Hydrodynamic Bend Instability of Motile Particles on a Substrate

Area of Science:

• Soft Matter Physics
• Active Matter Physics
• Fluid Dynamics

Background:

• Hydrodynamic bend instabilities are common in active particle systems.
• These instabilities are typically attributed to dipolar active stresses from self-propelled particles.
• Understanding instability origins is key for active matter applications.

Purpose of the Study:

• To investigate the emergence of hydrodynamic bend instabilities.
• To determine if instabilities can occur without dipolar active stress.
• To explore the role of self-propulsion in polar active units.

Main Methods:

• Linear stability analyses were employed.
• Numerical simulations were conducted.
• Analytical derivations were performed.

Main Results:

• A hydrodynamic bend instability was shown to emerge solely from self-propulsion forces in polar active units.
• A uniformly ordered state develops instability above a critical self-propulsion force.
• Increased self-propulsion leads to a disorderly flow state.

Conclusions:

• Hydrodynamic bend instabilities can be driven by self-propulsion alone, without dipolar stresses.
• This provides a new mechanism for instability in 2D self-propelled materials on substrates.
• The findings have implications for biological cell layers and synthetic active materials.