D. Richter et al., From Rouse dynamics to local relaxation: A neutron spin echo study on polyisobutylene melts, J CHEM PHYS, 111(13), 1999, pp. 6107-6120
We investigated the single chain motions of monodisperse polyisobutylene ch
ains in the melt by neutron spin echo spectroscopy. Thereby a wide range in
momentum space over a large dynamic range was covered. Motional processes
from the center of mass diffusion, the Rouse dynamics to the more local rel
axation processes which limit the validity of the standard Rouse model, wer
e elucidated. The observed dynamic structure factors were analyzed in terms
of relevant theoretical approaches addressing the limiting factors of the
Rouse model. We found that other than claimed in the literature effects of
local chain stiffness-they were treated in terms of the all rotational stat
es model and a bending force model-cannot account for the experimental obse
rvations. It appears that additional damping effects related to an internal
viscosity of the chain have to be involved, in order to explain the experi
mental results. (C) 1999 American Institute of Physics. [S0021-9606(99)5053
7-0].