Symmetry-breaking motility of penetrable objects in active fluids

Area of Science:

• Physics
• Soft Matter Physics
• Fluid Dynamics

Background:

• Active fluids exhibit unique properties due to self-propelling constituents.
• Object motility in active fluids is typically linked to fluid's orientational order (polar or nematic).
• Negative drag can induce motion in immersed objects.

Purpose of the Study:

• To investigate object motility in active fluids lacking preexisting order.
• To characterize the transitions leading to object self-propulsion.
• To explore the relationship between motility transitions and diffusion coefficients.

Main Methods:

• Theoretical analysis of a penetrable object in an active fluid.
• Investigation of symmetry-breaking bifurcations.
• Analysis of steady-state velocity and diffusion coefficients.

Main Results:

• Demonstrated motility of a symmetric object in an unordered active fluid.
• Identified continuous and discontinuous transitions in object velocity.
• Revealed a nonmonotonic dependence of the diffusion coefficient on particle size.

Conclusions:

• Object motility is achievable in active fluids without inherent order.
• Symmetry-breaking bifurcations govern the onset and nature of motility.
• Transitions influence the object's diffusive behavior, highlighting complex dynamics.