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@INPROCEEDINGS{Zorn:1023009,
      author       = {Zorn, Reiner and Chua, Yeong-Zen and Schmelzer, Jürn W. P.
                      and Holderer, Olaf and Zamponi, Michaela and Schick,
                      Christoph},
      title        = {{D}etermination of the cooperativity length in glass
                      forming liquids and polymers},
      reportid     = {FZJ-2024-01595},
      year         = {2023},
      abstract     = {Although the idea of a ‘characteristic’ or
                      ‘cooperativity’ length scale ξ related to the glass
                      transition is now wide-spread, there is much less consensus
                      on whether this length scale can be related to thermodynamic
                      fluctuations and, if yes, whether one has to consider
                      temperature fluctuations δT. The crucial experiment to this
                      end has to compare values of ξ from ‘thermodynamic’
                      formulae to independent values from structural-dynamics
                      experiments.An experiment with the aim of determining the
                      cooperativity length ξ in glass forming materials was
                      proposed some time ago by Ernst Donth [1]. The basic idea of
                      this experiment is to assign a length scale to the
                      AC-calorimetric relaxation time using the spatial resolution
                      of quasielastic neutron scattering. The main problem is to
                      find a range of relaxation times that is accessible by both
                      methods. From the very beginning it is clear that only
                      neutron-spin echo (NSE) is suited for this task. This raises
                      the additional problem that incoherent scattering has to be
                      measured. Therefore, significant progress in the performance
                      of NSE as well as AC calorimetry was required to conduct
                      this experiment.A first experiment of this kind was realised
                      on a glass-forming liquid, propylene glycol (PG) [2]. The
                      result was that agreement with the thermodynamic
                      calculations was better if temperature fluctuations were
                      accounted for. Nevertheless, in PG the difference between
                      the two thermodynamic estimates is small and the dynamics of
                      the methyl groups overlaps with the α relaxation.
                      Therefore, a material with a higher ‘contrast’ between
                      the alternatives was of interest and used in a second
                      experiment, poly(ethylmethacrylate) (PEMA). In addition,
                      neutron backscattering experiments showed that the methyl
                      group dynamics is better separated in PEMA. Finally, the
                      experiment benefitted from the upgrade of J-NSE with
                      superconducting coils. The new results show a clear
                      agreement with the thermodynamic calculation involving
                      temperature fluctuations.[1] E. Donth, Eur. Phys. J. E 12,
                      11 (2003).[2] Y. Z. Chua, R. Zorn, O. Holderer, J. W. P.
                      Schmelzer, C. Schick, E. Donth, J. Chem. Phys. 146, 104501
                      (2017).},
      month         = {Aug},
      date          = {2023-08-12},
      organization  = {9th International Discussion Meeting
                       on Relaxation in Complex Systems,
                       Makuhari Messe (Japan), 12 Aug 2023 -
                       18 Aug 2023},
      subtyp        = {Invited},
      cin          = {JCNS-1 / IBI-8},
      cid          = {I:(DE-Juel1)JCNS-1-20110106 / I:(DE-Juel1)IBI-8-20200312},
      pnm          = {632 - Materials – Quantum, Complex and Functional
                      Materials (POF4-632) / 6G4 - Jülich Centre for Neutron
                      Research (JCNS) (FZJ) (POF4-6G4) / 5251 - Multilevel Brain
                      Organization and Variability (POF4-525) / 5241 - Molecular
                      Information Processing in Cellular Systems (POF4-524)},
      pid          = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G4 /
                      G:(DE-HGF)POF4-5251 / G:(DE-HGF)POF4-5241},
      experiment   = {EXP:(DE-MLZ)J-NSE-20140101 / EXP:(DE-MLZ)SPHERES-20140101},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/1023009},
}