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:: Research Interests :: I am an engineer (PhD candidate, Harvard University) studying the fluid mechanics of microchannel and interfacial flows. Currently I am modeling and experimenting with the sorting and coating of magnetic micron-scale particles in lab-on-a-chip devices. I also have concurrent projects studying the deformation of a water-oil interface by magnetic spheres in an applied magnetic field. The inspiration for these physical problems arise from the biotechnology and water filtration industries, where magnetic particles are used to bind and sort biological material. Since July 2009, I have been a student visitor at Princeton University, working with Professor Howard A. Stone in the Complex Fluids Group. Here is a link to my publications and presentations. |
:: Information :: School of Engineering and Applied Sciences |
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:: Upcoming Presentation Schedule :: |
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11.11-17.2011 |
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:: Microfluidics ::
Microfluidic Immunomagnetic Multi-Target Sorting Sorting of cells and biological material is typically done using a fluorescence detection system that has a large footprint. Cells are also sorted by their attachment to antibody-coated magnetic beads in magnetic separation systems. Here, a microfluidic system is developed that uses a magnetic field to sort magnetic beads by deflecting them in the direction normal to the flow. A mathematical model is derived that predicts the magnitude of deflection based on the bead size and susceptibility, magnet strength, fluid speed and viscosity, and device geometry. The system can be applied to sort cells and biological materials by binding them to beads of different sizes and susceptibilities. (Collaborating with Ian Griffiths and Howard Stone) |
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Microfluidic Particle Conformal Coating Device Coating of cells with a layer of polymeric membrane can help protects the cells from the host's immune system during drug delivery. We demonstrate conformal coating of protein-bound, micron-size paramagnetic beads with a very thin O(1 micron) layer of coating fluid, by pulling the beads from an aqueous phase to an oil phase in a microfluidic co-flowing system and control the coating thickness with the aqueous phase viscosity. (Collaborating with Jason Wexler, Jiandi Wan and Howard Stone) |
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:: Interfacial Deformation :: Particle Collection and Hump Formation At A Liquid-Air Interface When a suspension of paramagnetic beads is in a sufficiently strong magnetic field gradient, a jet forms. Based on this approach, we report a technique for depositing an aggregate of paramagnetic beads on a substrate. In response to a weak magnetic field, all of the beads collect at the almost planar interface, which then deforms modestly as the field strength is increased to form a hump. Above a critical field strength, the hump where the beads have collected goes unstable to form a jet. We use high-speed videos to study the system’s hump-jet transition. We also propose an analytical scaling model that predicts the critical conditions for the transition by the balance of magnetic and capillary forces acting on the aggregate of beads. (Collaborating with Ian Griffiths, Zhenzhen Li, Pilnam Kim and Howard Stone) |
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Magnetic Capillary Rafts By balancing capillary attraction and magnetic repulsion, magnetized spheres form equilibrium patterns on an oil-water interface. The distance between particles is controlled by the magnitude of the magnetic field, which reaches a critical point when the field is sufficiently weak, the formation collapses, sinks, and drags some of the oil with it. (Collaborating with Krzysztof Sadlej and Howard Stone) |
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:: Capillarity Dynamics :: Droplet Splash Control With Tangential Velocity Drops falling onto a moving or inclined surface experience normal and tangential impact velocities. Asymmetrically triggering and inhibiting splashes is accomplished by varying the relative tangential velocity between the falling drop and the impacted surface. A model is developed that predicts the wetting to splashing transition, taking into account the tangential velocity. (Collaborating with Jacy Bird and Howard Stone) |
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Spreading and Jetting of Electrically Driven Films We study the electrically driven spreading of dielectric liquid films in wedge-shaped gaps across which a potential difference is applied. Our experiments are in a little-studied regime where the electrical relaxation time is long compared to the time for charge to be convected by the fluid motion. We observe that at a critical gap height, or critical normal electric field, the hump-shaped leading edge undergoes an instability in the form of a Taylor cone and periodic jetting ensues, after which traveling waves occur along the trailing thin film. We propose a convection-dominated mechanism for charge transport to describe the observed dynamics and rationalize the viscosity dependence of the dynamics. (Collaborating with Pilnam Kim, Camille Duprat and Howard Stone) |
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:: Publications and Presentations :: Peer-Reviewed Journal Publications
Peer-Reviewed Proceedings
Invited Talks and Seminars
Contributed Oral Presentations
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Copyright 2012 by Scott Tsai |
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