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 τ 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 δ of the powerlaw dependence of τ on the chain length N, τ ∞ Nδ, is estimated. For linear polymer brushes, δ 5.9, which is considerably larger than the value estimated in a previous simulation study. On the other hand, for ring polymer brushes, δ 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.
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