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arXiv · 2504.07050

Minimal mechanism for flocking in phoretically interacting active particles

Arvin Gopal Subramaniam·Sagarika Adhikary·Rajesh Singh
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Abstract

Coherent collective motion is a widely observed phenomenon in active matter systems. Here, we report a flocking transition mechanism in a system of chemically interacting active colloidal particles sustained purely by chemo-repulsive torques at low to medium densities. The basic requirements to maintain the global polar order are excluded volume repulsions and long-ranged repulsive torques. This mechanism requires that the time scale individual colloids move a unit length to be dominant with respect to the time they deterministically respond to chemical gradients, or equivalently, pair colloids sliding together a minimal unit length before deterministically rotating away from each other. Switching on the translational repulsive forces renders the flock a crystalline structure. Furthermore, liquid flocks are observed for a range of chemo-attractive inter-particle forces. Various properties of these two distinct flocking phases are contrasted and discussed. We complement these results with stability analysis of a hydrodynamic model, which admits the transition corresponding to destabilization of the flocking state observed in particle-based simulations.

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Arvin Gopal Subramaniam, Sagarika Adhikary, Rajesh Singh. 2025-04-09. Minimal mechanism for flocking in phoretically interacting active particles. https://doi.org/10.1039/d5sm01005e

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