Live soap: stability, order, and fluctuations in apolar active smectics

Area of Science:

• Soft Matter Physics
• Active Matter Physics
• Hydrodynamic Theories

Background:

• Active fluids exhibit complex behaviors driven by internal energy sources.
• Apolar smectics possess orientational and positional order, distinct from nematics.
• Understanding dynamic stability is crucial for active matter applications.

Purpose of the Study:

• To develop a hydrodynamic theory for noisy, apolar active smectics.
• To investigate their dynamic stability in bulk suspensions and on substrates.
• To predict their phase behavior and emergent properties.

Main Methods:

• Construction of a hydrodynamic theory.
• Analysis of systems in bulk suspension and on substrates.
• Investigation in two (d=2) and three (d=3) dimensions.

Main Results:

• Active apolar smectics are dynamically stable in Stokesian bulk suspensions.
• Smectic order is quasilong-ranged in d=2 and long-ranged in d=3.
• Predicted reentrant Kosterlitz-Thouless melting to an active nematic in d=2.
• Predicted nonzero second-sound speed parallel to layers in bulk suspensions.
• Absence of giant number fluctuations in both cases.

Conclusions:

• The developed theory provides a framework for understanding active apolar smectics.
• These systems exhibit unique stability and phase transitions not seen in passive or purely orientational active fluids.
• The findings have implications for designing and controlling active soft matter systems.