Decrease In Surface Potential Research Articles

Optimization of Laminated Bio-Polymer Fabrication for Food Packaging Application: A Sustainable Plasma-Activated Approach.

The current level of packaging consumption imposes a need to fabricate single-use food packaging with renewable and compostable materials, such as bio-polyesters (e.g., polylactic acid, PLA and polybutylene succinate, PBS) or cellulose, but their use is still problematic. Fabrication of bio-compostable composites can specifically address impeding challenges, and adhesive lamination, achieved with compostable glue, is becoming more and more popular with respect to the less versatile hot lamination. In this context, plasma activation, a chemical-free oxidation technique of a material's surface, is used to increase the affinity of three different biomaterials (cellulose, PLA and PBS) toward a compostable polyurethane adhesive to decrease its amount by gluing bio-polyesters to cellulose. Optical Microscopy reveals activation conditions that do not affect the integrity of the materials, while Water Contact Analyses confirm the activation of the surfaces, with contact angles decreased to roughly 50 deg in all cases. Unexpectedly, ζ-potential analyses and subtractive infrared spectroscopy highlight how the activation performed superficially etches cellulose, while for both PLA and PBS, a general decrease in surface potential and an increase in superficial hydroxyl group populations confirm the achievement of the desired oxidation. Thus, we rationalize continuous activation conditions to treat PLA and PBS and to glue them to neat cellulose. While no beneficial effect is observed with activated PLA, bi-laminate composites fabricated with activated PBS fulfill the benchmark for adhesion strength using less than before, while oxygen permeation analyses exclude plasma-induced etching even at a nanoscale.

Model of the Formation of a Fixed Charge in SiO<sub>2</sub>, Produced by Thermal Oxidation of Silicon

Solid-state recrystallization of the surface silicon layer after chemical and mechanical polishing with application of fast thermal treatment by pulses of one second duration is one of the feasible methods of improving the silicon surface properties. The purpose of this work is to explore the impact of fast thermal treatment resulting in solid state recrystallization of mechanically disrupted layer on generation of fixed charge in SiO2 at thermal oxidation of silicon. The results of studying P-doped electron silicon (KEF 4.5) and B-doped hole silicon (BDS 12) hole-type silicon of orientation <100> diameter 100 mm after chemical and mechanical polishing are provided. By the method of voltage-capacitance characteristic the flat zones voltage and charge density on the boundary of “silicon – silicon dioxide” were determined and by the method of scanning probe electrometry the surface distribution of these characteristic prior and after fast thermal treatment was determined. It has been ascertained that fast thermal treatment on silicon wafers KEF 4.5 and BDS 12 of orientation <100> due to solid state recrystallization of mechanically disrupted layer shall bring about 1.5 times decrease in surface potential along wafers area and residual fixed charge in silicon dioxide.

Noise spectroscopy based numerical modelling of chemisorption on SnO2 surface for CO gas sensing applications

The gas sensor response of the tin oxide (SnO2) semiconductor toward carbon monoxide (CO) gas has been simulated using the noise spectroscopy technique. The Wolkenstein gas adsorption model is used to calculate the surface coverage of environmental oxygen ions and target gas molecules. The interaction of CO gas molecules with the negatively charged oxygen ions has been incorporated in the numerical model. The equilibrium charge neutrality condition of the semiconductor material has been solved as a function of gas adsorption parameters like surface coverage, temperature, pressure and surface potential. Eventually, the power density spectrum (PDS) of the electrical conductance of the sensing layer was calculated before and after the gas adsorption conditions. It has been observed that the semiconductor band bending increases sharply at a certain concentration of environmental oxygen gas concentration (10−4 to 10−3 atm). At a temperature of 480 K, a steep decrease in surface potential was observed. This temperature range of maximum sensor response was optimized for calculating noise spectrum of electrical conductivity fluctuations at equilibrium condition of adsorption-desorption. The cutoff frequency (109 Hz) was calculated using normalized PDS of electrical conductance. The gas sensor response was calculated as a ratio of film conductance before and after the gas adsorption as a function of gas pressure and surface temperature at the calculated cutoff frequency. The increase in sensor response was observed with the increase in CO partial pressure as a function of temperature for a specific cut off frequency. The comparison of sensor response of the presented model has been demonstrated with another published numerical model. The presented model shows improved sensor response for higher (>10−8 atm) CO partial pressure.

Research on the Induced Electrostatic Discharge of Spacecraft Typical Dielectric Materials under the ESD Pulse Irradiation.

Based on polyimide (PI), epoxy resin (EP), polytetrafluoroethylene (PTFE) typical dielectric materials used in spacecraft, a research platform for charge-discharge experiment under strong field was established. The influence of irradiation field strength, beam energy, dielectric thickness, etc., on electrostatic discharge characters of dielectric materials were studied and summarized. The results show that with the increase of field strength, the frequency of induced electrostatic discharge increases, the accumulated charge on the dielectric surface decreases, and the dielectric surface potential decreases; Under the same conditions, PI has the lowest discharge frequency and the highest surface dynamic balance potential. The thicker the dielectric material, the lower the discharge frequency, the higher the surface dynamic equilibrium potential; The shape and size of the background electrodes also affect the discharge frequency. When the area is the same, the sharper the electrode edge, the higher the discharge frequency. When the shape is the same, the larger the grounding area, the higher the discharge frequency. By proposing the induced discharge test method, the function mechanism of spatial environmental factors on the electrostatic discharge of typical dielectric materials are obtained. Comparative analysis on electrostatic properties of different dielectric materials can provide data reference and technical support for spacecraft electrostatic safety and protection.

Adsorption of CTAB on Sapphire-c at High pH: Surface and Zeta Potential Measurements Combined with Sum-Frequency and Second-Harmonic Generation.

The adsorption of cetyltrimethylammonium bromide (CTA+Br-) on sapphire-c surfaces was studied at pH 10 below the surfactants' critical micelle concentration. The evolution of interfacial potentials as a function of CTAB concentration was characterized by surface and zeta potential measurements and complemented by molecular dynamic (MD) simulations as well as by second-harmonic (SHG) and vibrational sum-frequency generation (SFG) spectroscopy. The changes in interfacial potentials suggest that the negative interfacial charge due to deprotonated surface aluminols groups is neutralized and can be even overcompensated by the presence of CTA+ cations at the interface. However, SFG intensities from strongly hydrogen-bonded interfacial water molecules as well as SHG intensities decrease with both increasing CTAB concentration and the magnitude of the surface potential. They do not suggest a charge reversal at the interface, while the change in zeta potential is actually consistent with an apparent charge inversion. This can be qualitatively explained by results from MD simulation, which reveal adsorbed CTA+ cations outside a first strongly bound hydration layer of water molecules, where they can locally distort the structural order and replace some of the interfacial water molecules adjacent to the first layer. This is proposed to be the origin for the significant loss in SFG and SHG intensities with increasing CTAB concentration. Moreover, we propose that CTA+ can act as a counterion and enhance the occurrence of deprotonated surface aluminols that is consistent with the decrease in surface potential.

Effects of soluble organics on the settling rate of modified clay and development of improved clay formulations for harmful algal bloom control

For many years, the dispersal of modified clay (MC) has been used to control harmful algal blooms (HABs) in coastal waters of China. MC flocculation efficiency can be influenced by many factors in variable and complex natural environments, including high concentrations of dissolved organic matter (DOM) in the water to be treated. Since many HABs occur in nearshore waters where DOM concentrations are high, this is a significant problem that requires urgent attention. This study involved the use of humic acid as a representative form of DOM to study the influence of organic matter on the MC flocculation process. At high concentrations, humic acid was adsorbed onto MC particles, resulting in a decrease in surface potential and an increase in electrostatic repulsion between the clay particles; this decreased the MC settling rate and increased the water clarification time. Flocs were characterized by their relatively small particle size, high particle concentration, and low collision efficiency, which together resulted in slow clarification of the water after MC spraying. Based on the mechanism of the DOM-MC interaction and combined with the Derjaguin-Landau-Verwey-Overbeek theory and theoretical considerations of clay surface modification, the “ionic atmosphere compression” method was used to improve MC flocculation efficiency in high-organic water. This method increased the ionic strength of the clay stock solution by adding salt, thereby compressing the ionic atmosphere of MC particles and lowering the potential barrier, allowing the MC particles in the treated water to flocculate rapidly and form large flocs, followed by further floc growth and rapid settling via differential sedimentation. The settling rate of MCs improved by a factor of two and the removal efficiency of the HAB cells increased by 7–28%. This study provides important baseline information that will extend the application of MC to HAB control in water bodies with high organic loadings.

Physical mechanisms driving the reversible aggregation of Staphylococcus aureus and response to antimicrobials

Formation of non-sessile, auto-aggregated cells of Staphylococcus aureus contributes to surface colonization and biofilm formation, hence play a major role in the early establishment of infection and in tolerance to antimicrobials. Understanding the mechanism of aggregation and the impact of aggregation on the activity of antimicrobials is crucial in achieving a better control of this important pathogen. Previously linked to biological phenomena, physical interactions leading to S. aureus cellular aggregation and its protective features against antimicrobials remain unraveled. Herein, in-vitro experiments coupled with XDLVO simulations reveal that suspensions of S. aureus cells exhibit rapid, reversible aggregation (> 70%) in part controlled by the interplay between cellular hydrophobicity, surface potential and extracellular proteins. Changing pH and salt concentration in the extracellular media modulated the cellular surface potential but not the hydrophobicity which remained consistent despite these variations. A decrease in net cellular negative surface potential achieved by decreasing pH or increasing salt concentrations, caused attractive forces such as the hydrophobic and cell–protein interactions to prevail, favoring immediate aggregation. The aggregation significantly increased the tolerance of S. aureus cells to quaternary ammonium compounds (QAC). The well-dispersed cell population was completely inactivated within 30 s whereas its aggregated counterpart required more than 10 min.

Radiation Synthesis of Psyllium/Frankincense Essential Oil –Based Wound Dressing Hydrogels: Antimicrobial, Antioxidant and Wound Healing Performance

Abstract Innovative bioactive hydrogel dressings based on Psyllium (Pys) and Carbopol (Carp) supported with Frankincense essential oil (FO) were fabricated using γ- irradiation facility for crosslinking and sterilization. (Psy-Carp)/FO dressing’s characteristics, hemolytic potential, antioxidant efficiency, antimicrobial activity as well as their morphological features were evaluated. Wound healing efficacy was evaluated using a rat model. The results revealed that the gelation degrees increased by the increase of (Psy) concentration, Carbopol content, and irradiation dose. The incorporation of FO oil up to 5% improves the swelling ability as well as the dressing porosity as shown by SEM images. The incorporation of FO oil enhances the Water Vapor Transmission Rate (WVTR), increases the antioxidant activity. Antimicrobial activity and microbial barrier potency of (Psy-Carp)/FO dressing was tested against Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Candida albicans (C. albicans), the results showed that it attenuates microbial growth of all the tested strains after 18 h. by two log cycle and cause a high rate of microbial killing. A significant increase of protein release, decrease in Exopolysaccharides (EPS) content and decrease of membrane surface potential were noticed indicating alternation of cell membrane permeability leading to cell death. In vivo wound healing evaluation using rat model confirms that the tested dressings induce faster wound healing with improvement biochemical parameters compared with that of FO free (Psy-Carp) hydrogel. Based on the above-mentioned results, it can be concluded that (Psy-Carp)/FO hydrogel dressings demonstrate a promising potential as wound care candidates.

Extracellular ATP molecules effects the functional properties of granulocyte plasma membrane

Extracellular ATP is an auto- and paracrine regulator in the mechanisms of intercellular signaling. It is the trigger starting the purinergic signaling cascade also. The aim of this work to study the effect of extracellular ATP on the functional properties (rigidity, surface potential, adhesive properties and osmoregulatory capabilities of the membrane) of the plasma membrane and the migration activity of granulocytes in experiments in vitro. In the experiment, the granulocyte subpopulation separated from the venous blood of healthy people was used. The experiment samples were incubated with adenosine-5-triphosphate disodium salt trihydrate in concentration 10 мМ that matches of ATP concentration released from blood cells during deformation stress in the microvasculature vessels. The stiffness and surface potential of a cell, the adhesion force between erythrocyte and granulocyte was measured by using the method of atomic force microscopy, tests with hypoosmotic load were performed and the migration activity of granulocytes was studied. As a result of the experiment, a decrease in stiffness and surface potential was found by 53.2% and 32.5 % (р

Plasma expansion towards an electrically insulated surface

The problem of plasma expansion into a vacuum is revisited with the addition of a finite boundary condition; an electrically insulated surface. As plasma expands towards a charge-accumulating surface, the leading electron cloud charges the surface negatively, which in turn repels electrons and attracts ions. This plasma–surface interaction is shown to result in a feedback process which accelerates the plasma expansion. In addition, we examine the decrease in (negative) surface potential and associated near-surface electron density. To investigate this plasma coupling with an electrically floating surface, we develop an analytic model including four neighbouring plasma regions: (i) undisturbed plasma, (ii) quasi-neutral self-similar expansion, (iii) ion front boundary layer and (iv) electron cloud. A key innovation in our approach is a self-contained analytic approximation of the ion front boundary layer, providing a spatially continuous electric field model for the early phase of bounded plasma expansion.

Layer number dependence of the work function and optical properties of single and few layers MoS2: effect of substrate

We have examined the influence of flake-substrate effects that affect one and few layers of MoS2 in terms of their electrical and optical properties. In the measurements, we used SiO2/Si substrates with etched cavities and aluminum electrodes. Suspended areas are easily identifiable both on images depicting the topography and on the surface potential maps measured with the Kelvin probe force microscopy. Compared to the SiO2/Si supported material, surface potential decrease is observable at the membrane. The surface potential value of the flakes located on the electrodes is the lowest. PL measurements prove that single MoS2 monolayer was obtained. Suspended regions are also correlated with maps obtained as a result of Raman spectroscopy.

The nonlocal electron kinetics for a low-pressure glow discharge dusty plasma

The nonlocal electron kinetic model based on the Boltzmann equation is developed in low-pressure argon glow discharge dusty plasmas. The additional electron-dust elastic and inelastic collision processes are considered when solving the kinetic equation numerically. The orbital motion limited theory and collision enhanced collection approximation are employed to calculate the dust surface potential. The electron energy distribution function (EEDF), effective electron temperature Teff, and dust surface potential are investigated under different plasma and dust conditions by solving the Boltzmann and the dust charging current balance equations self-consistently. A comparison of the calculation results obtained from nonlocal and local kinetic models is made. It is shown that the appearance of dust particles leads to a deviation of the EEDF from its original profile for both nonlocal and local kinetic models. With the increase in dust density and size, the effective electron temperature and dust surface potential decrease due to the high-energy electron loss on the dust surface. Meanwhile, the nonlocal and local results differ much from each other under the same calculation condition. It is concluded that, for low-pressure (PR ≤ 1 cm*Torr) glow discharge dusty plasmas, the existence of dust particles will amplify the difference of local and nonlocal EEDFs, which makes the local kinetic model more improper to determine the main parameters of the positive column. The nonlocal kinetic model should be used for the calculation of the EEDFs and dusty plasma parameters.

Impact of nano-ZnO/grafted textile on the outer membrane permeability of some pathogenic bacteria

Cotton textile grafted by chitosan hydroxyethyl methacrylate has been prepared by gamma radiation as a polymeric stabilizer for ZnO nanoparticles (NPs). The grafting percent and swelling property of the prepared grafted polymer in bi-distilled water were studied and the results showed that the swelling percent of the plain textile is higher than that of all different compositions. The morphology and structure of plain textile, grafted textile and nano-ZnO/grafted textile were examined by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The presence of ZnO in the prepared samples was examined by energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The particle size of the formed ZnO NPs has been estimated by transmission electron microscopy (TEM). The results indicate the nanoscale of the ZnO particles. Nano-ZnO/grafted textile was tested against some pathogenic strains, and the results show that the nano-ZnO/grafted textile was able to attenuate bacterial growth of MRSA and Klebsiella pneumoniae after 24 h of direct contact. Also, release of potassium ions, loss of absorbing materials and decrease of membrane surface potential were noticed, indicating alteration of cell membrane permeability. Furthermore, SEM observation showed bacterial cell deformation for growth on the nano-ZnO/grafted textile. These results have been promising in the antibacterial field.

Surface flashover performance of epoxy resin microcomposites improved by electron beam irradiation

The influencing mechanism of electron beam irradiation on surface flashover of epoxy resin/Al2O3 microcomposite was investigated. Epoxy resin/Al2O3 microcomposite samples with a diameter of 50mm and a thickness of 1mm were prepared. The samples were irradiated by electron beam with energies of 10 and 20keV and a beam current of 5μA for 5min. Surface potential decay, surface conduction, and surface flashover properties of untreated and irradiated samples were measured. Both the decay rate of surface potential and surface conductivity decrease with an increase in the energy of electron beam. Meanwhile, surface flashover voltage increase. It was found that both the untreated and irradiated samples have two trap centers, which are labeled as shallow and deep traps. The increase in the energy and density of deep surface traps enhance the ability to capture primary emitted electrons. In addition, the decrease in surface conductivity blocks electron emission at the cathode triple junction. Therefore, electron avalanche at the interface between gas and an insulating material would be suppressed, eventually improving surface flashover voltage of epoxy resin microcomposites.

Effects of DC and pulse voltage combination on surface charge dynamic behaviors of epoxy resin

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 HVDC GIS and the safety of entire grid. Moreover, the influence on surface charge dynamic behavior under pulse voltage produced by switch overvoltage, accompanying with the DC voltage, is still unclear. In order to research the comprehensive effect of DC and pulse voltage on surface charge behavior, 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 and pulse polarities. When DC and pulse voltage with the same polarity are applied, smaller pulse voltage would push the original charges away, resulting in the decrease of initial surface potential. But a big pulse voltage could increase the surface potential. The speed of surface charge dissipation has an opposite tendency. When the pulse polarity becomes the opposite of DC voltage, surface potential at the sample center will be a heteropolar value at the beginning and then it gradually becomes consistent with the initial polarity. In addition, the surface charge change rate will rise with the increase of heteropolar pulse voltage. The Trap energy distributions were used to analyze charge decay process in the last section.

Simulation of low-energy electron beam irradiated PTFE based on bipolar charge transport model

Studies on charge transport properties of space grade insulating materials become popular recently because it is closely related to the safe operation of spacecraft. Taking charge carriers retrapping and hole injection into consideration, we simulated the surface charging and the space charge accumulation properties of PTFE under lowenergy electron-beam irradiation using bipolar charge transport model in this paper. Parameters for simulation were based on experiments and previous studies. The secondary electron yields of PTFE irradiated by electron-beam of different primary electron energies were measured, and experimental data were fitted with an empirical equation. Thermally stimulated current was measured, and the trap parameters of PTFE were analyzed from the current-temperature curve by initial-rise method. In order to investigate the space charge distribution and the surface potential of steady state, factors like primary electron energy, sample thickness, temperature and trap density were selected as variables separately. It is found that the steady surface potential is nearly linear with the primary electron energy, which also fits the experimental results. The simulation results show the sample thickness affects the charging rate of surface potential mostly, and the charging rate is slower in thinner samples. The steady surface potential fluctuates slightly in the case that temperature is not high, but it increases significantly when temperature is higher than 400 K. With the increase in trap density, the space charge accumulation tends to focus on the surface and the dielectric/electrode interface, and the steady surface potential decreases.

Effects of AC and pulse voltage combination on surface charge accumulation and decay of epoxy resin

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.

Observation of gold electrode surface response to the adsorption and oxidation of thiocyanate in acidic electrolyte with broadband sum-frequency generation spectroscopy

The adsorption and oxidation of thiocyanate (SCN−) on polycrystalline Au electrode surface in acidic electrolyte (10mM NaSCN/0.1M HClO4) have been investigated with broadband sum-frequency generation spectroscopy (BB-SFG). Potential-dependent behaviors of both the surface adsorbed species and the Au nonresonant (NR) electrode surface have been observed through BB-SFG band. A phase change of the S-bounded SCN− on the Au electrode surface occurs around 0.3V in both the anodic (increase of surface potential) and cathodic (decrease of surface potential) sweeps. At surface potentials >0.7V, oxidation and adsorption of the products (AuCN and Au(CN)2−) have been observed. Possible oxidation/reduction pathways have been discussed. The Stark slopes of the adsorbed SCN− SFG bands are significantly different in the anodic scan (before oxidation) from that in the cathodic scan (after the oxidation). The Au surface NR SFG band in the cathodic scan is much stronger than that in the anodic scan at the double layer surface potentials (−0.2V to 0.5V). The potential dependent Au surface NR BB-SFG band clearly shows that the adsorption/desorption and oxidation/reduction of surface species will affect the surface electronic structure.

Quantification Et Evolution Du Bilan De La Nappe Karstique De Saida (Nord-Ouest De l’Algerie)

The Northwest of Algeria, characterized by a semi-arid climate has seen in recent decades its surface and ground water potential decrease due to the scarcity of rainfall. Demographic pressure has increased the difficulties in the management of water resources, leading to problems of water scarcity in several areas of the country, especially in low-rainfall areas. From the hydrogeological point of view, the study area contains many karstic springs with great importance, which flows can exceed 50 l /s during flood periods. Aquifer recharge occurs primarily by rainwater.The main objective of this study was to evaluate the water balance of the karst aquifer situated near the city of Saida (North-West of Algeria) and to follow its evolution on several decades. In this region, the karst groundwater is important for drinking water supply, irrigation and industrial units.This approach to assessment will be based on the water balance equation by involving precipitation, evapotranspiration, infiltration and groundwater flow. The total volume of the groundwater reserves obtained from the balance method represent 45 million m3. These reserves have decreased with time.

Dust grains potential variation in a Vasyliunas Cairns-distributed plasmas with negative ions

Dust grains' potential variation is presented by using a non-equilibrium complex (dusty) plasma following the Vasyliunas Cairns (VC)-distribution, in which the components such as the electrons, ions [positive and negative], and dust grains have negative charge. For this reason, mathematical statement of currents is solved for dust grains having negatively charge to accomplish the equilibrium state value (viz., qd = constant) in the presence of VC-distributed plasmas. Indeed, the current balance equations are modified due to the streaming/nonequilibrium distributed negative ions. Numerically, it is assessed that the important plasma variable, for example, spectral index α, spectral index κ, negative ions streaming velocity (U0), and negative ions number density (ρ), significantly influences the dust grain surface potential (|ψd|) by: (i) increasing the value of spectral index kappa (κ) and negative ions density (ρ), the magnitude of dust surface potential (|ψd|) decreases and (ii) increasing the values of spectral index α and negative ions streaming velocity (U0), dust grains surface potential (|ψd|) increases. The relevance to low-temperature research center in a non-equilibrium dusty (complex) plasma is precisely discussed by associating oxygen ions (negative and positive) species.