Increase In Surface Charge Density Research Articles

Assessing charge accumulation and flashover phenomena on silicone rubber surface exposed to salt-containing droplets under direct current voltage

In damp and salt-fog environments, silicone rubber composite insulators are prone to forming dispersed droplets that absorb airborne salt nuclei, leading to charge accumulation and potentially causing flashovers that threaten transmission line stability. Regrettably, these concerns have not yet received sufficient attention from relevant researchers. This study examines the surface charge accumulation and flashover characteristics of silicone rubber insulators with droplets of varying electrical conductivity. The droplets can fix charges, as the conductivity of droplets on insulator surfaces increases, the migration rate of surface charges accelerates, causing distortion of the electric field and a significant increase the area of high-density charge regions on the sample surface. Compared with dry surfaces, increasing the equivalent salt density of salt-containing droplets attached to the surface from mild to severe (with conductivity increasing from 800 μS/cm to 2800 μS/cm) leads to a 25 %-40 % increase in the average surface charge density. After adsorbing charges, the salt droplets shorten the discharge development path, making it easier to trigger interface discharge. Compared with dry surfaces, the average flashover voltage of the salt droplets is reduced by at least 30 %. This study offers valuable analysis on charge accumulation and flashover for silicone rubber insulators in salt-fog environments.

The Role of Alkali Cations on the Selectivity of 5-Hydroxymethylfurfural Electroreduction on Glassy Carbon.

In the past decade, organic electrosynthesis has emerged as an atom- and energy-efficient strategy for harvesting renewable electricity that provides exceptional control over the reaction parameters. A profound and fundamental understanding of electrochemical interfaces becomes imperative to advance the knowledge-based development of electrochemical processes. The major strategy toward an efficient electrochemical system is based on the advancement in material science for electrocatalysis. Studies on the complex interplay among electrode surface, electrolyte, and transformation intermediates have only recently started to emerge. It involves acquiring atomic-scale insights into the electrochemical double layer, for which the identity and concentration of composing ions play a crucial role. In this study, we present how the identity and concentration of alkali cations impact the selectivity of aldehyde functionality electroreduction. As a case-study transformation, we set the electrochemical conversion of 5-hydroxymethylfurfural (HMF), a promising biomass-derived feedstock for the sustainable production of polymer or fuel precursors. Our findings reveal a consistent trend of the selectivity shift towards 2,5-bis(hydroxymethyl)furan (BHMF) as a function of cation size and concentration, rationalized by specific cation adsorption at the glassy carbon (GC), followed by the increase in the electrode surface charge density.

60Co-γ Irradiation-Induced Shift and Polarity Reversal in the Triboelectric Series of Poly(ether sulfone)s.

The sensitivity of triboelectric nanogenerators (TENGs) to the surface charge density highlights the significance of triboelectric materials and their modifications. Efforts have been directed toward developing effective strategies for increasing the surface charge density, expanding the potential applications of TENGs. This study proposes the use of irradiation technology for grafting to modify the electron-donating capability of poly(ether sulfone) (PES), thereby affording a dual benefit of enhancing the surface charge density and inducing a shift in the position of PES from negative to positive within the triboelectric series. The TENG based on grafted PES has resulted in a significant 3-fold increase in surface charge density compared to that of pristine PES, reaching 263 μC m-2. The surface charge density can be further increased to 502 μC m-2 through charge pumping. Notably, irradiation technology presents advantages over chemical grafting methods, particularly in terms of sustainability and environmental friendliness. This innovative approach shows great potential in advancing the domain of TENGs.

All porous Ecoflex and SEBS-based stretchable high-performance triboelectric nanogenerator for self-powered human activity monitoring

Achieving a high output performance by expanding the surface area of triboelectric materials is key to developing triboelectric nanogenerators (TENGs) for future versatile applications. Herein, highly porous Ecoflex and styrene-ethylene-butylene-styrene (SEBS) using chloroform are introduced to improve TENG performance. The triboelectric output increases significantly with increasing porosity, which can be attributed to the increase in the contact area, dielectric constant, and electrostatic induction in the porous structure, thereby resulting in additional surface charges on the porous surface and increased surface charge density of the friction materials. The TENG can stretch by up to 550 % with the designed fabric electrode configuration. Facilitated by the increased contact area of 3D printed microstructure and porous Ecoflex substrate, the fabricated TENG demonstrates a high voltage of 2280 V, corresponding to a power density of 18.8 W m−2, which is enough to power 460 light-emitting diodes and stopwatches. Demonstration of monitoring the walking steps of patients with Parkinson’s and blind people was also performed, which revealed outstanding sensing capabilities. In addition, the TENG-based self-powered sensor demonstrated an identification accuracy of 99.3 % and a motion detection accuracy of 98.2 % based on a deep learning model. Furthermore, by exploiting the outstanding ultrahigh sensitivity, the TENG was demonstrated for low-frequency football player motion monitoring. Therefore, the results of this study provide new insights into investigating porous materials and an efficient method to construct high-performance TENGs that can promote their practical application in the fields of smart healthcare and sports.

Heat and mass transfer of molten carbonates at charged electrode interface and its anisotropic behavior: A molecular dynamics study

Molten carbonates are broadly used in fuel cells with potential applications in reducing CO2 emission, while their heat and mass transfer properties near a charged electrode surface are less well understood. Using molecular dynamics (MD) simulations, the heat and mass transfer properties of molten Na2CO3-K2CO3 salts at charged nickel surfaces are revealed in this study. Simulation results indicates that when surface charge density increases, molten salt’s thermal transport exhibit anisotropic behavior: the interfacial thermal resistance show strong dependence on the surface charge while heat transfer parallel to surface is not sensitive to the surface charge. As for interfacial mass transfers, the shear viscosity of the carbonate tends to rise with external electric field, while the corresponding ion diffusion does not vary very much and exhibit position-dependent behavior. To further explore this, we find that the anisotropy of this heat and mass transfer properties is primarily attributed to the nonuniform ion distribution in the direction perpendicular to nickel surface with the increasing of charge, while the interatomic correlation does not vary much as surface charge increases. These results have suggested that the anisotropy of heat and mass transport properties of molten salt near electrode, which should be taken care of when modelling the macroscopic heat and mass transport of molten carbonate fuel cells in particular.

Surface charge manipulation for improved humidity sensing of TEMPO-oxidized cellulose nanofibrils

Cellulose-based humidity sensors have attracted great research interest due to their hydrophilicity, biodegradability, and low cost. However, they still suffer from relatively low humidity sensitivity. Due to the presence of negatively charged carboxylate groups, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibril (CNF) exhibits enhanced hydrophilicity and ion conductivity, which is considered a promising candidate for humidity sensing. In this work, we developed a facile strategy to improve the humidity sensitivity of CNF films by regulating their surface charge density. With the increase in surface charge density, both water uptake and charge carrier densities of the CNF films can be improved, enabling a humidity sensitivity of up to 44.5 % (%RH)−1, higher than that of most polymer-based humidity sensors reported in the literature. Meanwhile, the sensor also showed good linearity (R2 = 0.998) over the 15–75 % RH at 1 kHz. With these features, the CNF film was further demonstrated for applications in noncontact sensing, such as human respiration, moisture on fingertips, and water leakage, indicating the great potential of CNF film in humidity monitoring.

Unveiling the importance of surface ionization on desalination and ion-sieving performance of graphene oxide membranes

The experimental results have confirmed the negative surface charge of graphene oxide (GO) membranes. However, little work considered the influences of surface ionization on the performance of GO-based desalination or ion-sieving membranes. In this work, the surface charge of GO was included to explore its effects on the desalination performance adopting molecular dynamics (MD) simulation methods. The MD results indicated the enhanced interactions between GO nanochannel and water as well as ions with the increase in surface charge density. Consequently, the water flux enhanced but the ion rejection rate decreased with the increase in surface charge density. We further explored the influences of intercalated cations on the comprehensive desalination performance of GO membranes. The simulation results turned out that the performance of GO nanochannel was optimized at an appropriate interlayer distance. Among all the investigated cases, GO nanochannel intercalated with Mg2+ possesses the best desalination performance. It was found that surface charge density exerted little effect on optimizing the Li+/Mg2+ separation performance. However, Li+/Mg2+ separation performance could be optimized by narrowing the interlayer distance of GO nanochannel. The revealed mechanisms in this work might provide useful suggestions for designing strategies for nanosheet-based membranes to achieve better desalination and ion-sieving performance.

Feedstock and pyrolysis temperature influence biochar properties and its interactions with soil substances: Insights from a DFT calculation

The use of biochar for soil improvement and emission reduction has been widely recognized for its excellent performance. However, the choice of feedstock and pyrolysis temperature for biochar production significantly affects its surface parameters and interactions with soil substances. In this study, we retrieved 465 peer-reviewed papers on the application of biochar in reducing greenhouse gas emissions and nutrient losses in soil and analyzed the changes in biochar physicochemical parameters from different feedstock and pyrolytic temperatures. Molecular simulation computing technology was also used to explore the impacts of these changes on the interaction between biochar and soil substances. The statistical results from the peer-reviewed papers indicated that biochar derived from wood-based feedstock exhibits superior physical characteristics, such as increased porosity and specific surface area. Conversely, biochar derived from straw-based feedstock was found to contain excellent element content, such as O, N, and H, and biochar derived from straw and produced at low pyrolysis temperatures contains a significant number of functional groups that enhance the charge transfer potential and adsorption stability by increasing surface charge density, charge distribution and bonding orbitals. However, it should be noted that this enhancement may also activate certain recalcitrant C compounds and promote biochar decomposition. Taken together, these results have significant implications for biochar practitioners when selecting suitable feedstock and pyrolysis temperatures based on agricultural needs and increasing their understanding of the interaction mechanism between biochar and soil substances.

Plasma‐oxidized 2D MXenes subnanochannel membrane for high‐performance osmotic energy conversion

AbstractNanofluidic channels inspired by electric eels open a new era of efficient harvesting of clean blue osmotic energy from salinity gradients. Limited by less charge and weak ion selectivity of the raw material itself, energy conversion through nanofluidic channels is still facing considerable challenges. Here, a facile and efficient strategy to enhance osmotic energy harvesting based on drastically increasing surface charge density of MXenes subnanochannels via oxygen plasma is proposed. This plasma could break Ti–C bonds in the MXenes subnanochannels and effectively facilitate the formation of more Ti–O, C═O, O–OH, and rutile with a stronger negative charge and work function, which leads the surface potential of MXenes membrane to increase from 205 to 430 mV. This significant rise of surface charge endows the MXenes membrane with high cation selectivity, which could make the output power density of the MXenes membrane increase by 248.2%, reaching a high value of 5.92 W m−2 in the artificial sea‐river water system. Furthermore, with the assistance of low‐quality heat at 50°C, the osmotic power is enhanced to an ultrahigh value of 9.68 W m−2, which outperforms those of the state‐of‐the‐art two‐dimensional (2D) nanochannel membranes. This exciting breakthrough demonstrates the enormous potential of the facile plasma‐treated 2D membranes for osmotic energy harvesting.

High‐Efficiency Charge Injection with Discharge Mitigation Strategy for Triboelectric Dielectric Materials

AbstractThe high surface charge density of triboelectric dielectric materials is the core of high output performance triboelectric nanogenerators (TENGs). However, the increase in surface charge density enabled by the existing triboelectric material modification is still far from the saturation value (σBS) limited by air breakdown. Here, utilizing the directional high electric field generated by the charge excitation technology of the voltage‐multiplying circuit, an ultrafast charge self‐injection strategy is proposed. An ordinary contact‐separation TENG with a working frequency of 1.5 Hz can realize charge self‐injection on the surface of its dielectric layer to a saturation value within 22 s. Furthermore, the surface charge on the dielectric layer after excessive charge self‐injection can be retained to the maximum value by the step‐by‐step discharge mitigation strategy. Finally, by using a 7 µm thick polyimide film, a super‐high charge density of 1480 µC m−2 is achieved after charge injection, which is the historical high by modification of single layer material series currently. The charge self‐injection technology combined with discharge mitigation strategy proposed in this work is an important breakthrough in the field of triboelectric layer modification. In addition, this work also provides a systematic discussion on the σBS of dielectric layer related physical mechanism.

Cd(II) and As(V) removal from the multicomponent solutions in the presence of ionic polymers using carbonaceous adsorbents obtained from herbs

Abstract Biochars and activated carbons obtained from the nettle and the sage herbs were used for Cd(II), As(V), poly(acrylic acid) and polyethylenimine simultaneous adsorption from the multicomponent aqueous solutions. Electrokinetic studies proved that both activated carbons show acidic character of the surface. The point of zero charge of the sample obtained from the nettle herb occurs at pH 3.1, whereas that of the adsorbent obtained from the sage herb at pH 4.0. Cd(II) adsorption causes the decrease in the surface charge density and the zeta potential of both activated carbons, whereas As(V) addition results in the increase of solid surface charge density and its impact on the zeta potential value depends on adsorbent type. In case of the simultaneous presence of metals and polymers, the adsorbed macromolecules have greater influence on the surface charge density and the zeta potential values than the metal ions. Cd(II) and As(V) are well adsorbed on the examined activated carbons irrespective of the solution pH (changing in the range 3–9). Maximum adsorption were 218.27 mg/g for Cd(II) and 205.53 mg/g for As(V). The polymers presence causes a decrease (80–90 %) of both metal ions adsorbed amounts, whereas the poly(acrylic acid) and polyethylenimine adsorption mechanism in the presence of cadmium and arsenic ions depends on the adsorbent type and polymer-metal interactions.

A simplified model for the impact of dielectric polarization of a charged droplet on its diffusiophoresis

This study aims to quantify the impact of the dielectric permittivity of a droplet on its diffusiophoresis in different types of electrolytes. The dielectric droplet polarizes by the diffusion field along with the local electric field created by the interactions of the double layer with the imposed ionic concentration gradient, which generates an induced surface charge density anti-symmetrically distributed on the droplet surface. This induced surface charge influences both electrophoresis and chemiphoresis parts. Based on a low imposed concentration gradient, a simplified model is derived through a first-order perturbation technique. Dielectric polarization of the droplet attenuates the spinning force at the interface. This creates the mobility of a droplet of higher dielectric permittivity in the presence of a stronger diffusion field significantly higher than that of a perfectly dielectric droplet, and its value depends on the polarity of the droplet surface charge. In the absence of the diffusion field, the mobility of a conducting droplet remains a positive immaterial of the polarity of its surface charge density. We find that the impact of the dielectric polarization becomes significant as the surface charge density increases and attenuates with the increase in droplet viscosity. For a dielectric droplet at a thinner Debye length, a step-jump in mobility occurs at a higher value of the surface charge density. Such a type of step-jump in mobility does not appear for the conducting droplet due to the absence of the Maxwell stress at the interface.

Surface charge enhanced kinetically-limited evaporation in nanopores

Understanding the fundamentals of the kinetically-limited water evaporation in nanopores is of significant importance to improve the performance of modern evaporation-based thermal management devices. However, the ubiquitous existence of ions in aqueous solutions and charged function groups on solid walls have been ignored traditionally and the effect of surface charges on nanopore evaporation remains elusive. Herein, we consider the effect of surface charges on disjoining pressure and solve the system of equations governing the heat and mass transfer during the evaporation process from single nanopores numerically to yield the ultimate evaporation under various working conditions. Our results reveal that the surface charge, along with pore radius, wall temperature, and the relative humidity of ambient air, plays a critical role in determining the overall performance of the system. As the surface charge density increases, or as the pore radius decreases, the extended meniscus leads to a higher net rate of evaporation per unit pore area. Increasing the pore wall temperature increases the driving force for evaporation and results in a better performance despite the meniscus contracted. Results of this work provide new understanding of nanoscale phase-change heat transfer and is beneficial to applications requiring intensive evaporation, such as electronic cooling, forward osmosis, and membrane distillation.

Surface charge density governs the ionic current rectification direction in asymmetric graphene oxide channels.

Charged asymmetric channels are extensively investigated for the design of artificial biological channels, ionic diodes, artificial separation films, etc. These applications are attributed to the unique ionic current rectification phenomenon, where the surface charge density of the channel has a deep influence. In this work, we use molecular dynamics simulations to study the rectification phenomenon in asymmetric graphene oxide channels. A fascinating finding is that the ionic current rectification direction reverses from the negative to positive electric field direction with an increase in surface charge density. Specifically, at low charge density, the ionic flux reaches greater values in the negative electric field due to the enrichment of cations and anions, which provides a sufficient electrostatic shielding effect inside the channel and increases the possibility of ion release by the residues. However, at high charge density, the extremely strong residue attraction induces a Coulomb blockade effect in the negative electric field, which seriously impedes the ion transport and eventually leads to a smaller ionic current. Consequently, this ionic current order transition ultimately results in the rectification reversion phenomenon, providing a new route for the design of some novel nanofluidic devices.

Improving the Performance of the Lamellar Reduced Graphene Oxide/Molybdenum Sulfide Nanofiltration Membrane through Accelerated Water-Transport Channels and Capacitively Enhanced Charge Density.

Graphene is promising in the construction of next-generation nanofiltration membranes for wastewater treatment and water purification. However, the application of graphene-based membranes has still been prohibited by their deficiencies in permeability and ion rejection. Herein, regulating the 2D channel and enhancing the charge density are co-adopted for simultaneous enhancement of the water flux and salt rejection of reduced graphene oxide (rGO) membranes through the intercalation of molybdenum sulfide (MoS2) nanosheets and external electrical assistance. The fabricated rGO/MoS2 membranes possess expanded nanochannels with less friction and a higher water molecule transport velocity gradient (from 8.57 to 14.07 s-1) than those of rGO membranes. Consequently, their water permeance increases from 0.92 to 34.9 L m-2 h-1 bar-1. Meanwhile, benefiting from the high capacitance and negative potential of -1.1 V versus the saturated calomel electrode given to the membranes, their rejection rates toward NaCl reach 87.2% and those toward Na2SO4 reach 93.7%. The Donnan steric pore model analysis indicates that the capacitively and electrically increased surface charge density make great contributions to the higher ion rejection rate. This work gives new insights into membrane design for high water flux and salt rejection efficiency.

The electrophoretic motion of cylindrical macroions inside a nanochannel using molecular dynamics simulation

This paper examines the electrophoretic motion of a cylindrical macroion floating in a solution of water and NaCl inside a silicon nanochannel using molecular dynamics simulation. The aim is to investigate the effects of parameters like free movement, initial orientation, shape, aspect ratio, surface charge density and initial electrical charge of macroion on the electrophoretic motion. Findings suggest that any increase in surface charge density could give a rise to electrophoretic velocity of the solution. Considering the macroion free to move around, initial orientation does not play significant role in final results. Results also imply that macroion’s velocity does not change steadily by variations in surface charge density which is because of the multilayer structure of the Stern layer. Finally, average electrophoretic velocity of the solution for all scenarios in this study is witnessed to be the same. However, maximum electrophoretic velocity could be four times greater than average values. This must be taken into account in applications with limited maximum velocity.

Charge modifications of graphene oxide enhance the inhibitory effect on insulin amyloid fibrillation based on electrostatic interactions

Graphene oxide (GO) is a biocompatible nanomaterial that has an inhibitory effect on insulin amyloid fibrillation. In order to enhance the inhibitory effect of GO and explore the rules of electrostatic interactions on the inhibitory effect, carboxyl group, PEI and PEG were coupled to the GO nanoplatelet surface to prepare inhibitors of different surface electrical properties. The effects of surface electrical properties of inhibitors on insulin fibrillation were investigated. The results showed that GO, carboxyl group modified GO (GO-COOH), PEI modified GO (GO-PEI), and PEG modified GO (GO-PEG) inhibited insulin fibrillation in a dose-dependent manner. Compared with GO, positive charge-modified GO-PEI and negative charge-modified GO-COOH enhanced the inhibitory effect, while uncharged polymer-modified GO-PEG weakened the inhibitory effect. The inhibitory effect of the inhibitors increased with the increase of surface charge density. The difference in inhibitory effect between GO-PEI and GO-COOH was due to the different electrostatic interactions between inhibitors and insulin, and the different inhibition mechanisms. In addition, inhibitors mainly interact with insulin during the nucleation phase to hinder insulin fibrillation. The charge modifications of graphene oxide enhanced the inhibitory effect on insulin fibrillation based on electrostatic interactions, which will provide new thoughts for the development of anti-amyloid fibrillation drugs.

The Sensing Mechanism of InAlN/GaN HEMT

The sensing mechanism of InAlN/GaN high electron mobility transistors (HEMTs) is investigated systematically by numerical simulation and theoretical analysis. In detail, the influence of additional surface charge on device performance and the dependence of surface sensing properties on InAlN barrier thickness are studied. The results indicate that the saturation output drain current Idsat and two-dimensional electron gas (2DEG) concentration increase with the increase of positive surface charge density, which decrease with the increase of negative surface charge. The influence of negative surface charge on device performance is more remarkable than that of positive surface charge. Additionally, the modulation ability of surface charge on device performance increases with the decrease ofInAlN barrier thickness. The modulation of surface charge on device performance and the influence of barrier thickness on surface sensing sensitivity are mainly attributed to the variation of the energy band structure, surface potential and 2DEG concentration in the HEMT heterostructure. This work provides important support for structural optimization design of GaN-based HEMT sensors.

Effects of biased and unbiased illuminations on two-dimensional electron gases in dopant-free GaAs/AlGaAs

Illumination is performed at low temperature on dopant-free two-dimensional electron gases (2DEGs) of varying depths, under unbiased (gates grounded) and biased (gates at a positive or negative voltage) conditions. Unbiased illuminations in 2DEGs located more than 70 nm away from the surface result in a gain in mobility at a given electron density, primarily driven by the reduction of background impurities. In 2DEGs closer to the surface, unbiased illuminations result in a mobility loss, driven by an increase in surface charge density. Biased illuminations performed with positive applied gate voltages result in a mobility gain, whereas those performed with negative applied voltages result in a mobility loss. The magnitude of the mobility gain (loss) weakens with 2DEG depth, and is likely driven by a reduction (increase) in surface charge density. Remarkably, this mobility gain/loss is fully reversible by performing another biased illumination with the appropriate gate voltage, provided both $n$-type and $p$-type Ohmic contacts are present. Experimental results are modeled with Boltzmann transport theory, and possible mechanisms are discussed.

Quantification of pulsed electric field for the rupture of giant vesicles with various surface charges, cholesterols and osmotic pressures.

Electropermeabilization is a promising phenomenon that occurs when pulsed electric field with high frequency is applied to cells/vesicles. We quantify the required values of pulsed electric fields for the rupture of cell-sized giant unilamellar vesicles (GUVs) which are prepared under various surface charges, cholesterol contents and osmotic pressures. The probability of rupture and the average time of rupture are evaluated under these conditions. The electric field changes from 500 to 410 Vcm-1 by varying the anionic lipid mole fraction from 0 to 0.60 for getting the maximum probability of rupture (i.e., 1.0). In contrast, the same probability of rupture is obtained for changing the electric field from 410 to 630 Vcm-1 by varying the cholesterol mole fraction in the membranes from 0 to 0.40. These results suggest that the required electric field for the rupture decreases with the increase of surface charge density but increases with the increase of cholesterol. We also quantify the electric field for the rupture of GUVs containing anionic mole fraction of 0.40 under various osmotic pressures. In the absence of osmotic pressure, the electric field for the rupture is obtained 430 Vcm-1, whereas the field is 300 Vcm-1 in the presence of 17 mOsmL-1, indicating the instability of GUVs at higher osmotic pressures. These investigations open an avenue of possibilities for finding the electric field dependent rupture of cell-like vesicles along with the insight of biophysical and biochemical processes.