Phase behavior and surface tension of soft active Brownian particles

Area of Science:

• Soft Matter Physics
• Statistical Mechanics
• Active Matter Systems

Background:

• Active Brownian particles (ABPs) exhibit motility-induced phase separation (MIPS), forming dense clusters.
• Understanding the thermodynamic and structural properties of these dense phases is crucial.

Purpose of the Study:

• To develop a microscopic, analytical method for predicting dense phase structure in ABPs.
• To investigate the relationship between interparticle pressure, swim pressure, and macroscopic pressure.
• To analyze the intrinsic nature of surface tension in phase-separated ABP systems.

Main Methods:

• Microscopic analytical theory for predicting dense phase structure.
• Brownian dynamics simulations of quasi two-dimensional ABPs.
• Derivation of a continuum model for pressure analysis.

Main Results:

• Accurate predictions of dense cluster area fraction, interparticle pressure, and radius.
• Consistent pressure predictions between microscopic theory and continuum model when activity is treated as a body force.
• Demonstration that interface width and surface tension are intrinsic system properties.

Conclusions:

• The proposed pressure formulation accurately describes ABP systems.
• Surface tension in ABP systems is an intrinsic characteristic, independent of system size when activity is properly accounted for.
• This work provides a robust framework for understanding phase separation in active matter.