Fluidic dielectrophoresis: The polarization and displacement of electrical liquid interfaces (original) (raw)

Tunable pattern structures in dielectric liquids under high dc electric fields

IEEE Transactions on Dielectrics and Electrical Insulation, 2006

This work focuses on the abrupt changes that the application of large enough electric fields provokes in the internal structure of hematite/silicone oil suspensions. Experimental results reflect the existence of two well-defined structural patterns according to the strength of the field and the concentration of particles. At low electric fields, columns of particles between the electrodes can be observed when the concentration of solids exceeds a critical volume fraction. However, at higher fields, electrohydrodynamic convection and eventually electrophoretic migration take place, reflecting the relevance of the particle charge. A complete theoretical discussion is given to explain the origin of these so different behaviors. While the mismatch in the electrical properties (particularly, conductivity) of the solid and liquid phases, that is the Maxwell-Wagner polarization, can justify the chain-like structures of particles, it is necessary to take into an account the process of charge injection at the electrode/suspension interface to support the electrophoretic migration and deposition. The experimental conditions for which polarization or current effects predominate are elucidated in terms of the conductivity of the solid phase and the magnitude of the applied electric field.

Characterization and optimization of liquid electrodes for lateral dielectrophoresis

2007

Using the concept of insulator-based ''electrodeless'' dielectrophoresis, we present a novel geometry for shaping electric fields to achieve lateral deviation of particles in liquid flows. The field is generated by lateral planar metal electrodes and is guided along access channels to the active area in the main channel. The equipotential surfaces at the apertures of the access channels behave as vertical ''liquid'' electrodes injecting the current into the main channel. The field between a pair of adjacent liquid electrodes generates the lateral dielectrophoretic force necessary for particle manipulation. We use this force for high-speed deviation of particles. By adding a second pair of liquid electrodes, we focus a particle stream. The position of the focused stream can be swept across the channel by adjusting the ratio of the voltages applied to the two pairs. Based on conformal mapping, we provide an analytical model for estimating the potential at the liquid electrodes and the field distribution in the main channel. We show that the simulated particle trajectories agree with observations. Finally, we show that the model can be used to optimize the device geometry in different applications.

Interactions of electrical fields with fluids: laboratory-on-a-chip applications

Abstract: The area of ‘laboratory-on-a-chip’, miniaturised or microfluidic analysis systems, is a rapidly developing field. At the microscale, electrokinetic processes become enhanced, and the advent of AC electrokinetics (EK) in recent years further promotes the development of electrokinetic devices for microfluidics. ACEK has demonstrated to manipulate fluids and polarisable particles at low voltages without some of the disadvantages from DCEK, such as electrochemical reactions and the limitation of low ionic strength fluids. The three major mechanisms of ACEK, that is, dielectrophoresis, AC electro-osmosis and AC electrothermal effect, provide versatility and flexibility to interface with many current methods and technologies in multiple biological, chemical and physical disciplines. This paper gives an overview of ACEK and its applications, with an emphasis on fluid manipulation by electric fields.

Dielectrophoresis in aqueous suspension: impact of electrode configuration

Microfluidics and Nanofluidics, 2014

supplying a non-uniform electric field. When using alternating current and insulated electrodes this is possible in conducting media such as aqueous solutions. However, relatively high field strength is required that is discussed to induce also an undesired Joule heating effect. In this paper, we demonstrate boundary conditions for avoiding this side effect and suggest a novel design of an interdigitated electrode (IDE) configuration to reduce the power consumption. Numerical simulation using OpenFOAM demonstrated that, when replacing conventional plate IDE by cylindrical micro IDE in microchannel systems, the dielectrophoretic force field, i. e. the electric field gradient squared, becomes stronger and more homogeneously distributed along the electrodes array. Also the resulting particle DEP velocities were highest for the cylindrical IDE. The simulations were experimentally confirmed by measuring velocity of resin particle located at the subsurface of demineralized water. Surprisingly the fluid flow induced by electrothermal effect turned out to be negligible in microchannels when compared to the DEP effect and becomes dominant only for distances between particle and IDE larger than 6000 µm. The well agreed experimental and simulation results allow for predicting particle motion. This can be expected to pave the way for designing DEP microchannel-separators with high throughput and low energy consumption.

Particle Manipulation in Insulator Based Dielectrophoretic Devices1

Journal of Nanotechnology in Engineering and Medicine, 2013

Microfluidic devices can make a significant impact in many fields where obtaining a rapid response is critical, particularly in analyses involving biological particles, from deoxyribonucleic acid (DNA) and proteins, to cells. Microfluidics has revolutionized the manner in which many different assessments/processes are carried out, since it offers attractive advantages over traditional bench-scale techniques. Some of the advantages are: small sample and reagent amounts, higher resolution and sensitivity, improved level of integration and automation, lower cost and much shorter processing times. There is a growing interest on the development of techniques that can be used in microfluidics devices. Among these, electrokinetic techniques have shown great potential due to their flexibility. Dielectrophoresis (DEP) is an electrokinetic mechanism that refers to the interaction of a dielectric particle with a spatially non-uniform electric field; this leads to particle movement due to polar...

Electrokinetic actuation of low conductivity dielectric liquids

Sensors and Actuators B …, 2009

Whilst electrohydrodynamic (EHD) flow actuation of dielectric fluids has been widely demonstrated, the fundamental mechanisms responsible for their behaviour is not well understood. By highlighting key distinguishing features of the various EHD mechanisms discussed in the literature, and proposing a more general mechanism based on Maxwell (electric) pressure gradients that arise due to induced polarization, we suggest that it is possible to identify the dominant EHD mechanisms that are responsible for an observed flow. We demonstrate this for a class of low conductivity dielectric fluids -Electro-Conjugate Fluids (ECFs) -that have recently been shown to exhibit EHD flow phenomena when subjected to nonuniform fields of low intensities. Careful inspection of the salient attributes of the flow, at least at low field strengths (<1 kV/cm) -for example, the absence of a threshold voltage for the onset of flow, the quadratic scaling of the flow velocity with the applied voltage, and flow from the high to the low field region -eliminate the possibility of mechanisms based on space charge. Instead, we suggest that flow can be attributed to the existence of a Maxwell pressure gradient. This is further corroborated by good agreement between our experimental results and theoretical analysis.

Insulator-based dielectrophoresis of microorganisms: Theoretical and experimental results

ELECTROPHORESIS, 2011

Dielectrophoresis (DEP) is the motion of particles due to polarization effects in nonuniform electric fields. DEP has great potential for handling cells and is a non-destructive phenomenon. It has been utilized for different cell analysis, from viability assessments to concentration enrichment and separation. Insulator-based DEP (iDEP) provides an attractive alternative to conventional electrode-based systems; in iDEP, insulating structures are used to generate nonuniform electric fields, resulting in simpler and more robust devices. Despite the rapid development of iDEP microdevices for applications with cells, the fundamentals behind the dielectrophoretic behavior of cells has not been fully elucidated. Understanding the theory behind iDEP is necessary to continue the progress in this field. This work presents the manipulation and separation of bacterial and yeast cells with iDEP. A computational model in COMSOL Multiphysics was employed to predict the effect of direct current-iDEP on cells suspended in a microchannel containing an array of insulating structures. The model allowed predicting particle behavior, pathlines and the regions where dielectrophoretic immobilization should occur. Experimental work was performed at the same operating conditions employed with the model and results were compared, obtaining good agreement. This is the first report on the mathematical modeling of the dielectrophoretic response of yeast and bacterial cells in a DC-iDEP microdevice.

Screening of Coulomb interactions in liquid dielectrics

Journal of Physics: Condensed Matter, 2019

The interaction of charges in dielectric materials is screened by the dielectric constant of the bulk dielectric. In dielectric theories, screening is assigned to the surface charge appearing from preferential orientations of dipoles along the local field in the interface. For liquid dielectrics, such interfacial orientations are affected by the interfacial structure characterized by a separate interfacial dielectric susceptibility. We argue that dielectric properties of polar liquids should be characterized by two distinct susceptibilities responsible for local response (solvation) and long-range response (dielectric screening). We develop a microscopic model of screening showing that the standard bulk dielectric constant is responsible for screening at large distances. The potential of mean force between ions in polar liquids becomes oscillatory at short distances. Oscillations arise from the coupling of the collective longitudinal excitations of the dipoles in the bulk with the interfacial structure of the liquid around the solutes.

Electrohydrodynamics and dielectrophoresis in microsystems: scaling laws

Journal of Physics D-applied Physics, 2003

The movement and behaviour of particles suspended in aqueous solutions subjected to non-uniform ac electric fields is examined. The ac electric fields induce movement of polarizable particles, a phenomenon known as dielectrophoresis. The high strength electric fields that are often used in separation systems can give rise to fluid motion, which in turn results in a viscous drag on the particle. The electric field generates heat, leading to volume forces in the liquid. Gradients in conductivity and permittivity give rise to electrothermal forces and gradients in mass density to buoyancy. In addition, non-uniform ac electric fields produce forces on the induced charges in the diffuse double layer on the electrodes. This causes a steady fluid motion termed ac electro-osmosis. The effects of Brownian motion are also discussed in this context. The orders of magnitude of the various forces experienced by a particle in a model microelectrode system are estimated. The results are discussed in relation to experiments and the relative influence of each type of force is described.