Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session G34: Micro/Nano Particles: Magnetic Manipulation |
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Chair: Gabriel Caballero-Robledo, National Polytechnic Institute Room: 242 |
Sunday, November 20, 2022 3:00PM - 3:13PM |
G34.00001: The Impact of Polymer Fluid Microstructure on Achiral Microswimmer Propulsion David Quashie, Sophie Jermyn, David Gordon, Paige Nielsen, Shannon Kelley, Jamel Ali Rigid microscale swimmers consisting of geometries with two or fewer symmetrical axes offer a simple design approach for producing effective microswimmers. However, for efficient propulsion in complex media, swimmer geometry must also account for interactions within fluidic environments which often contain colloids and polymers that can alter swimming kinematics. Here we explore the effects of fluid microstructure on two geometrically distinct achiral microswimmers made of aggregated magnetic microbeads that have arc structures with a single axis of symmetry. Polymer solutions of varying number average molecular weight (Mn) are used to create Newtonian solutions with differing local microstructures. When actuated using a uniform rotational magnetic field, swimmer propulsion efficiency varies significantly with Mn. Local viscoelastic effects are proposed to contribute to the modulation of achiral swimmers’ gait and efficiency in high Mn polymer solutions. To investigate this, dilute polymer solutions that exhibit either predominantly shear thinning behavior or have significant elasticity are explored. Both types of viscoelastic fluid are observed to affect the achiral kinematics; however, these effects vary with swimmer geometry. This work provides insight into designing achiral microswimmers with enhanced propulsion efficiency given a priori knowledge of the fluidic environment. |
Sunday, November 20, 2022 3:13PM - 3:26PM |
G34.00002: Adjoint-based optimization of open loop control of a microfluidic acoustic flow Javier Lorente Macias, Matthew P Juniper Drop-on-demand inkjet printing is one of the most widespread applications of microfluidics. Within the printhead, ink continuously flows through multiple microchannels. Each microchannel contains a piezo-electric actuator on the top face and a nozzle on the opposite face. When the actuator pulses, a droplet is forced through the nozzle. Acoustic oscillations then reverberate within the microchannel until they are damped by viscous and thermal dissipation. If a droplet is ejected before the reverberations from the previous droplet have been sufficiently damped, its size is affected by the reverberations, which spoils the image being printed. In this study, we design open loop control of the actuator to eliminate these reverberations. First, we derive the governing equations of the thermoviscous acoustic flow by linearising the compressible Navier-Stokes equations. Then we derive the associated adjoint problem to obtain the gradient of the objective function (the acoustic energy after a given time) with respect to the actuator deformation. Finally we formulate an optimisation problem to find the actuator waveform that minimises the reverberations within a given time. |
Sunday, November 20, 2022 3:26PM - 3:39PM |
G34.00003: Magnetically-actuated thin films Navraj S Lalli, Li Shen, Daniele Dini, Andrea Giusti The application of a magnetic field (MF) to thin films (TFs) containing ferromagnetic nanoparticles (NPs) is explored as a means of acquiring control over the film drainage and stability. Freely-suspended TFs were created on a horizontal glass boundary from mixtures containing water, surfactant, glycerin and magnetite NPs. The film thickness is recorded via interferometry and the motion of aggregates can be traced as they appear white. In the absence of an external MF, drainage of the film is approximately axisymmetric and towards the borders of the film due to capillary suction; however, with an inhomogeneous external MF, there is an increase in the drainage rate towards the region of greater magnetic flux density (by magnitude) due to magnetite-surfactant aggregates moving, and dragging surrounding liquid, towards that region. The average film lifetime was significantly lower in this case. Overall, this may be the starting point for creating externally actuated TFs, which could encapsulate a substance such as a gaseous fuel or drug whose release could be induced through an external field. As a result of these findings, future work will focus on studying whether similar effects can be found with an electric field applied to TFs containing charged or electrically-polarisable NPs. |
Sunday, November 20, 2022 3:39PM - 3:52PM |
G34.00004: Capture of magnetic nanoparticles does not depend on the compaction of microparticles in a chip Gabriel A Caballero-Robledo, Keziah B Reynoso-Hernández, Pablo E Guevara-Pantoja, Harold O Ochoa-Gutiérrez Magnetic nanoparticles can be captured in a magnetized porous medium composed of ferromagnetic microparticles. But, how does the microparticles' packing state affect the nanoparticle capture? In this work, we present experiments of a magnetic trap in a microfluidic chip where we study the capture efficiency as a function of the compaction of the microparticles column. We also present a simple analytical model based on the competition of drag and magnetic forces. Our work can help optimize environmental and biomedical applications based on high-gradient magnetic nanoparticle separation. |
Sunday, November 20, 2022 3:52PM - 4:05PM |
G34.00005: Suppressing dendritic growth in electrochemical systems using magnetic fields Kirutiga Srikanda Prabanna Balan, Thomas C Underwood The growth of metal dendrites limits the efficiency of electrodeposition in electrochemical systems and constrains the lifetime of next-generation battery technologies. Strategies to tailor ionic transport have shown to be effective in delaying the onset of dendritic growth in electrolytic solutions. For example, imposing bulk flow is known to reduce boundary layer heights while enhancing the rate of ionic diffusion. Using a microfluidic reactor, we show how a magnetic field can also increase the deposition rate and energy efficiency of Cu electrodeposition using Lorentz forces. Magnetic fields are observed to induce vorticity, drive bulk flow, and enhance mixing near dendritic interfaces as they grow. These three-dimensional effects are distinct from imposed convection and offer a means to drive local transport around dynamic interfaces where current flows. Magnetic fields are shown to be a solution that enhances the extraction rate and energy efficiency of electrodeposition while limiting the height of metal dendrites. |
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