Surface tension between coexisting phases of active Brownian particles

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Phase-separated active Brownian particles exhibit stable interfaces but conflicting negative surface tension.
• Existing models for active surface tension face challenges reconciling mechanical and thermodynamic viewpoints.

Purpose of the Study:

• To derive a mechanical expression for active surface tension that resolves the confliction with stable interfaces.
• To investigate the relationship between intrinsic pressure and active surface tension in active Brownian systems.

Main Methods:

• Derivation of a mechanical expression for active surface tension based on the work required to create interfacial area.
• Calculation of interfacial profiles of intensive quantities while maintaining their invariance.
• Mechanical stability analysis of steady-state droplets and fluctuating interfaces.

Main Results:

• A novel mechanical expression for active surface tension was derived.
• The derived expression yields a significantly positive surface tension.
• Active surface tension increases with particle activity, supported by stability analyses.

Conclusions:

• The derived mechanical expression for active surface tension resolves the long-standing contradiction in active Brownian systems.
• The findings provide a robust framework for understanding interfacial phenomena in active matter.
• This work offers a promising resolution to debates surrounding the formula of active surface tension.