Formation of spiral coils among self-propelled chains

We study the dynamics of self-propelled chains with the excluded volume interaction via the Brownian dynamics simulation, in which the bending elasticity of chains is varied. The changes of the bending elasticity lead to various characteristics of the clustering behavior in the short-chain-only system. When a long self-propelled chain is mixed with these short chains, it can fold into the spiral coil, a steadily rotating spiral conformation, either at a high density of short chains or at a low density if the long chain itself is sufficiently flexible. Our results qualitatively support the speculation that the formation of the spiral coil in the swarm of Vibrio alginolyticus is triggered by collisions from the clusters of the shorter bacteria.