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Microbial Brazil nut effect
Atul Srivastava1, Kenji Kikuchi1,2, Takuji Ishikawa1,2
1Graduate School of Biomedical Engineering, Tohoku University, 6-6-01 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan. kenji@bfsl.mech.tohoku.ac.jp.
Soft Matter
|October 26, 2021
Summary
Microbes create gas bubbles that drive the Brazil nut effect (BNE), causing large particles to segregate in granular media. This microbial BNE was demonstrated in mixtures and for intruder segregation.
Area of Science:
- Physics
- Microbiology
- Geology
Background:
- The Brazil nut effect (BNE) describes the segregation of large particles in vibrated granular media.
- Previous studies primarily focused on mechanical vibrations and shears to induce BNE.
Purpose of the Study:
- To introduce and demonstrate a novel 'microbial Brazil nut effect' (mBNE).
- To investigate the segregation dynamics in granular mixtures and intruder transport induced by microbial activity.
Main Methods:
- Utilizing microbe-generated gas bubbles to induce granular fluctuations.
- Employing X-ray micro-computed tomography (μCT) for visualization.
- Applying scaling arguments to analyze segregation velocity.
Main Results:
- Demonstrated mBNE in both bidisperse granular mixtures and for intruder segregation.
- Clarified the transport mechanics of intruders within bubbly granular beds.
- Identified the role of microbial gas production in particle segregation.
Conclusions:
- Microbial activity can induce a Brazil nut effect in granular media.
- The findings suggest mBNE is a ubiquitous phenomenon in natural environments like wet sandy floors.
- This effect may influence material distribution in microbe-populated aquatic environments.
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