@article{BauerGogoneaBauerWirgesetal.2004,
  author    = {Bauer-Gogonea, Simona and Bauer, Siegfried and Wirges, Werner and Gerhard, Reimund},
  title     = {Dielectric investigation of photo-induced chromophore degradation in nonlinear optical side-chain polymer electrets},
  year      = {2004},
  abstract  = {Organic materials with non-centrosymmetric chromophores are known to be susceptible to a number of photochemical processes, including reversible isomerization reactions as well as irreversible photo-oxidation or photo- reduction reactions. Reversible isomerization is the basis for a variety of applications, such as photo-induced poling, optical data storage and optical grating formation. The irreversible processes that involve the destruction of the chromophores have been found useful for the fabrication of optical waveguides, but they also limit the life times of polymeric photonic devices. In this paper, it is demonstrated that dielectric measurements allow for an in-depth investigation of non-reversible chromophore degradation processes in a typical side-chain polymer. The time- and temperature-dependent dielectric function of the polymer at 1 kHz enables us to follow the chromophore-degradation kinetics and to monitor the bleaching depth as a function of time at room and elevated temperatures},
  language  = {en}
}
@article{WegenerBergweilerWirgesetal.2004,
  author    = {Wegener, Michael and Bergweiler, Steffen and Wirges, Werner and Pucher, Andreas and Gerhard, Reimund},
  title     = {Voided space-charge electrets : piezoelectric transducer materials for electro-acoustic applications},
  year      = {2004},
  language  = {en}
}
@article{WegenerWirgesFohlmeisteretal.2004,
  author    = {Wegener, Michael and Wirges, Werner and Fohlmeister, Jens Bernd and Tiersch, Brigitte and Gerhard, Reimund},
  title     = {Two-step inflation of cellular polypropylene films: Void-thickness increase and enhanced electromechanical properties},
  year      = {2004},
  abstract  = {In cellular, electromechanically active polymer films, the so-called ferroelectrets, the cell size and shape distributions can be varied through a controlled inflation process. Up to now, high-pressure treatments were usually performed at elevated temperatures. There are, however, significant experimental limitations and complications if the pressure and temperature treatments are performed at the same time. Here, we demonstrate the controlled inflation of cellular polypropylene films by means of sepal-ate pressure and temperature treatments. Separate procedures are Much easier to implement. Excellent electromechanical properties were achieved with Such a two-step inflation process. The technique has significant potential for inflating large-area transducer films for electromechanical and electroacoustical applications},
  language  = {en}
}
@article{WegenerWirgesGerhardetal.2004,
  author    = {Wegener, Michael and Wirges, Werner and Gerhard, Reimund and Dansachm{\"u}ller, M. and Schw{\"o}diauer, R. and Bauer-Gogonea, Simona and Bauer, Siegfried and Paajanen, Mika and Minkkinen, Hannu and Raukola, J.},
  title     = {Controlled inflation of voids in cellular polymer ferroelectrets : optimizing electromechanical transducer properties},
  year      = {2004},
  abstract  = {When exposed to sufficiently high electric fields, polymer-foam electret materials with closed cells exhibit ferroelectric-like behavior and may therefore be called ferroelectrets. In cellular ferroelectrets, the influence of the cell size and shape distributions on the application-relevant properties is not yet understood. Therefore, controlled inflation experiments were carried out on cellular polypropylene films, and the resulting elastical and electromechanical parameters were determined. The elastic modulus in the thickness direction shows a minimum with a corresponding maximum in the electromechanical transducer coefficient. The resonance frequency shifts as a function of the elastic modulus and the relative density of the inflated cellular films. Therefore, the transducer properties of cellular ferroelectrets can be optimized by means of controlled inflation. (C) 2004 American Institute of Physics},
  language  = {en}
}