Bulk Condensation by an Active Interface

Area of Science:

• Physics
• Materials Science
• Soft Matter Physics

Background:

• Understanding fluid dynamics and phase transitions is crucial in materials science.
• Self-assembly of active matter offers novel pathways for material organization.

Purpose of the Study:

• To investigate the role of motile grains in inducing bulk condensation of a hard-bead fluid.
• To explore the self-assembly dynamics and structural properties of the condensed phase.

Main Methods:

• Experimental observation of fluid condensation driven by motile grains.
• Mechanically detailed simulations to model the system's behavior.
• Development of a continuum theory based on the Cahn-Hilliard equation.

Main Results:

• A small population of orientable motile grains self-assembles into a moving polarized monolayer, inducing bulk condensation.
• In a quasi-1D geometry, two oppositely aligned layers of motile grains immobilize the condensed nonmotile component.
• The continuum theory, featuring a nonreciprocal Cahn-Hilliard structure, accurately predicts observed trends with varying packing fractions.

Conclusions:

• Motile grains can act as effective agents for inducing and controlling phase transitions in fluids.
• The observed phenomena can be described by a modified Cahn-Hilliard theory, highlighting the importance of nonreciprocity.
• This work provides insights into active matter systems and their potential for creating ordered structures.