Self-Assembly of Active Bivalent Patchy Particles

TL;DR

This study investigates how active patchy particles self-assemble into chains and novel structures like spirals and spinning crystals, revealing activity-driven aggregation behaviors and structural transitions at different temperatures and densities.

Contribution

It introduces the first detailed analysis of out-of-equilibrium polymerization of active bivalent patchy particles, highlighting activity effects on chain formation and novel aggregate states.

Findings

Active particles form aggregating chains unlike passive systems.

Low activity favors random self-assembly; high activity induces alignment.

At low temperature and high density, chains form motility-induced spirals (MISP).

Abstract

In the present work, with the intent of exploring the out-of-equilibrium polymerization of active patchy particles in linear chains, we study a suspension of active bivalent Brownian particles (ABBPs). At all studied temperatures and densities, ABBPs self-assemble in aggregating chains, as opposed to the uniformly space-distributed chains observed in the corresponding passive systems. The main effect of activity, other than inducing chain aggregation, is to reduce the chain length and favor alignment of the propulsion vectors in the bonding process. At low activities, attraction dominates over activity in the bonding process, leading self-assembly to occur randomly regardless of the particle orientations.Interestingly, we find that at the lowest temperature, as density increases, chains aggregate forming a novel state: MISP, i.e., Motility-Induced Spirals, where spirals are characterised by a finite angular velocity. On the contrary, at the highest temperature, density and activity, chains aggregate forming a different novel state (a spinning crystalline cluster) characterized by a compact and hexagonal ordered structure, both translating and rotating. The rotation arises from an effective torque generated by the presence of competing domains where particles self-propel in the same direction.