Diddo Diddens, Andreas Heuer
The Rouse model can be regarded as the standard model to describe the dynamics of a short polymer chain under melt conditions. In this contribution, we explicitly check one of the fundamental assumptions of this model, namely that of a uniform friction coefficient for all monomers, on the basis of MD simulation data of a PEO melt. This question immediately arises from the fact that in a real polymer melt the terminal monomers have on average more intermolecular neighbors than the central monomers. The mobilities are determined by our recently developed statistical method [Diddens et al., EPL 2010, 91 (6), 66005], which provides complementary information about the local polymer dynamics and thus contrasts standard quantities such as the mean square displacement (MSD) or the Rouse mode analysis. Within our analysis it turned out that the Rouse assumption of a uniform mobility is fulfilled to a good approximation for the PEO melt, although the underlying microscopic dynamics is highly affected by different contributions from intra- and intermolecular excluded volume interactions, which, each in itself, cannot be taken into account by a modified friction coefficient. However, in the sum, these non-trivial terms roughly cancel each other, and the overall dynamics corresponds to that of a phantom chain. These effects remain elusive when studying the dynamics with the MSD only, since this observable characterizes a sum over dynamical contributions due to the bare mobility, chain connectivity and more complicated local potentials.
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http://arxiv.org/abs/1211.3291
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