Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session BF: Microfluidics: Devices II |
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Chair: Axel Guenther, University of Toronto Room: 101F |
Sunday, November 22, 2009 10:30AM - 10:43AM |
BF.00001: Defining Microstructured Fluids and Soft Materials Bottom Up Lian Leng, Siavash Aslanbeigi, Axel Guenther We demonstrate a microfluidic strategy for the three-dimensional organization of soft bulk materials with a tunable microstructure. Two miscible fluid streams entered a massively-scaled microfluidic device and were distributed through an array of alternating channels. A soft lithography process was adapted to consistently define microchannels with a hydraulic diameter of 150microns in 500micron thin elastomer substrates, followed by bonding of up to ten such layers in the vertical direction. The resulting microfluidic device contained a total of one hundred microchannels. At the device exit, a complex fluid was continuously extruded as a matrix material where the pores contained the second fluid. Upon leaving the chip, the vascularized matrix was solidified and created a perfusable soft material. The material microstructure and its tunability were characterized using microscale computed tomography. [Preview Abstract] |
Sunday, November 22, 2009 10:43AM - 10:56AM |
BF.00002: Light-enabled digital microfluidics: A technology leading to a programmable lab on a chip Steven T. Wereley, Han-Sheng Chuang, Aloke Kumar We present a self-driven microfluidic device for droplet manipulations based on an open optoelectrowetting (O-OEW) technique. The proposed O-OEW features dynamic droplet maneuverability and great extensibility due to light-induced virtual electrodes and an open configuration. The device comprises coplanar interdigitated electrodes, a photoconductor, and an insulator on a single substrate. The mechanism behind the O-OEW is dependent on the impedance switching between the photoconductor and the insulator. The photoconductor works as a gate for the equivalent circuit. Under illumination the impedance of the photoconductor decreases, prompting an electrowetting effect due to a high voltage drop in the insulator. Without illumination the impedance of the photoconductor increases, shifting the voltage drop back to the photoconductor layer and shutting off the electrowetting. The illumination induces a localized hydrophilic region on an overall hydrophobic surface, causing an imbalance of surface tension forces and the subsequent liquid droplet movement. By selectively illuminating the platform surface, basic droplet operations are implemented, such as translation, merging, and simultaneous multi-droplet control. Immersing the liquid droplets in oil enhances the movements and prevents serious evaporation. For more high-end applications, an addressable light source, such as a DLP projector, can be employed. The integration will enable the realization of a programmable lab on a chip. [Preview Abstract] |
Sunday, November 22, 2009 10:56AM - 11:09AM |
BF.00003: Beyond Poiseuille: Over-limiting Fluid Flows through Macroscopically Long Carbon Nanochannels S. Sinha Ray, A.L. Yarin Nanotubes and nanochannels have tremendous potential in various fields like drug delivery, DNA segregation, capillary electrophoresis etc. Except coelectrospinning all the methods result in nanotubes sufficiently small in diameter (1-100 nm) but not longer than several micron precluding easy manipulation making them almost unsuitable for installing in nanofluidic devices for studying fluid flow characteristics. In this work we developed macroscopically long ($\sim $1 cm) carbon nanochannels and studied flow characteristics in them. Then, we demonstrated that bi-layer flows of liquid and gas can result in an over-limiting regime, where a higher flow rate of liquid can be achieved as compared to the case when the same liquid flows through the same tube subjected to the same pressure drop and occupies the whole bore. This paradoxical result is because the less viscous gas layer can flow much faster than the underlying liquid layer and entrain the latter via a significant shear stress. The present results show that the over-limiting liquid flows through nanotubes, seemingly resembling a deviation from the no-slip condition, in reality are entrained by a rapidly moving gas layer in bi-layer liquid/gas flows. This quasi-slip phenomenon happens in relatively large nanotubes ($\sim $500 nm) where the no-slip condition holds with sufficient accuracy, which can be beneficial in micro- and nanofluidics, nanoreactors and drug delivery systems, which are the current goals of this team. [Preview Abstract] |
Sunday, November 22, 2009 11:09AM - 11:22AM |
BF.00004: Inertial-Microfluidic Hydrodynamic Lens Young Won Kim, Jung Yul Yoo A hydrodynamic lens is the methodology to focus nano- and micro-particles suspended in liquid medium. We designed and tested a single-stage inertial-microfluidic hydrodynamic lens embodied in a microchip for biomedical and environmental applications. We adopted cylindrical micro-orifices with diameters of 100--300 $\mu$m, transporting micro-particles in sizes of 1--16 $\mu $m. A numerical study is conducted to provide optimum design rules of the lens system. The lens performances are evaluated in terms of Stokes number considering the particle size, the orifice diameter, and the flow Reynolds number. Micro-particle tracking velocimetry ($\mu $-PTV) adopting Nd:YAG lasers, which freeze flowing particles, are applied, and compared with the numerical simulation in terms of the focused beam diameter. The particle focusing method suggested in this work is fairly simple, sheathless, and free from necessity of other external forces. [Preview Abstract] |
Sunday, November 22, 2009 11:22AM - 11:35AM |
BF.00005: A Piezoelectric Micropumping Based on D31 Mode Yakut Ali, Cuifang Kuang, Jamil Kahn, Guiren Wang A micropumping device has been developed, which may find application in different areas such as blood pumping and chemical reagents dosing in bioengineering or as an efficient thermal management solution scheme in space-constrained electronic devices, due to some of their unique properties such as lower noise generation and ease of miniaturization. In this presentation, liquid pumping effect is reported using a simple valveless piezoelectric dynamic pump in D31 mode based on acoustic streaming principle. The actuator tip configuration is found to have a significant effect on the pumping performance. Quantitative results of maximum local velocity are presented for different tip configuration of the same actuator for comparison. In addition, this work also demonstrates the quantitative measurements of the pumping performance such as the flow rate and pressure head generated as a function of different relevant parameters such as applied electrical field, AC frequency and length of the actuator. [Preview Abstract] |
Sunday, November 22, 2009 11:35AM - 11:48AM |
BF.00006: Performance predictions for valveless impedance pumps in the microscale: wave speed and time response considerations for the Liebau phenomenon John Meier, Morteza Gharib Valveless pumping through periodic excitation of a pliant tube with geometric asymmetry was first noted by Liebau in 1954. Studies by Hickerson and Gharib (J. Fluid Mech. 2006) and Avrahami and Gharib (J. Fluid Mech. 2008) highlight the role of wave dynamics and resonance in valveless impedance pumps that exploit the Liebau phenomenon. While pulse propagation in fluid filled elastic tubes has been studied for centuries, there are fundamental scaling investigations missing from the literature that are necessary to understand impedance pump behavior. The pump has been shown to function down to scales of 250 $\mu $m in tubular systems by Rinderknecht et al. (J. Micromech. Microeng. 2005). We have recently shown that the pump also functions in a planar manifestation, fabricated using multilayer soft lithography, with pump thicknesses on the order of 200 $\mu $m. In this study we look at wave propagation and time response in both tubular and planar systems and discuss the effects of the scaling parameter $\lambda $/L in the pumping element and its affects on performance and fundamental impedance pump behavior. [Preview Abstract] |
Sunday, November 22, 2009 11:48AM - 12:01PM |
BF.00007: Numerical and experimental study of Newtonian and non-Newtonian flow in a spiral viscous pump Gustaf M{\aa}rtensson, Andreas Gustafsson The need to transport small volumes of viscous media is a vital part of microfluidic devices vital to applications in biotechnology, chemistry and electronics. A novel Archimedian viscous micropump was developed in an attempt to achieve precise and accurate delivery of fluid in a robust and industrially viable package. The pump consists of a two-disc system, where one is patterned with a spiral rectangular channel of variable width and the other is smooth and has a rate of rotation \( \Omega \) in order to pump the fluid. The width of the channel is variable along its length in order to achieve a constant local Reynolds number and avoid recirculation zones along the spiral, which is described $ r = a + b \theta ^{c} $, where \( r \) is the radius at the spiral centerline and \( \theta \) is the angle. Numerical and analytical studies of the proposed model will be presented, exhibiting a linear relationship between the flow \( Q \) and \( \Omega \). Results from experiments with a simplified prototype will also be presented supporting the analytical and numerical studies. [Preview Abstract] |
Sunday, November 22, 2009 12:01PM - 12:14PM |
BF.00008: Stabilization of ion concentration polarization using a heterogeneous nanoporous junction Pilnam Kim, Sung Jae Kim, Jongyoon Han, Kahp Y. Suh We demonstrate a recycled ion -- flux through heterogeneous nanoporous junctions, which induce stable ion concentration polarization (ICP) with an electric field. The nanoporous junctions are based on integration of ionic hydrogels whose surfaces are negatively- and positively- charged for cationic selectivity and anionic selectivity, respectively. It is shown that a `heterojunction' structure with cationic selective hydrogels (CSH) and anionic selective hydrogels (ASH) can be matched up in a way to achieve continuous ion-flux operation for stable concentration gradient or ionic conductance. Furthermore, the combined junctions can be used to accumulate ions on a specific region of the device. [Preview Abstract] |
Sunday, November 22, 2009 12:14PM - 12:27PM |
BF.00009: Analysis of Magnetohydrodynamic Flow in Microfluidics Yogendra Panta, Wei Lin Over the last three decades, numerical and experimental fluid dynamic studies have been well documented for optimization of device performance in general fluid dynamics, prediction and analysis of physiological flows, fluid-structure interactions in biological systems, and effectiveness of drug delivery systems in lab on chip devices. Magnetohydrodynamics (MHD) is a proven and a routinely used technology not only in various industries to heat, pump, stir and levitate fluids but also an innovative potential for making remarkable biosensors. Two typical pilot projects to test, analyze and optimize the MHD effects were designed. Microfluidics channels coupled with MHD in various shapes were fabricated from a thin brass sheet sandwiched between two polycarbonate sheets in which two platinum electrodes were patterned on the channel walls. Ionic solution colored with dye was introduced in the channel to visualize the fluid flow with or without the MHD. The induction and driving of fluid motion in the channel was accomplished by placing magnetic field normal to the applied electric field in order to induce Lorentz forces in the fluid contained in the channel. Experimental data and numerical results were obtained in a good agreement. Flow velocities were obtained linearly increasing with the higher magnetic flux densities. Future work will be focused on the development of MHD biosensors for chemical biology applications. [Preview Abstract] |
Sunday, November 22, 2009 12:27PM - 12:40PM |
BF.00010: Oscillatory Magnetogasdynamic Slip Flow in a Microchannel Ramesh Agarwal The problem of pressure driven Magnetogasdynamic (MGD) slip flow with small rarefaction through a long micro-channel is considered. The flow is driven by steady or oscillatory pressure gradient. The study of MGD flows in microchannels is of great interest since they occur in magnetic thin films and other electromagnetic micro-scale devices. In obtaining the micro-fluidic solutions in the presence of a magnetic field, some additional physical, mathematical and numerical issues need to be considered. These issues deal with the scaling laws for micro-scale MHD flows and the relevant parameters such as Mach number, Reynolds number, Hartmann number, magnetic Reynolds number, and Knudsen number. For planar constant area micro-channel, it is possible to obtain the analytical solutions for both steady and oscillatory pressure driven flows. As physically expected, the higher value of the magnetic field (higher Hartmann number) flattens the velocity profile in the channel. [Preview Abstract] |
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