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Hydrodynamic theory of flocking at a solid-liquid interface: Long-range order and giant number fluctuations
Niladri Sarkar1, Abhik Basu2, John Toner3
1Instituut-Lorentz, Leiden University, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
Physical Review. E
|January 15, 2022
Summary
Active particles at liquid-solid interfaces form stable flocks with long-range order. Stable systems exhibit giant number fluctuations and anomalous diffusion parallel to the interface.
Area of Science:
- Physics
- Soft Matter Physics
- Fluid Dynamics
Background:
- Coherent collective motion, or flocking, is observed in various biological and artificial systems.
- Understanding flocking behavior at interfaces is crucial for applications in microfluidics and materials science.
Purpose of the Study:
- To develop a hydrodynamic theory for flocking of active particles at a solid-liquid interface.
- To investigate the stability, order, and emergent phenomena in such systems.
Main Methods:
- Dynamic coupling of polar order parameter and particle concentration to the bulk fluid.
- Hydrodynamic theory construction.
Main Results:
- Stable flocking with long-range orientational order is achieved over a wide parameter range.
- Giant number fluctuations occur, scaling as the 3/4th power of the mean number in a given area.
- Anomalously rapid diffusion is observed parallel to the interface, while perpendicular diffusion remains nonanomalous.
Conclusions:
- The hydrodynamic theory successfully describes flocking at solid-liquid interfaces.
- Emergent phenomena like giant number fluctuations and anomalous diffusion are key characteristics of these systems.
- System stability and behavior are dependent on specific parameter regimes.
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