% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@INPROCEEDINGS{Unidad:189956,
      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        = {{P}acking length-dependence of the transition from
                      unentangled to entangled dynamics in polymer melts},
      reportid     = {FZJ-2015-02924},
      year         = {2015},
      abstract     = {It is well-known that the packing model (Fetters and
                      co-workers) shows the relationship between microscopic chain
                      properties (chain stiffness, monomer bulkiness) with
                      macroscopic rheological behavior via the entanglement
                      molecular weight (Me). However, what is less recognized is
                      that the critical molecular weight (Mc) and reptative
                      molecular weight (Mr) which denote transitions between
                      unentangled (Rouse) and entangled (tube) dynamics and
                      reptation-contour length fluctuations (CLF) to pure
                      reptation dynamics respectively, also show dependence on the
                      packing length (p). In this contribution, we highlight two
                      aspects of this dependence:1. Based on zero-shear viscosity
                      data for six different polymers, from our own measurements
                      and from literature, we show that there's a packing length
                      dependence of the two crossovers (Mc, Mr) and that the trend
                      is for the two to merge at a certain critical value of the
                      packing length (p*). Further, analysis of the loss moduli
                      (G'') for several well-entangled polymers with different
                      packing lengths reveals a p-dependence of the high-frequency
                      slope of the terminal peak contrary to the predicted value
                      of -1/4 by tube models with CLF.2. Based on preliminary
                      measurements of the dynamic structure factor by neutron spin
                      echo spectroscopy, we show that the onset for the effect of
                      entanglements on the dynamics (i.e. deviation from Rouse
                      behavior) starts in fact from Me and manifests by
                      suppression of long- wavelength modes. From measurements on
                      a series of polymers with different molecular weights
                      (around Mc) and with different packing lengths, we examine
                      how this deviation from Rouse behavior might proceed
                      differently depending on the packing length of the
                      polymer.Both aspects hint at possible missing ingredients in
                      the current modeling framework (tube model) for entangled
                      polymer melts, particularly on the understated importance of
                      the packing length (p).},
      month         = {Apr},
      date          = {2015-04-14},
      organization  = {10th Annual European Rheology
                       Conference, Nantes (France), 14 Apr
                       2015 - 17 Apr 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/189956},
}