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 - 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 - Rychkov, Dmitry A1 - Altafim, Ruy Alberto Pisani A1 - Qiu, Xunlin A1 - Gerhard, Reimund T1 - Treatment with orthophosphoric acid enhances the thermal stability of the piezoelectricity in low-density polyethylene ferroelectrets JF - Journal of applied physics N2 - Ferroelectrets have been fabricated from low-density polyethylene (LDPE) films by means of a template-based lamination. The temperature dependence of the piezoelectric d(33) coefficient has been investigated. It was found that low-density polyethylene ferroelectrets have rather low thermal stability with the piezoelectric coefficient decaying almost to zero already at 100 degrees C. This behavior is attributed to the poor electret properties of the polyethylene films used for the fabrication of the ferroelectrets. In order to improve the charge trapping and the thermal stability of electret charge and piezoelectricity, LDPE ferroelectrets were treated with orthophosphoric acid. The treatment resulted in considerable improvements of the charge stability in LDPE films and in ferroelectret systems made from them. For example, the charge and piezoelectric-coefficient decay curves shifted to higher temperatures by 60 K and 40 K, respectively. It is shown that the decay of the piezoelectric coefficient in LDPE ferroelectrets is governed by the relaxation of less stable positive charges. The treatment also leads to noticeable changes in the chemical composition of the LDPE surface. Infrared spectroscopy reveals absorption bands attributed to phosphorus-containing structures, while scanning electron microscopy shows new island-like structures, 50-200 nm in diameter, on the modified surface. Y1 - 2012 U6 - https://doi.org/10.1063/1.4729866 SN - 0021-8979 VL - 111 IS - 12 PB - American Institute of Physics CY - Melville ER -