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Interfacial instability in a viscoelastic microfluidic coflow system

Published online by Cambridge University Press:  04 December 2024

S. Hazra Open the ORCID record for S. Hazra [Opens in a new window] ,
L. Malik Open the ORCID record for L. Malik [Opens in a new window] ,
T. Sujith Open the ORCID record for T. Sujith [Opens in a new window]  and
A.K. Sen Open the ORCID record for A.K. Sen [Opens in a new window]
S. Hazra
Affiliation:
Micro Nano Bio Fluidics Unit, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
L. Malik
Affiliation:
Micro Nano Bio Fluidics Unit, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
T. Sujith
Affiliation:
Micro Nano Bio Fluidics Unit, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
A.K. Sen*
Affiliation:
Micro Nano Bio Fluidics Unit, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India
*
†Email address for correspondence: [email protected]
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Abstract

Understanding interfacial instability in a coflow system has relevance in the effective manipulation of small objects in microfluidic applications. We experimentally elucidate interfacial instability in stratified coflow systems of Newtonian and viscoelastic fluid streams in microfluidic confinements. By performing a linear stability analysis, we derive equations that describe the complex wave speed and the dispersion relationship between wavenumber and angular frequency, thus categorizing the behaviour of the systems into two main regimes: stable (with a flat interface) and unstable (with either a wavy interface or droplet formation). We characterize the regimes in terms of the capillary numbers of the phases in a comprehensive regime plot. We decipher the dependence of interfacial instability on fluidic parameters by decoupling the physics into viscous and elastic components. Remarkably, our findings reveal that elastic stratification can both stabilize and destabilize the flow, depending on the fluid and flow parameters. We also examine droplet formation, which is important for microfluidic applications. Our findings suggest that adjusting the viscous and elastic properties of the fluids can control the transition between wavy and droplet-forming unstable regimes. Our investigation uncovers the physics behind the instability involved in interfacial flows of Newtonian and viscoelastic fluids in general, and the unexplored behaviour of interfacial waves in stratified liquid systems. The present study can lead to a better understanding of the manipulation of small objects and production of droplets in microfluidic coflow systems.

JFM classification

Micro-/Nano-fluid dynamics: Microfluidics Instability: Instability Non-Newtonian Flows: Viscoelasticity
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 1000 , 10 December 2024 , A96
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Copyright
© The Author(s), 2024. Published by Cambridge University Press

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Footnotes

‡

These authors contributed equally to this work.

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Supplementary material: File

Hazra et al. supplementary movie

Observations of the unstable flow regimes: waviness along the interface and droplet formation from the low viscous fluid
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