Non-monotonic dependence of polymer chain dynamics on active crowder size.

Configuration dynamics of flexible polymer chains is of ubiquitous importance in many biological processes. Here, we investigate a polymer chain immersed in a bath of size-changed active particles in two dimensional space using Langevin dynamics simulations. Particular attention is paid to how the radius of gyration R of the polymer chain depends on the size σ of active crowders. We find that R shows nontrivial non-monotonic dependence on σ: The chain first swells upon increasing σ, reaching a fully expanded state with maximum R, and then, R decreases until the chain collapses to a compact coil state if the crowder is large enough. Interestingly, the chain may oscillate between a collapse state and a stretched state at moderate crowder size. Analysis shows that it is the competition between two effects of active particles, one stretching the chain from inside due to persistence motion and the other compressing the chain from outside, that leads to the non-monotonic dependence. Besides, the diffusion of the polymer chain also shows nontrivial non-monotonic dependence on σ. Our results demonstrate the important interplay between particle activity and size associated with polymer configurations in active crowding environments.