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Electrokinetic flow instabilities in shear thinning fluids with conductivity gradients
To-Lin Chen1,2, Mahmud Kamal Raihan2, Seyed Mojtaba Tabarhoseini2
1Department of Engineering Science, National Cheng Kung University, Tainan 70101, Taiwan. loudyfu@mail.ncku.edu.tw.
Soft Matter
|January 8, 2025
Summary
Fluid shear thinning, induced by xanthan gum (XG) in microchannel electrokinetic flows, lowers the electric field threshold for instabilities. However, wave properties like speed and amplitude decrease with increasing polymer concentration.
Area of Science:
- Fluid Dynamics
- Electrokinetics
- Microfluidics
Background:
- Electrokinetic instabilities (EKI) manifest as waves at fluid interfaces in microchannels under electric fields.
- Prior research primarily focused on Newtonian fluids, neglecting non-Newtonian behavior common in biological and chemical samples.
Purpose of the Study:
- To experimentally investigate the impact of fluid shear thinning on electrokinetic instabilities (EKI).
- To analyze the effects of xanthan gum (XG) concentration on EKI wave characteristics and onset thresholds.
Main Methods:
- Addition of xanthan gum (XG) to Newtonian buffer solutions to induce shear-thinning properties.
- Experimental observation and measurement of EKI wave onset, propagation speed, amplitude, and frequency in microchannels.
- Analysis of the critical electric Rayleigh number considering fluid property variations.
Main Results:
- The threshold electric field for EKI onset was significantly reduced in XG solutions compared to Newtonian solutions.
- Wave propagation speed, amplitude, and frequency were diminished in the presence of XG.
- Increasing XG concentration lowered the threshold electric field and critical electric Rayleigh number, indicating shear thinning enhances EKI.
Conclusions:
- Fluid shear thinning, achieved with xanthan gum, effectively lowers the electric field threshold for electrokinetic instabilities.
- While shear thinning enhances EKI onset, wave properties exhibit a non-monotonic trend with polymer concentration, diverging from predictions based solely on electroosmotic velocity.
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