Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session N21: Microfluidic Physics II |
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Sponsoring Units: DFD Chair: Patrick Tabeling, Ecole Supérieure de Physique et de Chimie Industrielles de la Ville de Paris Room: Baltimore Convention Center 318 |
Wednesday, March 15, 2006 8:00AM - 8:12AM |
N21.00001: Microfluidics with Gel Emulsions Craig Priest, Enkhtuul Surenjav, Stephan Herminghaus, Ralf Seemann Microfluidic processing is usually achieved using single phase liquids. Instead, we use monodisperse emulsions to compartment liquids within microchannel geometries. At low continuous phase volume fractions, droplets self-organize to form well-defined arrangements, analogous to foam. While it is well-known that confined geometries can induce rearrangement of foam compartments at the millimeter-scale, similar dynamics are also expected for gel emulsions. We have studied online generation, organization and manipulation of gel emulsions using a variety of microchannel geometries. ``Passive'' reorganization, based on fixed channel geometries, can be supplemented by ``active'' manipulation by incorporating a ferrofluid phase. A ferromagnetic phase facilitates reorganization of liquid compartments on demand using an electromagnetic trigger. Moreover, coalescence between adjacent compartments within a gel emulsion can be induced using electrical potential. Microfluidics using gel emulsions will be well-suited for combinatorial chemistry, DNA sequencing, drug screening and protein crystallizations. [Preview Abstract] |
Wednesday, March 15, 2006 8:12AM - 8:24AM |
N21.00002: In-situ Generation of Focal Conic Defects in Flow of Smectic-A Liquid Crystals in Microchannels Shahab Shojaei-Zadeh, Shelley Anna The response of ordered phases of layered liquids such as smectic-A liquid crystals to flow is often dominated not by the direct coupling of flow to molecular degrees of freedom, but by the driven motion of defects in these systems. This is because flow generates instabilities in these systems that lead to the formation of defects. Most attention to date focuses on the global viscoelastic behavior and shear alignment of layered liquids, while little work has been done to understand defect motion and defect/flow interaction in these systems. Here we introduce a new approach, which enables simultaneous generation and observation of focal conic defects in pressure-driven flow of smectic-A liquid crystals. We observe that introducing a sudden change in the cross-sectional area of a microchannel via a small obstacle leads to the formation of a steady stream of defects. Generated defects move along the microchannel and interact with each other and with the flow itself. We measure the pressure drop and defect velocity and relate these to observed defect size and microchannel geometry. These results provide a novel way of probing nonlinear behavior of layered fluids under flow. [Preview Abstract] |
Wednesday, March 15, 2006 8:24AM - 8:36AM |
N21.00003: Folding and swirling of viscous threads in microfluidics Thomas Cubaud, Thomas G. Mason We study miscible multiphase flows with large viscosity contrast in microchannels. We investigate the folding instability of a viscous thread surrounded by a less viscous liquid that flow into a diverging microchannel. In this situation, extensional viscous stresses cause the thread to bend and fold rather than dilating in order to minimize dissipation. We show that diffusive mixing at the boundary of the thread can significantly modify the folding flow morphologies. We relate the folding frequency to the characteristic shear rate. We also examine the hydrodynamic coupling between multiple threads and the threads' rupturing into arrays of viscous swirls, reminiscent of the Kelvin-Helmholtz instability. [Preview Abstract] |
Wednesday, March 15, 2006 8:36AM - 8:48AM |
N21.00004: Observations of Tipstreaming and Thread Formation in a Microfluidic Flow Focusing Device Shelley Anna, Hans Mayer We present a novel method of generating sub-micron scale droplets in a microfluidic device. In particular we utilize the interaction of fluid motion and surfactant transport during the tipstreaming mode of droplet formation, which is achieved using a flow focusing microfluidic design. Tipstreaming is a mode of drop breakup in which daughter droplets, usually orders of magnitude smaller than the parent drops, are ejected from the pointed tips of parent droplets or bubbles. An attractive characteristic of tipstreaming is that droplets produced are not limited by the device feature size. In this work we observe that tipstreaming occurs within a specific range of capillary number (Ca $\sim $ 0.1 to 1, consistent with literature values for tipstreaming), flow rate ratio, and surfactant concentration, and that tipstreaming is preceded by the formation of thin threads that follow the pinchoff of larger droplets. We measure the thread diameter and length as a function of dimensionless parameters and discuss our results with respect to surfactant diffusion and kinetic timescales relative to flow timescales. [Preview Abstract] |
Wednesday, March 15, 2006 8:48AM - 9:00AM |
N21.00005: Drops and Jets in two Phase Coaxial Flows Andrew Utada, Alberto Fernandez-Nieves, David Weitz We discuss the transition from dripping to jetting from a nozzle in a coaxially flowing fluid. The fact that the outer fluid is viscous and moving affects the transition from dripping to jetting as well jet shape and drop formation mechanism. We relate the physics of drop formation to a recently reported microcapillary device (1,2) that generates monodisperse double emulsions. (1) A. S. Utada, E. Lorenceau, D. R. Link, P. Kaplan, H. A. Stone, D. A. Weitz, Science 308, 537 (2005) (2) E. Lorenceau, A. S. Utada, D. R. Link, G. Cristobal, M. Joanicot, D. A. Weitz, Langmuir in press, (2005). [Preview Abstract] |
Wednesday, March 15, 2006 9:00AM - 9:12AM |
N21.00006: Geometrically controlled jet-like instabilities in microfluidic two-phase flows Katherine Humphry, Armand Ajdari, Howard Stone, Alberto Fernandez-Nieves, David Weitz We demonstrate effects of confinement in microfluidic devices with a two phase co-flowing system. When the flow rate of the inner fluid is small compared to the flow rate of the outer fluid, and the resulting width of the inner fluid is smaller than the height of the channel, the inner fluid breaks into droplets, as expected for a three-dimensional system. On the other hand, when the width of the second phase becomes comparable to the height of the microfluidic device, Rayleigh capillary instabilities are suppressed, and the inner fluid forms a jet that does not break, as might be expected for a purely two-dimensional system. We show that by changing the dimensions of the microfluidic channel we can transition from a stable co-flow to drop break-up. The experimental results are compared with of model of this two-phase flow. [Preview Abstract] |
Wednesday, March 15, 2006 9:12AM - 9:24AM |
N21.00007: Playing with Microfluidic Droplets and Actuators Patrick Tabeling, Valessa Barbier, Herv\'{e} Willaime In the lab-on a chips of the future, flows will be handled at the microscale through mazes of microchannels using actuators. Here we concentrate on PDMS based microfluidic systems and we use actuators to introduce localized perturbations on a chip, close to where droplets are formed, i.e. near the intersection of a main and a side channel along which oil and water flows are driven. We observe Arnold tongues and devil staircases leading to the formation of regular or quasiperiodic-like droplets. These behaviors are well accounted for by modelling the system as a non linear oscillator driven by an external forcing. The characteristics of the regimes that are observed depend on the flow-rate conditions. In some range of flow-rates, we show that the droplet sizes can be varied by one order of magnitude by changing the actuation frequency, without modifying the flow-rates.These findings are used to understand the complex behavior of droplet emittors placed in parallel. [Preview Abstract] |
Wednesday, March 15, 2006 9:24AM - 9:36AM |
N21.00008: Droplet Traffic Control at a simple T junction Pascal Panizza, Wilfried Engl, Annie Colin, Armand Ajdari A basic yet essential element of every traffic flow control is the effect of a junction where the flow is separated into several streams. How do pedestrians, vehicles or blood cells divide when they reach a junction? How does the outcome depend on their density? Similar fundamental questions hold for much simpler systems: in this paper, we have studied the behaviour of periodic trains of water droplets flowing in oil through a channel as they reach a simple, locally symmetric, T junction. Depending on their dilution, we observe that the droplets are either alternately partitioned between both outlets or sorted exclusively into the shortest one. We show that this surprising behaviour results from the hydrodynamic feed-back of drops in the two outlets on the selection process occurring at the junction. Our results offer a first guide for the design and modelling of droplet traffic in complex branched networks, a necessary step towards parallelized droplet-based ``lab-on-chip'' devices. [Preview Abstract] |
Wednesday, March 15, 2006 9:36AM - 9:48AM |
N21.00009: Manipulation and stretching of bacteria and liposomes by Microfluidics Eyal Zussman, Wael Salalha Microfluidic technology can be useful in lab-on-a-chip applications of biological assays, environmental monitoring, detection of toxic materials, as well as for assembly of nano- and micro-scale objects into more complex systems. In this work we focused on the orientation of rod-shaped bacteria (Bacillus) by employing shear flow and a high rate elongation flow, and stretching of giant liposomes with diameter size of tens of microns, which can be used as a simplified model for cell behavior. This was achieved by flows of dilute rod-like bacteria and liposome suspensions within a micro-channel by means of a capillary-driven motion. Fluidic alignment situations were tested, firstly by Venturi-like flow which produces a sufficiently converging and diverging flow, and secondly by sink-like flow in a converging microchannel. In the first method we found that the converging part of the flow aligns rod-like bacteria, whereas the diverging part disaligns them, while in the second method the rod-like bacteria can perfectly align along the streamlines. In addition we used the same technology to test liposome deformation while they are flowing through a Venturi-like microchannel. The microfluidics devices were fabricated from poly(dimethylsiloxane) (PDMS) by soft lithographic techniques. [Preview Abstract] |
Wednesday, March 15, 2006 9:48AM - 10:00AM |
N21.00010: Continuous separation of serum from human whole blood within a microfluidic device John Davis, David Inglis, James Sturm, Robert Austin We were able to demonstrate separation of red and white blood cells from their native blood plasma, using a technique known as deterministic lateral displacement. The device takes advantage of asymmetric bifurcation of laminar flow around obstacles. This asymmetry creates a size dependent deterministic path through the device. All components of a given size follow equivalent migration paths, leading to high resolution. A subsequent version of the device will focus on the removal of platelets from whole blood. Samples will be extracted from the microfluidic device and analyzed by conventional flow cytometry. [Preview Abstract] |
Wednesday, March 15, 2006 10:00AM - 10:12AM |
N21.00011: Reversible Dialysis in a Microfluidic Formulator. Seila Selimovic, Jung-uk Shim, Seth Fraden In order to facilitate the screening of conditions for protein crystallization, we have been using the Microfluidic Formulator chip (Stephen Quake, PNAS Vol. 101, 40 ). This PDMS device allows us to mix up to 40 different reagents and protein solutions. We use this combinatorial approach along with a ``drop-on-demand'' method whereby we employ on-chip positive displacement pumps to form aqueous droplets containing protein and separate them by plugs of oil. Subsequently, the aqueous drops containing protein are guided by surface tension forces into storage chambers. To control the chemical potential of these sub-nanoliter protein samples, we fabricate reservoirs underneath the storage compartments. A thin PDMS membrane that is permeable to water, but not to protein or salt, separates the reservoirs from the storage chambers. Water can permeate into or out of the stored samples until the chemical potentials of the reservoir and the protein solution are equal leading to protein crystallization in some chambers. [Preview Abstract] |
Wednesday, March 15, 2006 10:12AM - 10:24AM |
N21.00012: A noble microfluidic device for protein crystallizations. Jung-uk Shim, Seth Fraden A high throughput, low volume microfluidic device has been constructed out of poly(dimethylsiloxane) elastomer. We have demonstrated that sub-nanoliter water-in-oil drops of protein solutions of different composition can be rapidly stored in individual wells, which allows screening of 1000 conditions while consuming a total of only 1 microgram protein on a 20 cm$^{2}$ chip. This reduction in protein needed for crystal screens allows high-throughput crystallization of mammalian proteins expressed in tissue culture. A significant advance over current microfluidic devices is that each pot is in contact with a reservoir through a dialysis membrane which only water and other low molecular weight organic solvents can pass, but not salt, polymer or amphiphile. This enables the concentration of all solutes in a solution to be reversibly, rapidly, and precisely varied in contrast to current microfluidic methods, which are irreversible. This microfluidic dialysis technology solves a major problem in protein crystallization, the decoupling of nucleation from growth. The device will also be useful for general studies of the phase behavior of protein solutions. [Preview Abstract] |
Wednesday, March 15, 2006 10:24AM - 10:36AM |
N21.00013: Shear induced particle migration in binary colloidal suspensions Denis Semwogerere, Eric R. Weeks, Jeffrey F. Morris We present experimental investigations of the spatial and temporal evolution of particle migration in pressure driven flows of Brownian particle suspensions. Binary suspensions of 1 $\mu $m- and 3 $\mu $m-diameter colloidal particles at a variety of concentration ratios and volume fractions are pumped through a 50 $\mu $m x 500 $\mu $m rectangular-cross-section capillary tube. Shear rate gradients caused by the resulting parabolic velocity profile drive particles away from the walls towards the center of the channel where the shear rate is lowest. Size segregation is observed. We measure the development of the size segregation by tracking the evolution of the particle concentration down the center of the tube of the small and large sized particles. The flows are directly imaged using high-speed confocal microscopy (up to 300 images/second). [Preview Abstract] |
Wednesday, March 15, 2006 10:36AM - 10:48AM |
N21.00014: Using permeable microcapsules to deliver nanoparticles on substrates Rolf Verberg, Alexander Alexeev, Anna Balazs We present a novel algorithm to simulate nanoparticles in the presence of a substrate, microcapsules and an externally driven flow. Here, the microcapsules consist of an elastic shell that encloses a fluid with either a dissolved chemical component or a suspension of nanoparticles that are small enough to be treated as so-called tracer particles (mutually non-interacting particles without excluded volume). The model couples a lattice-Boltzmann model for the fluid flow, a lattice-spring model for the elastic shell, and a Brownian dynamics model to simulate tracer trajectories. We then apply the model to simulate the release of nanoparticles from a microcapsule as it rolls along a substrate, as well as the subsequent particle adsorption on the wall. We study the effect of flow conditions, reaction kinetics, capsule elasticity, and capsules-substrate interaction on the rate of deposition and the size of the area of deposition at the substrate. The results provide guidelines for designing effective micro-scale delivery systems. [Preview Abstract] |
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