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Braided mixing in confined chiral active matter
1Niels Bohr International Academy, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark. jonas.berx@nbi.ku.dk.
Soft Matter
|August 7, 2025
Summary
Active microswimmers stir fluids for efficient mixing at microscopic scales. Optimizing their patterns, like vortex droplets and oscillating phases, maximizes mixing efficiency by analyzing spacetime trajectory braids.
Area of Science:
- Physics
- Soft Matter Physics
- Fluid Dynamics
Background:
- Efficient fluid mixing is crucial for homogeneity in various applications.
- Microscopic systems face challenges with diffusion and turbulence for effective mixing.
- Active stirring or geometric boundary effects are common solutions for microscale mixing.
Purpose of the Study:
- To investigate chaotic mixing in microscopic systems using a modified chiral Vicsek model.
- To explore the role of confinement, chiral motion, and alignment interactions on mixing patterns.
- To optimize system parameters for maximum mixing efficiency.
Main Methods:
- Simulated a modified chiral Vicsek model with active microswimmers acting as moving rods.
- Analyzed mixing by computing the entanglement of particle spacetime trajectories, forming a braid.
- Optimized the finite-time braiding exponent to determine optimal system parameters.
Main Results:
- Identified specific patterns of microswimmer behavior that enhance mixing.
- Demonstrated that a combination of local stable vortex droplets and ordered oscillating phases yields maximal mixing.
- The braiding exponent serves as a quantitative measure for optimizing mixing.
Conclusions:
- A novel approach to achieving efficient microscale fluid mixing using active microswimmers has been presented.
- The study provides a method for optimizing mixing parameters by analyzing spacetime trajectory entanglement.
- The findings suggest that specific emergent patterns in active matter systems can lead to highly efficient mixing.
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