Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G7: Microfluids: Electro/Magnetic Manipulation |
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Chair: Paulo Arratia, University of Pennsylvania Room: 329 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G7.00001: Electrical manipulation of submicron particles by reservoir-based dielectrophoresis (rDEP). Herbert Harrison, Mark Johnson, Saurin Patel, Xiangchun Xuan Reservoir-based dielectrophoresis (rDEP) is a recently developed technique by our group that exploits the inherent electric field gradients at a reservoir-microchannel junction for particle and cell manipulations. It is based on the induced negative dielectrophoretic motion at the junction to focus, trap and sort micron particles and cells. In this talk we present the experimental and numerical results for the electrical manipulation of submicron particles by rDEP. We study and compare the transport of submicron particles from reservoir to microchannel with negative and positive rDEP, respectively. The effects of electric field and medium concentration are examined. The goal is to implement a continuous particle sorting by negative and positive rDEP. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G7.00002: Self-assembly and manipulation of particles on drop surfaces M. Janjua, I.S. Fischer, P. Singh We have recently shown that particles adsorbed on the surface of a drop can be self-assembled at the poles or the equator of the drop by applying a uniform electric field, and that this method can be used to separate on the surface of a drop particles experiencing positive dielectrophoresis from those experiencing negative dielectrophoresis. In this talk we show that the frequency of the electric field is an important parameter which can be used to modify the distribution of self-assembled monolayers. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G7.00003: Mathematical modeling of the motion of soft biological particles during insulator based dielectrophoresis Naga Neehar Dingari, Cullen R. Buie We present a theoretical model to investigate the effects of soft polyelectrolyte layers and bulk ionic concentration on the motion of biological particles such as bacteria in insulator based dielectrophoresis (iDEP) [1] devices. The polarizabilities and electrophoretic mobilities are calculated by solving modified Poisson-Nernst-Plank equations [2] (for ionic transport) and modified Stokes equations (for fluid flow) around the soft particle. The details of soft layer are modeled by including dissociation of ionogenic groups within soft layer and specific interactions with the background electrolyte. We consider two test cases: fibrillated and unfibrillated bacteria whose mobilities were analyzed theoretically and experimentally by Duval et.\textit{al} [3]. We consider a wide range of bulk electrolyte concentration to include thin and thick double layer cases. As a consequence of our analysis we highlight an interesting interplay between soft layer conductivity (function of pH, pKa of ionogenic groups) and double layer conductivity (function of bulk electrolyte concentration) on the particle trajectories in an iDEP device. \\[4pt] [1] Braff, W. a; Pignier, A.; Buie, C. R. \textit{Lab on a chip} \textbf{2012}, \textit{12}, 1327--31.\\[0pt] [2] Duval, J. F. L.; Ohshima, H. \textit{Langmuir }\textbf{2006}, \textit{22}, 3533--46.\\[0pt] [3] Duval, J. F. L.; Busscher, H. J.; van de Belt-Gritter, B.; van der Mei, H. C.; Norde, W. \textit{Langmuir }\textbf{2005}, \textit{21}, 11268--82. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G7.00004: Electric filed induced self-assembly of monolayers of sub-micron sized particles on flexible thin films K. Shah, M. Hossain, M. Janjua, N. Aubry, I.S. Fischer, P. Singh We present a technique that uses an electric field in the direction normal to the interface for self-assembling particle monolayers of sub-micron sized particles on fluid-liquid interfaces and freezing these monolayers onto the surface of a flexible thin film. The electric field gives rise to dipole-dipole and capillary forces which cause the particles to arrange in a triangular pattern. The technique involves assembling the monolayer on the interface between a UV-curable resin and another fluid by applying an electric field, and then curing the resin by applying UV light. The monolayer becomes embedded on the surface of the solidified resin film. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G7.00005: Electrical trapping and sorting of particles in an asymmetric ratchet microchannel Akshay Kale, Xinyu Lu, Xiangchun Xuan Ratchet microchannels have been demonstrated to implement the electrical focusing, trapping, and sorting of various particles. However, no work has thus far been done on the effects of the structure of ratchets on the transport and manipulation of particles in ratchet microchannels. In this talk we present our recent results of the electrokinetic particle trapping and sorting in an asymmetric ratchet microchannel. The ratchet effects (i.e., forward or backward motion) on the trapping effectiveness and location of particles are examined under various DC-biased AC electric fields. The discrepancies in the trapping voltage and location are utilized to demonstrate a continuous electrical sorting of particles by size. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G7.00006: Transport of microspheres across liquid-liquid interfaces Steffen Hardt, Ashok Sinha, Amlan Mollah, Ranjan Ganguly Experiments with magnetic microspheres crossing the interface between two immiscible polymer solutions under the influence of a magnetic field are reported. The liquids form a bilaminated configuration in a microchannel, allowing a detailed inspection of the liquid-liquid interface. The trajectories of the particles close to the interface are examined using bright-field microscopy and a high-speed camera. During the interaction phase the interface gets deformed and the particles ``snap in,'' indicating that a three-phase contact line is formed. The dependence of the particle-interface interaction on the size of the microspheres is studied, showing that via transfer across a liquid-liquid interface a size separation of particles can be achieved. Comparing the results for 1.29 micron diameter spheres with those for 4.69 micron spheres, it is found that the small particles are able to cross the interface more easily than what is expected from a simple scaling analysis taking into account the balance between magnetic and interfacial forces on the particles. The most likely explanation for this phenomenon involves the line tension that destabilizes smaller particles adsorbed to a liquid-liquid interface more than larger particles. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G7.00007: Self-assembled magnetocapillary swimmers Maxime Hubert, Geoffroy Lumay, Floriane Weyer, Noriko Obara, Nicolas Vandewalle Capillary driven self-assembly consists of suspending small objects at a water-air interface. Due to the effects of wetting, gravity and surface tension, the interface is slightly deformed, inducing a net force between the particles. In the experiments we present, we consider the presence of a vertical magnetic field acting on soft-ferromagnetic particles. Dipole-dipole repulsion competes with capillary attraction such that 2d ordered structures are self-assembling. By adding a secondary horizontal and oscillating magnetic field, periodic deformations of the assembly are induced. Pulsating particle arrangements start to swim, either translating or rotating. The physical mechanisms and geometrical ingredients behind this cooperative locomotion are identified. Furthermore, strategies to control the swimming dynamics are proposed. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G7.00008: Structure and dynamics of self-assembling colloidal monolayers in oscillating magnetic fields Alison Koser, Paulo Arratia Many fascinating phenomena such as large-scale collective flows, enhanced fluid mixing and pattern formation have been observed in so-called active fluids, which are composed of particles that can absorb energy and dissipate it into the fluid medium. For active particles immersed in liquids, fluid-mediated viscous stresses can play an important role on the emergence of collective behavior. Here, we experimentally investigate their role in the dynamics of self-assembling magnetically-driven colloidal particles which can form highly organized hexagonal lattices that span length scales much larger than a particle diameter. We find that viscous stresses reduce hexagonal ordering, generate smaller clusters, and significantly decrease down the rate of cluster formation, all while holding the system at constant number density. Furthermore, we show that time and length scales of cluster formation depend on and scale with the Mason number (\textit{Mn}) or ratio of viscous to magnetic forces. Our results suggest that viscous stresses hinder collective behavior in a self-assembling colloidal system. This work is supported by the Army Research Office through the award W911NF-11-1-0488. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G7.00009: Models of particle capture in high gradient magnetic separation Almut Eisentraeger, Ian Griffiths, Dominic Vella High gradient magnetic separation is an efficient way to remove magnetic and paramagnetic particles, such as heavy metals, from waste water. As the water flows through a mesh of magnetized steel wool, high magnetic gradients around the wires attract and capture the particles. We model such a system by considering a single point dipole travelling through a periodic array of magnetized cylinders. We show that there is a critical Mason number (dimensionless flow velocity) below which the particle is captured independent of its initial position. Above this threshold, particle capture is only partially successful and depends on the particle's initial position. We determine the relationship between the critical Mason number and geometry using numerical and asymptotical calculations. To develop these ideas further, we also discuss briefly the aggregation of particles into chains. [Preview Abstract] |
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