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Negative Drag Force on Beating Flagellar-Shaped Bodies in Active Fluids.

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Active particles (APs) create complex drag forces on flagellum-like objects. The force direction depends on object motion, driven by particle redistribution, with implications for micro-robotics.

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Area of Science:

  • Physics of active matter
  • Fluid dynamics
  • Soft robotics

Background:

  • Active particles (APs) exhibit self-propulsion or directed motion.
  • Interactions between active particles and immersed objects are crucial for understanding complex fluid behavior.
  • Phototaxis, or light-directed movement, is a key mechanism for controlling AP behavior.

Purpose of the Study:

  • To experimentally investigate the drag forces exerted by active particles on a flagellum-shaped object.
  • To explore how object motion (translation and beating) influences drag forces in active particle suspensions.
  • To understand the role of dynamic particle redistribution in generating these forces.

Main Methods:

  • Experimental investigation using a flagellum-shaped object and light-induced active particles.
  • Utilizing negative phototactic interactions to control particle behavior.
  • Employing numerical simulations and an analytical model for validation and generalization.

Main Results:

  • Observed both positive and negative drag forces on the flagellum-shaped object.
  • Drag force direction was found to depend on the beating frequency and translational velocity of the object.
  • Dynamic redistribution of active particles in response to object motion was identified as the driving mechanism.

Conclusions:

  • The interplay between object geometry changes and active particle density distribution is complex.
  • Findings provide insights into fluid-structure interactions in active baths.
  • Results have potential relevance for the design and control of microrobotic systems.