Conformation and Dynamics of a Long Active Polymer Chain Confined in a Circular Cavity

The conformational and dynamical properties of a long semi-flexible active polymer chain confined in a circular cavity are studied by using Langevin dynamics simulation method. Results show that the steady radius of gyration of the polymer decreases monotonically with increasing the active force. Interestingly, the polymer forms stable compact spiral with directional rotation at the steady state when the active force is large. Both the radius of gyration and the angular velocity of the spiral are nearly independent of the cavity size, but show scaling relations with the active force and the polymer length. It is further found that the formation of the stable compact spiral in most cases is a two-step relaxation process, where the polymer first forms a metastable swelling quasi spiral and then transforms into the stable compacted spiral near the wall of the cavity. The relaxation time is mainly determined by the transformation of the swelling quasi spiral, and shows remarkable dependence on the size of the cavity. Specially, when the circumference of the circular is nearly equivalent to the polymer length, it is difficult for the polymer to form the compacted spiral, leading to a large relaxation time. The underlying mechanism of the formation of the compacted spiral is revealed.