Pulsed Direct Current Electric Fields Research Articles

Electrokinetically-delivered persulfate and pulsed direct current electric field induced transport, mixing and thermally activated in situ for remediation of PAHs contaminated soil.

Herein, we proposed and proved a novel strategy that enhanced the delivery of persulfate (PS) to soil by electrokinetics (EK), and then applying a pulsed direct current (DC) electric field thermally activated the PS in situ, and synchronously promoted PS plume mixing, contaminants-free radicals reaction and continued to replenish PS to the soil, to achieve efficient degradation of contaminants in low permeability zones. Results showed that transport rate of PS in tested soil by EK was approximately 12.3 times than diffusion. Applying an irregular pulsed DC field maintained the targeted temperature (30-50℃) during activation phase, and generated two oxidative radicals (SO4∙-/∙OH). Concurrently, in the case, electromigration and electroosmosis have promoted the PS transport and the reactive mixing of PS/free radicals with polycyclic aromatic hydrocarbons (PAHs) contaminated soil and enhance the PAHs degradation. PS concentrations in pore fluid was characterized by an increase accompanied by continuous fluctuations. Eventually, in case of the long-term low-temperature activation (i.e., 30-40 ℃), a significant decreases (nearly 60%) in average concentration of PAHs in the whole soil cell was observed over 10 days. These results demonstrates that the novel strategy has great potentiality in the remediation of low permeability contaminated soil.

On the investigation of electroanaesthesia in Labeo rohita under DC and PDC electric field

This study investigates electroanaesthesia under Direct Current (DC) and three low frequency Pulsed Direct current (PDC) of 1 Hz, 3 Hz and 6 Hz in Labeo rohita. All the current types in this study were effective in anaesthetizing L. rohita with fast induction and rapid recovery period in all fishes. The threshold value of voltage gradient (V cm–1) for inducing anaesthesia was higher in DC than PDCs. Opercular movements were significantly lower during anaesthesia, significantly higher one minute after recovery in all current types and reduced significantly in DC, PDC 1 Hz and PDC 3 Hz after 10 min of recovery from anaesthesia. Blood glucose level returned to the near control values after 8 hours of exposure in all current types in this study. DC sharp rise and PDC 3Hz may be preferred for inducing anaesthesia considering the recommended criteria of anaesthetic induction and recovery time. Result of this study indicates that electroanaesthesia technique with fast induction and rapid recovery may proffer a cost effective, safe and ecofriendly alternative for aquaculture activities in L. rohita.

Electrocoalescence of two charged nanodroplets under different types of external electric fields

Droplet coalescence induced by an external electric field has been extensively applied in industries. However, the coalescence dynamics of droplets under three common types of electric fields, direct current (DC), alternative current (AC), and pulsed DC electric fields, and the corresponding coalescence mechanisms are unsatisfactorily explored. This study applied molecular dynamic simulations to investigate the coalescence dynamics of two charged droplets under these three types of electric fields. At the same field strengths, the contact time by applying the DC electric field is noted as the shortest among the three studied electric fields, and this is followed by the AC and the pulsed DC electric field. The DC and AC electric fields always possess the same critical field strengths, which are much lower than that of the pulsed DC electric field. The critical field strength is noted to be independent of the period under the AC electric field, whereas would decrease with increasing the period under the pulsed DC electric field. Despite the different dependence of critical field strength on pulse period, interestingly, the critical field strength, Ec, under the pulsed DC electric field is approximately equal to that under the AC electric field at a long period limit; conversely, the critical root-mean-square (RMS) field strength, ERMS,c, under the pulsed DC electric field is close to that under the AC electric fields at a short period limit.

Convergence effect of droplet coalescence under AC and pulsed DC electric fields

The coalescence behaviors of two neutral droplets suspended in silicone oil under the alternating current (AC) and pulsed direct current (DC) electric fields are investigated by experiments and numerical simulations. The distribution evolutions of electric force and velocity field during the droplet coalescence under the AC and pulsed DC electric fields are analyzed. The relationship between electric field excitation and droplet interface response is illustrated. The equivalent response mechanism of droplets under the high-frequency AC and pulsed DC electric fields and under the DC electric fields is revealed. The relationship of droplet dynamic behaviors under the DC electric field and under the AC and pulsed DC electric fields are established. The critical electric field frequencies above which the shortest distance curves no longer change under the AC and pulsed DC electric fields are obtained. These new findings are significant for the optimization of electrostatic coalescence.

Charge-Transfer-Induced Noncoalescence and Chain Formation of Free Droplets under a Pulsed DC Electric Field.

Electrocoalescence technology is an important method for the demulsification of crude oil emulsion, but its development is restricted by the short circuit caused by droplet chain formation. To reveal the formation mechanism of droplet chains, the electrocoalescence behaviors of two droplets and droplet clusters under pulsed direct current (DC) electric fields are experimentally studied. The two droplets usually successively undergo complete coalescence, partial coalescence, and noncoalescence as the electric field strength increases. The critical electric field strengths for complete coalescence under pulsed DC electric fields with different frequencies are obtained. The effects of the electric field waveform and frequency on the noncoalescence characteristics of two droplets and the stability of droplet chains are explored. The droplet chains under a high-frequency electric field are more stable and longer than those under a low-frequency electric field due to the reduction of the movement distance and the generation of daughter droplets from tip streaming. The reversal of the composition of electric forces due to charge transfer is the fundamental mechanism of noncoalescence of two droplets and chain formation in the emulsion under a pulsed DC electric field.

Electro-coalescence of two charged droplets under pulsed direct current electric fields with various waveforms: A molecular dynamics study

Electrocoalescence has been extensively used to remove water droplets in water-in-oil emulsions. Pulsed direct current (DC) electric fields were found to be more effective than DC electric fields. However, as an essential process in electro-dehydration, coalescence dynamics of two charged droplets and corresponding coalescence mechanisms under pulsed DC electric fields have remained poorly understood. In this work, such coalescence dynamics behaviors are investigated via molecular dynamics simulations. The contact time of droplets, deformation ratio of coalescing droplets, and critical field strength are compared among square, sinusoidal, and triangular waves. The results show that, with the same pulse amplitude, the contact time is the shortest for the square wave, the following are sinusoidal and triangular waves. Sinusoidal and triangular waves have similar waveforms and they significantly differ from the square wave. However, it is astonishing that the contact times are very close for the square and sinusoidal waves, which are far less than that for the triangular wave. This seemingly abnormal result is reasonably explained by the equivalent field strength or RMS (root mean square) field strength. The square and sinusoidal waves have the same RMS field strength, whereas the triangular wave has a smaller RMS field strength. After two droplets coalesce into a large droplet, the coalescing droplet undergoes periodic deformation. The deformation ratio significantly depends on waveforms. As compared with sinusoidal and triangular waves, the deformation is much drastic for the square wave. The critical field strengths are also evaluated for the three waveforms. The result shows that the square and sinusoidal waves have almost the same critical field strength, whereas the triangular wave has a much higher critical field strength. Further analysis demonstrates that the RMS critical electric fields are actually the same for the three waveforms.

Droplet dynamic response in low‐viscosity fluid subjected to a pulsed electric field and an alternating electric field

AbstractDroplet dynamic response in low‐viscosity fluid under a pulsed direct‐current (DC) electric field and a sinusoidal electric field is investigated by experiments and numerical simulations. The coupled level set and volume of fluid method is employed to capture moving interface and the numerical method is validated by experimental results. This article focuses on the effects of waveform, frequency and initial phase on the dynamic response. The deformation period is identical with the electric period for the pulsed DC electric field but the deformation period is half of the electric period for the sinusoidal electric field. As the frequency increases, the maximum deformation degree Dmax first climbs steadily to a peak value, then decreases steeply and finally approaches an equilibrium value. The maximum Dmax appears at f = 50 Hz for the pulsed DC electric field and appears at f = 100 Hz for the sinusoidal electric field according to numerical results. These results are helpful for the optimization of electro‐coalescence.

Keratinocyte electrotaxis induced by physiological pulsed direct current electric fields

Endogenous electric fields (EFs) direct the migration (electrotaxis) of keratinocytes in skin wounds, and the exogenous application of EFs may therefore improve wound healing, but the potential benefits are limited by the side effects of constant direct current (DC) passing through tissues. In contrast, with pulsed DC (characterized by intermittent output), parameters can be adjusted to minimize the adverse effects of electric currents. However, it remains unknown whether pulsed DC can reliably induce keratinocyte electrotaxis. In this study, using primary keratinocytes in an electrotaxis chamber, we found that a pulsed DCEF at physiological strength (EF = 150 mV/mm, duty cycle = 60%, frequency = 0.1 Hz) could induce robust electrotaxis. This effect was dependent on both voltage and duty cycle, but not on frequency. As predicted, fewer electrochemical reactions and cytotoxic reactions were detected with pulsed DCEF than with constant DCEF. In summary, we here demonstrate for the first time, that pulsed DCEF can trigger keratinocyte electrotaxis comparable to that induced by constant DCEF, while minimizing the electrochemical side effects. These findings support the future development of a pulsed DCEF device to improve wound healing in human patients.

Electric Pulses Can Influence Galvanotaxis of Dictyostelium discoideum.

Galvanotaxis, or electrotaxis, plays an essential role in wound healing, embryogenesis, and nerve regeneration. Up until now great efforts have been made to identify the underlying mechanism related to galvanotaxis in various cells under direct current electric field (DCEF) in laboratory studies. However, abundant clinical research shows that non-DCEFs including monopolar or bipolar electric field may also contribute to wound healing and regeneration, although the mechanism remains elusive. Here, we designed a novel electric stimulator and applied DCEF, pulsed DCEF (pDCEF), and bipolar pulse electric field (bpEF) to the cells of Dictyostelium discoideum. The cells had better directional performance under asymmetric 90% duty cycle pDCEF and 80% duty cycle bpEF compared to DCEF, with 10 Hz frequency electric fields eliciting a better cell response than 5 Hz. Interestingly, electrically neutral 50% duty cycle bpEF triggered the highest migration speed, albeit in random directions. The results suggest that electric pulses are vital to galvanotaxis and non-DCEF is promising in both basic and clinical researches.

Enhanced DC-Operated Electroluminescence of Forwardly Aligned p/MQW/n InGaN Nanorod LEDs via DC Offset-AC Dielectrophoresis.

We introduce an orientation-controlled alignment process of p-GaN/InGaN multiquantum-well/n-GaN (p/MQW/n InGaN) nanorod light-emitting diodes (LEDs) by applying the direct current (DC) offset-alternating current (AC) or pulsed DC electric fields across interdigitated metal electrodes. The as-forwardly aligned p/MQW/n InGaN nanorod LEDs by a pulsed DC dielectrophoresis (DEP) assembly process improve the electroluminescence (EL) intensities by 1.8 times compared to the conventional AC DEP assembly process under DC electric field operation and exhibit an enhanced applied current and EL brightness in the current-voltage and EL intensity-voltage curves, which can be directly used as the fundamental data to construct DC-operated nanorod LED devices, such as LED areal surface lightings, scalable lightings (micrometers to inches) and formable surface lightings. The enhancement in the applied current, the improved EL intensity, and the increased number of forwardly aligned p/MQW/n InGaN nanorods in panchromatic cathodoluminescence images confirm the considerable enhancement of forwardly aligned one-dimensional nanorod LEDs between two opposite electrodes using DC offset-AC or a pulsed DC electric field DEP assembly process. These DC offset-AC or pulsed DC electric field DEP assembly processes suggest that designing for these types of interactions could yield new ways to control the orientation of asymmetric p/MQW/n InGaN diode-type LED nanorods with a relatively low aspect ratio.

Understanding the response of pulsed electric field on osteoblast functions in three-dimensional mesh structures

The endogenous electric field plays a determining role in impacting biological functions including communication with the physiological system, brain, and bone regeneration by influencing cellular functions. From this perspective, the objective of the study described here is to elucidate the effect of external electric field under dynamic conditions, in providing a guiding cue to osteoblasts in terms of cell-cell interactions and synthesis of prominent adhesion and cytoskeleton proteins. This was accomplished using pulsed direct current electric field of strength 0.1-1 V/cm. The electric field provided guided cue to the cells to migrate toward cathode. Membrane blebbing or necrosis was nearly absent in the vicinity of cathode at 0.1 and 0.5 V/cm electric field strength. Moreover, a higher cell proliferation as well as higher expression of vinculin and densely packed actin stress fibers was observed. At anode, the cells though healthy but expression of actin and vinculin was less. We underscore for the first time that the biological functionality can be favorably modulated on 3D printed scaffolds in the presence of electric field and under dynamic conditions with consequent positive effect on cell proliferation, growth, and expression level of prominent proteins.

Pulsed DC Electric Field-Induced Differentiation of Cortical Neural Precursor Cells.

We report the differentiation of neural stem and progenitor cells solely induced by direct current (DC) pulses stimulation. Neural stem and progenitor cells in the adult mammalian brain are promising candidates for the development of therapeutic neuroregeneration strategies. The differentiation of neural stem and progenitor cells depends on various in vivo environmental factors, such as nerve growth factor and endogenous EF. In this study, we demonstrated that the morphologic and phenotypic changes of mouse neural stem and progenitor cells (mNPCs) could be induced solely by exposure to square-wave DC pulses (magnitude 300 mV/mm at frequency of 100-Hz). The DC pulse stimulation was conducted for 48 h, and the morphologic changes of mNPCs were monitored continuously. The length of primary processes and the amount of branching significantly increased after stimulation by DC pulses for 48 h. After DC pulse treatment, the mNPCs differentiated into neurons, astrocytes, and oligodendrocytes simultaneously in stem cell maintenance medium. Our results suggest that simple DC pulse treatment could control the fate of NPCs. With further studies, DC pulses may be applied to manipulate NPC differentiation and may be used for the development of therapeutic strategies that employ NPCs to treat nervous system disorders.

Electro-coalescence of two charged droplets under constant and pulsed DC electric fields

In the presence of electric field induced by either constant or pulsed direct current (DC), a critical electric strength (Ec) exists for the transition from full coalescence to partial coalescence of adjacent charged droplets. In this study, the electro-coalescence behaviors of two charged droplets under constant and pulsed DC electric fields are studied via molecular dynamics simulations. The results show that the two droplets experience an attractive force when the constant DC electric field is applied, which causes an accelerated approach from one another before contact. However, under the pulsed DC electric field, the approach velocities of the two droplets accelerate within the pulse duration, while remain approximately constant during the pulse interval. Thus, the value of Ec for full coalescence and partial coalescence of the two droplets under the pulsed DC electric field becomes larger as compared with the constant DC electric field, which significantly reduces the time required for bringing the two droplets into contact. Hence, higher electro-coalescence efficiency is achieved. Furthermore, for a given pulse period, Ec is inversely proportional to the pulse duration; for a given duty ratio, Ec reduces with the increase in the pulse period.

Pulsed Direct Current Electric Fields Enhance Osteogenesis in Adipose-Derived Stromal Cells

Adipose-derived stromal cells (ASCs) constitute a promising source of cells for regenerative medicine applications. Previous studies of osteogenic potential in ASCs have focused on chemicals, growth factors, and mechanical stimuli. Citing the demonstrated role electric fields play in enhancing healing in bone fractures and defects, we investigated the ability of pulsed direct current electric fields to drive osteogenic differentiation in mouse ASCs. Employing 50 Hz direct current electric fields in concert with and without osteogenic factors, we demonstrated increased early osteoblast-specific markers. We were also able to establish that commonly reported artifacts of electric field stimulation are not the primary mediators of the observed effects. The electric fields caused marked changes in the cytoskeleton. We used atomic force microscopy-based force spectroscopy to record an increase in the cytoskeletal tension after treatment with electric fields. We abolished the increased cytoskeletal stresses with the rho-associated protein kinase inhibitor, Y27632, and did not see any decrease in osteogenic gene expression, suggesting that the pro-osteogenic effects of the electric fields are not transduced via cytoskeletal tension. Electric fields may show promise as candidate enhancers of osteogenesis of ASCs and may be incorporated into cell-based strategies for skeletal regeneration.

The Effect of Pulsed Direct Current Field on the Membrane Flux of a New Style of Membrane Bioreactor

AbstractThe effect of a pulsed direct current electric field on the membrane flux of an antifouling Membrane Bioreactor (MBR) designed and built in the laboratory was studied. The results showed that a pulsed direct current electric field had a significant effect on the membrane flux. The average membrane flux when using a pulse direct current electric field was between that of a steady electric field and that of no electric current under a trans‐membrane pressure drop of ΔP = 0.1 MPa and a pulsed direct current electric field strength of 20 V/cm. There was an optimum value of pulse intensity and pulse duration for the membrane flux. The shorter the pulse interval time was, the higher the frequency of power‐on, and the higher the average stable membrane flux of the MBR. This may have resulted from the fact that charged coarse particles and colloids account for 80 % of CODcr and BOD5 in urban domestic sewage. These particles and colloids moved away from the membrane surface at a certain electrical field strength, gradually thinning the particle sedimentary layer, reducing the membrane filtration resistance, and increasing the membrane flux significantly. However, the formation of a sedimentary layer on the membrane surface needed a significant amount of time and an appropriate pulse frequency while the MBR is powered on. This could save energy while keeping the membrane clean.

Electro-hydrodynamic separation of aqueous drops from flowing viscous oil

In a number of industrial processes, gravitation usually plays a significant role in the separation of dispersed particles or drops from another immiscible liquid. This separation, taking place in large tanks, provides low operating cost when the residence time of the liquid–liquid system is long and the density difference between the two phases is large. However, the situation becomes complicated for small liquid drops dispersed in another liquid when the density difference is very small and the carrier liquid is at high velocity. In this paper, using a novel compact electrocoalescer-separator that has been developed recently, an externally applied electric field has been shown to significantly enhance the separation of aqueous drops in a flowing viscous oil, with low concentrations of the dispersed phase. The separation efficiency increases with the electric field strength until a limit, above which, drop deformation and break-up occur. Using pulsed direct current electric fields, an optimum electric field and frequency exist for the enhancement of drop–drop and drop–interface coalescence, thus producing an optimum separation efficiency for the system. The separation efficiency increases with drop size up to a certain diameter, as larger drops have been observed to deform and short-circuit the system. Short-circuiting can be avoided by optimising the electric field. From a force balance on a single sphere, a parameter IP is defined which describes the acceleration of the sphere under an electric field. The parameter IP can predict the behaviour of the system qualitatively up to the limit where drop break-up and electrical short-circuiting occur.

Electrostatic and hydrodynamic separation of aqueous drops in a flowing viscous oil

In various industrial processes, sedimentation often plays a significant role in the separation of dispersed particles or drops from another immiscible liquid. This separation, taking place in large tanks, provides low operating cost when the residence time of the liquid–liquid system is long and the density difference between the two phases is large. However, the situation becomes complicated for small liquid drops dispersed in another liquid when the density difference is very small and the carrier liquid is at high velocity. In this paper, using a novel compact electrocoalescer-separator that has been developed recently, an externally applied electric field has been shown to significantly enhance the separation of aqueous drops in a flowing viscous oil, with very low concentrations of the dispersed phase. The separation efficiency increases with the electric field strength until a limit, above which, drop deformation and break-up occur. Using pulsed direct current electric fields, an optimum electric field and frequency exist for the enhancement of drop–drop and drop–interface coalescence, thus producing an optimum separation efficiency for the system. The separation efficiency increases with drop size up to a certain diameter, as larger drops have been observed to deform and short-circuit the system. Short-circuiting can be avoided by optimising the electric field. From a force balance on a single sphere, a parameter I P is defined which describes the acceleration of the sphere under an electric field. The parameter I P can predict the behaviour of the system qualitatively up to the limit where drop break-up and electrical short-circuiting occur.

Electrostatic enhancement of coalescence of water droplets in oil: a review of the technology

The technology for electrostatic enhancement of coalescence of water droplets in oil emulsions is critically reviewed. Historically, the electrostatic coalescer was invented for the petroleum-related industries in California [US Patent 987 115 (1911)]. Nowadays, this technology is generally considered for the separation of an aqueous phase dispersed in a dielectric oil phase with a significantly lower dielectric constant than that of the dispersed phase. Various designs have been introduced, with most using alternating current (AC) electric fields with mains frequency (50 or 60 Hz). The direct current (DC) electric field has been less common in the past as compared to the AC. In 1981, the concept of pulsed DC electric fields was introduced, together with insulated electrodes [Trans. IChemE 59 (1981) 229–237; UK Patent 217 1031A (1986)]. Since then, this has become more common in the electrocoalescence technology. Pulsed DC and AC fields are especially useful, when the aqueous phase content of the emulsion is high, to prevent short-circuiting between the pair of electrodes. Processing of oil from old wells is a good example, where the volumetric water content could vary significantly. Reported work by some workers indicates the existence of an optimum frequency, which depends on the electrode coating material, its thickness and the liquid emulsion composition. This is however, a contentious issue which has not been completely resolved. The characteristics and geometry of the electrode system (generally cylindrical or plate) influence the performance of the electrostatic coalescer, and are closely related to the type of the applied electric field and the emulsion used. There are basically two types of electrode: uninsulated electrode and insulated electrode. Combination of electrocoalescence and mechanical separation (e.g., centrifugal force) has also been introduced. Heating and the addition of chemicals have been shown to further enhance the electrocoalescence of water droplets. Other methods that can be combined with the electrical treatment are filtration, methods employing high pressure and temperature, and mixing. This review paper also looks at some of the current specific industrial applications using the electrocoalescence technology. Besides the oil and petroleum industries, this technology has potential applications in the edible oil industries such as palm oil, sunflower oil and vegetable oil processing. Most of the currently available equipment is very big and bulky, having a large inventory of emulsion. Therefore, we see the future trend for new developments to be in the direction of inventing small portable devices, incorporating features such as optimum electric fields and combined electrical and centrifugal forces to further enhance the separation of water-in-oil emulsions. Furthermore, a better understanding of the fundamentals of electrocoalescence will enable a better design of the geometry of the electrodes, of the flow field with respect to the electric fields, the type of dispersion used and the type of the applied electric field.

The physical properties of polyisocyanates in solution

Electric birefringence measurements have been made on four samples of poly-n-butyl isocyanate in three solvents. The value of M W/ M N for three of the samples was 1·2. A description of the apparatus and of its use with both alternating and pulsed direct current electric fields is given. The method has been used to obtain molecular relaxation times and dipole moments. These data have been analysed, together with the results of dielectric experiments reported in the literature, in terms of both rigid helices and weakly bending helices. The results indicate that flexibility is encountered for molecular weights in excess of 5 × 10 4. This is somewhat lower than had previously been reported from other relaxation experiments. Below this molecular weight, the observed molecular relaxation times, which were associated with an end-over-end rotation due to the helices having a permanent dipole moment along their helical axis, were related to a number average molecular weight. Data were consistent with a helix monomer projection length of 1·3 Å and a diameter of 11 Å. In the range 5 × 10 4 < M N < 10 5 , the data have been interpreted in terms of Hearst's recent theory for weakly bending rods. These results were consistent with the worm-like chain model, used to interpret the data for molecular weights in excess of 100,000. It was shown that the assignment of a specific persistence length was unreliable even for molecular weights as high as 5 × 10 5. The study demonstrates the merits and sensitivity of the electric birefringence method. It is the first time that the “double frequency” component of the birefringence, which is generated when alternating fields are applied to the solutions, has been detected and used to determine molecular parameters for a synthetic polymer.