Is The Distribution Of Entanglements Homogeneous In Polymer Melts
APPLICATION OF SCATTERING METHODS TO THE DYNAMICS OF POLYMER SYSTEMS(1993)
摘要
Neutron-scattering experiments have been performed on elongated polystyrene melts consisting of relatively short labelled
chains (MM>106), which were not labelled. Important anomalies with respect to the theoretical predications have been observed. In particular,
the iso-intensity lines exhibit, in a large range of relaxation times, striking butterfly shapes and an unexpected orientation: the long axis of these patterns is oriented parallel to the stretching direction. As
a working assumption, we propose to relate this phenomenon to a non-homogeneous arrangement of chain entanglements in the
melts. As a matter of facts, it has been proposed that elongated gels should exhibit butterfly patterns (The whole solvent
being labelled) as a result of a sort of anisotropic unscreening of cross-linking heterogeneities. Experiments were performed
on samples synthesized specially in order to match the assumptions of the model and butterfly patterns have effectively been
observed. The same type of mechanism can be driven by an heterogeneity of chain entanglement in the case of assymetrical melts:
the short labelled chains may behave as a kind of polymeric solvent and accumulate, during the relaxation, in the less entangled
regions (which should be also regions of lower constraint).
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关键词
POLYMER,MELTS,GELS,PERCOLATION,CLUSTERS,NEUTRON SCATTERING
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