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 D7: Microfluidics: Methods and Devices II |
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Chair: Manu Prakash, Stanford University Room: 24C |
Sunday, November 18, 2012 2:15PM - 2:28PM |
D7.00001: Simultaneous measurement of the geometry and the internal 3D velocity field of a micron sized droplet confined in a channel using Astigmatism-PTV Tobias Mack, Christian Cierpka, Christian J. K\"{a}hler Astigmatism-PTV is a method that allows to measure with a single camera the fully three-dimensional, three-component velocity field. The technique is ideally suited for microfluidic velocity measurements without errors due to in-plane and out-of-plane averaging (Cierpka et al. Meas Scie Tech 21, 2010). Recently it was shown, that the interface between two fluids or the surrounding fluid and droplets or bubbles can be estimated as well with the technique (Rossi et al., Meas Scie Tech 22, 2010). In this contribution the advantages of both techniques are combined to measure the shape of a droplet inside a micro channel along with the internal 3D flow field of the droplet induced by the surrounding fluid. For the current investigation, particles were only distributed within oil-droplets. Therefore the shape of the droplet could be later reconstructed by the volumetric particle positions and the velocity can be estimated tracking the same particles in consecutive frames of the same dataset. The procedure allows the simultaneous determination of the shape and the droplet velocity as well as the inner flow field and offers a great potential for current research. [Preview Abstract] |
Sunday, November 18, 2012 2:28PM - 2:41PM |
D7.00002: Correlation Force Spectroscopy for Single Molecule Measurements Milad Radiom, Brian Robbins, John Walz, Mark Paul, William Ducker The sensitivity of force measurements in single molecule force spectroscopy is limited by noise resulting from thermal vibration of microcantilevers as well as hydrodynamic interaction with surrounding fluid. The thermal noise is particularly important in biomolecular studies since many biomolecular events have energy similar to the thermal noise: for a cantilever of spring constant k$_{s}\sim $0.1N/m the thermal noise sets a bound on force noise level of order (k$_{s}$k$_{B}$T)$^{1/2}\sim $20pN where k$_{B}$ and T are the Boltzmann constant and temperature. We describe a new technique which characterizes single polymer chains through measurement of correlations between thermally-stimulated vibrations of two closely spaced microcantilevers in fluid. We call this technique Correlation Force Spectrometry. CFS has lower noise than its counterpart single cantilever techniques since thermal noise in CFS only arises from the region where the two cantilevers interact due to fluid coupling, rather than from the entire cantilever. When a molecule is straddled between the two cantilevers, the correlation arises from the solvent as well as stiffness and internal damping of the molecule. We will present our results showing the effect of coupling through a single molecule of dextran. [Preview Abstract] |
Sunday, November 18, 2012 2:41PM - 2:54PM |
D7.00003: Micro-Particle Image Velocimetry using Microfabricated Diode Lasers Nicholas Judy Microfabricated diode lasers are interfaced with PDMS microchannels using in-plane waveguides. This allows for micro-PIV measurements to be obtained in the microchannel, without the requirement of large external Nd:YAG lasers, which are commonly used in traditional micro-PIV. The microfabricated diode laser has a peak wavelength of 532nm and produces up to 200mW of power. PDMS waveguides are designed in-plane and perpendicular as a part of the PDMS microdevices and coupled to the microfabricated laser using an optical fiber. Two types of waveguides are designed: a PDMS waveguide and a microfluidic waveguide. The PDMS waveguide involves a two-step soft-lithography process to give a difference in index, while the microfluidic waveguide uses oil as the waveguide medium. Limitations of the current technique and its potential impact on the future of micro-PIV will be presented. [Preview Abstract] |
Sunday, November 18, 2012 2:54PM - 3:07PM |
D7.00004: ABSTRACT WITHDRAWN |
Sunday, November 18, 2012 3:07PM - 3:20PM |
D7.00005: Simple and inexpensive micro-capillary devices for generating composite emulsions Erqiang Li, Jiaming Zhang, Sigurdur Thoroddsen All-glass microfluidic devices have attracted recent attention due to their excellent chemical robustness, bio-compatibility, optical properties and the ease of modifying their surface wettability. Herein we report the usage of a single tapered cylindrical glass capillary and microscope slides to fabricate simple and inexpensive all-glass microfluidic devices that are capable of producing monodisperse double emulsions. Triple emulsion droplets of water-in-oil-in-water-in-oil (W/O/W/O) or O/W/O/W phases can also be stably generated by adding another cylindrical capillary next to the outlet of the first capillary. In addition, by careful controlling the wettability of the inner surface of the first capillary, multi-component emulsion droplets of (gas and water)-in-oil-in-water ((G+W)/O/W) phases can also be stably produced. Such gas-laden emulsion drops may be beneficial for bio-related applications where oxygen supply is required. The relationship between the flow parameters and the resulting number of encapsulated droplets and the emulsion droplet sizes, have been investigated, for all of these various higher order emulsions. [Preview Abstract] |
Sunday, November 18, 2012 3:20PM - 3:33PM |
D7.00006: Pumpless Transport of Low Surface Tension Liquids in Surface Tension Confined (STC) Tracks Constantine Megaridis, Thomas Schutzius, Mohamed Elsharkawy, Manish Tiwari Surfaces with patterned wettability have potential applications in microfluidics, fog capture, pool boiling, etc. With recent fabrication advancements, surfaces with adjacent superhydrophobic and superhydrophilic regions are feasible at a reasonable cost; with properly designed patterns, one can produce microfluidic paths (a.k.a. surface tension confined or STC tracks) where a liquid is confined and transported by surface tension alone. The surface tension of water is relatively high (72 mN/m), as compared with oils ($\sim $25 mN/m) and organic solvents ($\sim $20 mN/m). This makes the design of STC channels for oils and organic solvents far more difficult. In this study, open STC tracks for pumpless transport of low-surface tension liquids (acetone, ethanol, and hexadecane) on microfluidic chips are fabricated using a large-area, wet-processing technique. Wettable, wax-based, submillimeter-wide tracks are applied by a fountain-pen procedure on superoleophobic, fluoroacrylic carbon nanofiber (CNF) composite coatings. The fabricated anisotropic wetting patterns confine the low-surface tension liquids onto the flow tracks, driving them with meniscus velocities exceeding 3 cm/s. Scaling arguments and Washburn's equation provide estimates of the liquid velocities measured in these tracks, which also act as rails for directional sliding control of mm-sized water droplets. The present facile patterned wettability approach can be extended to deposit micrometer-wide tracks. [Preview Abstract] |
Sunday, November 18, 2012 3:33PM - 3:46PM |
D7.00007: Selective pumping in a network: A novel bioinspired flow transport paradigm Yasser Aboelkassem, Anne Staples We present a new paradigm for selectively pumping and controlling fluids at the microscale in a complex network of channels, which we call ``selective pumping in a network.'' The approach is inspired by internal flow distributions induced by rhythmic wall contraction phenomena in insect tracheal networks. The selective pumping concept presented enables fluids to be transported, controlled and directed into specific branches in networks while avoiding other possible branching routes, without the use of any mechanical valves. The results presented here might help guide efforts to fabricate novel microfluidic devices with improved efficiency for mixing purposes and targeted drug delivery applications. In this study, both theoretical analysis and Stokeslets-meshfree computational methods are used to solve for the 2D viscous flow transport in an insect-like tracheal network of channels with prescribed moving wall contractions. The derived theoretical analysis is based on both lubrication theory and quasi-steady approximations at low Reynolds numbers. The meshfree numerical method is based on the method of fundamental solutions (MFS) that uses a set of singularized force elements ``Stokeslets'' to induce the flow motions. Moreover, the passive particle tracking simulation [Preview Abstract] |
Sunday, November 18, 2012 3:46PM - 3:59PM |
D7.00008: Hand-powered microfluidics: A membrane pump with a patient-to-chip syringe interface Brendan MacDonald, Max Gong, Trung Nguyen, David Sinton In this talk, an on-chip hand-powered membrane pump with a robust patient-to-chip syringe interface is presented. This approach enables safe sample collection, sample containment, integrated sharps disposal, high sample volume capacity, and controlled downstream flow with no electrical power requirements. Sample is manually injected into the device via a syringe and needle. The membrane pump inflates upon injection and subsequently deflates, delivering fluid to downstream components in a controlled manner. The device is fabricated from poly(methyl methacrylate) (PMMA) and silicone, using CO$_2$ laser micromachining. Pump performance is experimentally demonstrated and the behavior is subsequently modeled with reference to a resistor-capacitor electrical circuit analogy. Downstream output of the membrane pump is regulated, and scaled, by connecting multiple pumps in parallel. The device provides precisely controlled pumping rates and high volume throughput without any electrical power requirements. [Preview Abstract] |
Sunday, November 18, 2012 3:59PM - 4:12PM |
D7.00009: Digitally controlled droplet microfluidic system based on electrophoretic actuation Do Jin Im, Byeong Sun Yoo, Myung Mo Ahn, Dustin Moon, In Seok Kang Most researches on direct charging and the subsequent manipulation of a charged droplet were focused on an on-demand sorting in microchannel where carrier fluid transports droplets. Only recently, an individual actuation of a droplet without microchannel and carrier fluid was tried. However, in the previous work, the system size was too large and the actuation voltage was too high (1.5 kV), which limits the applicability of the technology to mobile use. Therefore, in the current research, we have developed a miniaturized digital microfluidic system based on the electrophoresis of a charged droplet (ECD). By using a pin header socket for an array of electrodes, much smaller microfluidic system can be made from simple fabrication process with low cost. A full two dimensional manipulation (0.4 cm/s) of a droplet (300 nL) suspended in silicone oil (6 cSt) and multiple droplet actuation have been performed with reasonable actuation voltage (300 V). By multiple droplet actuation and coalescence, a practical biochemical application also has been demonstrated. We hope the current droplet manipulation method (ECD) can be a good alternative or complimentary technology to the conventional ones and therefore contributes to the development of droplet microfluidics. [Preview Abstract] |
Sunday, November 18, 2012 4:12PM - 4:25PM |
D7.00010: Puch Card Programmable Microfluidics George Korir, Manu Prakash Microfluidic technology has emerged as a powerful means of manipulating fluids at the micro-scale with many promising applications, but universal programmability is still dependent on external control systems. With a focus on global-health and field applications, external control and pumps significantly hamper the use of microfluidic devices in harsh conditions. Punch Cards (simple tapes of paper) have been used to program early computers before the advent of electronic memory. With this analogy, we present a novel universal programming scheme for microfluidics using paper Punch Card tapes. We further characterize our devices as a function of readout speed, bit-error rate for a given operating conditions (Capillary and Reynolds number). A lumped element model was built to characterize the flow and serve as a predictive template for future designs. Operated by hand, the system requires no external sources of electricity or pumps. We demonstrate that Punch Cards provide an innumerable number of ways to program fluids including running complex protocols in the field with minimal training. [Preview Abstract] |
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