Active sorting to boundaries in active nematic-passive isotropic fluid mixtures.

Area of Science:

• Soft matter physics
• Active matter physics
• Fluid dynamics

Background:

• Active nematic fluids exhibit self-propulsion and orientational order.
• Confined fluid mixtures can display emergent behaviors at interfaces.
• Boundary conditions significantly influence fluid phase behavior.

Purpose of the Study:

• To investigate the boundary accumulation of active nematic fluids in a mixture with passive isotropic fluids.
• To understand the role of fluid activity (extensile vs. contractile) and boundary anchoring on spatial distribution.
• To explore the mechanisms driving active fluid sorting at interfaces.

Main Methods:

• Utilizing a two-fluid theoretical model.
• Simulating the behavior of active nematic and passive isotropic fluids in confinement.
• Analyzing the effects of planar and homeotropic boundary anchoring conditions.

Main Results:

• Extensile active fluids accumulate at planar boundaries but decrease in concentration at homeotropic boundaries.
• Contractile active fluids show reversed accumulation behavior compared to extensile fluids.
• Active fluid sorting is driven by nematic order gradients, influenced by imposed or spontaneous anchoring.

Conclusions:

• The sorting of active fluids at boundaries is predictable and depends on activity type and anchoring.
• Nematic order gradients are key to understanding active fluid segregation.
• Findings are relevant for experiments with microtubule-kinesin systems and biological phenomena like cell colony sorting.