Activity Driven Orientational Order in Active Nematic Liquid Crystals on an Anisotropic Substrate

Area of Science:

• Physics
• Soft Matter Physics
• Fluid Dynamics

Background:

• Active nematics exhibit complex dynamics driven by self-propelled constituent elements.
• Anisotropic substrates can influence the behavior of materials by introducing directional preferences.
• Understanding defect dynamics is crucial for predicting active matter behavior.

Purpose of the Study:

• To investigate how anisotropic substrates affect the turbulent dynamics of two-dimensional active nematics.
• To determine the role of anisotropic friction and viscosity in defect ordering.
• To elucidate the mechanisms driving defect alignment.

Main Methods:

• Simulated a two-dimensional active nematic system.
• Introduced anisotropic friction and viscosity defined by the substrate.
• Analyzed the emergence and alignment of topological defects.
• Examined the active flow generated by individual defects.

Main Results:

• Global nematic order of topological defects emerged and was controlled by viscosity anisotropy and active stress magnitude.
• Passive liquid crystals with anisotropic properties did not show global defect alignment.
• Active flow kinetic energy depended on defect orientation relative to the substrate.
• A torque was observed, aligning defects with substrate anisotropy.

Conclusions:

• Active stress, not passive properties, drives defect ordering in anisotropic environments.
• Substrate anisotropy dictates defect alignment through orientation-dependent active flow and resulting torques.
• The findings provide insights into controlling active matter organization using surface properties.