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@ARTICLE{Bras:172776,
      author       = {Bras, Ana and Fonseca, Isabel M. and Dionísio, Madalena
                      and Schönhals, Andreas and Affouard, Frédéric and
                      Correia, Natália T.},
      title        = {{I}nfluence of {N}anoscale {C}onfinement on the {M}olecular
                      {M}obility of {I}buprofen},
      journal      = {The journal of physical chemistry / C},
      volume       = {118},
      number       = {25},
      issn         = {1932-7455},
      address      = {Washington, DC},
      publisher    = {Soc.},
      reportid     = {FZJ-2014-06217},
      pages        = {13857 - 13868},
      year         = {2014},
      abstract     = {The molecular mobility of ibuprofen confined to a
                      mesoporous silica host (MCM-41) of 3.6 nm pore diameter is
                      investigated by dielectric relaxation spectroscopy. It is
                      confirmed that crystallization is suppressed; therefore,
                      depending on the temperature, the guest exists in the glassy
                      and supercooled state inside of the pores. A detailed
                      relaxation map is provided where multiple processes are
                      dynamically characterized, comprised of three processes that
                      are also found for the bulk and two additional ones. The
                      bulk-like processes include two secondary processes, a
                      simple thermally activated one, a γ process and a
                      Johari–Goldstein βJG process, and the one associated with
                      the dynamic glass transition of molecules located in the
                      pore center (α process). In confinement, all of these
                      processes display deviations in its dynamical behavior
                      relative to the bulk, the most dramatic one undergone by the
                      α process, which exhibits Arrhenius-like temperature
                      dependence upon approaching the glass transition instead of
                      Vogel/Fulcher/Tammann/Hesse (VFTH) scaling as obeyed by the
                      bulk. The two additional relaxations are associated with the
                      dynamical behavior of hydrogen-bonded ibuprofen molecules
                      lying in an interfacial layer near the pore wall, an S
                      process for which the mobility is strongly reduced relative
                      to the α process and a Debye-like D process for which the
                      dynamics is closely correlated to the dynamics of the
                      interfacial process, both exhibiting VFTH temperature
                      dependencies. The comparison with the behavior of the same
                      guest in the analogous host, SBA-15, with a higher pore
                      diameter (8.6 nm) leads to the conclusion that the bulk-like
                      mobility associated with the dynamic glass transition
                      undergoes finite size effects being accelerated upon a
                      decrease of the pore size with a concomitant reduction of
                      the glass transition temperature relative to the bulk, 22
                      and 32 K, respectively, for the 8.6 and 3.6 nm pore
                      diameters. The continuous decrease in the separation between
                      the α- and βJG-trace with pore size decrease allows one to
                      conclude that confined ibuprofen is a suitable guest
                      molecule to test the Coupling Model that predicts a
                      transformation of the α process into a βJG-mode under
                      conditions of an extreme nanoconfinement. The overall
                      behavior inside of pores is consistent with the existence of
                      two distinct dynamical domains, originated by ibuprofen
                      molecules in the core of the pore cavity and adjacent to the
                      pore wall, from which a clear picture is given by molecular
                      dynamics simulation.},
      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:000338184300062},
      doi          = {10.1021/jp500630m},
      url          = {https://juser.fz-juelich.de/record/172776},
}