Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session LC: Microfluidics: Electrophoresis and Electroosmosis I |
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Chair: Frederic Bottausci, University of California, Santa Barbara Room: Hilton Chicago Grand Ballroom |
Tuesday, November 22, 2005 8:00AM - 8:13AM |
LC.00001: Induced charge electroosmosis in microfluidic devices Yuxing Ben, Jeremy Levitan, Howard Stone, Todd Thorsen, Martin Bazant Induced charge electroomosis (ICEO) is an attractive way to pump and mix fluid in microfluidic devices. Such devices have the advantages of low voltages and low power consumptions. It is easy to control and manipulate fluid with an AC electric field. In this paper, we study ICEO around a cylinder between flat plates. An analytic solution for this geometry is obtained. More complicated geometries are exploited by finite element simulations for optimal pumping down a channel. In all cases, we compare with experiments where devices are fabricated by electroplating gold on glass in polymer micrchannels, and flow is visualized by microPIV, with reasonable agreement. [Preview Abstract] |
Tuesday, November 22, 2005 8:13AM - 8:26AM |
LC.00002: Electrolyte transport in neutral polymer gels embedded with charged inclusions Reghan Hill Ion permeable membranes are the basis of a variety of molecular separation technologies, including ion exchange, gel electrophoresis and dialysis. This work presents a theoretical model of electrolyte transport in membranes comprised of a continuous polymer gel embedded with charged spherical inclusions, e.g., biological cells and synthetic colloids. The microstructure mimics immobilized cell cultures, where electric fields have been used to promote nutrient transport. Because several important characteristics can, in principle, be carefully controlled, the theory provides a quantitative framework to help tailor the bulk properties for enhanced molecular transport, microfluidic pumping, and physicochemical sensing applications. This talk focuses on the electroosmotic flow driven by weak electric fields and electrolyte concentration gradients. Also of importance is the influence of charge on the effective ion diffusion coefficients, bulk electrical conductivity, and membrane diffusion potential. [Preview Abstract] |
Tuesday, November 22, 2005 8:26AM - 8:39AM |
LC.00003: Electro-osmotic flow in a non-uniformly charged cavity David Halpern, Hsien-Hung Wei Electro-osmotic flow (EOF) has recently received growing attention in view of its potential means to manipulate flows within microfluidic devices. In this work, the EOF in an open, rectangular cavity is investigated theoretically. In the limit of a thin Debye screening layer adjacent a charged surface, the EOF is characterized by the Smoluchowski-slip velocity at the walls with prescribed zeta potentials because of an electric field. It is well known that an EOF with a uniform zeta potential does not give rise to flow separation due to its irrotational nature, as opposed to the classical problem of shear flow past a cavity. This study explores how a non-uniform charge distribution along the cavity surface affects the EOF therein. Assuming Stokes flow, a boundary element method is employed to determine the fluid motion and electric field in the cavity. The results show that the system can be susceptible to flow separation, and exhibit various flow patterns, depending on the distributions of zeta potentials and the aspect ratio of the cavity. This work might provide guidance for developing optimal strategies on achieving effective mixing using microdevices without appealing to complicated designs. This research is supported by Grant NSC 94-2214-E-006-008 of the National Science Council of Taiwan. [Preview Abstract] |
Tuesday, November 22, 2005 8:39AM - 8:52AM |
LC.00004: Flow-regulated dielectrophoretic manipulation of submicron particles Hsien-Hung Wei, Meng-Juan Lee The motion of submicron particles under the condition of simultaneous flow and dielectrophoresis (DEP) is investigated experimentally using a microfluidic approach. Experiments are conducted within a PDMS microchannel integrated with arrays of castellated microelectrodes. Submicron latex particles are suspended in an electrolyte aqueous solution. The response of dielectrophoretic particle motion to the change in the dielectric properties is carried out using different electrolyte concentrations. Results show that particle aggregation patterns are different from those of conventional DEP.Various new patterns of particle aggregation are identified, depending on the flow rate, the frequency of an applied electric field and the electrolyte conductivity. A scaling analysis is devised to explain the effects at work in accordance with experimental observations. The study provides new strategies for manipulating submicron particles in a continuous manner. This research is supported by Grant NSC 94-2214-E-006-008 of the National Science Council of Taiwan. [Preview Abstract] |
Tuesday, November 22, 2005 8:52AM - 9:05AM |
LC.00005: Electrokinetic micropumps for microfluidics Gaurav Soni, Carl Meinhart We have designed and fabricated novel electrokinetic micropumps for producing unidirectional flows in microchannels. These pumps utilize very small voltages (15 Volts) to create significant flow velocities (100 microns/s). Low voltages reduce the problem of electrolysis and bubble formation inside the microchannels. One type of the pump is based on DC electroosmosis and requires a DC voltage drop across a serpentine wire. This serpentine shaped wire is located at the bottom of a microchannel. Application of a DC potential drop produces induced charges close to the wire surface. Induced charge moves under the influence of local electric field produced by the DC voltage. The serpentine wire is based on the design reported by Gagnon et al., 05. [Preview Abstract] |
Tuesday, November 22, 2005 9:05AM - 9:18AM |
LC.00006: Manipulation of nanoparticles using dielectrophoresis and fluid flow. Sophie Loire, Igor Mezic We present numerical simulations on dielectrophoretic (DEP) separation and trapping performed in a titanium-based microchannel linear electrode array. The use of electric field and in particular dielectrophoresis (DEP) have a great potential to help miniaturize and increase the speed of biomedical analysis. Precise control and manipulation of micro/nano/bio particles inside those miniaturized devices depend greatly on our understanding of the phenomena induced by AC electric field inside microchannels and how we take advantage of them. The device is designed to generate inhomogeneities in electric- field magnitude. This allows positive and negative DEP (p-DEP and n-DEP). Moreover, it can also produce inhomogeneities in electric-field phase, hence authorizing traveling wave DEP (twDEP). We show that fluid flow effects are substantial and can affect the particle motion in a positive (enhanced trapping) and negative (trapping when separation is desired) way. An advection-diffusion equation is used to numerically simulate the system. The study of the combination of the three electrical effects with diffusion, predicts the location of the trapping regions. We finally investigate the limits of particle size that can be accurately controlled. [Preview Abstract] |
Tuesday, November 22, 2005 9:18AM - 9:31AM |
LC.00007: Dielectro-kinetic concentration of Quantum dots Frederic Bottausci, Yanting Zhang, Igor Mezic We report experimental results on dielectrokinetic concentration of 10-15 nanometers in diameter particles performed in a planar electrodes chip using bulk titanium micro-fabrication. The device consists of an array of 24 electrodes sitting on the bottom of a 200 microns wide, 30 microns deep and 6 millimeters long titanium channel. The electrodes are 20 microns wide with a pitch of 40 microns. With appropriate voltage amplitude and frequency, we show the concentration of nanometer particles onto the middle of the electrodes despite strong Brownian motion whereas bigger particles tend to accumulate at the edges of the electrodes due to stronger dielectrophoretic force. The concentration process takes place in few hundreds of milliseconds. This experiment is the first step for control of nanometers particles. We discuss the advantage of nano-concentration and present quantitative results. [Preview Abstract] |
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