Dynamic Properties of Densely Grafted Polymer Brushes Investigated by Multistep Relaxation Mode Analysis

The relaxation processes of densely grafted linear and ring polymer brushes in thermal equilibrium are studied via coarse-grained molecular dynamics simulations and relaxation mode analysis (RMA). Good solvent conditions and the free-draining limit are assumed. The longest relaxation time tau( )of a polymer is evaluated via multistep RMA, where the relaxation modes and rates estimated in the previous RMA step are used in the next step. The exponent Delta of the power-law dependence of tau on the chain length N, tau proportional to N-Delta, is estimated. For linear polymer brushes, Delta similar or equal to 5.9, which is considerably larger than the value estimated in a previous simulation study. On the other hand, for ring polymer brushes, Delta similar or equal to 3.7, which is consistent with previous work. The physical nature of the slow relaxation modes and the difference between linear and ring brushes are discussed.