@article{WangLackXieetal.2012,
  author    = {Wang, Feipeng and Lack, Alexander and Xie, Zailai and Fr{\"u}bing, Peter and Taubert, Andreas and Gerhard, Reimund},
  title     = {Ionic-liquid-induced ferroelectric polarization in poly(vinylidene fluoride) thin films},
  series = {Applied physics letters},
  volume    = {100},
  journal   = {Applied physics letters},
  number    = {6},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0003-6951},
  doi       = {10.1063/1.3683526},
  pages     = {4},
  year      = {2012},
  abstract  = {Thin films of ferroelectric beta-phase poly(vinylidene fluoride) (PVDF) were spin-coated from a solution that contained small amounts of the ionic liquid (IL) 1-ethyl-3-methylimidazolium nitrate. A remanent polarization of 60 mC/m(2) and a quasi-static pyroelectric coefficient of 19 mu C/m(2)K at 30 degrees C were observed in the films. It is suggested that the IL promotes the formation of the beta phase through dipolar interactions between PVDF chain-molecules and the IL. The dipolar interactions are identified as Coulomb attraction between hydrogen atoms in PVDF chains and anions in IL. The strong crystallinity increase is probably caused by the same dipolar interaction as well.},
  language  = {en}
}
@article{FruebingWangWagener2012,
  author    = {Fr{\"u}bing, Peter and Wang, Feipeng and Wagener, Michael},
  title     = {Relaxation processes and structural transitions in stretched films of polyvinylidene fluoride and its copolymer with hexafluoropropylene},
  series = {Applied physics : A, Materials science \& processing},
  volume    = {107},
  journal   = {Applied physics : A, Materials science \& processing},
  number    = {3},
  publisher = {Springer},
  address   = {New York},
  issn      = {0947-8396},
  doi       = {10.1007/s00339-012-6838-1},
  pages     = {603 -- 611},
  year      = {2012},
  abstract  = {Relaxation processes and structural transitions in nonstretched and uniaxially stretched films of poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) and its homopolymer polyvinylidene fluoride (PVDF) for comparison were investigated with the aim of understanding the electromechanical properties of this lower-modulus ferroelectric copolymer. The mechanical and the dielectric response at the glass transition ( relaxation) exhibit similar temperature dependence of the relaxation time, whereas mechanical and dielectric processes above the glass transition are not related. They represent a continuous softening process within the amorphous phase and the dielectric relaxation, respectively. The latter is attributed to conformational changes of VDF segments in lamellae of spherulites constituting the nonpolar crystalline phase. Furthermore, there is a contribution from melting of secondary crystallites formed in the amorphous phase during annealing or storage. Mechanically, this transition appears in nonstretched and stretched films as an accelerated decrease of the elastic modulus that terminates the rubber plateau. Dielectrically, this transition becomes visible as a frequency-independent loss peak only in stretched films, because stretching removes the relaxation, which superimposes the transition in nonstretched films. Melting of secondary crystallites is shown to appear in the homopolymer, too, though less pronounced because of more complete primary crystallisation. Stretching increases the modulus above the glass transition only slightly, and it does not significantly influence the softening process. On the other hand, stretching causes a spontaneous polarisation and introduces order within the amorphous phase, rendering it more polar. Melting of secondary crystallites provides an additional contribution to the polarisation. These findings may explain the relatively high electromechanical activity of P(VDF-HFP) but also its relatively low thermal stability. Moreover, they may be important for correct procedure and analysis of temperature-dependent dielectric measurements on partially crystalline polymers, in particular on those with less favourable sterical conditions for primary crystallisation.},
  language  = {en}
}
@article{KollscheKalbitzKappeletal.2012,
  author    = {Kollsche, Matthias and Kalbitz, Rene and Kappel, Marcel and Fr{\"u}bing, Peter and Gerhard, Reimund},
  title     = {Vermittlung von Schl{\"u}sselkompetenzen f{\"u}r Biologen in der Studieneingangsphase},
  isbn      = {978-3- 937026-77-0},
  year      = {2012},
  language  = {de}
}