Defect self-propulsion in active nematic films with spatially varying activity.

Area of Science:

• Physics
• Soft Matter Physics
• Complex Fluids

Background:

• Active nematic films exhibit dynamic topological defects.
• Understanding defect behavior in non-uniform active environments is crucial.

Purpose of the Study:

• Investigate topological defect dynamics in active nematic films with spatially varying activity.
• Analyze the effects of constant activity gradients and sharp activity jumps on defect motion and orientation.

Main Methods:

• Theoretical modeling of active nematic hydrodynamics.
• Numerical simulations of topological defect dynamics.
• Analysis of defect trajectories, velocities, and orientations.

Main Results:

• Constant activity gradients induce finite vorticity in +1/2 defects, aligning them with the gradient.
• +1/2 defects retain self-propulsion, while -1/2 defects remain non-motile under constant gradients.
• Sharp activity jumps act as barriers, trapping and altering the motion of both +1/2 and -1/2 defects.
• -1/2 defects exhibit self-propulsion towards activity interfaces and preferred orientation due to vorticity-induced torques.

Conclusions:

• Spatially varying activity significantly impacts topological defect dynamics in active nematics.
• The observed behavior of defects near activity interfaces explains the accumulation of negative topological charge.
• These findings provide insights into defect organization in complex active matter systems.