Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session BA: Micro Fluids: Fluidic Devices II |
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Chair: Carl Meinhart, University of California, Santa Barbara Room: Salt Palace Convention Center 150 A-C |
Sunday, November 18, 2007 10:34AM - 10:47AM |
BA.00001: Rapid Generation of Bionanoparticles Using Surface Wave Atomization and Nonuniform Evaporation Mar Alvarez, Leslie Yeo, James Friend We present the generation of relatively monodisperse nanoparticles via a two-step process, combining surface wave atomization through MHz-order Rayleigh instabilities induced on a source fluid and nonuniform evaporation post-atomization to obtain loosely bound agglomerations of biocompatible and degradable polymer nanoparticles. The process forms particles from the source fluid in fractions of a second, far faster than with other formation techniques, and we illustrate methods for controlling the particle diameter and morphology through a combination of polymer concentration, critical micelle concentration templating, and surface wave frequency and standing wave ratio, all in a handheld microdevice. High-speed microvideography, along with TEM, SEM, AFM and scanning mobility particle sizer data provides evidence to support our modelling of the atomization process, and the use of the technique to encapsulate bovine serum albumin (BSA), fluor-tagged biotin and fluorescent polystyrene particles demonstrate useful applications of the method. [Preview Abstract] |
Sunday, November 18, 2007 10:47AM - 11:00AM |
BA.00002: Evaluation of microfluidic Chips for Cell-sorting Applications Carolyn Ren, Jay Taylor, G.D. Stubley The design of a miniaturized cell-sorting device must follow strict parameters such as applied voltage, efficiency of cell-separation, repeatability, size, flow control, and cost, among others. Current designs have achieved successful levels of cell-isolation. However, further improvements in the microfluidic chip design are important for incorporation into larger systems. This study evaluates specific design modifications that contribute to reduce required applied potential aiming for portable devices, improved operation reliability by minimizing induced pressure disturbance when electrokinetic pumping is employed and incorporating online filters to reduce channel blockage, and improved flow control by incorporating directing streams achieving dynamic sorting and counting. The chip designs fabricated in glass and polymeric materials include asymmetric channel widths for sample focusing, nonuniform channel depth for minimizing induced pressure disturbance, directing streams to assist particle flow control, and online filters for reducing channel blockage. Fluorescence-based visualization of electrokinetic focusing, flow field phenomena, and dynamic cell-sorting demonstrate the advantages of the chip design. [Preview Abstract] |
Sunday, November 18, 2007 11:00AM - 11:13AM |
BA.00003: Driving Cell Seeding Using Vibration Induced Surface Waves Haiyan Li, James Friend, Leslie Yeo The ability to load cells into scaffold matrices is an important step in\textit{ in-vitro} cell culturing. Efficient and rapid cell seeding is however difficult and has traditionally been carried out using a static method by allowing gravity to drive the perfusion of the cell suspension into the porous scaffold. Nevertheless, due to the large capillary pressures associated with the small scaffold pore dimensions, the static cell seeding method is both slow and inefficient; the majority of cells are distributed close to the surface of the scaffold due to the inability of the fluid to penetrate deep into the scaffold. By driving the liquid into the scaffold using small amplitude surface vibrations on a piezoelectric substrate, we demonstrate that the cells can be infused much quicker (approximately 10 seconds) than if allowed to perfuse by gravity alone, which requires seeding times in excess of 30 minutes. Greater penetration of the fluid and hence the cells into the scaffold is also achieved with the vibration forcing, thus giving rise to a more uniform cell distribution within the scaffold. Moreover, we have verified that 80{\%} of the yeast cells seeded by the surface waves remained viable. [Preview Abstract] |
Sunday, November 18, 2007 11:13AM - 11:26AM |
BA.00004: Nature-inspired polymer actuators for micro-fluidic mixing. Jaap M.J. den Toonder, Femke Bos, Judith de Goede, Patrick Anderson One particular micro-fluidics manipulation mechanism ``designed'' by nature is that due to a covering of beating cilia over the external surface of micro-organisms (e.g. Paramecium). A cilium can be viewed as a small hair or flexible rod (in protozoa: typical length 10 microns and diameter 0.1 microns) which is attached to the surface. We have developed polymer micro-actuators, made with standard micro-technology processing, which respond to an applied electrical or magnetic field by changing their shape. The shape and size of the polymer actuators mimics that of cilia occurring in nature. Flow visualization experiments show that the cilia can generate substantial fluid velocities, in the order of 1 mm/s. In addition, using specially designed geometrical configurations of the cilia, very efficient mixing is obtained. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices. [Preview Abstract] |
Sunday, November 18, 2007 11:26AM - 11:39AM |
BA.00005: Manipulating a Bouncing Drop by the Use of Virtual Drops Marcos Caballero, Michael Schatz Coalescence of a droplet with a fluid bath can be inhibited by oscillating the bath vertically. We propose a form of transport for this system that is non-destructive, reprogrammable, and near-frictionless. Below the Faraday threshold, stable bouncers can be moved using a pulsed infrared laser impinging on the fluid surface. The motion is similar to the interaction of two stable bouncing drops except it is repulsive at short range. The pulsed laser deformation, a virtual bouncer, can form a bound state with a single bouncing droplet. Near the Faraday threshold, walkers can be redirected using selective heating of the substrate. Laser pulses act as singular sources of waves; virtual bouncers. Through this wave interaction, non-trivial trajectories are observed. The transport of these nanoliter sized droplets is quite fast when compared to other forms of transport, on the order of centimeters per second. [Preview Abstract] |
Sunday, November 18, 2007 11:39AM - 11:52AM |
BA.00006: Concentration of Micro and Nanoparticles in Sessile Droplets Using Asymmetric Surface Wave Irradiation James Friend, Leslie Yeo, Haiyan Li A rapid particle concentration method in sessile droplets and confined fluid chambers has been developed using asymmetric surface wave propagation on a substrate upon which the droplet is placed. Nanometre-order vibration induced along the substrate at frequencies from 8 to 125 MHz generate a combination of forces upon suspended particles and the fluid droplet itself via diffraction to provide localized agglomeration of nanoparticles into microstructures, followed by rapid collection of the microstructures to a single point at the centre of the droplet in about 2 to 30 seconds. This is far faster than other currently available particle concentration mechanisms due to the large convective velocities achieved using the device. The ability to control the collection via surface wave power and the effect of scale on the collection time and scheme of agglomeration are explained via a physical model, verified using fluorescent polystyrene particles from 20 nm to 45 microns in diameter. The usefulness of the method for bioparticles is illustrated through rapid concentration of yeast and mouse mesenchymal stem cells which remain viable and functional after concentration. [Preview Abstract] |
Sunday, November 18, 2007 11:52AM - 12:05PM |
BA.00007: Remote Detection of Explosive Molecules by a Microfluidic SERS Device Brian Piorek, Seung Joon Lee, Martin Moskovits, Sanjoy Banerjee, Carl Meinhart Free-surface microfluidics (FSF) is combined with surface-enhanced Raman spectroscopy (SERS) to detect trace explosives vapors at room temperature and pressure. A free surface, with a large surface to volume ratio, is created using an open microchannel. Since surface tension is a dominant force at the microscale, it can be used to confine the fluid in the microchannel and create a pressure gradient to drive the flow with velocities ranging from $\sim $ 1um/s - 1mm/s. The curvature of the free surface is measured by confocal microscopy in order to determine the local Laplace pressure in the free-surface microchannel flow. The system has been used for the molecular-specific detection of vapor emanated from explosives such as DNT, TNT and picric acid. The system does not show signs of performance degradation from common interferents such as saturated gasoline vapor and perfume. [Preview Abstract] |
Sunday, November 18, 2007 12:05PM - 12:18PM |
BA.00008: Microfluidic Evaporation for Phase Diagram Screening Patrick Moreau, Jean-Baptiste Salmon, Jacques Leng We use a pervaporation-based microfluidic device to concentrate solutions in a controlled way. This allows us to develop chips for phase diagram screening,and to study both fundamental and technological issues, such as the impact of kinetic pathway of concentration on a variety of aqueous solutions (colloids, surfactants, polymers and mixtures of thereof). The first part of the presentation will deals with the characterization of the concentration process (including analytical results, numerical simulations, and experimental observations). It will be shown that our device is well suited for a wide range of particle sizes in the colloidal range. In the second part, we will present results obtained on several systems during (along) the concentration process (surfactants and polymers). On-chip FRAP (fluorescence recovery after photobleaching) and microrheology measurements will be presented in addition to optical and fluorescence microscopy. [Preview Abstract] |
Sunday, November 18, 2007 12:18PM - 12:31PM |
BA.00009: Controlling PDMS surfaces properties in microfluidic systems: a way to control multiphase flows Herv\'e Willaime, Valessa Barbier, Pol Grasland-Mongrain, Yves Hennequin, Nicolas Pannacci, Patrick Tabeling, Michael Tatoulian PDMS is a popular material, well adapted for the rapid fabrication of microfluidic systems. Its disadvantages are known: one of them is an inability to offer reliable and convenient-to-control surface properties. For multiphase flows, this induces limitations on the type of emulsions we may produce, since the external phase must in all cases fully wet the channels walls. In this paper we propose different methods for coating PDMS surfaces to make the surface hydrophilic. We propose 2 different methods to polymerize acrylic acid on PDMS: the first is a coating by plasma (dry) and the second is an in situ coating (first proposed by Eugenia Kumacheva's group) by flowing a solution of acrylic acid and benzophenon as UV photoinitiator. Both methods permit a localized coating, and it is so possible to pattern PDMS surfaces by alterning hydrophilic and hydrophobic surfaces. We will show examples of applications obtained in textured microchannels. [Preview Abstract] |
Sunday, November 18, 2007 12:31PM - 12:44PM |
BA.00010: A Microfluidic Network for Investigating the Flow of Layered Liquids under Confinement Shahab Shojaei-Zadeh, Shelley L. Anna The flow response of ordered phases of layered liquids such as smectic-A liquid crystals is dominated by the driven motion of defects in these systems. Shearing motions lead to dilatation of the layers, which generates an instability that develops into defects. While this basic concept is accepted, little experimental work exists to quantify defect motion and defect-flow interactions once the instabilities have developed. We probe these motions using pressure-driven flow in PDMS-based microchannels. The microchannel surfaces are treated such that a specific molecular anchoring is imposed. Confinement, combined with specific surface anchoring, leads to the formation of well-ordered static defect textures with characteristic sizes in the tens of microns. To establish and control a known pressure difference across a microchannel filled with liquid crystal, we introduce a simple microfluidic network capable of controlling both flow rate and pressure drop across a target microchannel segment. By introducing a known input flow rate to this network, we establish a known pressure difference across the target segment. We measure this pressure difference along with the defect velocity and relate these to the initial defect size and arrangement. These results demonstrate a novel method for probing nonlinear flow behavior of microstructured liquids. [Preview Abstract] |
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