Electrical characteristics of a millisecond pulsed glow discharge

A μs and ms pulsed argon glow discharge was investigated with respect to the breakdown condition (Paschen curve). Moreover, current–voltage profiles were acquired for different discharge frequencies, pulse durations, cathode–anode spacing and discharge pressures. The breakdown voltage was dependent on the cathode material (Cu, steel, Ti and Al). No severe change in the breakdown voltage was observed for a 1 ms pulse at different frequencies. However, the theoretical breakdown curve, calculated based on the Paschen equation did not fit the experimental data. The current plots for different cathode–anode spacing showed a maximum at intermediate distance (8–10 mm). These data were consistent with mass spectrometric data acquired using the same instrument in a GC-GD-TOFMS chemical speciation study.     

Differential Ion Mobility Separations in up to 100 % Helium Using Microchips

The performance of differential IMS (FAIMS) analyzers is much enhanced by gases comprising He, especially He/N₂ mixtures. However, electrical breakdown has limited the He fraction to ~50 %–75 %, depending on the field strength. By the Paschen law, the threshold field for breakdown increases at shorter distances. This allows FAIMS using chips with microscopic channels to utilize much stronger field intensities (E) than “full-size” analyzers with wider gaps. Here we show that those chips can employ higher He fractions up to 100 %. Use of He-rich gases improves the resolution and resolution/sensitivity balance substantially, although less than for full-size analyzers. The optimum He fraction is ~80 %, in line with first-principles theory. Hence, one can now measure the dependences of ion mobility on E in pure He, where ion-molecule cross section calculations are much more tractable than in other gases that form deeper and more complex interaction potentials. This capability may facilitate quantitative modeling of high-field ion mobility behavior and, thus, FAIMS separation properties, which would enable a priori extraction of structural information about the ions.

Nonlinear current-voltage characteristics of conductive polyethylene composites with carbon black filled pet microfibrils

Current-voltage electrical behavior of in situ microfibrillar carbon black (CB)/poly(ethylene terephthalate) (PET)/polyethylene (PE) (m-CB/PET/PE) composites with various CB concentrations at ambient temperatures was studied under a direct-current electric field. The current-voltage (I-V) curves exhibited nonlinearity beyond a critical value of voltage. The dynamic random resistor network (DRRN) model was adopted to semi-qualitatively explain the nonlinear conduction behavior of m-CB/PET/PE composites. Macroscopic nonlinearity originated from the interfacial interactions between CB/PET micro fibrils and additional conduction channels. Combined with the special conductive networks, an illustration was proposed to interpret the nonlinear I-V characteristics by a field emission or tunneling mechanism between CB particles in the CB/PET microfibers intersections.     

First-principles study of field emission properties of gas adsorption on the carbon nanotubes

Carbon-containing gases usually present when preparing carbon nanotubes, and can affect the field emission of carbon nanotubes. Water vapor is also an important kind of gas for field emission, concerned by both experimental and theoretical studies. Under strong electric field, the gas molecules may be decomposed to radicals. Using DMol3 code based on density-functional theory, we calculated the adsorption of the gas molecules CH₄, CO and H₂O and the CH₃ and OH radicals under emission conditions. We found that the H₂O and the methyl have advantages to field emission and the CH₄, CO and the hydroxyl have disadvantages. The results of H₂O and CO are consistent with experiments, and the enhancement of current by CH₄ in the experiment may be due to the methyl decomposed from the CH₄.     

Conversion of natural gas to C_2 hydrocarbons via cold plasma technology

The plasma technology served as a tool in unconventional catalysis has been used in natural gas conversion,because the traditional catalytic methane oxidative coupling reaction must be performed at high temperature on account of the stability of methane molecule.The focus of this research is to develop a process of converting methane to C2 hydrocarbons with non-equilibrium plasma technology at room temperature and atmospheric pressure.It was found that methane conversion increased and the selectivity of C2 hydrocarbons decreased with the voltage.The optimum input voltage range was 40-80 V corresponding to high yield of C2 hydrocarbons.Methane conversion decreased and the selectivity of C2 hydrocarbons increased with the inlet flow rate of methane.The proper methane flow rate was 20-40 ml/min (corresponding residence time 10-20 s).The experimental results show that methane conversion was 47% and the selectivity of C2 hydrocarbons was 40% under the proper condition using atmospheric DBD cold plasma technology.It was found that the breakdown voltage of methane VB was determined by the type of electrode and the discharge gap width in this glow discharge reactor.The breakdown voltage of methane VB,min derived from the Paschen law equation was established.     

Conversion of natural gas to C2 hydrocarbons via cold plasma technology

The plasma technology served as a tool in unconventional catalysis has been used in natural gas conversion, because the traditional catalytic methane oxidative coupling reaction must be performed at high temperature on account of the stability of methane molecule. The focus of this research is to develop a process of converting methane to C2 hydrocarbons with non-equilibrium plasma technology at room temperature and atmospheric pressure. It was found that methane conversion increased and the selectivity of C2 hydrocarbons decreased with the voltage. The optimum input voltage range was 40-80 V corresponding to high yield of C2 hydrocarbons. Methane conversion decreased and the selectivity of C2 hydrocarbons increased with the inlet flow rate of methane. The proper methane flow rate was 20-40 ml/min (corresponding residence time 10-20 s). The experimental results show that methane conversion was 47% and the selectivity of C2 hydrocarbons was 40% under the proper condition using atmospheric DBD cold plasma technology. It was found that the breakdown voltage of methane VB was determined by the type of electrode and the discharge gap width in this glow discharge reactor. The breakdown voltage of methane VB,min derived from the Paschen law equation was established.     

Electric Field Effects on Photoconductivity and Electronic Absorption Spectra of Photogeneration Sites in Amorphous Molecular Semiconductors

Field dependences of photogeneration quantum yields of charge carriers in films of amorphous molecular semiconductors at high external electric field strengths cannot be always explained in terms of the Onsager or the Poole–Frenkel model, which do not consider the effect of an electric field on basic parameters of these materials. It is assumed that an external electric field shifts the electron density in molecules from its equilibrium distribution, thus altering the probability of electronic transitions. The assumption has been verified in studying the effect of an external electric field on the absorption spectra of poly(N-epoxypropylcarbazole) films doped with a merocyanine dye. Correlation between the theoretical and experimental results has been obtained.     

Improved Antimicrobial Potency through Synergistic Action of Chitosan Microparticles and Low Electric Field

Techniques to inhibit gram-negative bacteria such as Shiga toxin-producing Escherichia coli are valuable as the prevalence of large-scale industrial food preparation increases the likelihood of contamination. Chitosan, the deacetylated derivative of chitin, has been demonstrated to inhibit bacteria growth in acidic environments, but is significantly less effective in preventing bacteria grown at pH?>7.0. Pulsed electric fields, constituting another method of bacteria inhibition, are difficult to generate at sufficient strength due to the high electric potentials required. This study utilizes adsorption of particulate chitosan in a very low electric field for an increased inhibition of gram-negative bacteria in neutral or alkaline pH conditions. Chitosan microparticles are demonstrated to flocculate E. coli, inhibit growth, and exhibit increased efficacy when combined with a low voltage electric field applied over 2-min intervals. Using sustained pulses of approximately 100?V/cm, it is demonstrated that bacteria viability is reduced by several orders of magnitude. The degree of bacterial inhibition is increased when chitosan microparticles are introduced to the system prior to imposing a small electric field.     

Micro-gas-discharges as source of cathodic electroluminescence in non-aqueous solutions

The cathodic light emission observed during electrolysis of solutions of simple inorganic salts (e.g. LiClO₄, NaBF₄ and Tb³⁺ salts) in solvents such as dimethylformamide, dimethylsulphoxide, and POCl₃ at potentials higher than 6 V has been analyzed using spectroscopic, microscopic and electroanalytical techniques.Experimental results indicate that insulating (“passive”) layers on the cathode play an essential role in the mechanism of this electroluminescence. High current densities in the pores of these layers heat the solution and finally lead to local vaporization and decomposition of the solvent, thus creating insulating gas-filled cavities in the pores. If the applied voltage is sufficiently high, an electrical breakdown can develop across this cavity producing the observed luminescence phenomena.The luminescence emission spectra are indicative of excited gaseous species. Insulating model-layers obtained by glow-discharge polymerization were deposited on the cathode and used as models for electrodes with passive layers. Light emission was significantly more reproducible at such electrodes and allowed us to obtain reproducible voltage—current—light curves which support the proposed mechanism. The luminescence from Tb³⁺-ions occurs by energy transfer from the gas discharge.     

Determination of the lipid bilayer breakdown voltage by means of linear rising signal

Electroporation is characterized by formation of structural changes within the cell membrane, which are caused by the presence of electrical field. It is believed that "pores" are mostly formed in lipid bilayer structure; if so, planar lipid bilayer represents a suitable model for experimental and theoretical studies of cell membrane electroporation. The breakdown voltage of the lipid bilayer is usually determined by repeatedly applying a rectangular voltage pulse. The amplitude of the voltage pulse is incremented in small steps until the breakdown of the bilayer is obtained. Using such a protocol each bilayer is exposed to a voltage pulse many times and the number of applied voltage pulses is not known in advance. Such a pre-treatment of the lipid bilayer affects its stability and consequently the breakdown voltage of the lipid bilayer. The aim of this study is to examine an alternative approach for determination of the lipid bilayer breakdown voltage by linear rising voltage signal. Different slopes of linear rising signal have been used in our experiments (POPC lipids; folding method for forming in the salt solution of 100 mM KCl). The breakdown voltage depends on the slope of the linear rising signal. Results show that gently sloping voltage signal electroporates the lipid bilayer at a lower voltage then steep voltage signal. Linear rising signal with gentle slope can be considered as having longer pre-treatment of the lipid bilayer; thus, the corresponding breakdown voltage is lower. With decreasing the slope of linear rising signal, minimal breakdown voltage for specific lipid bilayer can be determined. Based on our results, we suggest determination of lipid bilayer breakdown voltage by linear rising signal. Better reproducibility and lower scattering are obtained due to the fact that each bilayer is exposed to electroporation treatment only once. Moreover, minimal breakdown voltage for specific lipid bilayer can be determined.     

On the role of intermembrane contact in cell electrofusion

The question: is cell electrofusion mediated by a long-lived fusogenic state or does the electric field fuse the membranes directly, was investigated by a new centrifugal approach. Mouse L-cells were brought into contact by a special centrifuge device allowing high voltage pulses to be applied upon the cell pellet during centrifugation. Both stages, membrane contact and electrical breakdown of cell membranes, were controlled. The degree of cell-to-cell compression and corresponding intermembrane contact area were estimated by measuring the low-voltage resistance R of the cell pellet which grows sharply with the increase of centripetal acceleration G. The extent of electrical membrane poration and critical pulse parameters were detected by recording the breakdown current. Supercritical pulse delivery to a cell pellet compressed by intensive centrifugation (400–600 g) leads to polycaryon mass formation. The pulse amplitude required for efficient fusion (2–3 kV/cm, 20–50 μs: fusion index F ∼ 25–35%) was found to be several times higher than the amplitude sufficient to induce noticeable breakdown (300 V/cm). The shapes of the F(G) and R(G) dependences were similar, which revealed a correlation between the area of intermembrane contact and fusion probability. Fusion was negligible if the moment of pulsation and the period of intensive centrifugation were separated in time. The data obtained allow us to conclude that in the case of fusion of L-cells the action of the electric field is not mediated by any long-lived fusogenic state. The process of the common membrane surface formation driven directly by the electric field is discussed.     

Effects of electric field on confined electrolyte in a hexagonal mesoporous silica

In an electrowetting experiment on a surface treated hexagonal mesoporous silica, it is noticed that the effective solid-liquid interfacial tension is quite insensitive to the applied voltage, while the accessible nanopore volume decreases significantly as the voltage is increased. When the voltage is higher than 900 V, the liquid infiltration cannot be detected. The liquid defiltration is quite insensitive to the electric field. These unique phenomena may be attributed to the field responsive ion behaviors in the confining nanoenvironment.     

I/V characteristics of a molecular switch

We present a study of the conduction properties of a class of aromatic compounds, whose conformation can be modulated with a transverse electric field, with strong effects on the molecular transport properties. The theoretical method includes the molecule–electrode interaction in a simple, although effective way: the coupling matrix elements are considered independent from the energy of the continuum spectrum of the lead. This results in a simple expression for the molecular Green’s function with a significant simplification in the expression of the transmission function. The effects of the voltage bias on the electronic molecular density is included through a uniform effective electric field. A simplified but accurate method for the evaluation of the molecular response to the field, which spares lengthy computations for each value of the voltage, is presented. The proposed method is calibrated on the widely studied benzene-1,4-dithiol molecule. The calculations on the selected molecular wire (a tetracyano derivative of 4,4′-di(mercaptoethynyl)tolan) show that conductivity is low for perpendicular rings, whereas conduction is allowed for the planar conformation, which corresponds to the equilibrium geometry in the absence of the transverse electric field.     

A theoretical study of atmospheric propagation of laser and return light for stand-off laser induced breakdown spectroscopy purposes

A theoretical study of atmospheric extinction mechanisms of optical radiation (molecular/aerosol scattering and absorption) has been carried out in order to assess their influences on stand-off laser-induced breakdown spectroscopy (LIBS) measurements. The atmospheric extinction of laser radiation at wavelengths commonly used in laser-induced breakdown spectroscopy (1064 nm and 532 nm) and of the laser-induced breakdown spectroscopy plasma emission beyond 250 nm is small compared to the attenuation with range due to the inverse square law. The fundamental problem with light propagation through the atmosphere is that the atmospheric transmittance does not remain constant within the whole spectral interval, and that this variation results in a change in the spectral distribution of the light received by the detector. Knowledge of atmospheric transmittance would allow for compensation of this effect.     

Direct observation by laser scanning confocal microscopy of microstructure and phase migration of PVC gels in an applied electric field

The fluorescent probe lucigenin was incorporated in poly(vinyl chloride) (PVC) gels, and laser scanning confocal microscopy (LSCM) was used to clarify the internal structures of the gels. From the two-dimensional and three-dimensional information by LSCM, we first observed the internal structure of the PVC gel at a wet status, where the PVC gels comprised a polymer-rich phase and a polymer-poor phase uniformly with a three-dimensional network structure. After an electric field was applied, an effect of the electric field resulted in the change of internal structure in the gels. The polymer-poor phase moved from the cathode to the anode and the polymer-rich phase formed linelike arrangement between electrodes due to the attraction force. On the other hand, the freeze-dried PVC gels with/without in-situ dc voltage casting were particularly fabricated to confirm above results by the field emission scanning electron microscopy (FE-SEM). It was found that many craters remained on the surface of the gel near the anode due to sublimation in freeze-drying. This phenomenon did not appear on the surface near the cathode. The results of in-situ dc voltage casting also suggested that a substantial amount of polymer-poor phase was moved and fixed at the anode. Thus, results of both LSCM and in-situ dc voltage casting corresponded to the effect of electric field on PVC gels and provided a convincing evidence for the interpretation of the deformation mechanism of PVC gel actuators by an applied electric field.     

Prediction of Dielectric Properties of Air Plasma for Circuit Breaker Application Based on a Chemically Non-equilibrium Model

Dielectric properties of air plasma in a model circuit break were investigated. A chemically non-equilibrium (non-CE) model was used to simulate the arc dynamic behavior inside the nozzle during current zero period. Distribution of the critical breakdown electric field E_cr of hot air was derived from the electron energy distribution function by solving the Boltzmann transport equation, using calculated temperature, pressure and species composition. Then, the electric field at applied recovery voltage (E_a) was calculated. The probability of dielectric breakdown inside the nozzle can be predicted by comparing E_a and E_cr. The results show that neglect of departure from chemical equilibrium may lead to the overestimation of the dielectric recovery strength of circuit breaker arc during the first several hundred microseconds after current zero.     

Saturation Magnetization and Law of Approach to Saturation for Self-formed Ionic Ferrofluids Based on MnFe2O2 Nanoparticles

The magnetization curves of MnFe₂O₂ nanoparticles and self-formed ferrofluids based on these particles have been measured at room temperature. The median size of the particlesis 13.67 nm. The specific saturation magnetization is less than the theoretical value for theferrofluids. In the high field range from 5 kOe to 10 kOe, the higher the particle volume fraction is, the steeper the slope of the magnetization curves is when it approaches saturation.The behavior of the saturation magnetization and the law of approach to saturation are due to the presence of self-assembled aggregates of ring-like micelle structures which form in the absence of the magnetic field and field-induced aggregates, respectively. The field-induced aggregates have a dissipative structure, so that at high field, the law of approach to saturation magnetization is different from the one described using Langevin paramagnetism theory. The large particles in the ferrofluids result in apparent hysteresis.     

Stark beats of Lyman-α emission of foil-excited hydrogen atom

The Stark beats of Lyman-α emission due ton=1 ? 2 transition of hydrogen atom have been studied by the beam-foil method. After passage through a thin carbon foil, the static electric field of 500 V/cm was applied to the beam in the direction either parallel to or anti-parallel to the the beam velocity. The linearly polarized emission was measured by using a toroidal mirror at a Brewster's angle reflection. When the direction of the applied electric field is reversed, an appreciable phase shift was observed. The analysis of the data leads to the complete determination of the density matrix of the H(n=2) atoms at the time of their production.     

Convective flow in the liquid crystal heat switch

The 'heat switch' is based on the fact that in some liquid crystal (LC) materials heat transfer depends on the voltage applied between two parallel electrodes containing the sample. The rate of heat transfer depends on the voltage rather than the electric field intensity, but is not understood. Since the heat switch can involve electric field intensities up to at least the breakdown field of air, it is important to understand the mechanism responsible for heat transfer. Results are presented indicating that a mechanism described earlier is involved. A proposal for a refrigerator using LC heat switches is also made.     

Electric birefringence of solutions of aromatic poly(amide hydrazide) in dimethyl sulphoxide

Birefringence in a pulsed electric field has been investigated for solutions of para-aromatic polyamid hydrazide (PAH) in dimethyl sulphoxide. The values of the specific Kerr constant K extrapolated to zero concentration have been determined. The experimental data are adequately described by the theoretical dependence of K on the contour length of the PAH molecules for kinetically rigid wormlike chains. The angle formed by the dipole moment of the monomer unit and the direction of the PAH chain was found to be 61.5 ± 1.5°. Comparison between relaxation times obtained from the curves of the decay of birefringence after the end of the electric pulse and the intrinsic viscosities of some PAH samples confirm the conclusion about high kinetic rigidity of PAH macromolecules.