Rouse reorientation time

Doi and Edwards [ 1, Eq. 4.37 and parenthetical remark after Eq. 4.157] use the symbol T, for the Rouse reorientation time (or rotational relaxation time), which is twice the quantity defined by Eq. 6.3. Note that since N = M/Mq, % is proportional to for a given polymer. 

Rouse reorientation (rotational) time Rouse stress relaxation time... 

Before turning to dynamics, we should hke to point out that, because no solvent is explicitly included, the Rouse model [37,38] (rather than the Zimm model [39]) results in the dilute limit, as there is no hydrodynamic interaction. The rate of reorientation of monomers per unit time is W, and the relaxation time of a chain scales as [26,38]... 

One example of mapping by chain diffusion involved the case of lOmers of polyisoprene at 413 K. A dynamic mapping between a fully atomistic and a very simple coarse-grained model was demonstrated. Only chain stiffness was used to perform the mapping in that study. The local chain reorientation in both simulations was the same after the time scales had been determined by the diffusion coefficient. The decay times of the Rouse modes, however, were not equal, indicating that mapping by stiffness alone is too simplistic. 

In the extreme case where this subchain for high Rouse modes becomes only a single monomer, we end up with the segmental relaxation time, i.e., the reorientation dynamics on the monomer scale. This time scale can almost always be used for mapping, and it can also be used for comparison with and calibration to NMR experiments. If we use the Rouse model for mapping time scales, we should make sure that the Rouse model is a reasonable description for the system under study. 

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