Propagation of active nematic-isotropic interfaces on substrates

Area of Science:

• Physics
• Soft Matter Physics
• Biophysics

Background:

• Bacterial swarms exhibit complex interface dynamics, as observed in active-passive interfaces of Serratia marcescens.
• Active nematics, characterized by self-propelled constituents with orientational order, display unique emergent behaviors.

Purpose of the Study:

• To investigate the propagation dynamics of active-passive interfaces using a hydrodynamic multiphase model.
• To characterize the statistical dynamics of active nematics and their relationship to experimental swarm data.
• To explore the influence of substrate friction on active nematic behavior and interface stability.

Main Methods:

• Development and application of a hydrodynamic multiphase model.
• Calculation of spatial and temporal autocorrelation functions and energy spectrum.
• Analysis of circular and flat active-passive interface propagation under varying activity levels.
• Investigation of substrate friction effects on active nematic pattern formation.

Main Results:

• The closing time of circular passive domains shows a quadratic decay with increasing activity.
• The structure factor of flat interfaces mirrors swarm data, with an activity-dependent exponent.
• Substrate friction introduces an activity-dependent threshold, leading to either isolated turbulent islands or expanding active nematics.
• Friction gradients can induce static interfaces.

Conclusions:

• The hydrodynamic model successfully captures key statistical dynamics of active nematic interfaces, consistent with bacterial swarm experiments.
• Interface propagation and pattern formation are highly sensitive to the balance between internal activity and external friction.
• Active nematic systems exhibit distinct regimes of behavior based on activity and substrate properties, including isotropic, expanding, and island-forming states.