Configuration dynamics of a flexible polymer chain in a bath of chiral active particles.

We investigate the configuration dynamics of a flexible polymer chain in a bath of active particles with dynamic chirality, i.e., particles rotate with a deterministic angular velocity ω besides self-propulsion, by Langevin dynamics simulations in a two dimensional space. Particular attention is paid to how the radius of gyration Rg changes with the propulsion velocity v0, the angular velocity ω, and the chain length N. We find that in a chiral bath with a typical nonzero ω, the chain first collapses into a small compact cluster and then swells again with increasing v0, in quite contrast to the case for a normal achiral bath (ω = 0) wherein a flexible chain swells with increasing v0. More interestingly, the polymer can even form a closed ring if the chain length N is large enough, which may oscillate with the cluster if v0 is large. Consequently, the gyration radius Rg shows nontrivial nonmonotonic dependences on v0, i.e., it undergoes a minimum for relatively short chains and two minima with a maximum in between for longer chains. Our analysis shows that such interesting phenomena are mainly due to the competition between two roles played by the chiral active bath: while the persistence motion due to particle activity tends to stretch the chain, the circular motion of the particle may lead to an effective osmotic pressure that tends to collapse the chain. In addition, the size of the circular motion R0 = v0/ω plays an important role in that the compact clusters and closed-rings are both observed at nearly the same values of R0 for different ω.