Bubble Transfer by Electrostatic Force.

A new technology of the electric-field manipulation by dielectric particles in dielectric liquids and drops has been developed in the last decades. To simulate electromechanics of microparticles in a weaklyconducting dielectric drop the Taylor's leaky-dielectric model is extended. To achieve this electric-potential distribution inside and outside a weakly-conducting dielectric sphere embedded in a weakly-conducting dielectric in an electric field is determined taking into account the interfacial current. The conventional definition of the total, bulk plus surface, conductance of the sphere is detailed allowing for its dependence on the angular distribution of the external electric field. Technology of microparticles moving over the interface of the drop is based on the application of electrohydrodynamic (EHD) drag and dielectrophoretic (DEP) forces. The surface conductivities of the drop and individual microparticles can have a significant influence on the surface charge and thereby on the DEP and EHD drag forces. Thus, we show that recent explanation of manipulation by microparticles trapped at the interface of a silicone-oil drop immersed in castor oil is misleading. Taking into account the surface conductivity of the microparticles, we find that EHD drag and DEP forces are of the same direction but not opposite at zero or low frequencies as stated previously. Due to the reversal of the DEP force with the field frequency the motion of microparticles turns back. Surface conductivity of the drop can also explain experiments in which the prolate deformation persists after liquids of the drop and ambient medium are interchanged.

In previous our research, we introduced attachment or detachment of 25nm diameter quantum dots (QDs) manipulating method and 100nm diameter polystyrene (PS) nano-beads at nano sized metal structures by dielectrophoretic (DEP) force. The metal nano-structures were connected with micro electrode to apply the DEP force for trapping the nanoparticles. The DEP force is easily controllable by frequency and intensity of applied electric field. And the DEP force is very sufficient to manipulate the fluorescent nanoparticles at specific nanostructures, due to the large difference of electric fields inducement around nanostructures. The trapped fluorescent nanoparticles at nano metal structures which can be considered and called as a composited structure of photon emitting nanoparticles and nano structures could be utilized in study of coupling photons to plasmon waveguides as a real single photon generator. And the nanoparticle manipulating method could accomplish the additional composite structures without any chemical reactions as a lithographic method of fluorescent nanoparticles which can be used in QD display. The QDs are the most important and remarkable candidates nanoparticles to produce photon-emitting in quantum devices and display. However, the previous research had limitations such as limiting the variety of nanostructure, degree of freedom, and attaching sites due to the connected microelectrodes. And additional fabrication steps should be needed after the manipulation of nanoparticles to metal structures. In this paper, we introduced the manipulation of QD which is composed with cadmium selenide, the semiconducting materials at the nanostructures by DEP force for plasmonic applications and QD display. For the high degree of freedom, the nanostructures didn’t connect with microelectrodes. Various shapes of nano structures which is made of gold are accomplished between the micro electrodes. The microelectrodes were not connected with the nano-structures. Wire, Y-branch and vertex shape of nanostructure were fabricated with e-beam lithography and lift-off process. The distance between microelectrodes and nanostructures was also calculated to optimize the condition of QD trapping with multiphysics simulation. Possibility of selective manipulation of QDs was also performed through the theoretical approaches at various shape of nanostructures by using the DEP force. Each shape of structures was considered to manipulate the QDs at the nanostructures. The selective manipulation which is attaching-side, position, end-facet selective in nanostructures provide the three degrees of freedom in attachment in the same structure. Consequently, the semiconductor materials based fluorescent nanoparticles, QDs, are successfully manipulated at nano-structures without any connecting with microelectrodes.

The research in this paper extends previous liquid film flow boiling studies by including the effect of an additional electrohydrodynamic (EHD) force, namely the dielectrophoretic (DEP) force. Rather than using only EHD conduction pumping of the liquid film to electro-wet the heater surface, a localized non-uniform electric field above the heater surface is also used to generate a dielectrophoretic force for improved vapor bubble extraction during the nucleate boiling regime. The effect of liquid film height and applied potential are studied as a function of heater superheat and heat flux. The study considers the sole and combined effect of DEP with EHD conduction pumping. A brief analytical study is also used to estimate the expected dielectrophoretic force magnitude and explain the results. All of the above studies are also used to quantify the enhancement in heat transfer that can be achieved when heat transport systems are driven or augmented by these electrohydrodynamic phenomena. The results show remarkable enhancement of up to 1217% in heat flux and boiling heat transfer coefficient for a given superheat when both mechanisms are used simultaneously. The experimental data are important for applications in thermal management in terrestrial and micro-gravity conditions.

The dielectrophoretic (DEP) choking phenomenon is revisited for Janus particles that are transported electrokinetically through a microchannel constriction by a direct-current (DC) electric field. The negative DEP force that would block a particle with a diameter significantly smaller than that of the constriction at its inlet is seen to be relaxed by the rotation of the Janus particle in a direction that minimizes the magnitude of the DEP force. This allows the particle to pass through the constriction completely. An arbitrary Lagrangian-Eulerian (ALE) numerical method is used to solve the nonlinearly coupled electric field, flow field, and moving particle, and the DEP force is calculated by the Maxwell stress tensor (MST) method. The results show how Janus particles with non-uniform surface potentials overcome the DEP force and present new conditions for the DEP choking by a parametric study. Particle transportation through microchannel constrictions is ubiquitous, and particle surface properties are more likely to be non-uniform than not in practical applications. This study provides new insights of importance for non-uniform particles transported electrokinetically in a microdevice.

The small gap distance separating a spherical colloidal particle in electrophoretic motion from a planar nonconducting surface is a required parameter for calculating its electrophoretic mobility. In the presence of an externally applied electric field, this gap distance is determined by balancing the van der Waals, electrical double layer interaction, and gravitational forces with a dielectrophoretic (DEP) force. Here, the DEP force was determined analytically by integration of the Maxwell stress over the surface of the particle. The account of this force showed that its previous omission from the analysis always resulted in underpredicted gap distances. Furthermore, the DEP force dominated under conditions of low particle density or high electric field strength and led to much higher gap distances on the order of a few microns. In one particular case, a combination of low particle density and small particle size produced two possible equilibrium gap distances for the particle. However, the particle was unstable in the second equilibrium position when subjected to small perturbations. In general, larger particles had smaller gap sizes. The effects of four other parameters on gap distance were studied, and gap distances were found to increase with lower particle density, higher electric field strength, higher particle and wall zeta potentials, and lower Hamaker constants. Retardation effects on van der Waals attraction were considered.

A new control mechanism to realize tunable microsphere resonators suspended in liquid is proposed. Via adjusting the bias voltage across an inhomogeneous dielectric structure (a rib waveguide plus microsphere), the microsphere resonator is attracted and levitated on top of the single-mode rib waveguide via an repulsive dielectrophoretic (DEP) force, where the coupling gap between the microsphere resonator and the waveguide is precisely controlled. The tunable gap spacing is analyzed by calculating the dielectrophoretic force through Maxwell stress tensor.

A conductivity-difference-based method for increasing dielectrophoretic (DEP) force for particle separation in a microfluidic chip is presented in this paper. By applying a direct-current (DC) voltage across two immiscible electrolyte solutions with a conductivity difference, an enhanced electric field gradient is generated at the liquid-liquid interface. Theoretical analysis based on equivalent circuit theory found that the gradient of the electric field squared increases with the decrease in the conductivity ratio of the two liquids (main channel to the side channel). As a result, the particle separation distance (an indicator of DEP force) increases with the decrease in the conductivity ratio, which is both numerically predicted and experimentally verified. Numerical simulations also show that the separation distance increases with the increase in the magnitude of the electric field and the decrease in the width of the orifice. The method presented in this paper is simple and advantageous for increasing DEP force without applying higher DC voltages or fabricating smaller orifices.

A major problem for analysis of bio-nanoparticles such as the influenza viruses (size is about 100 nm) is that sample concentration is low. We developed manipulation of the single virus using optical tweezers supported by dielectrophoretic concentration of the viruses in a microfluidic chip. The microfluidic chip made of poly (dimethyl siloxane) (PDMS) is useful to achieve stable manipulation of the virus. The chip has the independent sample chamber and analysis chamber to make the quantitative analysis of the functions of the virus before and after infection to the target cell. Dielectrophoretic (DEP) force worked inside the sample chamber concentrates the virus. DEP force was also worked for avoiding virus adhesion to the glass substrate. Concentrated virus was flown to the sample selection part and was trapped by optical tweezers. Trapped virus was transported to the analysis chamber and contact to the target cell for infection. In this paper, we described the DEP virus concentration for single virus infection to a specific cell. We succeeded in the DEP concentration of the influenza virus, transport of the single virus transport, and contact to the specific H292 cell.

The ongoing development of modern electronic systems leads to smaller, more powerful devices that are expected to operate in complex environments. Due to this, advanced thermal management technologies are required to meet the growing demand, especially in space where two-phase thermal systems are limited by the absence of gravity. Electrohydrodynamic (EHD) and dielectrophoretic (DEP) forces can be used to sustain stable liquid film boiling in micro-gravity, which is otherwise impractical due to the lack of a required buoyancy force to initiate bubble departure. EHD and DEP are phenomena that are represented by the interaction between electric fields and fluid flow. The DEP force especially is characterized by the unique ability to act on liquid/vapor interfaces due to a high gradient of electrical permittivity, allowing for two phase operation. This study investigates the effect of EHD conduction pumping coupled with DEP vapor extraction on liquid film flow boiling during a microgravity parabolic flight, and it characterizes the future two-phase microgravity heat transport technology prior to testing on the International Space Station (ISS). The results of this study show that EHD and DEP raise critical heat flux, lower heater surface temperature, and successfully sustain boiling in micro-gravity all at the cost of low power consumption. Additionally, the heat transfer data captured in terrestrial, microgravity, and 1.8 g conditions compare well, indicating that this technology can provide thermal enhancement independent of gravity. This study paves the way for future implementation of EHD-driven two-phase heat transport devices into space and aeronautical electronics applications.

Dielectrophoresis polishing (DEPP) is a novel flat polishing technology which utilizes the dielectrophoretic (DEP) effect to reduce the centrifugal force on the slurry and to obtain a higher polishing efficiency. The mechanism of the DEPP was analyzed in this paper; the motion of slurry being acted upon by DEP force in non-uniform electric field was captured in real-time with a specially designed video recording system to show the influence of electric field intensity and frequency upon DEP force. DEPP and traditional CMP were investigated. These processes were carried out in sequence on the same machine with the same slurry. Compared with traditional CMP, the efficiency of DEPP was improved by about onefold and the better surface uniformity of silicon wafer was obtained. The final surface roughness Ra of silicon wafer was measured at 1.2 nm.

The ongoing development of modern electronic systems leads to smaller, more powerful devices that are expected to operate in complex environments. Due to this, advanced thermal management technologies are required to meet the growing demand, especially in space where two-phase thermal systems are limited by the absence of gravity. Electrohydrodynamic (EHD) and dielectrophoretic (DEP) forces can be used to sustain stable liquid film flow boiling in the absence of gravity, which is otherwise impractical due to the lack of a required buoyancy force to initiate bubble departure. EHD is a phenomenon that is represented by the interaction between electric fields and fluid flow. The DEP force is characterized by its ability to act on liquid/vapor interfaces due to a high gradient of electrical permittivity. This study investigates the heat transfer characteristics of EHD conduction pumping driven liquid film flow boiling coupled with DEP vapor extraction during a microgravity parabolic flight and on the ground. The results of this study show that EHD and DEP raise the critical heat flux, lower heater surface temperature, and successfully sustain boiling in both microgravity and on the ground with low power consumption. Additionally, the heat transfer data captured in terrestrial, microgravity, and 1.8 g conditions compare well, indicating that combining these mechanisms can provide thermal enhancement independent of gravity. This study provides fundamental understanding of electrically driven liquid film flow boiling in the presence of phase change, paving the way toward developing next-generation heat transport devices for space and terrestrial applications.

This paper extends previous liquid film flow boiling studies by including the effect of an additional electrohydrodynamic (EHD) force, namely, the dielectrophoretic (DEP) force. Rather than using only EHD conduction pumping of the liquid film to electro-wet the heater surface, a localized nonuniform electric field above the heater surface is established to generate a DEP force for improved vapor bubble extraction during the nucleate boiling regime. The effects of liquid film height and applied potential are studied as a function of heater superheat and heat flux. A brief analytical study is also used to estimate the expected DEP force magnitude to explain the results. All of the above studies are also used to quantify the enhancement in heat transfer that can be achieved when heat transport systems are driven or augmented by these two EHD mechanisms. The results show remarkable enhancement of up to 1217% in boiling heat transfer coefficient at a given superheat when both mechanisms are used simultaneously. The experimental data are important for applications in thermal management in terrestrial and space conditions.

To achieve high-precision dielectrophoretic (DEP) assembly of carbon nanotubes (CNTs) for nanoelectronic circuits and nanoelectromechanical systems (NEMS), a technique is investigated both theoretically and experimentally for shaping the local geometries of nanoelectrodes to control the electrohydrodynamic behavior of CNTs. Motion trajectories and positions of CNTs assembled on electrodes are predicted based on calculated DEP forces and torques. Both simulation and experimental results show that the geometries of two opposing electrodes significantly affect the precision and robustness with which CNTs can be deposited. Experimental investigation of an electrode array demonstrates that the spacing between neighboring electrode pairs should be larger than twice the width of electrodes to avoid overlapping electric fields and unstable DEP forces; otherwise, unequally distributed electric fields and DEP forces induce a significant number of assembly failures in the array.

In this paper, we fabricated quantum dot (QD) aggregates at desired locations using dielectrophoretic (DEP) forces induced in the carbon nanotube (CNT) nanogap created by Joule heating-induced electrical breakdown. Nanogaps with a size of at least 20–30 nm can be effectively fabricated in the ambient condition, and fabrication yield can be monitored through in-situ electrical signal without post morphological analysis. The geometry of CNT electrodes with high aspect ratio as well as the gap size of the electrodes to a few tens of nanometers scale enabled the derivation of sufficiently high DEP forces that facilitate the trapping of QD in the CNT nanogap. Above all, we were able to fabricate a conducting crack-free QD aggregates by exchanging the ligands on the surface of the QDs in the presence of a DEP force and this approach showed the possibility of being applied as a QD based optoelectronic devices.

The paper presents theoretical analysis of flow dynamics in a heated microchannel in which flow rate may be controlled by dielectrophoretic (DEP) forces. Proposed model equations were derived in terms of lumped parameters characterising the system comprising of DEP controller and the microchannel. In result, an equation for liquid height of rise in the controller was obtained from momentum balances in the two elements of the considered system. In the model, the boiling process in the heated section of microchannel is taken into account through a pressure drop, which is a function of flow rate and uniform heat flux. Presented calculation results show that the DEP forces influence mainly the flow rate in the microchannel. In this way, by proper modulation of voltage applied to the DEP controller, it is possible to lower the frequency of Ledinegg instabilities.