Relaxation of Rouse modes for unentangled polymers obtained by molecular simulations

Although the Rouse model has been widely used to describe unentangled polymer dynamics, there are some experimental and simulation results, in which the local chain dynamics is not fully consistent with the Rouse predictions. In this study, molecular simulations by a few different molecular models were conducted to reveal the effects of inter-molecular interactions on the relaxation of Rouse modes. Kremer-Grest bead-spring simulations exhibited that the second and third Rouse modes relaxations deviate from the Rouse prediction even though the first Rouse mode relaxation is fairly consistent with the Rouse behavior. A similar deviation was observed for full-atomistic simulations of polybutadiene and polyisoprene. For dissipative particle dynamics simulations, the magnitude of deviation was much smaller. Additional Kremer- Grest simulations with various molecular weights and full-atomistic simulations without excluded volume interactions suggest that the chain rigidity and the hard-core inter-beads interactions are attributable to the deviation through short-time relaxations induced by inter-beads collisions.