Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session Q13: Particle Assembly and Self-orientationParticles
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Chair: Enkeleida Lushi, Simons Foundation and New York University Room: 506 |
Tuesday, November 21, 2017 12:50PM - 1:03PM |
Q13.00001: Flow-driven alignment of carbon nanotubes during floating evaporative self assembly Arganthael Berson, Katherine Jinkins, Jason Chan, Gerald Brady, Kjerstin Gronski, Padma Gopalan, Harold Evensen, Michael Arnold Individual semi-conducting single-wall carbon nanotubes (s-SWCNTs) exhibit exceptional electronic properties, which makes them promising candidates for the next generation of semi-conductor electronics. In practice, field-effect transistors (FETs) are fabricated from arrays of s-SWCNTs deposited onto a substrate. In order to achieve high electronic performance, the s-SWCNTs in these arrays must be densely packed and well aligned. Floating Evaporative Self Assembly (FESA) is a new deposition technique developed at the UW-Madison that can achieve such high-quality s-SWCNT alignment. For example, it was used to fabricate the first s-SWCNT-based FETs to outperform gallium arsenide and silicon FETs. In FESA, a droplet of ink containing the s-SWCNTs is deposited onto a pool of water. The ink spreads on the water surface towards a substrate that is vertically pulled out of the water. A band of aligned s-SWCNTs is deposited with each drop of ink. High-speed imaging is combined with cross-polarized microscopy to elucidate the mechanisms behind the exceptional alignment of s-SWCNTs. Two key mechanisms are 1) the collection of s-SWCNTs at the ink-water interface and 2) the depinning of the air-ink-substrate contact line. Avenues for scaling up FESA will be presented. [Preview Abstract] |
Tuesday, November 21, 2017 1:03PM - 1:16PM |
Q13.00002: A hydrodynamic mechanism for spontaneous formation of ordered drop arrays in confined shear flow Sagnik Singha, Mauricio Zurita-Gotor, Michael Loewenberg, Kalman Migler, Jerzy Blawzdziewicz It has been experimentally demonstrated [Phys. Rev. Lett. 86, 1023 (2001)] that a drop monolayer driven by a confined shear flow in a Couette device can spontaneously arrange into a flow-oriented parallel chain microstructure. However, the hydrodynamic mechanism of this puzzling self-assembly phenomenon has so far eluded explanation. In a recent publication [Soft Matter 8, 7495 (2012)] we suggested that the observed spontaneous drop ordering may arise from hydrodynamic interparticle interactions via a far-field quadrupolar Hele–Shaw flow associated with drop deformation. To verify this conjecture we have developed a simple numerical-simulation model that includes the far-field Hele–Shaw flow quadrupoles and a near-field short-range repulsion. Our simulations show that an initially disordered particle configuration self-organizes into a system of particle chains, similar to the experimentally observed drop-chain structures. The initial stage of chain formation is fast; subsequently, microstructural defects in a partially ordered system are removed by slow annealing, leading to an array of equally spaced parallel chains with a small number of defects. The microstructure evolution is analyzed using angular and spatial order parameters and correlation functions. [Preview Abstract] |
Tuesday, November 21, 2017 1:16PM - 1:29PM |
Q13.00003: Dynamics of flexible fibers transported in confined viscous flows Jean Cappello, Camille Duprat, Olivia Du Roure, Mathias Nagel, François Gallaire, Anke Lindner The dynamics of elongated objects has been extensively studied in unbounded media as for example the sedimentation of fibers at low Reynolds numbers. It has recently been shown that these transport dynamics are strongly modified by bounding walls. Here we focus on the dynamics of flexible fibers confined by the top and bottom walls of a microchannel and transported in pressure-driven flows. We combine well-controlled microfluidic experiments and simulations using modified Brinkmann equations. We control shape, orientation, and mechanical properties of our fibers using micro-fabrication techniques and in-situ characterization methods. These elastic fibers can be deformed by viscous and pressure forces leading to very rich transport dynamics coupling lateral drift with shape evolution. We show that the bending of a perpendicular fiber is proportional to an elasto-viscous number and we fully characterize the influence of the confinement on the deformation of the fiber. Experiments on parallel flexible fibers reveal the existence of a buckling threshold. [Preview Abstract] |
Tuesday, November 21, 2017 1:29PM - 1:42PM |
Q13.00004: Lens and dendrite formation during colloidal solidification Grae Worster, Jiaxue You Colloidal particles in suspension are forced into a variety of morphologies when the suspending fluid medium is frozen: soil is compacted between ice lenses during frost heave; ice templating is a recent and growing technology to produce bio-inspired, micro-porous materials; cells and tissue can be damaged during cryosurgery; and metal-matrix composites with tailored microstructure can be fabricated by controlled casting. Various instabilities that affect the microscopic morphology are controlled by fluid flow through the compacted layer of particles that accumulates ahead of the solidification front. By analysing the flow in connection with equilibrium phase relationships, we develop a theoretical framework that identifies two different mechanisms for ice-lens formation, with and without a frozen fringe, identifies the external parameters that differentiates between them and the possibility of dendritic formations, and unifies a range of apparently disparate conclusions drawn from previous experimental studies. [Preview Abstract] |
Tuesday, November 21, 2017 1:42PM - 1:55PM |
Q13.00005: Stable Systems of Charged Sedimenting Particles Christopher Trombley, Maria Ekiel-Jezewska The behavior of charged particles settling in a fluid is qualitatively different from the behaviors of settling particles without a fluid or without charge. A foundational qualitative result on the behavior of charged particles in a vacuum is Earnshaw's Theorem, which states that no configuration of particles can be a stable equilibrium. In contradistinction, an explicit example of a stable equilibria for charged particles in a Stokes flow is given. Furthermore, necessary conditions for Lyapunov stability of two interacting charged particles settling in a Stokes fluid are derived from the point force model. The physical parameters of the system are explored to find conditions where stable equilibria can or cannot exist. It is shown that the parameters corresponding to stable equilibria form an open, bounded and connected set. The existence of stable systems of charged sedimenting particles is significant from both fundamental and practical perspectives. [Preview Abstract] |
Tuesday, November 21, 2017 1:55PM - 2:08PM |
Q13.00006: Clustering and propulsion of isotropic catalytic swimmers Akhil Varma, Thomas D Montenegro-Johnson, Sebastien Michelin Catalytic micro-swimmers such as phoretic particles use local gradients in solute concentration for propulsion. An isolated isotropic phoretic particle generates a uniform concentration field on its surface and hence cannot propel on its own. Symmetry of this field is broken by the presence of at least another similar particle in the system, which leads to phoretic attraction or repulsion. Phoretic attraction drives the clustering of identical homogeneous particles into stable clusters of various configurations which may self-propel or rotate due to their geometric asymmetry. Using full numerical simulations and analytic approximations based on pairwise interactions of the particles, we study the cluster formation and its impact on the statistics of the propulsion properties. We finally analyze the effect of background noise on the results. [Preview Abstract] |
Tuesday, November 21, 2017 2:08PM - 2:21PM |
Q13.00007: Universal emergent dynamics of micro-spinners above a wall Enkeleida Lushi, Michael Shelley We study the collective behavior in ensembles of micro-spheres driven to rotate above a wall. This many particle system is Hamiltonian and the ensemble rotates about its center of mass. Using large-scale computations that resolve the interactions with the wall, hydrodynamics and particle collisions, we study the emergence of collective rotation, edge currents and universal behaviors that depend on the density. [Preview Abstract] |
Tuesday, November 21, 2017 2:21PM - 2:34PM |
Q13.00008: ABSTRACT WITHDRAWN |
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