Classical Nucleation Theory for Active Fluid Phase Separation.

Area of Science:

• Physics
• Chemical Engineering
• Materials Science

Background:

• Classical Nucleation Theory (CNT) explains phase-change kinetics in passive fluids using a free-energy landscape.
• Nucleation in nonequilibrium systems is complex due to the absence of free energy, requiring numerical computation of a quasipotential.
• Active systems, which self-propel or consume energy, exhibit unique phase-separation behaviors.

Purpose of the Study:

• To extend Classical Nucleation Theory (CNT) to active phase-separating systems.
• To analytically compute the quasipotential and nucleation barrier for liquid-vapor phase separation in active systems.
• To investigate the role of detailed balance in active nucleation.

Main Methods:

• Utilized a minimal field-theoretic model (Active Model B+) for active phase separation.
• Applied analytical methods within the small noise and supersaturation limits of CNT.
• Identified the instanton trajectory and its properties, including the nuclear radius as the reaction coordinate.

Main Results:

• Successfully extended CNT to a class of active phase-separating systems.
• Analytically computed the quasipotential and nucleation barrier for liquid-vapor phase separation.
• Demonstrated that detailed balance, though broken microscopically, is restored along the instanton trajectory.

Conclusions:

• The study provides an analytical framework for understanding nucleation in active systems, bridging a gap in current theories.
• The findings enable predictions of phase-separation kinetics in active matter, relevant for various applications.
• Restoration of detailed balance along the instanton trajectory offers a key insight into the dynamics of active nucleation.