Relaxation of Self-Entangled Many-Arm Star Polymers

: We present a description of the relaxation of star polymers based on the conformational scaling properties predicted by Daoud and Cotton and confirmed in our recent simulations. We identify three typical relaxation mechanisms. The first describes elastic deformation of the overall shape. Its relaxation time is nearly independent of f. A second type of relaxation occurs via rotational diffusion. We predict that the relaxation time should scale with N^2v+1ƒ^2-cv where v is the correlation length exponent. A third relaxation process is the disentanglement of two or more arms. Here the longest relaxation time should increase exponentially with f^1/2. We measure various relaxation processes by molecular-dynamics simulations of star polymers with many (6 < f < 50) arms. The observed relaxation times are consistent with our predictions but do not give strong confirmation. We also discuss how the observed scaling behavior should be modified by hydrodynamic interactions, which are not treated in the simulations.