Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session R10: Microscale Flows: Particle Sorting and Control |
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Chair: Claire Hur, Harvard University Room: 3005 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R10.00001: Separation of polymers by length in rotational flow Faihan Alfahani, Jennifer Kreft Pearce We use a lattice-Boltzmann based Brownian dynamics simulation to determine if polymers of different lengths can be separated by a combination of a trapping force and fluid flow. We produce two counter-rotating vortices in the simulation, similar to the work of HIlgenfeldt, et al., that used rotational flow to separate colloids of different size. We can achieve separation of polymers that differ in length by as little as 30{\%}. We expect that this technique could be used in a microfluidic device to analyze the size of long DNA fragments produced in common molecular biological tests. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R10.00002: High throughput sorting of spherical particles in inertial microfluidics Phanindra Tallapragada, Senbagaraman Sudarsanam, Nilesh Hasabnis The fundamental problem of sorting sphere like particles by size in flows at low Reynolds numbers in confined geometries is one which is frequently encountered in microfluidic engineering. The inertial sorting of particles in Dean flows, demonstrated in pioneering work by Papautsky and Bhagat et.al and DiCarlo et.al is specific to particular sizes of particles and it is not apparent how particles of different or larger sizes could be sorted. This is because the phenomena of particle focusing across a large parametric regime is poorly understood. Additionally the unexplored case where larger particles need to be sorted by size is especially important in applications involving large cells such as Islet cells whose diameter can vary from $50$ $\mu$m to $200$ $\mu$m. We characterize the transitions in particle focusing with changing channel Reynolds number, particle Reynolds number and the Dean number and exploit these transitions to sort particles by size. Based on such transitions, particles across size ranges of 3 $\mu$m to 100 $\mu$m in various 2-particle mixtures are sorted. We also find that this separation occurs in a narrow range of channel Reynolds number. We demonstrate our findings by sorting particles in different mixtures. [Preview Abstract] |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R10.00003: Kinetics of colloidal gold nanoparticle chain assembly via \textit{in situ} liquid cell electron microscopy observations Taylor Woehl, Tanya Prozorov Various types of colloidal nanoparticles are known to self-assemble into hierarchical mesostructures via anisotropic interparticle interactions. Previous modeling and experiments have suggested that dipolar interactions may be responsible for assembly of one dimensional nanoparticle chain structures; however, due to a lack of \textit{in situ }observations little is known about the kinetics of the self-assembly. Here we use real-time nanoscale observations to measure the self-assembly kinetics of colloidal gold nanoparticles into one dimensional chains. Gold nanoparticles suspended in acetate buffer were observed via\textit{ in situ} liquid electron microscopy to self-assemble into chains of 5-10 nanoparticles over a time of minutes. Self-assembly is initiated upon irradiation of the nanoparticles with the imaging electron beam. Measurements of the self-assembly kinetics revealed that the chains formed \textit{via} second order aggregation kinetics during the first tens of seconds. We investigate the effects of the electron beam current and ionic strength of the buffer solution on the effective aggregation rate and chain formation mechanism. Our observations suggest that the aggregation rate increases with the effective diffusivity of the nanoparticles. [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R10.00004: Solution-based electric-field-assisted assembly of vertically aligned CNT membranes Richard Castellano, Cevat Akin, Jerry Shan Carbon-nanotube (CNT) membranes are of interest due to experiments and simulations showing flow through nanotubes to be 3 to 5 orders of magnitude faster than predicted by viscous flow theory. Thus, membranes incorporating vertically aligned CNTs (VACNTs) as through-pores offer promise as highly efficient and permeable membranes for a variety of filter and separation processes. However, current membrane-fabrication techniques utilizing CVD-grown VACNT arrays are costly and difficult to scale up. We are developing a solution-based, electric-field-assisted approach as a cost-effective and scalable method to producing large-area VACNT membranes and composites. Post-growth nanotubes are first dispersed in a polymeric matrix and then aligned with an AC electric field. A DC component induces electrophoresis to the CNTs to significantly increase the VACNT number density. This composite field also introduces complex fluid motion caused by induced-charge electro-osmosis and the electrochemistry of the fluid/electrode interface. We experimentally probe all of these effects and consider factors affecting the number density and spatial uniformity of VACNT membranes. We also consider the basic electrokinetics of nanotube alignment under spatially uniform AC electric fields, making quantitative comparison with classical models of the dynamics of polarizable, 1D particles under the combined effects of electric fields, hydrodynamic drag, and Brownian motion. We conclude by discussing the implications of these fundamental electrohydrodynamic studies for producing large-area membranes containing aligned CNTs. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R10.00005: Solution-Based Electro-Orientation Spectroscopy for the Automated, Quantitative Characterization and Sorting of 1D Nanomaterials Cevat Akin, Jerry Shan, Jingang Yi, Leonard Feldman, Corentin Durand, An-Ping Li The electrical-transport properties of 1D nanomaterials are often poorly known and vary with size and surface effects. Traditional quantitative characterization methods require specialized facilities and are usually slow, invasive and not suitable for the large number of measurements needed to statistically characterize samples with a heterogeneous distribution of properties. Here, we introduce a contactless, solution-based method to rapidly and quantitatively measure the electrical properties of 1D nanomaterials based on their transient alignment behavior in AC electric fields of different frequencies. The electro-orientation method can be automated and is compatible with further solution-based techniques for nanowire alignment and assembly, including electrophoresis, dielectrophoresis and flow control. We demonstrate the accuracy of the solution-based method using a variety of insulating, semiconducting and metallic nanowires, and show that electro-orientation spectroscopy can detect true nanoscale surface effects on the electrical conductivity of 1D nanomaterials. We further discuss our progress toward implementing the method in a microfluidic device capable of automated electrical characterization and sorting of nanowires and nanotubes. [Preview Abstract] |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R10.00006: Rapid Electrokientic Patterning of Metal Nanoparticles and Nanowires Avanish Mishra, Stuart Williams, Steven Wereley Rapid Electrokinetic Patterning (REP) combines electric field and laser induced heating for particle trapping on an electrode surface. This technique utilizes two planar transparent indium tin oxide (ITO) electrodes separated by a colloidal solution of suitable thickness. When an infrared (1064 nm) laser beam is projected on the electrode surface, due to interaction between AC electric field and laser induced heating, a toroidal electrothermal (ET) vortex is generated. It traps particles and brings them closer to the electrode surface where particles are captured by particle-electrode interactions. In this work, we demonstrate trapping of metal nanoparticles and discuss its application in Surface Enhanced Raman Scattering for trace analyte detection. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R10.00007: Viscous flow within an embedded serpentine channel as a mechanism to create time-dependent deformation patterns of elastic beams Yoav Matia, Amir Gat We analyze the time dependent interaction between the flow-field and the elastic deformation-field of a viscous liquid within a long serpentine channel, embedded in an elastic beam. The channel is positioned asymmetrically with regard to the midplane of the elastic beam. We focus on creeping flows and small deformations of the elastic beam and obtain, in leading order, a diffusion equation governing the pressure-field within the serpentine channel. The deformation of the beam is then related to the propagation of pressure within the channel. We thus obtain a viscous-elastic equation governing the deformation of the beam due to the viscous flow within the serpentine channel. This equation enables to design complex time-dependent deformation patterns of beams with embedded channel networks, relevant to soft-robotic applications. Our theoretical results were illustrated and verified using numerical computations. [Preview Abstract] |
(Author Not Attending)
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R10.00008: Different modes of self-assembly for same-stream and cross-stream microparticles in inertial microflows Soroush Kahkeshani, Dino Di Carlo Understanding parameters affecting dynamic self-assembly of particles in microchannels can enable control of particle density for applications such as flow cytometry and tissue printing. Inertial lift forces and repulsive viscous interactions have been shown to have important effects on inter particle spacing and dynamic particle pairwise interactions. Based on the aspect ratio of the channel, particles inertially focus to two or four positions in finite Reynolds number flows. In this work, we show that in channels with aspect ratio of two or greater, where we have predominantly two focused streams of particles, there is a favored same-stream spacing as well as favored cross-stream spacing between particles. We studied how channel geometry, particle size, concentration of particles, orientation of the neighboring particles, and Reynolds number can affect both cross-stream and same-stream spacing. In addition, based on our simulations, for the first time we showed that particle size and position of the particle in the channel significantly affect the shape of reversing streamlines behind and in front of the particles, however Reynolds number does not have a controlling effect on shape of these reversing streamlines. These results show unique features of particle interactions. [Preview Abstract] |
Tuesday, November 25, 2014 2:49PM - 3:02PM |
R10.00009: Rapid Electrokinetic Patterning for Vertical Stacking and Manipulation of Particles Katherine Clayton, Avanish Mishra, Steven Wereley A variety of optical and optoelectrical-based microfluidics techniques have been used for the trapping and manipulation of particles in a colloidal solution. Rapid Electrokinetic Patterning (REP) is one such technique. It uses laser activated electrothermal flow to trap particles in a monolayer. Particles can be manipulated on the substrate by steering the laser. In this work we show that by a careful selection of parameters, particles can be rapidly trapped in a tower configuration instead of a monolayer. Moreover, this vertical tower can be manipulated and stationed at any desirable place on the chip. We intend to discuss underlying physical mechanism and potential applications in biology. [Preview Abstract] |
Tuesday, November 25, 2014 3:02PM - 3:15PM |
R10.00010: Dielectric Decrement Effects on Nonlinear Electrophoresis of Ideally Polarizable Particles Jeffrey L. Moran, Wai Hong Ronald Chan, Cullen R. Buie, Bruno Figliuzzi We present numerical simulations of nonlinear electrophoresis of ideally polarizable particles that specifically include the effects of a spatially non-uniform dielectric permittivity near the particle surface. Models for this dielectric decrement phenomenon have been developed by several authors, including Ben-Yaakov et al. [J. Phys. Condens. Matter 2009] Hatlo et al. [EPL 2012], and Zhao {\&} Zhai [JFM 2013]. We extend this work to ideally polarizable particles and include the effects of surface conduction and advective transport in the electric double layer. By numerically solving for the coupled velocity field, electric potential, and ionic concentration distributions in the bulk solution surrounding the particle, we demonstrate that the dielectric decrement model predicts ionic saturation around the particle and thus physical implications that resemble those resulting from the steric model developed by Kilic et al. [PRE 2007], albeit with differences that reflect the nonlinearity of the modified Poisson-Boltzmann equation. In addition, we develop a generalized condensed layer model that approximates both the steric and dielectric decrement models in the limits of strong electric fields and negligible surface conduction to obtain more physical insights into these models. We demonstrate that the mobility in both models asymptotically scales as the square root of the electric field at high fields, recovering the result of Bazant et al. [Adv. Colloid Interface Sci 2009]. [Preview Abstract] |
Tuesday, November 25, 2014 3:15PM - 3:28PM |
R10.00011: Continuous Nanoparticle Size Separation Using Microfluidic Technology Bushra Tasadduq, Gonghao Wang, Wenbin Mao, Wilbur Lam, Alexander Alexeev, Todd Sulchek High throughput size based separation of nanoparticles is important to better understand and improve diagnosis of diseases that involve nanoparticles. We propose a novel microfluidic device capable of continuous size-dependent separation of particles. The separation device consists of a microchannel with periodically arranged diagonal ridges. The key to the separation is that these diagonal ridges create helical flow fields. Simultaneously, inertial particle migration alters the particle height in a size-dependent manner, which then exposes the particle to different secondary flows. The height-dependent secondary flows then cause particles with different sizes to migrate transversely with unique trajectories. We have characterized the separation results utilizing forward and side scatter flow cytometric analysis. We are able to separate 4 micrometer particles from 7 micrometer; 0.5 micrometer from 5 micrometer; and platelets from RBCs and WBCs with a substantial enrichments of number densities of 29-fold, 227-fold, and 53-fold respectively .We demonstrate there exists a z-position dependent phenomena which affects particle trajectories and hypothesize that controlling the particle z-position, we can further improve the efficiency of size based sorting. [Preview Abstract] |
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