| 1. |
- Hemachandran, E., et al.
(author)
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Bulk Acoustic Wave Activated Droplet Generation and Isolation
- 2023
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In: Fluid Mechanics and Fluid Power (Vol. 3)- Select Proceedings of FMFP 2021. - 2195-4364 .- 2195-4356. - 9789811962691 ; , s. 145-150
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Conference paper (peer-reviewed)abstract
- On-demand droplet generation from a continuously flowing stream of aqueous phase has profound applications in dropletbased microfluidics for rare event encapsulation studies. Here, we present acoustic relocation-based droplet generation from co-flowing immiscible fluids in an on-demand manner using bulk acoustic wave (BAW). After on-demand droplet generation, droplets are isolated using the same acoustic force resulted from BAW. Two different acoustic relocation regimes are observed, namely, stream to droplet relocation and stream to stream relocation regime. Our experimental observation reveals that to generate droplets from co-flowing fluids, the following conditions must be satisfied. First, the co-flowing immiscible stream should be maintained in acoustic relocation conditions (Cac > 1); Second, the capillary instability should be triggered during the relocation process, which happens at capillary numbers of the co-flowing fluids should be less than 0.2 (CaL and CaH < 0.2). Finally, using BAW microfluidic chip, droplets containing microparticle were produced ondemand from co-flowing streams wherein the microparticles are added in one of the phases.
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| 2. |
- Hemachandran, E., et al.
(author)
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Continuous Droplet Coalescence in a Microchannel Coflow Using Bulk Acoustic Waves
- 2019
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In: Physical Review Applied. - 2331-7019. ; 12:4
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Journal article (peer-reviewed)abstract
- The coalescence of liquid droplets with a liquid stream has profound importance in various emerging applications, such as biochemical assays. Acoustic force-based droplet manipulation, which offers unique advantages, is consequently gaining attention. However, the physics of acoustics-driven coalescence of liquid droplets with a liquid stream is not well understood. Here, we unravel the mechanism of coalescence of aqueous droplets flowing in an immiscible (oil) phase with a coflowing aqueous stream, when the system is exposed to acoustic radiation force due to bulk acoustic waves. Our study reveals that the acoustic coalescence phenomenon is governed by the interplay between two important timescales, acoustic migration timescale (τac) and advection timescale (τadv), that underpin the phenomenon. We find that the phenomenon is also governed by the acoustic capillary number (Cac) and relative widths of the coflowing oil and aqueous streams (i.e., Waq and Woil). Our results show that, if Cac<0.9 and Waq>Woil are satisfied to ensure the stability of the streams and positioning of the acoustic node in the aqueous phase, respectively, continuous coalescence is observed for (τadv/τac)≥0.85. We exploit the phenomenon for the extraction of droplet contents (beads and cells) into an aqueous stream.
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| 3. |
- Hemachandran, E., et al.
(author)
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Relocation of coflowing immiscible liquids under acoustic field in a microchannel
- 2019
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In: EPL. - : IOP Publishing. - 1286-4854. ; 125:5
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Journal article (peer-reviewed)abstract
- We report the dynamics of coflowing immiscible liquid streams exposed to an acoustic standing wave in a microchannel. Relocation of the liquid streams is experimentally demonstrated and a theoretical model that explains the underlying phenomena is presented. Our experiments and theoretical model suggest that the relocation phenomena are governed by the interplay between the primary acoustic radiation force F ac and the interfacial tension force F int-which is represented in terms of a new dimensionless number called "acoustocapillary number", . Using various combinations of immiscible liquids, we show that relocation of the higher acoustic impedance liquid stream to the pressure node occurs above a critical acoustocapillary number . The understanding of the above phenomena provides a new paradigm related to the manipulation of immiscible liquids under acoustic field.
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| 4. |
- Hemachandran, E., et al.
(author)
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Reversible Stream Drop Transition in a Microfluidic Coflow System via on Demand Exposure to Acoustic Standing Waves
- 2021
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In: Physical Review Letters. - 0031-9007. ; 127:13
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Journal article (peer-reviewed)abstract
- Transition between stream and droplet regimes in a coflow is typically achieved by adjusting the capillary numbers (Ca) of the phases. Remarkably, we experimentally evidence a reversible transition between the two regimes by controlling exposure of the system to acoustic standing waves, with Ca fixed. By satisfying the ratio of acoustic radiation force to the interfacial tension force, , experiments reveal a reversible stream drop transition for , and stream relocation for . We explain the phenomenon in terms of the pinching, advection, and relocation timescales and a transition between convective and absolute instability from a linear stability analysis [P. Guillot, Phys. Rev. Lett.99, 104502 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.104502].
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