TY - JOUR A1 - Yilmaz, Sükrü A1 - Wirges, Werner A1 - Bauer-Gogonea, Simona A1 - Bauer, Siegfried A1 - Gerhard, Reimund A1 - Michelotti, F. A1 - Toussaere, E. A1 - Levenson, R. A1 - Liang, J. A1 - Zyss, Joseph T1 - Dielectric, pyroelectric and electro-optic monitoring of the cross-linking process and photo-induced poling of Red Acid Magly Y1 - 1997 ER - TY - JOUR A1 - Wirges, Werner A1 - Wegener, Michael A1 - Voronina, Olena A1 - Zirkel, Larissa A1 - Gerhard, Reimund T1 - Optimized preparation of elastically soft, highly piezoelectric, cellular ferroelectrets from nonvoided poly(ethylene terephthalate) films N2 - Electrically charged cellular polymer films can exhibit very high piezoelectric activity and are therefore more and more often employed in advanced electromechanical and electro-acoustical transducers. In this paper, we report an optimized sequence of steps for preparing such ferroelectrets from commercial nonvoided ploy(ethylene terephthalate) (PETP) films by means of foaming with CO2 biaxial mechanical stretching, controlled void inflation, and bipolar electric charging. The nonvoid PETP films foamed with supercritical CO2 at a suitably high pressure and subsequently annealed for stabilization. The cellular foam structure was further optimized by means of well controlled biaxial stretching in a commercial stretcher and sometimes subsequent inflamation in a pressure chamber. Bipolar electric charging of the internal voids was achieved through the application of high electric fields in an SF0 atmosphere. The new optimized PETP ferroelectric exhibit quite large piezoelectric coefficients up to almost 500 pCN(-1), for which unusually low elastic stiffness of only around 0.3 MPa are essential. The PETP foam ferroelectrics posses unclamped thickenss-extension resonance frequences between approximately 120 and 250 kHz, and are thus highly suitable for several established as well as novel ultrasonic-transductant applications. Y1 - 2007 UR - http://onlinelibrary.wiley.com/doi/10.1002/adfm.200600162/pdf U6 - https://doi.org/10.1002/adfm.200600162 ER - TY - JOUR A1 - Wirges, Werner A1 - Raabe, Sebastian A1 - Qiu, Xunlin T1 - Dielectric elastomer and ferroelectret films combined in a single device how do they reinforce each other? JF - Applied physics : A, Materials science & processing N2 - Dielectric elastomers (DE) are soft polymer materials exhibiting large deformations under electrostatic stress. When a prestretched elastomer is stuck to a flat plastic frame, a complex structure that can be used as an actuator (DEA) is formed due to self-organization and energy minimization. Here, such a DEA was equipped with a ferroelectret film. Ferroelectrets are internally charged polymer foams or void-containing polymer-film systems combining large piezoelectricity with mechanical flexibility and elastic compliance. In their dielectric spectra, ferroelectrets show piezoelectric resonances that can be used to analyze their electromechanical properties. The antiresonance frequencies ( ) of ferroelectret films not only are directly related to their geometric parameters, but also are sensitive to the boundary conditions during measurement. In this paper, a fluoroethylenepropylene (FEP) ferroelectret film with tubular void channels was glued to a plastic frame prior to the formation of self-organized minimum-energy DEA structure. The dielectric resonance spectrum (DRS) of the ferroelectret film was measured in-situ during the actuation of the DEA under applied voltage. It is found that the antiresonance frequency is a monotropic function of the bending angle of the actuator. Therefore, the actuation of DEAs can be used to modulate the of ferroelectrets, while the can also be taken for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets brings a number of possibilities for application. Y1 - 2012 U6 - https://doi.org/10.1007/s00339-012-6833-6 SN - 0947-8396 SN - 1432-0630 VL - 107 IS - 3 SP - 583 EP - 588 PB - Springer CY - New York ER - TY - JOUR A1 - Wirges, Werner A1 - Przyrembel, G. A1 - Brinker, Walter A1 - Gerhard, Reimund A1 - Klemberg-Sapieha, J. A1 - Martinu, L. A1 - Poitras, D. A1 - Wertheimer, M. R. T1 - Metallised viscoelastic control layers for light-valve projection displays Y1 - 1995 ER - TY - JOUR A1 - Wertheimer, Michael R. A1 - St-Georges-Robillard, Amelie A1 - Lerouge, Sophie A1 - Mwale, Fackson A1 - Elkin, Bentsian A1 - Oehr, Christian A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Amine-rich organic thin films for cell culture - possible electrostatic effects in cell-surface interactions JF - Japanese journal of applied physics N2 - In recent communications from these laboratories, we observed that amine-rich thin organic layers are very efficient surfaces for the adhesion of mammalian cells. We prepare such deposits by plasma polymerization at low pressure, atmospheric pressure, or by vacuum-ultraviolet photo-polymerization. More recently, we have also investigated a commercially available material, Parylene diX AM. In this article we first briefly introduce literature relating to electrostatic interactions between cells, proteins, and charged surfaces. We then present certain selected cell-response results that pertain to applications in orthopedic and cardiovascular medicine: we discuss the influence of surface properties on the observed behaviors of two particular cell lines, human U937 monocytes, and Chinese hamster ovary cells. Particular emphasis is placed on possible electrostatic attractive forces due to positively charged R-NH3+ groups and negatively charged proteins and cells, respectively. Experiments carried out with electrets, polymers with high positive or negative surface potentials are added for comparison. Y1 - 2012 U6 - https://doi.org/10.1143/JJAP.51.11PJ04 SN - 0021-4922 VL - 51 IS - 11 PB - Japan Soc. of Applied Physics CY - Tokyo ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Tiersch, Brigitte T1 - Porous polytetrafluoroethylene (PTFE) electret films : porosity and time dependent charging behaviour of the free surface N2 - Electrically charged porous polytetrafluoroethylene (PTFE) films are often discussed as active layers for electromechanical transducers. Here, the electric charging behavior of open-porous PTFE films with different porosities is investigated. Optimized electric charging of porous PTFE films is determined by variation of charging parameters such as electric fields and charging times. Maximum surface potentials are depending on the porosity of the PTFE films. Suitable charging leads to high surface potentials observed on non-stretched or slightly stretched porous PTFE films. Further increase of charging fields yields decreasing values of the surface potential accompanied with an increase of conductivity. Y1 - 2006 UR - http://www.springerlink.com/content/601u86x365560515/ U6 - https://doi.org/10.1007/s10934-006-9015-0 ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Richter, Kristin A1 - Künstler, Wolfgang A1 - Gerhard, Reimund T1 - Charge stability and piezoelectric properties of porous fluoro-polymer space-charge electrets in layer systems Y1 - 2001 ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Paajanen, Mika A1 - Gerhard, Reimund T1 - Charging behaviour and thermal stability of porous and non-porous polytetrafluoroethylene (PTFE) electrets Y1 - 2007 SN - 978-1-4244-1482-6 ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Dansachmüller, M. A1 - Schwödiauer, R. A1 - Bauer-Gogonea, Simona A1 - Bauer, Siegfried A1 - Paajanen, Mika A1 - Minkkinen, Hannu A1 - Raukola, J. T1 - Controlled inflation of voids in cellular polymer ferroelectrets : optimizing electromechanical transducer properties N2 - 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 Y1 - 2004 ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Piezoelectric polyethylene terephthalate (PETP) foams : specifically designed and prepared ferroelectret films Y1 - 2005 ER -