Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H6: Microfluidics: General II |
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Chair: David Saintillan, University of Illinois at Urbana-Champaign Room: 24B |
Monday, November 19, 2012 10:30AM - 10:43AM |
H6.00001: Development of a modified Hess-Murray law for non-Newtonian fluids in bifurcating micro-channels David Emerson, Robert Barber Microfluidic manifolds frequently require the use of bifurcating channels and these can be used to create precise concentration gradients for chemical applications. More recently, novel devices have been attempting to replicate vasculatures or bronchial structures occurring in nature with the goal of creating artificial bifurcations that mimic the basic principles of designs found in nature. In previous work, we have used the biological principles behind the Hess-Murray Law, where bifurcating structures exhibit a constant stress profile and follow a third-power rule, to enable rectangular or trapezoidal micro-channels to be fabricated using conventional lithographic or wet-etching techniques. Using biological principles to design man made devices is generally referred to as biomimetics and this approach has found success in a range of new and emerging topics. However, our previous work was limited to Newtonian flows. More recently, we have used the Rabinovitsch-Mooney equation to be able to extend our analysis to non-Newtonian fluids. This has allowed us to develop a new rule that can provide a design criterion to predict channel dimensions for non-Newtonian flows obeying a constant stress biological principle. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H6.00002: Fluidic Control by Capillary and Maxwell Stresses for Liquid Printing of Small Metallic Structures Gerry Della Rocca, Sandra Troian Liquid dosing strategies for microfluidic applications normally rely on interior flow driven by external pressure gradients. To maintain a constant flow rate, the effective pressure drop over a given length conduit must scale inversely as the fourth power in the conduit radius, as prescribed by the Hagen-Poiseuille relation. For micron scale capillaries, this constraint requires enormous pressure gradients enforced by large pumps, cascades of tubing material, and electronic sensors. This burden, coupled with the likelihood of occlusions due to gas bubbles, contaminant or carrier particles, limits the usefulness of enclosed flow for transporting very small fluid volumes. Capillary flow on substrates etched with slender open grooves provides a much simpler, less expensive, efficient and reliable method of transport. When coupled with flow modulation by remote electric fields, the flow can be metered effectively and much more rapidly. We discuss the steady state, transient and oscillatory flow of a perfectly conducting liquid within an open conduit subject to a spatially and temporally varying electric field. The geometry investigated is geared toward applications involving liquid printing of small metallic elements for large-area circuits and photovoltaic displays. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H6.00003: The hydrodynamic interaction between a soft particle and a permeable surface Guy Ramon, Herbert Huppert, Howard Stone Practical experience has shown that permeable surfaces are more prone to deposition and, consequently, foul more than other non-permeable surfaces. This is due to the presence of an additional velocity component perpendicular to the surface. A particle will translate towards the surface at the same velocity as the background fluid; however, at close approach, particle interaction with the surface creates additional forces resulting from electrostatic, dispersion, polar and, the focus of this work, hydrodynamic interactions. A lubrication approximation is used to derive an equation for the pressure field; coupling with the elastic response of the particle allows evaluation of elastic interaction when the particle and/or surface are not completely rigid (e.g., soft polymer interfaces, bacteria cells, etc.). Useful asymptotic forms are derived, offering a clear and intuitive understanding of the force acting on a particle at close approach to a surface and its dependence on particle size, shape, the background flow and permeability of the surface. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H6.00004: Numerical analysis of radiation- and streaming-induced microparticle acoustophoresis Rune Barnkob, Peter Barkholt Muller, Henrik Bruus, Mads Jakob Herring Jensen We present a numerical analysis of the acoustophoretic motion of microparticles suspended in a liquid-filled microchannel excited with an ultrasound field tuned to resonance. The imposed first-order ultrasound field generates second-order fields leading to two particle forces with a non-zero time-average: the acoustic radiation force from sound-wave scattering off the particles and the Stokes drag force from the induced acoustic streaming flow. We consider a viscous heat-conducting liquid and non-interacting spherical particles. The model is based on the thermoviscous acoustic equations and takes into account the micrometer-thin but crucial viscous boundary layers at rigid walls. Using a numerical tracking scheme, we quantify the acoustophoretic particle velocities for experimentally relevant parameters. We characterize the transition from radiation- to streaming-dominated acoustophoretic motion as function of particle size, channel geometry, and material properties. See also Muller \textit{et al.}, Lab Chip \textbf{12}, in press (2012). [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H6.00005: Experimental analysis of radiation- and streaming-induced microparticle acoustophoresis Massimiliano Rossi, Alvaro Marin, Christian J. K\"{a}hler, Per Augustsson, Thomas Laurell, Peter B. Muller, Rune Barnkob, Henrik Bruus We present an experimental analysis of the acoustophoretic motion of microparticles suspended in a liquid-filled acoustofluidic microchannel. This analysis intends to provide an experimental validation and support to very recent numerical and analytical models of radiation- and streaming-induced microparticle acoustophoresis (see Muller et al., Lab Chip 12, in press, 2012). For the experiments, we used a suspension of water and spherical polystyrene particles in a straight microchannel with rectangular cross section, actuated in its 1.94-MHz resonance by means of a piezoelectric transducer. The particles were labeled with a fluorescent dye and their motion was observed using an epifluorescent microscope. For the analysis, the Astigmatism Particle Tracking Velocimetry (APTV) technique was used to measure the three-dimensional trajectories and velocities of the particles with high precision and resolution (Cierpka et al., Meas Sci Technol 22, 2011). The experiments were performed for different particle sizes, ranging from 0.5-$\mu$m particles, dominated by the Stokes drag force induced by the acoustic streaming of the flow, to 5-$\mu$m particles, dominated by the acoustic radiation force. The results agree well with the analytical and numerical predictions. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H6.00006: Inertial particle trapping and transport in viscous streaming Kwitae Chong, Jeff D. Eldredge A probe undergoing rectilinear oscillation creates a steady large-scale circulatory flow, which is conventionally called viscous streaming. This streaming flow, generated by the nonlinear interaction of the primary oscillatory motion, can provide an appealing option in micromanipulation, such as trapping, positioning and transport of a discrete particle. In this study, the streaming flow around a circular cylinder is obtained from previous analytical solution (by asymptotic expansion in small amplitude). The motion of an inertial particle in this flow is obtained by integrating the Maxey-Riley equation, in which the wall effect is newly considered. It has been observed in our previous work that, under certain conditions, the inertial particle is trapped inside the center of a streaming cell near the probe; here, the manner of trapping is re-explored under various choices of physical parameters, such as Reynolds number, particle size and density. We also extend the study to various arrangements of multiple oscillating probes by using high-fidelity computations to simulate particle transport between probes. In particular, we demonstrate systematic particle transport between probes by selectively stopping and starting the oscillatory motion of adjacent probes. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H6.00007: Drops subjected to surface acoustic waves: flow dynamics Philippe Brunet, Michael Baudoin, Olivier Bou Matar Ultrasonic acoustic waves of frequency beyond the MHz are known to induce streaming flow in fluids that can be suitable to perform elementary operations in microfluidics systems. One of the currently appealing geometry is that of a sessile drop subjected to surface acoustic waves (SAW). Such Rayleigh waves produce non-trival actuation in the drop leading to internal flow, drop displacement, free-surface oscillations and atomization. We recently carried out experiments and numerical simulations that allowed to better understand the underlying physical mechanisms that couple acoustic propagation and fluid actuation. We varied the frequency and amplitude of actuation, as well as the properties of the fluid, and we measured the effects of these parameters on the dynamics of the flow. We compared these results to finite-elements numerical simulations. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H6.00008: Surface Acoustic Wave (SAW) based Microfluidics for Particle and Droplet Manipulation Ye Ai, Babetta L. Marrone Acoustics has emerged as one of the most promising non-invasive techniques for particle and droplet manipulation in microfluidics. Surface acoustic wave (SAW) based microfluidic devices are developed to manipulate micron-sized particles and discrete droplets. When solid particles are immersed in a standing SAW, the resulting acoustic radiation force acting on the particles can drive the particles into the pressure node, resulting in particle focusing phenomenon. The amplitude of the acoustic radiation force highly depends on the particle properties, leading to different acoustic responses for different types of particles. Separation of two types of fluorescent particles is demonstrated using the developed SAW-based microfluidic device. Numerical simulations are performed to study the generation of the standing SAW and the particle separation which is in good agreement with the experimental results. When a SAW propagates through a droplet in contact with the piezoelectric substrate, the SAW partially leaks into the droplet and exerts an acoustic streaming force in the droplet, which can move the droplet in the direction of SAW propagation. It is further found that a curved SAW transducer is able to focus SAW into a very narrow beam and in turn focus randomly distributed droplets into a specific target. It is demonstrated that focused SAWs can be more efficient than uniform SAWs for droplet actuation in microfluidics. [Preview Abstract] |
Monday, November 19, 2012 12:14PM - 12:27PM |
H6.00009: Buckling and Transport of Semiflexible Filaments in Cellular Flows Harishankar Manikantan, David Saintillan A slender elastic filament placed in a lattice of counter-rotating vortices is known to move as a random walker. Such a cellular flow has also been compared to experiments on actin transport across myosin beds. We present numerical results that for the first time include the effect of Brownian fluctuations on these transport properties. A semiflexible filament is modeled based on slender-body theory for Stokes flow, and incorporates Euler-Bernoulli elasticity as well as thermal fluctuations. We consider inextensible biopolymers of length of the order of persistence length (actin, microtubules etc). In a hyperbolic external flow, such an elastic filament is susceptible to a buckling instability that drives it between stagnation points in the lattice. The velocity distribution of the filament is bimodal in the non-Brownian case, and systematically flattens out with thermal fluctuations. Also, filaments are shown to spend time waiting in a cell before being pushed out by a random fluctuation. Such a waiting time distribution might indicate sub-diffusive transport as against diffusive transport seen in the non-Brownian case. We also study the distribution of mass of the filament across the lattice, and discuss how persistence length affects its preferred position in a unit cell. [Preview Abstract] |
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