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Copyright Brian J. Kirby. With questions, contact Prof. Kirby here. This material may not be distributed without the author's consent. When linking to these pages, please use the URL http://www.kirbyresearch.com/textbook.

This web posting is a draft, abridged version of the Cambridge University Press text. Follow the links to buy at Cambridge or Amazon or Powell's or Barnes and Noble. Contact Prof. Kirby here. Click here for the most recent version of the errata for the print version.

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Jump To: [Kinematics] [Couette/Poiseuille Flow] [Fluid Circuits] [Mixing] [Electrodynamics] [Electroosmosis] [Potential Flow] [Stokes Flow] [Debye Layer] [Zeta Potential] [Species Transport] [Separations] [Particle Electrophoresis] [DNA] [Nanofluidics] [Induced-Charge Effects] [DEP] [Solution Chemistry]

17.5 Supplementary reading [DEP top]

Excellent references on the electromechanics of particles include [2023738]. These sources discuss dielectrophoresis and electrorotation in detail, including particle-particle interactions, detailed multipolar analysis, and double layer effects. Jones [38] treats magnetophoresis in detail as well as dielectrophoresis. Dielectrophoresis involves induced surface charge, and in that sense has similarities to the AC electrokinetic effects described in Chapter 16; however, in the case of DEP, the surface charge is caused by a discontinuity of material properties in lossy dielectrics as compared to a spatial gradient of material properties (e.g., electrothermal effects) or discontinuity between a lossy dielectric and an ideal conductor (e.g., induced-charge electroosmosis, AC electroosmosis).

Dielectrophoretic analysis often involves constant decisions between which level of analysis to use, ranging from the Maxwell stress tensor to the effective dipole. In real systems, analytical solutions are either numerical or approximate. With specific reference to dielectrophoresis, Wang, et al. [203204] have developed an analytical formalism for DEP forces and torques derived from the Maxwell stress tensor expression [205206207204]. A more significant body of work is devoted to numerical simulations and solutions for the DEP force and particle trajectories [208209205206210207211]. These findings indicate that the Maxwell stress tensor must be integrated to find accurate solutions when the particle size approaches (within an order of magnitude) the characteristic length scale of spatial variations of the electric field. Multipolar descriptions are described in detail in [38212]. Several different geometries have been considered in detail [20621321421521673217218207]. While we restrict ourselves in this chapter to spherically-symmetric and isotropic materials, DEP and electrorotation have been used to gain insight into internal structure or composition [219220221222223224225226227216228229230].

Dielectrophoresis applications range from fractionating particles based upon their “electrical phenotype” [195] to precise manipulation of single particles for property interrogation to new strategies for the creation of engineered tissues and organs. A number of dielectrophoretic trapping techniques have been employed; examples of separation by cell types can be found in [231194186]. Cell populations have been used to discern physiologic differences such as activation of mitosis [232], cell-cycle phase [233], exposure to drugs [234235], induced cell differentiation [203236], and cell death [237238185239240]. Using DEP-based devices to potentially separate the same type of cells based upon physiologic parameters is a powerful tool to identify responses of cells to various soluble agents. Multiple frequency techniques are presented in [185241242]. A subset of the published work uses “electrodeless” techniques, in which the electric field nonuniformity is created through constrictions in the channel geometry [196240197]. Many of these techniques are suitable for continuous-flow separation, also implemented with electrodes in [243244245]. These continuous flow separations have been applied for polystyrene spheres [197246], bacteria [247], yeast [248], and mammalian cells [233]. Individual cells have been addressed in DEP electrode arrays to facilitate single cell capture, analysis, and release, both in solution [249250251] and in photopolymerized gels [252].

This chapter omits dielectric spectroscopy, which can be used on colloidal suspensions to infer double layer and particle properties. The dielectric spectroscopy community describes many of the phenomena described in this chapter using different terminology—for example, the terms alpha and beta relaxations are used to describe the low- and moderate-frequency changes in the dielectric response owing to double layer asymmetry and fluid flow (alpha dispersion) or Maxwell-Wagner polarization (beta dispersion).

Some examples of digital microfluidics are presented in [201253].

[Return to Table of Contents]



Jump To: [Kinematics] [Couette/Poiseuille Flow] [Fluid Circuits] [Mixing] [Electrodynamics] [Electroosmosis] [Potential Flow] [Stokes Flow] [Debye Layer] [Zeta Potential] [Species Transport] [Separations] [Particle Electrophoresis] [DNA] [Nanofluidics] [Induced-Charge Effects] [DEP] [Solution Chemistry]

Copyright Brian J. Kirby. Please contact Prof. Kirby here with questions or corrections. This material may not be distributed without the author's consent. When linking to these pages, please use the URL http://www.kirbyresearch.com/textbook.

This web posting is a draft, abridged version of the Cambridge University Press text. Follow the links to buy at Cambridge or Amazon or Powell's or Barnes and Noble. Contact Prof. Kirby here. Click here for the most recent version of the errata for the print version.


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