Active Brownian filaments: deviations from blob scaling theory and dynamics inside cavities

Active filaments have become the subject of intense scrutiny in recent years because of their biological implications, and their role as a minimal model where the competition between thermal, elastic and active forces can be systematically studied.

Scaling arguments used to predict the radius of gyration of passive self-avoiding flexible polymers have been shown to hold even under the influence of active fluctuations. Via a numerical study we establish how the standard blob scaling theory representations of a polymer breaks down when dealing with active polymers under confinement. We find that the predicted exponents hold only whenever the persistence length generated on the polymer by the active forces is much smaller than the size of the characteristic blob in the scaling theory. Further, when the activity is directed along the backbone of a semi-flexible filament, while confined in a spherical cavity, a highly dynamic scenario emerges. The filament is capable of escaping local and global energy minima and sample, in a quasi-periodic fashion, an ensemble of conformations usually associated to higher bending energies, and previously observed for passive filaments only under very different degrees of confinement or identified as glassy metastable states.