Traveling Strings of Active Dipolar Colloids.

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Active Matter Physics

Background:

• Investigating self-assembled active colloidal systems is crucial for understanding emergent behaviors in complex fluids.
• Janus particles in electric fields offer a tunable platform for creating directed motion and ordered structures.

Purpose of the Study:

• To explore the self-assembly and collective dynamics of 3D colloidal polymers formed by Janus particles under electric fields.
• To investigate the transition from self-propelled columns to a string phase and analyze their dynamics.

Main Methods:

• Experimental realization of 3D self-assembled structures from Janus particle suspensions.
• Explicit numerical simulations combining dipolar interactions and active self-propulsion.
• Analytical modeling using an anisotropic Rouse model adapted for active driving.

Main Results:

• Observed self-assembly into 3D columns that exhibit 2D self-propulsion.
• Identified an activity-dependent transition to a string phase with increasing dipole strength.
• Characterized collective string dynamics and center-of-mass motion, showing consistency across experiments, simulations, and theory.
• Discovered long-range correlations in string fluctuations that grow with active persistence time.

Conclusions:

• The study elucidates the formation and behavior of novel active colloidal polymers.
• The findings highlight the role of active driving and dipolar interactions in phase transitions and collective dynamics.
• Demonstrated the predictive power of the anisotropic Rouse model for active systems and revealed purely active phenomena like growing long-range correlations.