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@ARTICLE{Hofmann:187532,
      author       = {Hofmann, M. and Kresse, B. and Privalov, A. F. and Willner,
                      L. and Fatkullin, N. and Fujara, F. and Rössler, E. A.},
      title        = {{F}ield-{C}ycling {NMR} {R}elaxometry {P}robing the
                      {M}icroscopic {D}ynamics in {P}olymer {M}elts},
      journal      = {Macromolecules},
      volume       = {47},
      number       = {22},
      issn         = {1520-5835},
      address      = {Washington, DC},
      publisher    = {Soc.},
      reportid     = {FZJ-2015-01161},
      pages        = {7917 - 7929},
      year         = {2014},
      abstract     = {Field-cycling (FC) 1H and 2H NMR relaxometry is applied to
                      linear polybutadiene (PB) of different molar mass (M) in
                      order to test current polymer theories. Applying earth field
                      compensation, five decades in the frequency dependence of
                      the spin–lattice relaxation rate T1–1(ν) = R1(ν) are
                      accessed (200 Hz - 30 MHz), and we focus on the crossover
                      from Rouse to entanglement dynamics. A refined evaluation is
                      presented, which avoids application of
                      frequency–temperature superposition as well as Fourier
                      transformation. Instead, the power-law exponent ε in the
                      entanglement regime is directly determined from the
                      susceptibility representation χNMR″(ω) = ω/T1(ω) ∝
                      ωε by a derivative method. Correspondingly, a power-law
                      t–ε characterizes the decay in the time domain, i.e., the
                      dipolar correlation function. For the total 1H relaxation,
                      comprising intra- and intermolecular relaxation, a high-M
                      exponent εtotal = 0.31 ± 0.03 is found. An isotope
                      dilution experiment, which yields the intramolecular
                      relaxation reflecting solely segmental reorientation,
                      provides an exponent εintra = 0.44 ± 0.03. It agrees with
                      that of FC 2H NMR (εQ = 0.42 ± 0.03) probing only
                      segmental reorientation. The fact that εintra > εtotal
                      demonstrates the relevance of intermolecular relaxation in
                      the entanglement regime (but not in the Rouse regime), and
                      εintra is significantly higher than predicted by the
                      tube-reptation (TR) model (εTR = 0.25) and, the latter
                      being supported also by recent simulations. The ratio of
                      inter- to intramolecular relaxation grows with decreasing
                      frequency, again in contradiction to the TR model and
                      results from double quantum 1H NMR. We conclude that no
                      clear evidence of a tube is found on the microscopic level
                      and the so-called return-to-origin hypothesis is not
                      confirmed. Studying the influence of chain end dynamics by
                      FC 1H NMR we compare differently chain end deuterated PB.
                      For the dynamics of the central part of the polymer the
                      exponent drops from εintra = 0.66 ± 0.03 down to εcent =
                      0.41 ± 0.03 for M = 29k which is very close to the high-M
                      value εintra. Thus, the protracted transition to
                      entanglement dynamics reported before is not found when the
                      polymer center is probed; instead full entanglement dynamics
                      appears to set in directly with M > Me.},
      cin          = {ICS-1 / Neutronenstreuung ; JCNS-1},
      ddc          = {540},
      cid          = {I:(DE-Juel1)ICS-1-20110106 / I:(DE-Juel1)JCNS-1-20110106},
      pnm          = {451 - Soft Matter Composites (POF2-451) / 54G - JCNS
                      (POF2-54G24)},
      pid          = {G:(DE-HGF)POF2-451 / G:(DE-HGF)POF2-54G24},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000345552700024},
      doi          = {10.1021/ma501520u},
      url          = {https://juser.fz-juelich.de/record/187532},
}