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@INPROCEEDINGS{Unidad:189954,
      author       = {Unidad, Herwin Jerome and Zamponi, Michaela and Ivanova,
                      Oxana and Willner, Lutz and Pyckhout-Hintzen, Wim and
                      Wischnewski, Andreas and Richter, Dieter and Fetters, Lewis
                      J.},
      title        = {{C}hain {D}ynamics near the {U}nentangled-{E}ntangled
                      {T}ransition of {P}olymer {M}elts},
      reportid     = {FZJ-2015-02922},
      year         = {2015},
      abstract     = {It is well-known that the transition between unentangled to
                      entangled dynamics occurs at a critical molecular weight
                      (Mc), typically assumed to be twice the entanglement
                      molecular weight (Me). Recently, we have reiterated a
                      previous finding that the ratio between Mc and Me doesn't
                      assume a universal value of 2 for all polymer melts but in
                      fact shows a dependence on the packing length (p). Not
                      withstanding, the physical picture behind the independent
                      existence of Me and Mc remains unclear.Here, we
                      reinvestigate the problem by probing the microscopic
                      dynamics of polybutadiene melts near the transition by
                      neutron spin echo spectroscopy. We analyze the dynamic
                      structure factor within the framework of the Rouse model
                      with modified mode spectrum. We find that suppression of
                      long-wavelength modes in the spectra already occurs for
                      melts with molecular weight above Me, even if they are still
                      below Mc. We rationalize these results based on earlier
                      ideas on entanglement formation. We also apply this
                      framework in confronting our viscosity data for various
                      polymers.},
      month         = {Mar},
      date          = {2015-03-15},
      organization  = {79th Annual Meeting of the DPG and DPG
                       Spring Meeting, Berlin (Germany), 15
                       Mar 2015 - 20 Mar 2015},
      subtyp        = {Other},
      cin          = {JCNS (München) ; Jülich Centre for Neutron Science JCNS
                      (München) ; JCNS-FRM-II / Neutronenstreuung ; JCNS-1},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-1-20110106},
      pnm          = {6215 - Soft Matter, Health and Life Sciences (POF3-621) /
                      6G15 - FRM II / MLZ (POF3-6G15) / 6G4 - Jülich Centre for
                      Neutron Research (JCNS) (POF3-623)},
      pid          = {G:(DE-HGF)POF3-6215 / G:(DE-HGF)POF3-6G15 /
                      G:(DE-HGF)POF3-6G4},
      experiment   = {EXP:(DE-MLZ)J-NSE-20140101},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/189954},
}