Neutron Scattering

Arrhenius temperature dependence with a same activation energy as that of the corresponding
dielectric /-process .
-il
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3 3.5 4 4.5 5 5 .5 6
1000 / T(K)
Figure 15 .9 : Relaxation rates at the first and second structure factor peak of PB in an
Arrhenius representation . Solid lines : a- and ßtraces for this polymers .
An evaluation of the structure factor following Eq.
[15 .6] and [15 .7] reveals a jump distance
for the fi-process of d - 1.5A . It also shows that the assumption of statistically independent a-
and relaxations is supported by the temperature and momentum transfer dependent spectra .
15 .3 Entropy driven dynamies - the Rouse regime
As outlined in the introduction, the conformational entropy of a chain acts as a resource for
restoring forces for chain conformations, deviating from thermal equilibrium .
In this Chapter
we deal with these entropy driven dynamics in terms of the Rouse model and present NSE
results on the space-time evolution of the Rouse relaxation and fmally discuss recent
molecular dynamic simulations which have been performed in parallel to NSE experiments,
in order to explore the limits of the Rouse picture.
15- 12