Arm retraction and escape transition in semi-flexible star polymer under cylindrical confinement.

We studied the structure and dynamics of star-shaped polymers by means of coarse-grained molecular dynamics simulations and analysis of structural transitions of semi-flexible macromolecules confined in nano-channels. The conformation of star arms in narrow channels is given by the channel width, arm flexibility and number of arms aligned together in the given region along the channel. We focused on the conformation transition, where all arms are initially stretched in one direction of the narrow channel and were interested in the process of how individual arms escape into a free volume region of channel. We found that the escape transition does not proceed from arm ends but progresses by extension of a loop starting from the branch point; the arms escape in individual steps and the extension of arms depends on how many arms align in parallel in the channel.