Influence Of Electrode Polarization Research Articles

Printed Dielectrophoretic Electrode‐Based Continuous Flow Microfluidic Systems for Particles 3D‐Trapping

AbstractInkjet‐printing is used to fabricate dielectrophoretic electrodes able to trap polystyrene (PS) microparticles as well as model planktonic cells. The possibility of rapid prototyping offered by inkjet‐printing allows the rational design of microchannels with tailored electric field distributions experienced by the suspended particles, which in turn provides a handle to drive them towards target regions. Specifically, this goal is achieved using two facing substrates constituting the bottom and the top walls of the channel, with a pair of interdigitated electrodes previously patterned by inkjet‐printing on each side. Influence of electrode polarization (magnitude and frequency of the input signal) is investigated both theoretically, by modeling the electric field distribution inside the channel, and experimentally using confocal fluorescence microscopy. The printed device is able to sort circulating PS particles as a function of their size, with diameters ranging from 0.5 to 5 µm, as well as to separate planktonic species according to their composition (Alexandrium minutum versus Prorocentrum micans). This work paves the way for the development of large‐area, microstructured dielectrophoretic electrodes able to separate the constituents of samples at flow rates up to 150 µL mn−1.

Electrode polarity effects in electrospinning organic/inorganic hybrid nanofibers

In this study, organic/alumina hybrid nanofibers were successfully prepared using polyvinylpyrrolidone (PVP) and polyvinyl butyral (PVB) polymers. The influence of electrode polarity on fiber morphology was discussed for the preparation of high-performance nanofibers. The morphology of PVB/alumina fibers varied greatly with the change of voltage especially in the case of the negative pole. However, the diameters of PVP/alumina nanofibers remained largely unchanged, and the negatively charged fibers were more uniform. TEM and FT-IR results proved that polymers, crosslinked with inorganic particles, can effectively improve the stability and uniformity of the morphology and microstructure of organic/inorganic hybrid fibers.

Influence of electrode polarization on the potential of DC electrical exploration

The accuracy of data obtained with the Direct Current (DC) electrical method is reduced by the electrode polarization effect, which is caused by current stimulation when the electrodes of the multi-electrode acquisition system are alternately used as the current and the potential electrodes. With the purpose of studying the characteristics of electrode polarization, the continuous potential responses of the electrodes in a conventional multi-electrode acquisition system (single-mode multi-electrode acquisition system) and the proposed double-mode multi-electrode acquisition system were adopted before and after current stimulation, by varying the electrode material, voltage amplitude and current duration. The results showed that for the single-mode acquisition system the electrode polarization was stronger and the electrodes possessed a stronger chemical activity, a longer current duration and a higher voltage amplitude that increased rapidly and then decayed after current stimulation. The average time for the potential to be restored to the background level was greater than 1.5h, and the electrode polarization of a stainless steel electrode was found to be stronger than a copper one. Thus, along with the action of current stimulation, the potential data was significantly influenced by the electrode polarization when adopting a conventional multi-electrode acquisition system. The results also demonstrated that the electrode polarization had a relatively weak influence on the resistivity data due to the data reprocessing.

Reliability of Constant Charge Method for Molecular Dynamics Simulations on EDLCs in Nanometer and Sub‐Nanometer Spaces

AbstractThe constant charge method (CCM) and constant potential method (CPM) are two major techniques to apply electric charges on electrodes for molecular dynamics (MD) simulations on electric double‐layer capacitors (EDLCs). Compared with CCM, CPM is more realistic since the influence of electrode polarization is taken into account, although computationally more expensive. In this work, the reliability of CCM for MD simulations on EDLCs in nanometer and sub‐nanometer spaces is investigated. Particular attention is paid to the comparison of CCM and CPM for modeling EDLCs in terms of ion concentration and EDL structures in such nano/sub‐nano confined spaces, which are widely found in graphene‐based materials. The deviation for ion concentration calculated from CCM and CPM was found to be significant in both neutral and charged confined spaces (e. g., deviation ratio of 40.27 % and 11.18 % for Cl− ions in neutral and charged 9 Å space, respectively), which is different from previous observations in bulk solutions. This result could be attributed to the strong electrode polarization in nano/sub‐nano confined spaces. Although CCM and CPM yielded essentially similar EDL structures, the time evolution of electrode charge with a potential difference could be conducted only with CPM. The findings of the current work could provide useful insights for choosing appropriate methods for MD simulation on EDLCs in nano/sub‐nano confined spaces.

Influence of methanol, ethanol and cypermethrin on the Glutathione S-tranferase catalyzed reaction of Glutathione with 1-chloro-2,4-dinitrobenzene: A method for detection and quantification of cypermethrin

This article describes application of normal mediatorless cyclic voltammetry and UV-visible spectroscopy to study the Glutathione S-tranferase (GST) catalyzed reaction of reduced glutathione(GSH) with 1-chloro-2,4-dinitrobenzene(CDNB) in two solvents methanol and ethanol, and influence of pyrethroid cypermethrin on it. The course of the reaction between CDNB and GSH in presence of GST differs in the two solvents, viz., methanol and ethanol. Unlike the case when ethanol was used as the solvent, in methanol GSH got transformed to an electro active state under the influence of electrode polarization. This electro active intermediate undergoes oxidation at 0.3V, sufficiently stable (more than two hours) and reacts with CDNB to form UV active but electro inactive final product. The same electro active intermediate is also formed by non-electrochemical process in presence of CDNB in methanol and the formation is catalyzed by GST. The said reaction is quantitatively affected by cypemethrin. A 25ppb cypermethrin solution can suppress completely the cyclic voltammetric peak as well as the UVpeak obtained from a 1:1 millimolar mixture of GSH and CDNB in presence of 20μL (0.02mg) of GST. Based on this, an electrochemical method for quantification of cypermethrin has been proposed that can detect cypermethrin down to 2ppb.The work has opened up new possibilities for electrochemical study of detoxification processes carried out by GSH.

The influence of electrode polarization on corrosion beneath paint

A Zn–Fe bi-electrode coated with different clear lacquers was exposed to NaCl solution, so that a well-defined galvanic cell was established with the current directly measured by a zero-resistance ammeter (ZRA). Electrochemical impedance spectroscopy (EIS) was periodically used to monitor the two coated electrodes individually or coupled together. Transient potentiostatic current measurements were also made after applying potential steps of different amplitudes to the individual metals, from which polarization curves were plotted. The ohmic potential drop in the paint was corrected using film resistance values determined by EIS. Evans diagrams were thus plotted from the iR-corrected polarization curves to make the first experimental determination of Evans diagrams as used by Mayne11J.E.O. Mayne, Chem. Ind. (London, UK), 293 (1951). to illustrate his resistance inhibition model.

Influence of electrode polarization on the capacitance of an electric double layer at and around zero surface charge

The influence of polarization of the electrode on the interfacial capacitance of a restricted primitive model planar double layer at and around zero surface charge is studied using a modified Poisson–Boltzmann theory for 1:1 electrolytes. The polarization, which occurs due to a dielectric discontinuity at the electrode–electrolyte interface, is treated by imagining fictitious image charges within the electrode, which mimic surface polarization charges. Specifically, the cases (i) when the electrode is a metallic conductor with infinite relative permittivity and (ii) when the electrode is a low relative permittivity insulator are investigated. The capacitance around zero surface charge is seen to undergo a gradual transition from having a camel-shaped form with a minimum at low electrolyte concentrations to having a maximum at higher concentrations consistent with the trends observed in earlier works in the absence of surface polarization. However, the transition envelope shifts to the lower concentration side relative to the no polarization situation for case (i), while it shifts to the higher concentration side for case (ii). The overall capacitance behaviour for both the situations indicates that the effect of the image interactions can be substantial, especially at low temperatures.

Dielectric properties of glucose in bulk aqueous solutions: Influence of electrode polarization and modeling

Impedance spectroscopy was applied to determine glucose concentration in the interstitial fluid for its potential use in diabetic monitoring. For this purpose, the changes in the measured dielectric properties due to the presence of glucose in water and saline solutions were examined between 40 Hz and 110 MHz. Electrode polarization (EP) was a dominant factor which shaped the spectrum at low frequencies. A theoretical model of EP using a constant phase-angle-element produced excellent matches to the measured data. By fitting the measured data to the model, the relative permittivity ( ɛ h ) and conductivity ( σ l ) were obtained. For deionized water, the relative permittivity dropped from 80.1 to 73.2 and conductivity ranged between 0.142 and 0.212 mS/m when the glucose concentration was increased from 0 to 32 g/dl. For the same variation of glucose level in 0.15 M NaCl, ɛ h was reduced from 79.8 to 71.5 and σ l decreased from 1.384 to 0.522 S/m. Glucose level produced a definite change in dielectric properties. However, the changes within the physiological range of glucose (less than a few hundred mg/dl) were small and appeared to be within the measurement error.

Fractal and Voltammetric Study of Linoleic Acid Adsorption at the Mercury/Electrolyte Solution Interface

A new method, size scaling of the hanging mercury drop electrode, is introduced and used to determine the fractal properties of the adsorbed layer and its dependence on fractional electrode coverage. Simultaneously, the adsorption process of linoleic acid at a mercury electrode surface has been studied by means of phase-sensitive ac voltammetry in 0.5 M NaCl electrolyte solution, pH 8.3, simulating seawater conditions. Three concentration domains that exhibit different fractal behavior characterize the adsorption process. In the first domain, corresponding to the fractional electrode coverage theta < 0.5, the fractal dimension of the adsorbed layer D 2. Further increase in surface concentration (electrode coverage) is followed by a swift change in fractal dimension, reaching the peak value D approximate to 2.4. This indicates that, at fractional electrode coverage of 0.7-0.8, depending on adsorption conditions, a second-order phase change in the adsorbed layer of linoleic acid takes place. In the third domain, the fractal dimension rapidly decreases to D approximate to 2.0 and remains stable regardless of bulk concentration increase, reflecting formation of a rather uniform and homogeneous layer of perpendicularly oriented molecules of linoleic acid. The observed changes of fractal dimension are a result of restructuring of the adsorbed layer and a change in the orientation of adsorbed molecules due to molecular interactions. The influence of electrode polarity on the adsorption process of linoleic acid and fractal properties of the adsorbed layer is discussed. Comparison with the apparent isotherm, obtained in a classical voltammetric way, shows that the analysis of fractal properties of the adsorbed layer provides a useful tool for studies of the adsorption process and a sensitive method for detection of phase changes.

Characteristics of the Amperometric Oxygen Sensor

Some important characteristics of the amperometric oxygen sensor are examined in detail with particular emphasis on the influence of electrode polarization on sensor behavior. First, we briefly discuss the theoretical framework describing the operation of the amperometric sensor and then describe operational characteristics and observations of anomalous behavior in light of that framework. For the experimental work, a double‐cell configuration with a drilled cover was used; the second cell served both as the diffusion barrier and as a potentiometric sensor for monitoring the oxygen partial pressure inside the cavity. It was found that the oxygen partial pressure varied significantly from the cavity entrance to the pumping cell cathode surface. Oxygen depletion inside the cavity strongly influenced the cathode polarization and sensor behavior. Upon application of increasing applied voltage, the maximum pumping capacity of the cathode decreased with oxygen depletion until it became equal to the diffusion‐limited current enforced by the diffusion barrier. Upon application of even higher voltages, oxygen could not be further depleted at the cathode surface; no further changes in the system occurred until the onset of electronic conduction in the cell electrolyte, where the current increased once again. Electronic conduction was shown to be the cause of anomalous behavior for the sensor where higher current was observed for lower oxygen concentration. A linear response for the amperometric sensor was realized only for oxygen concentrations in the range 0.1 to 25%.

Cell proliferation and intercellular communication in precision cut tissue slices

This article describes application of normal mediatorless cyclic voltammetry and UV-visible spectroscopy to study the Glutathione S-tranferase (GST) catalyzed reaction of reduced glutathione(GSH) with 1-chloro-2,4-dinitrobenzene(CDNB) in two solvents methanol and ethanol, and influence of pyrethroid cypermethrin on it. The course of the reaction between CDNB and GSH in presence of GST differs in the two solvents, viz., methanol and ethanol. Unlike the case when ethanol was used as the solvent, in methanol GSH got transformed to an electro active state under the influence of electrode polarization. This electro active intermediate undergoes oxidation at 0.3 V, sufficiently stable (more than two hours) and reacts with CDNB to form UV active but electro inactive final product. The same electro active intermediate is also formed by non-electrochemical process in presence of CDNB in methanol and the formation is catalyzed by GST. The said reaction is quantitatively affected by cypemethrin. A 25 ppb cypermethrin solution can suppress completely the cyclic voltammetric peak as well as the UVpeak obtained from a 1:1 millimolar mixture of GSH and CDNB in presence of 20 μL (0.02 mg) of GST. Based on this, an electrochemical method for quantification of cypermethrin has been proposed that can detect cypermethrin down to 2 ppb.The work has opened up new possibilities for electrochemical study of detoxification processes carried out by GSH.

The Influence of Electrode Polarity and Welding Current on Mechanical Properties of Submerged Arc Weld (SAW) in C-Mn Steels

An experimental study has been carried to study the effect of electrode polarity and welding current on mechanical properties of multipass SAW welds made by using C-Mn filler wire and basic flux. Weld deposits were characterised on the basis of tensile properties, hardness and charpy impact toughness Hardness survey of the weld revealed that higher hardness occured in the coarse microstructural region than the reheat refined region. For a given polarity there was an improvement in weld impact toughness as the current decreased from 700 A to 500 A. However the trend was reverse for tensile to be better for DCEP compared to DCEN.

The Influence of Electrode Polarity and Welding Current on Mechanical Properties of Submerged Arc Weld

The Influence of Electrode Polarity and Welding Current on Mechanical Properties of Submerged Arc Weld