Creep Behavior for Combined Rouse-Reptation Mechanism

Recoverable creep compliance JR(t) was analytically calculated for polymer chains relaxing through the Rouse and reptation mechanisms at short and long time scales, respectively. The ratio of the longest relaxation times of these mechanisms, rτ = τRouse/τrep, was varied from 0.056 to 0.0033. The calculation indicated that the effect of the fast Rouse mechanism on the distribution of slow modes of JR(t) decreases with decreasing rτ but a considerable effect remains even for rτ as small as 0.0033, i.e., even for the case of reptation-dominance in the terminal relaxation behavior. This result demonstrates an important difference between the creep and relaxation processes, the former being associated with a correlation (or interplay) of eigenmodes of chain motion due to the constant stress requirement.