Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L40: Microscale Flows: Microfluidic Devices I |
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Chair: Sangjin Ryu, University of Nebraska-Lincoln Room: Sheraton Back Bay D |
Monday, November 23, 2015 4:05PM - 4:18PM |
L40.00001: Corn-on-a-chip: Mini-channel Device for Corn Root Growth Kevin Kreis, Sangjin Ryu Plant growth heavily relies on interactions between the root and the soil environment, but it is impossible to observe such interactions because of opaqueness of soil. Microfluidics has been successfully utilized to monitor the root growth behaviors of Arabidopsis. In this study we have chosen Maize as a model plant because of its economic significance, and aim to develop transparent mini-channel devices accommodating the root growth of corn seedlings in a controlled environment. To mimic aspects of the soil environment, we try to impose concentration gradients of key chemical ions to the growing root using the device, and to investigate how the root responds to the applied stimuli. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L40.00002: Flow fraction in charged rectangular microchannel to optimally design hydrodynamic filtration chip for cell sorting Myung-Suk Chun, Sohyun Jeong, Jae Hun Kim, Tae Seok Lee Among the passive separations, hydrodynamic filtration (HDF) can perform the fractionation of cells or particles by selective extraction of streamlines controlled by the flow fraction at each branch. Only the stream near the sidewall enters the branches as the focusing, with the amount of fluid leaving the main channel being determined by the flow distribution related to the hydraulic flow resistances. Its understanding is important, but in-depth consideration has not been treated until now. The virtual boundary of the fluid layer should be first specified, and the parabolic velocity profile starts to form from the steady state flow with high P\'eclet numbers. We computed the 3-dimensional flow profile at the rectangular cross-section with any aspect ratios, by considering electrokinetic transport coupled with the Poisson-Boltzmann and Navier-Stokes equations. The chip was designed with the parameters rigorously determined by the complete analysis of laminar flow for flow fraction and complicated networks of main and multi-branched channels for cell sorting into the finite number of subpopulations. For potential applications to the precise sorting, our designed microfluidic chip can be validated by applying model cells consisting of heterogeneous subpopulations. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L40.00003: Deformability-based capsule sorting Anne Le Goff, Nadege Munier, Pauline Maire, Florence Edwards-Levy, Anne-Virginie Salsac Many microfluidic devices have been developed for cancer diagnosis applications, most of which relying on costly antibodies. Since some cancer cells display abnormal mechanical properties, new sorting tools based on mechanical sensing are of particular interest. We present a simple, passive pinched flow microfluidic system for capsule sorting. The device consists of a straight microchannel containing a cylindrical obstacle. Thanks to a flow-focusing module placed at the channel entrance, capsules arrive well-centered in the vicinity of the obstacle. Pure size-sorting can be achieved at low shear rate. When increasing the shear rate, capsules are deformed in the narrow space between the pillar and the wall. The softer the capsule, the more tightly it wraps around the obstacle. After the obstacle, streamlines diverge, allowing for the separation between soft capsules, that follow central streamlines, and stiff capsules, that drift away from the obstacle with a wider angle. This proves that we have developed a flexible multipurpose sorting microsystem based on a simple design. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L40.00004: Multiphase ferrofluid flows for micro-particle sorting Ran Zhou, Cheng Wang Utilizing negative magnetophoresis, ferrofluids have demonstrated great potential for sorting nonmagnetic micro-particles by size. Most of the existing techniques use single phase ferrofluids by pushing micro-particles to channel walls; the sorting speed is thus hindered. We demonstrate a novel sorting strategy by co-flowing a ferrofluid and a non-magnetic fluid in microchannels. Due to the magnetic force, the particles migrate across the ferrofluid stream at size-dependent velocities as they travel downstream. The laminar interface between the two fluids functions as a virtual boundary to accumulate particles, resulting in effective separation of particles. A stable and sharp interface is important to the success of this sorting technique. We investigate several factors that affect sorting efficiency, including magnetic field, susceptibility difference of the fluids, flow velocity, and channel geometry. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L40.00005: Electrohydrodynamic manipulation of particles adsorbed on the surface of a drop Edison Amah, Kinnari Shah, Ian Fischer, Pushpendra Singh In our previous studies we have shown that particles adsorbed on the surface of a drop can be concentrated at its poles or equator by applying a uniform electric field. This happens because even when the applied electric field is uniform the electric field on the surface of the drop is nonuniform, and so particles adsorbed on the surface are subjected to dielectrophoretic (DEP) forces. In this paper, we study the behavior of adsorbed particles at low electric field frequencies when the drop and ambient liquids are weakly conducting dielectric liquids, and model it using a leaky dielectric model. The electrohydrodynamic (EHD) flow which arises because of the accumulation of charge on the surface of the drop can be from pole-to-equator or equator-to-pole depending on the properties of the drop and ambient liquids. The flow however diminishes with increasing frequency and there is a critical frequency at which the drag force on a particle due to the EHD flow becomes equal to the DEP force, and above the critical frequency the DEP force dominates. When the fluid and particles properties are such that the EHD and DEP forces are in the opposite directions, particles can be can be collected at the poles or the equator, and also can be moved from the poles to the equator, or vice versa, by varying the frequency. Also, it is possible to separate the particles of a binary mixture when the critical frequencies of the two types of particles are different. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L40.00006: Magnetophoretic control of water droplets in bulk ferrofluid Georgios Katsikis, Alexandre Bréant, Manu Prakash We present a microfluidic platform for 2-D manipulation of water droplets immersed in bulk oil-based ferrofluid. Although non-magnetic, the droplets are exclusively controlled by magnetic fields, without any pressure-driven flow. The diphasic fluid layer is trapped in a submillimeter Hele-Shaw chamber that includes permalloy tracks on its substrate. An in-plane rotating magnetic field magnetizes the permalloy tracks, thus producing local magnetic gradients, while an orthogonal magnetic field magnetizes the bulk ferrofluid. To minimize the magnetostatic energy of the system, droplets are attracted towards the locations of the tracks where ferrofluid is repelled. Using this technique, we demonstrate synchronous propagation of water droplets, analyze PIV data of the bulk ferrofluid flow and study the kinematics of propagation. In addition, we show droplet break-up, merging and derive relevant scaling laws. Finally, we discuss future applications owing to the biocompatibility of the droplets. [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L40.00007: Contactless, high-throughput determination of electrical conductivity of one-dimensional nanomaterials by solution-based electro-orientation spectroscopy Cevat Akin, Jingang Yi, Leonard Feldman, Jerry Shan, Corentin Durand, Saban Hus, An-Ping Li, Michael Filler The electrical-transport properties of nanowires of the same composition (and even fabricated within the same batch) often vary by orders of magnitude. Existing characterization methods are slow, making the large number of measurements needed to statistically characterize highly variable samples essentially impossible. Here, we demonstrate a contactless, solution-based method to efficiently determine the electrical conductivity of individual 1D nanomaterials. This new method, electro-orientation spectroscopy, is based on the transient alignment behavior of fluid-suspended nanowires in AC electric fields of different frequencies. Comparison with direct transport measurements by probe-based scanning tunneling electron microscopy shows that electro-orientation spectroscopy can quantitatively measure nanowire conductivity over a 6-order-of-magnitude range, 10$^{\mathrm{-5}}$ -- 10 S/m. We demonstrate an automated microfluidic device capable of measuring and sorting hundreds of nanowires per hour. With this device, we statistically characterize the conductivity of a variety of nanowires and find significant variability in Si nanowires grown from the same wafer by metal-assisted chemical etching. Finally, we discuss the potential of the electro-orientation approach to be integrated with other solution-based methods for scalable positioning of nanowires for post-growth device assembly. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L40.00008: A modular and lowcost 3D-printed microfluidic device with assembly of capillaries for droplet mass production A. A. Aguirre-Pablo, J. M. Zhang, E. Q. Li, S. T. Thoroddsen We report a new 3D-printed microfluidic system with assembly of capillaries for droplet generation. The system consists of the following parts: 3Dprinted Droplet Generation Units (DGUs) with embedded capillaries and two 3D-printed pyramid distributors for supplying two different fluid phases into every DGU. A single DGU consists of four independent parts: a top channel, a bottom channel, a capillary and a sealing gasket. All components are produced by 3dprinting except the capillaries, which are formed in a glass-puller. DGUs are independent of the distributor and from each other; they can easily be assembled, replaced and modified due to its modular design which is an advantage in case of a faulty part or clogging, eliminating the need to fabricate a complete new system which is cost and time demanding. We assessed the feasibility of producing droplets in this device varying different fluid parameters, such as liquid viscosity and flow rate, which affect droplet size and generation frequency. The design and fabrication of this device is simple and low-cost with the 3D printing technology. Due to the modular design of independent parts, low-cost fabrication and easy parallelization of multiple DGU’s, this system provides great flexibility for industrial applications. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L40.00009: Hydrodynamics and Mass Transfer Characteristics of Laminar Bioelectrochemical Systems, a Summary Way Lee Cheng, Reza Sadr Hydrodynamics and diffusion characteristics of laminar bioelectrochemical systems (BES) with common micro-channel configuration are summarized. Computational fluid dynamics (CFD) simulations are performed to supplement literature results and to provide a comprehensive summary for the flow and diffusion characteristics in these systems in terms of dimensionless parameters. The results show that decreasing the fluid velocity enhances mixing between the two parallel flow streams with a stronger mixing in the near wall region. Reducing the ratio of channel width to channel height enhances mixing. Changing the angle between the inlet channels, in general, does not have a strong effect on the flow field, except when the angle is larger than about 135$^{\circ}$. Furthermore, fluid mixing is substantially different for 60$^{\circ}$ and 180$^{\circ}$ angle between the two inlet channels. For the 60$^{\circ}$ case, the length of mixing zone does not depends on the Reynolds number and it converges asymptotically as channel width-to-height ratio decreases. On the other hand, for the 180$^{\circ}$ case, this length depends on the flow Reynolds number and decreases monotonically at small ratio of channel width-to-heights ratio. The results show that asymmetric growth of a bio-layer on the channel wall increases shear stress substantially as one side of the channel as its height reduces compare to the other side. Moreover, this asymmetry causes a traverse velocity field that highly skews the mixing zone towards the side of the channel with larger height. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L40.00010: Valve-less microdispenser Ming Kwang Tan, Wang Xin, Weng Kent Lee We demonstrate the concept of valve-less microdispenser to control of the liquid flow through the nozzle, by incorporating Leidenfrost effect into the nozzle design. When the nozzle is heated above the Leidenfrost point, a thin vapor layer is formed between the heated substrate and the liquid above it. The vapor pressure due to the presence of the vapor layer, together with the effect of surface tension of the liquid, exerted on the liquid-vapor interface, preventing the flow of the liquid through the nozzle. The experimental results shown that nozzles of diameter 400 micrometer and below, the nozzle temperature of 150 degree Celsius is sufficient to prevent the continuous flowing of the liquid, whereas for nozzles of diameter between 400 to 500 micrometer, the nozzle temperature needs to increase to 160 degree Celsius in order to prevent the continuous flowing of the liquid. When nozzle temperature below 160 degree Celsius, intermittent ejection of microdroplets, whose size is a function of nozzle temperature, is observed. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L40.00011: Design of an Efficient Turbulent Micro-Mixer for Protein Folding Experiments Venkatesh Inguva, Blair Perot Protein folding studies require the development of micro-mixers that require less sample, mix at faster rates, and still provide a high signal to noise ratio. Chaotic to marginally turbulent micro-mixers are promising candidates for this application. In this study, various turbulence and unsteadiness generation concepts are explored that avoid cavitation. The mixing enhancements include flow turning regions, flow splitters, and vortex shedding. The relative effectiveness of these different approaches for rapid micro-mixing is discussed. Simulations found that flow turning regions provided the best mixing profile. Experimental validation of the optimal design is verified through laser confocal microscopy experiments. [Preview Abstract] |
Monday, November 23, 2015 6:28PM - 6:41PM |
L40.00012: Fabrication and characterization of vertically aligned carbon-nanotube membranes Richard Castellano, Cevat Akin, Matt Purri, Jerry Shan, Sangil Kim, Francesco Fornasiero Membranes having vertically-aligned carbon-nanotube (VACNT) pores offer promise as highly efficient and permeable membranes for use as breathable thin films, or in filtration and separation applications, among others. However, current membrane-fabrication techniques utilizing chemical-vapor-deposition-grown VACNT arrays are costly and difficult to scale up. We have developed a solution-based, electric-field-assisted approach as a cost-effective and scalable method to produce large-area VACNT membranes. Nanotubes are dispersed in a liquid polymer, and aligned and electrodeposited with the aid of an electric field prior to crosslinking the polymer to create VACNT membranes. We experimentally examine the electrodeposition process, focusing on parameters including the electric field, composition of the solution, and CNT functionalization that can affect the nanotube number density in the resulting membrane. We characterize the CNT pore size and number density and investigate the transport properties of the membrane. Size-exclusion tests are used to check for defects and infer the pore size of the VACNT membranes. Dry-gas membrane permeability is measured with a pressurized nitrogen-flow system, while moisture-vapor-transfer rate is measured with the ASTM-E96 upright-cup test. We discuss the measured transport properties of the solution-based, electric-field-fabricated VACNT membranes in reference to their application as breathable thin films. [Preview Abstract] |
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