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 A7: Microfluidics: Methods and Devices I |
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Chair: Amir Hirsa, Rensselaer Polytechnic Institute Room: 24C |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A7.00001: Microfluidic synthesis of crimped fibers Janine Nunes, Hannah Constantin, Talal Al-Housseiny, Howard Stone Flexible high aspect ratio microstructures, such as microfibers, are of considerable interest for potential textile, rheological and life science applications. This research is focused on the microfluidic synthesis of wavy or crimped polymeric microfibers. It is known that highly viscous liquid threads sheathed by a low viscosity continuous phase liquid can buckle when allowed to flow through a microchannel where there is an increase in channel cross-sectional dimensions. These structures are transient and evolve during flow to form piles, relax to straight threads or coalesce. Here we present the first example where buckling is triggered by the initiation of a polymerization reaction in a liquid thread that does not initially exhibit buckling (because of the low viscosity ratio between thread and continuous phase), and the subsequent preservation of the buckled morphology through completion of the crosslinking reaction. The resulting microfibers have highly uniform and reproducible morphology. By changing the location in the channel where the reaction is initiated, as well as the flow rates, the degree of waviness of the microfibers can be controlled. Current efforts are focused on developing a physical understanding of this process. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A7.00002: The use of sequences of pillars to engineer fluid cross-sectional shape \textit{via} inertial flow deformations Hamed Amini, Mahdokht Masaeli, Elodie Sollier, Yu Xie, Baskar Ganapathysubramanian, Howard A. Stone, Dino Di Carlo Control of fluid streams is useful in biological processing, chemical reaction engineering, and creating structured materials. We use cylindrical pillars to induce significant deformations in laminar flow. Numerical simulations predict that as fluid passes centrally positioned pillars in a straight microchannel, the fluid parcels near the channel centerline move towards the side walls, while fluid parcels near the top and bottom walls move towards the center. This inertial phenomenon (1 $\la$ \textit{Re} $\la$ 100) in effect creates a set of \textit{net} rotational secondary flows within the channel. The existence of four dominant operating modes (based on the number and direction of the induced secondary flows) is also demonstrated. We show how using the basic deformations on miscible co-flows of water and fluorescent dye we can manipulate and shape the cross-section of the colored stream. Hierarchical flow deformation operations can be integrated to execute sophisticated programs and render complex flow-shapes. We can numerically predict the deformation near a single pillar with high precision and accordingly, predict the total transformation function of any potential program. Consequently, a user can use a library of pre-simulated motions and engineer a flow-shape of interest quickly, at a low cost, and with high accuracy, an ability which we demonstrate. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A7.00003: Using in-fiber fluid instabilities for the scalable production of structured spherical particles Ayman Abouraddy, Joshua Kaufman, Guangming Tao, Soroush Shabahang, Esmaeil-Hooman Banaei, Daosheng Deng, Xiangdong Liang, Steven Johnson, Yoel Fink Developing efficient pathways to the fabrication of spherical particles is needed for a wide range of applications ranging from drug delivery to cosmetics. A heretofore unanswered technological challenge is the development of a single process for fabricating particles over a wide range of sizes, from a variety of materials, and in different structures. Here we harness the high-volume process of fiber drawing to create a scalable nanomanufacturing approach to address this challenge. We make use of a new class of multi-material fibers drawn from a macroscopic ``preform'' combined with the recent observation of an in-fiber Plateau-Rayleigh capillary instability (PRI). A macroscopic cylindrical preform is drawn into an extended fiber and subsequent thermal treatment induces the PRI at the heterogeneous interfaces along the fiber, causing the core to break up into a necklace of uniformly sized spheres held stationary in isolation in a cladding matrix. This process enables the fabrication of structured spherical particles from a variety of materials spanning an unprecedented range of sizes: from 2 mm down to 20 nm. By structuring the core at the preform stage, we produce multi-material core-shell particles, ``Janus'' particles, and multi-sectioned ``beach ball'' particles. By combining multiple cores in the same fiber we demonstrate an exceptionally high level of parallelization, rendering the process scalable. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A7.00004: Flow-induced protein crystallization: Macroscopic effects on 2D crystals James Young, David Posada, Amir Hirsa, Juan Lopez Proteins must first be crystallized before their molecular structure can be studied in detail. However, crystallizing protein is a challenging task which is often met with limited success. Although 2-D protein crystals at the air/water interface are usually obtained under quiescent conditions, it was recently shown that crystallization can be enhanced by a shearing flow. Here we examine the relationship between Reynolds number and the crystal growth process using the deep-channel surface viscometer geometry. It consists of an annular region bounded by stationary inner and outer cylinders and driven by a constant rotation of the floor. The interfacial velocity measurements are compared to Navier-Stokes computations with the Boussinesq-Scriven surface model. The interfacial film is lifted onto a solid substrate, and the protein crystals are observed via optical and atomic force microscopy. For a particular protein surface concentration, a Reynolds number threshold has been identified for flow-induced crystallization. This flow geometry also allows for the determination of the surface shear viscosity, which provides a quantitative measure of the mesoscale interactions associated with protein crystallization. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A7.00005: The Correlated Dynamics of a Pair of Tethered Microcantilevers in a Viscous Fluid Brian Robbins, Milad Radiom, John Walz, William Ducker, Mark Paul Understanding the dynamics of biomolecules or polymers in a fluid environment is an important challenge. One approach is to tether a molecule between the ends of two Brownian driven microcantilevers and to measure the change in their correlated dynamics. However, the cantilever dynamics is also correlated due to the motion of the intervening viscous fluid. An important question is whether the correlations due to a tethered molecule can be measured in the presence of the fluid coupling for configurations accessible to experiment. We present experimental measurements of the correlated motion of two microcantilevers in water without a tethered molecule. Using the fluctuation-dissipation theorem with deterministic finite-element simulations we compute the correlated dynamics for laboratory conditions. Our numerical results show very good agreement with experimental measurement. We next include a linear spring between the cantilever tips to model a tethered molecule and quantify the dynamics of the cantilever pair for a wide range of conditions. Our results provide physical insights into the signature of a tethered molecule and quantify the force, time, and length scales that are accessible to current technologies. [Preview Abstract] |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A7.00006: Measuring ultralow interfacial tensions with magnetic particles in microchannels Scott Tsai, Jason Wexler, Jiandi Wan, Howard Stone Ultralow interfacial tension solutions have interfacial tensions 1,000 times, or more, smaller than typical oil-water solutions. We describe a technique that measures ultralow interfacial tensions by magnetically deflecting paramagnetic spheres in a co-flow microfluidic device. Our method involves tuning of the distance between the co-flowing interface and the magnetic field source, and observing the behavior of the magnetic particles as they approach the liquid-liquid interface -- the particles either pass through or are trapped. We demonstrate the effectiveness of this technique for measuring very low interfacial tensions by testing solutions of different surfactant concentrations, and we show that our results are comparable with measurements made using a spinning drop tensiometer. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A7.00007: Ferrodroplets: a Global Clock for Droplet Microfluidics Georgios Katsikis, Manu Prakash A fluidic analogue to magnetic bubble computer memory is proposed as a novel propagation mechanism for droplet microfluidics. We designed a prototype microfluidic device where ferrofluid droplets are actuated along a 2-D plane using soft magnet patterns under the influence of rotating magnetic fields. The state of the system is dependent on occupancy of fluid droplets and the track geometry. The propagation characteristics of droplets are studied experimentally by varying operation parameters such as the magnitude and frequency of in-plane magnetic fields and the length scale of the device. The experimental findings are juxtaposed with scaling arguments and numerical simulations. Applications for this device as a universal clocking mechanism for droplet microfluidics are discussed.~ [Preview Abstract] |
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