle rib structure. The spatial potential and particle density in the discharge bulk showed that the Waffle ribs could weaken the striation phenomenon, which could be explained by the decrease in the particle numbers in the discharge cell. The simulation results of the ion incident angle showed that most ions impacted the sustained dielectric layer in the normal stripe rib cell with an incident angle in the range of 6° to 19° while with the Waffle rib structure the incident angle of most ions was in the range of 4° to 19°. The Waffle rib structure did not affect the angle distribution of incident ions significantly.展开更多
基金supported by the National Key Research and Development Plan of China(No.2021YFE0114700)National Natural Science Foundation of China(No.52377145).
文摘Secondary electron emission(SEE)induced by the positive ion is an essential physical process to influence the dynamics of gas discharge which relies on the specific surface material.Surface charging has a significant impact on the material properties,thereby affecting the SEE in the plasma-surface interactions.However,it does not attract enough attention in the previous studies.In this paper,SEE dependent on the charged surface of specific materials is described with the computational method combining a density functional theory(DFT)model from the first-principle theory and the theory of Auger neutralization.The effect ofκ-Al2O3 surface charge,as an example,on the ion-induced secondary electron emission coefficient(SEEC)is investigated by analyzing the defect energy level and band structure on the charged surface.Simulation results indicate that,with the surface charge from negative to positive,the SEEC of a part of low ionization energy ions(such as Ei=12.6 eV)increases first and then decreases,exhibiting a nonlinear changing trend.This is quite different from the monotonic decreasing tendency observed in the previous model which simplifies the electronic structure.This irregular increase of the SEEC can be attributed to the lower escaped probability of orbital energy.The results further illustrate that the excessive charge could cause the bottom of the conduction band close to the valence band,thus leading to the decrease of the orbital energy occupied by the excited electrons.The nonlinear change of SEEC demonstrates a more realistic situation of how the electronic structure of material surface influences the SEE process.This work provides an accurate method of calculating SEEC from specific materials,which is urgent in widespread physical scenarios sensitive to surface materials,such as increasingly growing practical applications concerning plasma-surface interactions.
基金part of the European project KEROGREEN,which has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement no.763909funding from the initiative“Computational Sciences for Energy Researcah”of Shell and the Netherlands Organization for Scientific Research(NWO)grant no.15CSTT05。
文摘Electrocatalytic and plasma-activated processes receive increasing attention in catalysis. Density functional theory(DFT) calculations are state-of-the-art tools for the fundamental study of reaction mechanisms and predicting the performance of catalytic materials. Proper application of DFT-based methods is crucial when investigating charge-doped electrode surfaces during electrocatalytic and plasma-activated reactions. Here, as a model electrode for plasma-activated CO2 splitting, we studied the interactions of O, CO, and CO2 with the neutral and progressively charged Ag(111) metal surfaces. We show that the application of correction procedures is necessary to obtain accurate adsorption energy profiles of O atoms,CO and CO2 molecules on Ag surfaces that are under the influence of additional electrons. Interestingly,the oxidation of CO is found to shift from a Langmuir–Hinshelwood mechanism on a neutral electrode to an Eley–Rideal mechanism on charged electrodes. Furthermore, we show that the surface charging of Ag(111) electrodes increase their CO2 reduction performance by enhancing the adsorption of O atoms and desorption of CO molecules. A further increase in the absolute charge-state of the electrode surface is expected to waive the thermodynamic barriers for the CO2 splitting reaction.
基金supported by National Natural Science Foundation of China (Nos. 51777026 and 11705075)。
文摘The surface charge characteristics in a three-electrode surface dielectric barrier discharge(SDBD)are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the most commonly used SDBD structure for airflow control, with an exposed electrode supplied with sinusoidal AC high voltage, a grounded encapsulated electrode and an additional exposed electrode downstream supplied with DC voltage. The ionic wind velocity and thrust can be significantly improved by increasing DC voltage although the plasma discharge characteristics are virtually unaffected. It is found that the negative charges generated by the discharge of the three-electrode structure accumulate on the dielectric surface significantly further downstream in an AC period compared to the actuator with a two-electrode structure. The negative charges in the downstream region increase as the DC voltage increases.In addition, the DC voltage affects the time required for the positive charge filaments to decay.The positive DC voltage expands the ionic acceleration zone downstream to produce a greater EHD force. The amplitude of the DC voltage affects the electric field on the dielectric surface and is therefore a key factor in the formation of the EHD force. Further research on the surface charge characteristics of a three-electrode structure has been conducted using a pulse power to drive the discharge, and the same conclusions are drawn. This work demonstrates a link between surface charge characteristics and EHD performance of a three-electrode SDBD actuator.
基金supported in part by National Natural Science Foundation of China(Nos.50937004,50777051)
文摘Surface charges greatly affect the discharge/flashover development process across an insulator. The relationship between surface charge distribution on insulating materials and measurement data based on Pockels technique is discussed, and an improved algorithm is built to calculate the real surface charge density from original data. In this algorithm, two-dimensional Fourier transform technique and Wiener filter are employed to reduce the amount of numerical calculation and improve the stability of computation, Moreover, this algorithm considers not only the influence of sample＇s thickness and permittivity, but also the impact of charges at different positions. The achievement of this calibration algorithm is demonstrated in details. Compared with traditional algorithms, the improved one supplies a better solution in the calibration of surface charge distribution on different samples with different thickness.
基金supported by National Natural Science Foundation of China(No.51777076)the Self-topic Fund of State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources(No.LAPS2019-21)。
文摘In this paper,plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface.The physicochemical characteristics of samples are investigated and the electrical performances measured.The obtained results show that compared with untreated and single treated samples,the samples treated by step gradient modification significantly improve the flashover performance.According to experiment and simulation,the mechanism explanations are summarized as follows.First,it is found that the step gradient conductivity can effectively optimize the electric field distribution of a needle-needle electrode.Then,step gradient modification suppresses the accumulation of surface charge at the triple junction and makes the charge distribution more uniform.Furthermore,it can accelerate the surface dissipation on a high electrical field region and control the dissipation rate on a low electrical field region.All these results can restrain surface discharge and increase the flashover voltage.The step gradient modification method proposed in this paper provides a new idea for improving the surface insulation performance.
基金supported by National Natural Science Foundation of China under contract No.11575194the National Basic Research Program of China(973 Project) under contract No.2014CB239505-3+2 种基金Natural Science Foundation of Hebei Province under contract No.E2015502081the Fundamental Research Funds for the Central Universities under contract No.2016ZZD07the Young Scholar of the Chang Jiang Scholars Program,Ministry of Education,China
文摘Non-thermal plasma surface modification for epoxy resin（EP）to improve the insulation properties has wide application prospects in gas insulated switchgear and gas insulatedtransmission line.In this paper,a pulsed Ar dual dielectrics atmospheric-pressure plasma jet（APPJ）was used for Si CxHyOzthin film deposition on EP samples.The film deposition was optimized by varying the treatment time while other parameters were kept at constants（treatment distance：10 mm,precursor flow rate：0.6 l min-（-1）,maximum instantaneous power：3.08 k W and single pulse energy：0.18 m J）.It was found that the maximum value of flashover voltages for negative and positive voltage were improved by 18%and 13%when the deposition time was3 min,respectively.The flashover voltage reduced as treatment time increased.Moreover,all the surface conductivity,surface charge dissipation rate and surface trap level distribution reached an optimal value when thin film deposition time was 3 min.Other measurements,such as atomic force microscopy and scanning electron microscope for EP surface morphology,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy for EP surface compositions,optical emission spectra for APPJ deposition process were carried out to better understand the deposition processes and mechanisms.The results indicated that the original organic groups（C–H,C–C,C=O,C=C）were gradually replaced by the Si containing inorganic groups（Si–O–Si and Si–OH）.The reduction of C=O in ester group and C=C in p-substituted benzene of the EP samples might be responsible for shallowing the trap level and then enhancing the flashover voltage.However,when the plasma treatment time was longer than 3 min,the significant increase of the surface roughness might increase the trap level depth and then deteriorate the flashover performance.
基金supported by the National Key Research and Development Program(Grant No.2016YFB0900900)National Natural Science Foundation of China(Grant No.51577064)
文摘The ion flow field on the ground is one of the significant parameters used to evaluate the electromagnetic environment of high voltage direct current（HVDC） power lines.HVDC lines may cross the greenhouses due to the restricted transmission corridors.Under the condition of ion flow field,the dielectric films on the greenhouses will be charged,and the electric fields in the greenhouses may exceed the limit value.Field mills are widely used to measure the groundlevel direct current electric fields under the HVDC power lines.In this paper,the charge inversion method is applied to calculate the surface charges on the dielectric film according to the measured ground-level electric fields.The advantages of hiding the field mill probes in the ground are studied.The charge inversion algorithm is optimized in order to decrease the impact of measurement errors.Based on the experimental results,the surface charge distribution on a piece of quadrate dielectric film under a HVDC corona wire is studied.The enhanced effect of dielectric film on ground-level electric field is obviously weakened with the increase of film height.Compared with the total electric field strengths,the normal components of film-free electric fields at the corresponding film-placed positions have a higher effect on surface charge accumulation.
基金the financial support from National Natural Science Foundation of China (No. 51607128)Natural Science Foundation of Hubei Province (No. 2016CFB111)China Postdoctoral Science Foundation (No. 2016M602353)
文摘In an insulating system including solid and gas dielectrics, discharge type has a strong impact on charge accumulation at the interface between two dielectrics, and hence charge decay. In order to clarify the influence, a surface charge measurement system was constructed, and three types of discharge, i.e. surface discharge, and low intensity and high intensity coronas, were introduced to cause surface charge accumulation. The decay behavior of surface charges after different types of discharge was obtained at various temperatures. It was found that total surface charges monotonically decreased with time, and the decay rate became larger as temperature increased. However, after a surface discharge or a high intensity corona, surface charge density in the local area appeared to fluctuate during the decay process. Compared with this, the fluctuation of surface charge density was not observed after a low intensity corona. The mechanisms of surface charge accumulation and decay were analysed. Moreover, a microscopic physical model involving charge production, accumulation, and decay was proposed so that the experimental results could be explained.
基金supported by the National Natural Science Foundation of China(Grant Nos.11375031 and 11335003)
文摘The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes(CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid–liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results,we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work.
基金Project supported by the Joint Funds of Xinjiang Natural Science Foundation,China(Grant No.2015211C298)
文摘Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows： i） when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii）for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii） when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.
基金the Graduate Student Research Innovation Project of Chongqing(No.CYB22016)National Natural Science Foundation of China(Nos.52237010,52277135,51907011)。
文摘The surface charge accumulation on polymers often leads to surface flashover.Current solutions are mainly based on the introduction of inorganic fillers.The high-cost process and low compatibility remain formidable challenges.Moreover,existing researches on all-organic insulation focus on capturing electrons,contrary to alleviating charge accumulation.Here,an all-organic modification coating was prepared on polystyrene(PS)with the large-scale atmospheric-pressure plasma,which exhibits outperformed function in mitigating surface charge accumulation.The surface charge dissipation rate and surface conductivity are promoted by about 1.37 and 9.45 times,respectively.Simulation and experimental results show that this all-organic modification coating has a smaller electron affinity potential compared with PS.The decrease of electron affinity potential may result in accelerated surface charge decay of PS,which has never been involved in previous works.Moreover,this coating also has good reliability in a repeated surface flashover.This facile and large-scale approach brings up a novel idea for surface charge regulation and the manufacture of advanced dielectric polymers.
基金supported by National Natural Science Foundation of China (No. 51777076)the Self-topic Fund of the State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources (No. LAPS2019-21)
文摘This work treats the Al_(2)O_(3)-ER sample surface using dielectric barrier discharge fluorination(DBDF),DBD silicon deposition(DBD-Si),atmospheric-pressure plasma jet fluorination(APPJ-F)and APPJ silicon deposition(APPJ-Si).By comparing the surface morphology,chemical components and electrical parameters,the diverse mechanisms of different plasma modification methods used to improve flashover performance are revealed.The results show that the flashover voltage of the DBDF samples is the largest(increased by 21.2%at most),while the APPJ-F method has the worst promotion effect.The flashover voltage of the APPJ-Si samples decreases sharply when treatment time exceeds 180 s,but the promotion effect outperforms the DBD-Si method during a short modified time.For the mechanism explanation,firstly,plasma fluorination improves the surface roughness and introduces shallow traps by etching the surface and grafting fluorine-containing groups,while plasma silicon deposition reduces the surface roughness and introduces a large number of shallow traps by coating Si Oxfilm.Furthermore,the reaction of the DBD method is more violent,while the homogeneity of the APPJ modification is better.These characteristics influence the effects of fluorination and silicon deposition.Finally,increasing the surface roughness and introducing shallow traps accelerates surface charge dissipation and inhibits flashover,but too many shallow traps greatly increase the dissipated rate and facilitate surface flashover instead.
基金Project supported by the National Key R&D Program of China(Grant No.2018YFB0904400)the National Natural Science Foundation of China(Grant No.51977187)+3 种基金the“Science and Technology Innovation 2025”Key Project of Ningbo City,China(Grant No.2018B10019)the Natural Science Foundation of Zhejiang Province,China(Grant No.LY18E070003)the State Key Laboratory of HVDC,Electric Power Research Institute,China Southern Power Grid(Grant No.SKLHVDC-2019-KF-18)the Fundamental Research Funds for the Central Universities,China(Grant No.2018QNA4017).
文摘We present the variations of electrical parameters of dielectric barrier discharge(DBD)when the DBD generator is used for the material modification,whereas the relevant physical mechanism is also elaborated.An equivalent circuit model is applied for a DBD generator working in a filament discharging mode,considering the addition of epoxy resin(EP)as the plasma modified material.The electrical parameters are calculated through the circuit model.The surface conductivity,surface potential decay,trap distributions and surface charge distributions on the EP surface before and after plasma treatments were measured and calculated.It is found that the coverage area of micro-discharge channels on the EP surface is increased with the discharging time under the same applied AC voltage.The results indicate that the plasma modified material could influence the ignition of new filaments in return during the modification process.Moreover,the surface conductivity and density of shallow traps with low trap energy of the EP samples increase after the plasma treatment.The surface charge distributions indicate that the improved surface properties accelerate the movement and redistribution of charge carriers on the EP surface.The variable electrical parameters of discharge are attributed to the redistribution of deposited surface charge on the plasma modified EP sample surface.
基金This work was supported in part by a grant from Russian Scientific Foundation(Project No.17-75-30064).
文摘Up to now,the DNA molecule adsorbed on a surface was believed to always preserve its native structure.This belief implies a negligible contribution of lateral surface forces during and after DNA adsorption although their impact has never been elucidated.High-resolution atomic force microscopy was used to observe that stiff DNA molecules kinetically trapped on monomolecular films comprising one-dimensional periodically charged lamellar templates as a single layer or as a sublayer are oversaturated by sharp discontinuous kinks and can also be locally melted and supercoiled.We argue that kink/anti-kink pairs are induced by an overcritical lateral bending stress(>30 pNnm)inevitable for the highly anisotropic 1D-1D electrostatic interaction of DNA and underlying rows of positive surface charges.In addition,the unexpected kink-inducing mechanical instability in the shape of the template-directed DNA confined between the positively charged lamellar sides is observed indicating the strong impact of helicity.The previously reported anomalously low values of the persistence length of the surface-adsorbed DNA are explained by the impact of the surface-induced low-scale bending.The sites of the local melting and supercoiling are convincingly introduced as other lateral stress-induced structural DNA anomalies by establishing a link with DNA high-force mechanics.The results open up the study in the completely unexplored area of the principally anomalous kinetically trapped DNA surface conformations in which the DNA local mechanical response to the surface-induced spatially modulated lateral electrostatic stress is essentially nonlinear.The underlying rich and complex in-plane nonlinear physics acts at the nanoscale beyond the scope of applicability of the worm-like chain approximation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12025407,11934003,9185012011774328)+1 种基金the Key R&D Program of China(Grant No.2016YFA0300902)the Chinese Academy of Sciences。
文摘Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry.Electric control is widely used to modify interfacial water,where the influence of surface charges is inevitable.Here we obtain positively and negatively charged surfaces using Li Ta O_(3) crystals and observe that a large net surface charge up to 0.1 C/m;can nominally change the contact angles of pure water droplets comparing to the same uncharged surface.However,even a small amount of surface charge can efficiently increase the water contact angle in the presence of aerosols.Our results indicate that such surface charges can hardly affect the structure of interfacial water molecular layers and the morphology of the macroscopic droplet,while adsorption of a small amount of organic contaminants from aerosols with the help of Coulomb attraction can notably decrease the wettability of solid surface.Our results not only provide a fundamental understanding of the interactions between charged surfaces and water,but also help to develop new techniques on electric control of wettability and microfluidics in real aerosol environments.
基金supported by Science Foundation of Hunan University
文摘A surface charge measuring system using the capacitive probe method is analysed. The present study shows that the measuring system cannot have a steady-state output and that the error resulting from the finite leakage resistance of the measuring system will be accumulated during the measuring process. Based on the theoretical analysis a new type probe with a low charge leakage and high resolution is designed. The surface charge accumulated on the Teflon insulator under a DC voltage is measured using this new probe and some phenomena of the surface charging are reported.
文摘Foam stability tests were performed using sodium dodecyl sulfate(SDS)surfactant and SiO2 nanoparticles as foaming system at different asphaltene concentrations,and the half-life of CO_(2) foam was measured.The mechanism of foam stability reduction in the presence of asphaltene was analyzed by scanning electron microscope(SEM),UV adsorption spectrophotometric concentration measurement and Zeta potential measurement.When the mass ratio of synthetic oil to foam-formation suspension was 1:9 and the asphaltene mass fraction increased from 0 to 15%,the half-life of SDS-stabilized foams decreased from 751 s to 239 s,and the half-life of SDS/silica-stabilized foams decreased from 912 s to 298 s.When the mass ratio of synthetic oil to foam-formation suspension was 2:8 and the asphaltene mass fraction increased from 0 to 15%,the half-life of SDS-stabilized foams decreased from 526 s to 171 s,and the half-life of SDS/silica-stabilized foams decreased from 660 s to 205 s.In addition,due to asphaltene-SDS/silica interaction in the aqueous phase,the absolute value of Zeta potential decreases,and the surface charges of particles reduce,leading to the reduction of repulsive forces between two interfaces of thin liquid film,which in turn,damages the foam stability.
文摘Drilling is a most important and crucial operation in the excavation industries.With the objective of looking into the enhancement of diamond drilling performance detailed laboratory investigations were carried out on phosphate rock.The effect of Poly（Ethylene Oxide）（PEO） added to the drilling water was studied by varying machine parameters and PEO concentration.The responses were rate of penetration and torque at the bit rock interface.Slake durability tests were also performed to understand the slaking behavior of phosphate rock in PEO solutions.
基金Supported by National High Technology R&D Program(SS2013AA041104)
文摘This paper investigated the dependence of out-of-plane electret-based vibration energy harvesters’output power,frequency bandwidth,and resonance frequency on surface charge density and load resistance.As the external acceleration amplitude and electret size were held constant,the following results are predicted by the numerical investigation：（1）An optimum value exists in the surface charge density to maximize the output power.As the surface charge density is increasing,electrostatic forces are enhanced,which emphasizes that the soft spring effect widens the frequency bandwidth and lowers the resonance frequency.（2）Different surface charge densities correspond to different optimum initial air gaps,resonance frequency,and optimum load resistance.（3）With the attenuation of the surface potential,the output power,frequency drift,and frequency bandwidth decreased.（4）An optimum value exists in the load resistance to maximize the output power.As the load resistance is decreasing,electrostatic force is enhanced,which lowers the resonance frequency.（5）A maximum frequency bandwidth exists with further load resistance increasing,and the initial air gap is smaller,the greater the frequency bandwidth.
文摘To investigate the effect of the rib structure on the discharge characteristics of the plasma display panel, the potential distribution, particles density distribution and ions incident angle distribution were examined by simulation of a two-dimensional particle-in-cell/Monte Carlo collision, with two kinds of rib structure： the stripe rib structure and the Waffle rib structure. The results showed that the distribution of electric potential at the corner of the discharge cell was almost the same for these two rib structures while in the centre there was a difference between these two rib structures. The striation phenomenon could be observed in both cases. The distribution of density also indicated that the striation phenomenon was accompanied by the firing of discharge, and the Waffle rib structure might reduce the density humps. In the cell with a stripe rib structure, the profiles of the surface charge density along the sustained dielectric layer presented a better fluctuating distribution than that in the cell with a Waffle rib structure. The spatial potential and particle density in the discharge bulk showed that the Waffle ribs could weaken the striation phenomenon, which could be explained by the decrease in the particle numbers in the discharge cell. The simulation results of the ion incident angle showed that most ions impacted the sustained dielectric layer in the normal stripe rib cell with an incident angle in the range of 6° to 19° while with the Waffle rib structure the incident angle of most ions was in the range of 4° to 19°. The Waffle rib structure did not affect the angle distribution of incident ions significantly.
