TY - JOUR A1 - Altafim, Ruy Alberto Pisani A1 - Altafim, Ruy Alberto Pisani A1 - Qiu, Xunlin A1 - Raabe, Sebastian A1 - Wirges, Werner A1 - Basso, Heitor Cury A1 - Gerhard, Reimund T1 - Fluoropolymer piezoelectrets with tubular channels resonance behavior controlled by channel geometry JF - Applied physics : A, Materials science & processing N2 - Ferro- or piezoelectrets are dielectric materials with two elastically very different macroscopic phases and electrically charged interfaces between them. One of the newer piezoelectret variants is a system of two fluoroethylenepropylene (FEP) films that are first laminated around a polytetrafluoroethylene (PTFE) template. Then, by removing the PTFE template, a two-layer FEP structure with open tubular channels is obtained. After electrical charging, the channels form easily deformable macroscopic electric dipoles whose changes under mechanical or electrical stress lead to significant direct or inverse piezoelectricity, respectively. Here, different PTFE templates are employed to generate channel geometries that vary in height or width. It is shown that the control of the channel geometry allows a direct adjustment of the resonance frequencies in the tubular-channel piezoelectrets. By combining several different channel widths in a single ferroelectret, it is possible to obtain multiple resonance peaks that may lead to a rather flat frequency-response region of the transducer material. A phenomenological relation between the resonance frequency and the geometrical parameters of a tubular channel is also presented. This relation may help to design piezoelectrets with a specific frequency response. Y1 - 2012 U6 - https://doi.org/10.1007/s00339-012-6848-z SN - 0947-8396 VL - 107 IS - 4 SP - 965 EP - 970 PB - Springer CY - New York ER - TY - JOUR A1 - Altafim, Ruy Alberto Pisani A1 - Rychkov, Dmitry A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Basso, Heitor Cury A1 - Altafim, Ruy Alberto Pisani A1 - Melzer, Martin T1 - Laminated tubular-channel ferroelectret systems from low-density Polyethylene Films and from Fluoroethylene-propylene Copolymer Films - A comparison JF - IEEE transactions on dielectrics and electrical insulation N2 - A template-based lamination technique for the manufacture of ferroelectrets from uniform electret films was recently reported. In the present work, this technique is used to prepare similar ferroelectret structures from low-density polyethylene (LDPE) films and from fluoro-ethylene-propylene (FEP) copolymer films. A comparative analysis of the pressure-, temperature-, and frequency-dependent piezoelectric properties has been performed on the two ferroelectret systems. It is observed that the FEP ferroelectrets exhibit better piezoelectric responses and are thermally more stable. The difference between the piezoelectric d(33) coefficients of the two ferroelectret systems is partially explained here by their different elastic moduli. The anti-resonance peaks of both structures have been investigated by means of dielectric resonance spectroscopy and electroacoustic sound-pressure measurements. A difference of more than 10 kHz is observed between the anti-resonance frequencies of the two ferroelectret systems. KW - Ferroelectrets KW - piezoelectrets KW - piezoelectricity KW - electro-mechanical transducers KW - static-pressure dependence KW - temperature dependence KW - frequency response Y1 - 2012 SN - 1070-9878 VL - 19 IS - 4 SP - 1116 EP - 1123 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Fang, Peng A1 - Hollaender, Lars A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Piezoelectric d(33) coefficients in foamed and layered polymer piezoelectrets from dynamic mechano-electrical experiments, electro-mechanical resonance spectroscopy and acoustic-transducer measurements JF - Measurement science and technology N2 - Piezoelectrets are novel transducer materials which can be widely applied in sensors and actuators. Here, three techniques for determining piezoelectric d(33) coefficients of piezoelectrets are reviewed and compared. Two types of piezoelectrets, polyethylene-naphthalate (PEN) polymer-foam piezoelectrets and fluorinated ethylene-propylene (FEP) copolymer-layer piezoelectrets, have been prepared and measured by means of dynamic, resonance, and acoustical methods. The dynamic measurements show that the d(33) coefficient of PEN-foam samples clearly decreases with increasing stress, but 80% of the initial d(33) can be retained after 1800 cycles of a continuous dynamic measurement in a mechanical fatigue test. The resonance measurements demonstrate that both PEN-foam and FEP-layer samples exhibit clear electro-mechanical resonances. PEN-foam samples show elastic moduli in the range from 1 to 12 MPa and d(33) values up to 500 pC N-1, while FEP-layer samples show homogeneous elastic moduli of about 0.3 MPa and d(33) values of about 280 pC N-1. The acoustical measurements reveal that both PEN-foam and FEP-layer samples exhibit stable frequency responses in the range from 5.7 to 20 kHz. In addition, d(33) coefficients obtained with different experimental methods are in good agreement with each other, which confirms the reliability of all three techniques. KW - piezoelectret KW - ferroelectret KW - dielectric resonance spectroscopy KW - piezoelectric measurements KW - acoustic-transducer materials KW - polyethylene naphthalate (PEN) KW - fluorinated ethylene-propylene copolymer (FEP) Y1 - 2012 U6 - https://doi.org/10.1088/0957-0233/23/3/035604 SN - 0957-0233 VL - 23 IS - 3 PB - IOP Publ. Ltd. CY - Bristol 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 - 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 -