Hydrodynamic Interactions Destroy Motility-Induced Phase Separation in Active Suspensions

Area of Science:

• Active matter physics
• Soft condensed matter
• Hydrodynamics

Background:

• Motility-induced phase separation (MIPS) is a key phenomenon in active matter, driven by self-propulsion.
• Its occurrence in wet systems with fluid-mediated hydrodynamic interactions (HIs) remains debated.
• Understanding MIPS in fluidic environments is crucial for active matter applications.

Purpose of the Study:

• To investigate whether MIPS can occur in wet active systems.
• To identify the mechanisms by which hydrodynamic interactions affect MIPS.
• To explore methods for restoring MIPS in fluidic environments.

Main Methods:

• Theoretical analysis
• Large-scale active fast Stokesian dynamics simulations
• Utilizing the squirmer model for active particles

Main Results:

• Collision-induced pusher force dipoles, even in neutral squirmers, disrupt MIPS when HIs are present.
• Both rotational and translational HIs independently suppress phase separation.
• Surface coatings can tune HIs to recover MIPS in fluidic systems.

Conclusions:

• Hydrodynamic interactions are critical in suppressing MIPS in wet active systems.
• Understanding and controlling HIs is key to achieving MIPS in fluidic environments.
• Surface modification offers a viable strategy to restore MIPS by tuning HIs.