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 M37: Field Manipulation in the MicroscaleElectro Micro
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Chair: Jerry Shan, Rutgers University Room: 303 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M37.00001: Numerical Investigation of Force-Free Magnetophoresis of Nonspherical Microparticles Jie Zhang, Cheng Wang Our group recently demonstrated novel force-free magnetophoresis to separate nonspherical particles by shape. In this approach, a uniform magnetic field is used to generate a magnetic torque, which breaks the rotational symmetry of the particles and leads to shape-dependent lateral migration of the particles. We use direct numerical simulations to gain a better understanding of this magnetophoresis mechanism by focusing on ellipsoidal microparticles - a representative type of nonspherical particles encountered in biomedical engineering. We study key effects that influence the rotational and translational behaviors, including particle-wall separation distance, direction and strength of the magnetic field, particle aspect ratio and size. The numerical results show that the lateral migration is negligible in the absence of the magnetic field. When the magnetic field is applied, the particles migrate laterally. The migration direction depends on the direction of external magnetic fields, which controls the symmetry property of the particle rotation. These findings agree well with experiments. Our numerical simulations yield a comprehensive understanding of particle migration mechanism, and provide useful guidelines on design of separating devices for non-spherical micro-particles. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M37.00002: Magnetophoresis-tuned diamagnetic particle focusing in ferrofluids. Qi Chen, Di Li, Xiangchun Xuan Focusing and aligning particles into a tight stream is often a necessary step prior to detecting them. Magnetic fluids including paramagnetic solutions and ferrofluids have been increasingly used for label free manipulation of diamagnetic particles in microfluidic devices. However, the current techniques for three-dimensional diamagnetic particle focusing in magnetic fluids requires the use of either two opposing magnets or a sheath flow focusing. We demonstrate in this work a sheath-free single-stream focusing of polystyrene particles in a ferrofluid flow through the use of a single permanent magnet. Moreover, the equilibrium position of the particle stream can be readily varied by changing the location of the magnet. This active magnetic focusing can potentially be combined with the passive inertial focusing for efficient three-dimensional particle alignment in a large range of flow rates. [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M37.00003: Dynamics of Ellipsoidal Particles in Simple Shear Flows under the Influence of Uniform Magnetic Fields Christopher Sobecki, Yanzhi Zhang, Cheng Wang Our recent experiments demonstrated a ``torque''-based method to separate nonspherical particles by combining shear flows and uniform magnetic fields. Experiments showed correlation between the lateral migration of the particle and the asymmetry of the particle rotation. To further understand the effect of magnetic field on the particle rotation, we study the rotational dynamics of an ellipsoidal particle, in an unbounded simple shear flow at zero-Reynolds numbers, subject to a uniform magnetic field. A dimensionless parameter,$\mbox{S}$, is defined to represent the relative strength between the magnetic and hydrodynamic torques. Without magnetic fields, the particle completes a family of periodic rotations known as Jeffery's Orbit. With a magnetic field, we find that there exists a critical value of $\mbox{S}$ ($\mbox{S}_{cr} )$. The particle is able to execute complete rotations for a weak magnetic field ($\mbox{S}$\textless $\mbox{S}_{cr} )$, and the particle rotation is impeded for a strong magnetic field ($\mbox{S}_{cr} )$. We study the effect of the direction of the magnetic field on the particle rotation. For $\mbox{S}$\textless $\mbox{S}_{cr} $, we obtain the relationship between the direction of the magnetic field and the symmetry property of the particle rotation. For $\mbox{S}$\textgreater $\mbox{S}_{cr} $, we determine the steady-state angles of the particle, and analyze their stability. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M37.00004: Streaming and particle motion in acoustically-actuated leaky systems Nitesh Nama, Rune Barnkob, Tony Jun Huang, Christian Kahler, Francesco Costanzo The integration of acoustics with microfluidics has shown great promise for applications within biology, chemistry, and medicine. A commonly employed system to achieve this integration consists of a fluid-filled, polymer-walled microchannel that is acoustically actuated via standing surface acoustic waves. However, despite significant experimental advancements, the precise physical understanding of such systems remains a work in progress. In this work, we investigate the nature of acoustic fields that are setup inside the microchannel as well as the fundamental driving mechanism governing the fluid and particle motion in these systems. We provide an experimental benchmark using state-of-art 3D measurements of fluid and particle motion and present a Lagrangian velocity based temporal multiscale numerical framework to explain the experimental observations. Following verification and validation, we employ our numerical model to reveal the presence of a pseudo-standing acoustic wave that drives the acoustic streaming and particle motion in these systems. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M37.00005: Self-Similar Taylor Cone Formation in Conducting Viscous Films: Computational Study of the Influence of Reynolds Number Theodore Albertson, Sandra Troian Previous studies by Zubarev (2001) and Suvorov and Zubarev (2004) have shown that above a critical field strength, an \textit{ideal} (inviscid) conducting fluid film will deform into a singular profile characterized by a conic cusp. The governing equations for the electrohydrodynamic response beneath the cusp admit self-similar solutions leading to so-called blow-up behavior in the Maxwell pressure, capillary pressure and kinetic energy density. The runaway behavior in these variables reflects divergence in time characterized by an exponent of -2/3. Here we extend the physical system to include viscous effects and conduct a computational study of the cusp region as a function of increasing electrical Reynolds number $Re_E$. We employ a finite element, moving mesh algorithm to examine the behavior of the film shape, Maxwell pressure and capillary pressure upon approach to the blow-up event. Our study indicates that self-similarity establishes at relatively low $Re_E$ despite the presence of vorticity, which is localized to the cusp surface region. With increasing $Re_E$, the period of self-similiarity extends further in time as the exponent changes from about -4/5 to the ideal value of -2/3, with slightly different values distinguishing the Maxwell and capillary stresses. [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M37.00006: Solution of the Inverse Problem for Thin Film Patterning by Electrohydrodynamic Forces} Chengzhe Zhou, Sandra Troian Micro- and nanopatterning techniques for applications ranging from optoelectronics to biofluidics have multiplied in number over the past decade to include adaptations of mature technologies as well as novel lithographic techniques based on periodic spatial modulation of surface stresses. We focus here on one such technique which relies on shape changes in nanofilms responding to a patterned counter-electrode. The interaction of a patterned electric field with the polarization charges at the liquid interface causes a patterned electrostatic pressure counterbalanced by capillary pressure which leads to 3D protrusions whose shape and evolution can be terminated as needed. All studies to date, however, have investigated the evolution of the liquid film in response to a \textit{preset} counter-electrode pattern. In this talk, we present solution of the inverse problem for the thin film equation governing the electrohydrodynamic response by treating the system as a transient control problem. Optimality conditions are derived and an efficient corresponding solution algorithm is presented. We demonstrate such implementation of film control to achieve periodic, free surface shapes ranging from simple circular cap arrays to more complex square and sawtooth patterns. [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M37.00007: Study of Dynamic Membrane Behavior in Applied DC Electric Field Prashanta Dutta, Adnan Morshed, Mohammad Hossan Electrodeformation of vesicles can be used as a useful tool to understand the characteristics of biological soft matter, where vesicles immersed in a fluid medium are subjected to an applied electric field. The complex response of the vesicle membrane strongly depends on the conductivity of surrounding fluid, vesicle size and shape, and applied electric field We studied the electrodeformation of vesicles immersed in a fluid media under a short DC electric pulse. An immersed interface method is used to solve the electric field over the domain with conductive or non-conductive vesicles while an immersed boundary scheme is employed to solve fluid flow, fluid-solid interaction, membrane mechanics and vesicle movement. Force analysis on the membrane surface reveals almost linear relation with vesicle size, but highly nonlinear influence of applied field as well as the conductivity ratios inside and outside of the vesicle. Results also point towards an early linear deformation regime followed by an equilibrium stage for the membranes. Moreover, significant influence of the initial aspect ratio of the vesicle on the force distribution is observed across a range of conductivity ratios. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M37.00008: Solution-Based Electro-Orientation Spectroscopy (EOS) for Contactless Measurement of Semiconductor Nanowires Wuhan Yuan, Amar Mohabir, Gozde Tutuncuoglu, Michael Filler, Leonard Feldman, Jerry Shan Solution-based, contactless methods for determining the electrical conductivity of nanowires and nanotubes have unique advantages over conventional techniques in terms of high throughput and compatibility with further solution-based processing and assembly methods. Here, we describe the solution-based electro-orientation spectroscopy (EOS) method, in which nanowire conductivity is measured from the AC-electric-field-induced alignment rate of the nanowire in a suspending fluid. The particle conductivity is determined from the measured crossover frequency between conductivity-dominated, low-frequency alignment to the permittivity-dominated, high-frequency regime. We discuss the extension of the EOS measurement range by an order-of-magnitude, taking advantage of the high dielectric constant of deionized water. With water and other fluids, we demonstrate that EOS can quantitatively characterize the electrical conductivities of nanowires over a 7-order-of-magnitude range, 10$^{\mathrm{-5}}$ to 10$^{\mathrm{2}}$ S/m. We highlight the efficiency and utility of EOS for nanomaterial characterization by statistically characterizing the variability of semiconductor nanowires of the same nominal composition, and studying the connection between synthesis parameters and properties. [Preview Abstract] |
Tuesday, November 21, 2017 9:44AM - 9:57AM |
M37.00009: Electric field induced self-assembly of monolayers of gold nanoparticles for surface enhanced Raman scattering applications. Suchandra Das, Naga Musunuri, Pavel Kucheryavy, Jenny Lockard, Ian Fischer, Pushpendra Singh We present a technique that uses an electric field in the direction normal to the interface for self-assembling monolayers of gold nanoparticles on fluid-liquid interfaces and freezing these monolayers onto the surface of a flexible thin film. The electric field gives rise to dipole-dipole and capillary forces which cause the particles to arrange in a triangular pattern. The technique involves assembling the monolayer on the interface between a UV-curable resin and another fluid by applying an electric field, and then curing the resin by applying UV light. The monolayer becomes embedded on the surface of the solidified resin film. We are using these films for surface enhanced Raman scattering (SERS) applications. Initial measurements indicate improved performance over commercially available SERS substrates. [Preview Abstract] |
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