Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D20: Focus Session: Microfluidics and Nanofluidics III - Pattern Formation and Droplets |
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Sponsoring Units: DPOLY DFD GSNP Chair: John Royer, NIST Room: 405 |
Monday, March 3, 2014 2:30PM - 3:06PM |
D20.00001: Whipping of electrified jets Invited Speaker: Alberto Fernandez-Nieves Whipping is a non-axisymmetric instability characteristic of electrified jets. It is exploited in electrospinning to reduce the average diameter of the fibers that result in this process. In air, it usually manifests in a chaotic fashion and thus, its structure and properties have been hard to quantify experimentally. We show that by applying electric fields to coflowing liquids, we can generate steady-state whipping structures. This allows for a detailed characterization of this non-axisymmetric instability. In addition, we will also discuss other emission regimes not typically seen in electrospray. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D20.00002: Ferrofluid-based reconfigurable optofluidic switch Gianna Valentino, Eric Mongeau, Yu Gu We present a low-cost, reconfigurable optofluidic switch exploiting both the optical and magnetic properties of a water-based ferrofluid. This switch is composed of an integrated waveguide orthogonally crossing a microfluidic channel containing high-index oil and a ferrofluid plug. The switch is turned ``ON'' or ``OFF'' by the movement of the ferrofluid plug in response to an external magnetic field. Each switch exhibits a high contrast ratio and millisecond response time. Parallel geometries for both mode and multi-mode waveguides are shown. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D20.00003: Macroscale Boltzmann statistics: Recreating statistical mechanics with a mechanically derived temperature Kyle Welch, Eric Corwin We use chaotic Faraday waves to create a macroscopic 2D pseudothermal environment in which we study surface tension mediated interactions between buoyant particles. The chaotic surface waves create an effective temperature that is proportional to the driving amplitude. We use Boltzmann statistics to measure interparticle potentials by tracking the distribution of particle separations. This allows us to study interparticle interactions without interfering with the dynamics of the system. We explore various systems of multiple interacting particles, focusing particularly on systems of particles linked together in a chain with stiff links, in analogy to polymers. We explore the response of these systems to changes in parameters such as effective temperature, particle size, shape and wetting properties, as well as linker spacing and total chain length. We report on the effective entropic spring-like behavior of such systems in the limit of large chain length. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D20.00004: Pattern formation of Dictystelium discoideum in the presence of laminar flow and cAMP pulses Azam Gholami, Oliver Steinbock, Vladimir Zykov, Eberhard Bodenschatz Dictyostelium discoideum (D.d) amobae undergo starvation-induced multicellular development in which single cells aggregate chemotactically towards cAMP signals emitted periodically from an aggregation center. We are investigating spatiotemporal pattern formation of D.d. cells under the presence of a laminar flow. Starved cells are loaded into a straight millifluidic device with an external flow and cell response to the signaling molecule cAMP is monitored indirectly using dark-field microscopy. The observed contraction waves develop simultaneously over the entire channel, are propagating only in flow direction, and have curved wave fronts resembling the parabolic flow profile. The wave dynamics analysis shows that the wave velocity is locked to the flow velocity and yields a wave period of T0~6 min, which matches the typical oscillation period of extracellular cAMP in spatial homogeneous, well-stirred systems. We apply a small cAMP perturbation at the inlet region of the channel and observe the spatiotemporal response of the cells as the pulse is propagating down the channel. The results show that D.d. cells are in the oscillatory regime and the system can be forced within resonance tongue. We compared our results with analytical and numerical analysis of Goldbeter model. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 4:18PM |
D20.00005: Microfluidic Droplet Dehydration for Concentrating Processes in Biomolecules Invited Speaker: Shelley Anna Droplets in microfluidic devices have proven useful as picoliter reactors for biochemical processing operations such as polymerase chain reaction, protein crystallization, and the study of enzyme kinetics. Although droplets are typically considered to be self-contained, constant volume reactors, there can be significant transport between the dispersed and continuous phases depending on solubility and other factors. In the present talk, we show that water droplets trapped within a microfluidic device for tens of hours slowly dehydrate, concentrating the contents encapsulated within. We use this slow dehydration along with control of the initial droplet composition to influence gellation, crystallization, and phase separation processes. By examining these concentrating processes in many trapped drops at once we gain insight into the stochastic nature of the events. In one example, we show that dehydration rate impacts the probability of forming a specific crystal habit in a crystallizing amino acid. In another example, we phase separate a common aqueous two-phase system within droplets and use the ensuing two phases to separate DNA from an initial mixture. We further influence wetting conditions between the two aqueous polymer phases and the continuous oil, promoting complete de-wetting and physical separation of the polymer phases. Thus, controlled dehydration of droplets allows for concentration, separation, and purification of important biomolecules on a chip. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D20.00006: Chiral Double Emulsions: Breaking Symmetry with Microfluidics Laura Adams, Thomas Kodger, Jiawei Yang, David Weitz We will present a new microfluidic encapsulation technique for generating chiral double emulsions, drops inside of drops, with a specific handedness. In presenting the data, we will discuss the effect of the number, size and composition of encapsulated drops on the double emulsion structure before and after pinching off from an injection capillary in a microfluidic device. These results support theoretical models in which the pinch-off mechanism is in direct analogy to boundary layer considerations. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D20.00007: Droplet based microfluidics for highthroughput screening of antibody secreting cells Liheng Cai, John Heyman, Linas Mazutis, Lloyd Ung, Rodrigo Guerra, Donald Aubrecht, David Weitz We present a droplet based microfluidic platform that allows highthroughput screening of antibody secreting cells. We coencapsulate single cells, fluorescent probes, and detection beads into emulsion droplets with diameter of 40 micron. The beads capture antibodies secreted by cells, resulting in a pronounced fluorescent signal that activates dielectrophoresis sorting at rate about 500 droplets per second. Moreover, we demonstrate that Reverse Transcription Polymerase Chain Reaction (RT-PCR) can be successfully applied to the cell encapsulated in a single sorted droplet. Our work highlights the potential of droplet based microfluidics as a platform to generate recombinant antibodies. [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D20.00008: Mechanical response of tumor cells flowing through a microfluidic capillary Zeina S. Khan, Nabiollah Kamyabi, Fazle Hussain, Siva A. Vanapalli Circulating tumor cells, the primary cause of cancer metastasis, are transported throughout the body to distant organs by blood flow. Despite the importance of cell transport and deformability in the vasculature for cancer metastasis, quantitative understanding of the hydrodynamic interactions between the cells and the blood vessel walls is lacking. Using a model microfluidic capillary of rectangular cross-section with an on-chip manometer coupled with high speed video imaging, we quantitatively investigate the hydrodynamic behavior via the cell excess pressure drop. By characterizing our device with simple model systems including viscous drops and soft elastic particles, we find that the excess pressure drop shows no apparent dependence on elastic modulus or interfacial tension, but depends significantly on internal viscosity for moderate confinements and shear stresses within the physiological range of 1-10 Pa. This suggests that the metastatic potential of circulating cells can be characterized by the effective viscosity. We test this hypothesis with several tumor cell lines and find that the effective cell viscosity determined from excess pressure drop measurements can be used to differentiate highly from lowly invasive cells. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D20.00009: A pressure actuated microfluidic system with real time feedback control of droplet length in a T junction microfluidic channel Wen Zeng A pressure actuated microfluidic system using microvalves is designed for droplet generation in a T junction microfluidic channel. Here, we mainly focus on the influence flow rates of continuous and dispersed phase has on the droplet formation. By using pressure actuation for droplet generation in a T junction microfluidic channel, uniform production of monodisperse droplet is achieved. By using the curve fitting, linearized equation which describes the linear relationship of droplet length and flow rate ratio is obtained. With real time feedback, a closed-loop control system of droplet generation is constructed. The mathematical model between pressure and flow rates of continuous and dispersed phase is built, and the control accuracy of droplet length is analyzed. Compared with syringe pump actuation, the droplet formation can be much steadier and the length of individual droplet can be controlled more precisely by pressure actuation, especially at lower flow rates. Based on pressure actuation, monodisperse droplet formation with volume range from microliter to nanoliter scale can be achieved. [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D20.00010: Effect of surfactant on bubble/liquid transport in a T-junction microchannel with sudden contraction Kuo-Long Pan, Huai-Jhu Chen We studied the effect of surfactant on the transport phenomena of bubbles in microfluidic devices. A T-junction microchannel with a sudden contraction section was used in the experiment, and the channel dimensions were 200 by 100 $\mu $m. Variations in the transport velocities of different bubbles were observed when they passed the sudden contraction area. Different liquids were adopted as the continuous phase. The work is composed of three parts First, the commercial software, Fluent, was used to analyze the effect of surface tension on the transport phenomena in the microchannel. Second, the roles of surface tension and viscosity were investigated by changing the concentration of ethanol solution. Third, the effects of surfactant type were studied by adding S111n (anionic) and S131 (amphoteric) respectively in water. Experimental results showed that when the concentration of surfactant exceeded the critical micelle concentration (CMC) limit while at the same surface tension, the bubbles would exhibit distinct patterns. Specifically, the wetting behaviors of the bubbles were different using the two dissimilar types of surfactant solutions, for which the wettability of S131 was higher than that of S111n. As a consequence, the transport velocities of the bubbles in S131 solutions were faster than that in S111n solutions [Preview Abstract] |
Monday, March 3, 2014 5:18PM - 5:30PM |
D20.00011: Inversion of the electric field driven by ionic solvation energy Guillermo Guerrero Garcia, Francisco Solis, Monica Olvera de la Cruz In previous studies, Monte Carlo simulations have suggested the possibility of inverting the electric field near a liquid/liquid interface due to excluded volume effects, ionic size asymmetry, and image charges at high electrolyte concentrations in the absence of ion transfer. In this work, we develop a mean field theory and coarse grained simulations to study the ion transfer between the two immiscible electrolytes in the presence of an electric field. Our calculations suggest a novel mechanism to invert the electric field near confined oil/water interfaces based on differences of the ionic solvation energy in both liquid media. [Preview Abstract] |
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