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 G01: Focus Session: Acoustofluidics I |
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Chair: James Friend, UC San Diego Room: Sagamore 123 |
Sunday, November 20, 2022 3:00PM - 3:13PM |
G01.00001: On the heating and patterning dynamics in acoustic tweezers based on surface acoustic waves Jörg König, Zhichao Deng, Robert Weser, Vijay Kondalkar, Alexandre Darinskii, Hagen Schmidt, Christian Cierpka Acoustic tweezers enable a non-invasive, label- and contact-free method for the precise manipulation of micro objects, which is of particular importance for biological cells to avoid (cross-)contamination and to prevent cell death. Although, cells are subjected to mechanical and thermal stress, acoustic tweezers are usually considered as biocompatible. In this presentation, the correlation between acoustic fields and acoustophoretic motion of particles as well as heating effects caused by inherent energy conversion processes are revealed, applying laser Doppler vibrometry, astigmatism particle tracking velocimetry and luminescence lifetime imaging in parallel. In situ measurements with high spatial and temporal resolution reveal not only a 3D particle patterning coinciding with the experimentally assisted numerical result of the acoustic radiation force distribution, but also a significant and very rapid temperature rise of up to 55°C depending on acoustic power and position of the particles within the microfluidic chamber. Besides, while particle patterning establishes within less than 2 seconds, temperature rises within a few tens of seconds. |
Sunday, November 20, 2022 3:13PM - 3:26PM |
G01.00002: Interactions between electrical double layers and MHz-frequency surface acoustic waves: Revisiting the electroacoustic phenomenon near a planar substrate Oles Dubrovski, Sudeepthi Aremanda, Ofer Manor The electrical double layer of ions (EDL) to appear next to charged surfaces in electrolyte solutions is fundamental across countless natural and artificial systems and may considerably vary in properties between one system to another. Its applications range from supporting electrophoresis and electrowetting to governing the kinetics of particulate coagulation and from governing the folding structures of proteins and the surface properties of membranes to determining the rate of particulate adsorption onto a substrate. However, the generic nature of the EDL and the interplay between intimate physical mechanisms therein is still an enigma even now, more than a century since it was discovered. A main difficulty in investigating dynamic EDL effects is the short EDL length scale of usually several nanometers and the EDL relaxation time of nano- to micro-seconds. We employ a MHz-frequency mechanical vibration near the surface of a solid substrate, i.e., a Rayleigh type surface acoustic wave (SAW), to excite the EDL within its length and time scales and hence obtain dynamical information about the physics therein. |
Sunday, November 20, 2022 3:26PM - 3:39PM |
G01.00003: Baroclinic acoustic streaming Remil Mushthaq, Gregory Chini, Guillaume Michel Chini et al. [J. Fluid Mech., 744 (2014), pp. 329-351] showed that baroclinically-produced fluctuating vorticity resulting from the interaction of an acoustic wave with a stratified fluid can drive time-mean flows that are orders of magnitude stronger than those realized in classical Rayleigh streaming. Subsequently, Michel & Chini [J. Fluid Mech., 858 (2019), pp. 536-564] demonstrated the potential for fully two-way coupling between a standing acoustic wave and the streaming flow driven by the wave in a thin channel with an imposed cross channel temperature gradient. More recently, Abdul-Massih (UNH dissertation, 2022) extended the work of Michel & Chini (2019) by quantifying the forced convective heat-transfer enhancement arising in baroclinic acoustic streaming as a function of the streaming-cell aspect ratio. The present investigation continues this line of inquiry by examining the structure of the wave/mean-flow coupling and concomitant heat transport in the large aspect-ratio regime, i.e., when the channel height is large relative to the wavelength of the imposed standing acoustic wave. The ultimate aim is to assess the potential for baroclinic acoustic streaming to be employed as a practical means of enhancing transport in fluid systems with imposed density variations. |
Sunday, November 20, 2022 3:39PM - 3:52PM |
G01.00004: Leaky wave coupling strength prescribes rigid kinematics and acoustic streaming in superhydrophobically stabilized droplets. Kha Nguyen, Jeremy Orosco, James Friend Acoustofluidics at micro- to nano-scales opens new doors to lab-on-a-chip technologies as it enables the introduction of chaotic advection and turbulence into fluidics systems in which low Reynolds number flows dominate. This technology relies on surface acoustic waves (SAWs), generated on piezoelectric substrates like lithium niobate, propagating along the surface and emitting energy into the fluid domains they encounter. However, the underlying physics is often obscured as existing theories fail to explain the complex, enigmatic behaviors observed at these extreme spatiotemporal scales. In this work, we demonstrate an easy-to-replicate system involving traveling SAWs introduced into a well-understood geometry—a spherical droplet stabilized on a superhydrophobic surface—through a microscopic circular defect mediating the transduction of the acoustic waves at the fluid-substrate interface: from internal streaming to bulk kinematic motion of the droplet, with interpolated behaviors marrying these extremes. We show that this continuously varying behavior is a function of specific system geometry and is independent of input power. Furthermore, we perform numerical simulations of the droplet's acoustic field to complement analysis and experiment, providing additional information to help understand the resulting hydrodynamics. |
Sunday, November 20, 2022 3:52PM - 4:05PM |
G01.00005: Surface acoustic wave activated droplet sorting in microfluidics using absorbance. Esther S Richter, Thomas Franke Microfluidic sorting is a powerful high-throughput screening tool in biotechnologies, including directed evolution, drug screening and single cell analysis. Drops can be sorted sorted in many ways, such as electric or magnetic fields. We use interdigitated transducers to create acoustic streaming in microfluidic channels to deflect drops. The generated travelling surface acoustic wave changes the flow streaming, and sorts subpopulations. Populations can be sorted independent of an object's properties and responsive particles, or dielectric components. The decision to select a subpopulation can be based on various criteria. Fluorescent detection is widely used, yet it requires labelling. Here we provide a label free technique using absorbance. Absorbance detection is often used to analyse biological samples, provides quantitative data and is particularly useful to sort drops. Based on Beer-Lamberts law, monodisperse drops have a fixed optical pathlength to measure absorbance. We have integrated label free absorbance detection and acoustically activated drop deflection with kHz sorting rates. |
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