Microstorms in Cellular Polymers: A Route to Soft Piezoelectric Transducer Materials with Engineered Macroscopic Dipoles

Wegener, Michael; Bauer, Siegfried

doi:10.1002/cphc.200400517

Cited by 180 publications

(142 citation statements)

References 46 publications

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“…The laboratory template consisted of a 100 m thick Teflon PTFE film with an area of 30ϫ 40 mm 2 and with parallel rectangular openings ͑area 1.5ϫ 30 mm 2 ͒ cut into the PTFE films by means of computer-controlled laser ablation. The PTFE separations between adjacent openings also had a width of 1.5 mm.…”

Section: Sample Preparationmentioning

confidence: 99%

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

Altafim¹,

Qiu²,

Wirges³

et al. 2009

Journal of Applied Physics

144

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Polarization switching at the nanoscale in ferroelectric copolymer thin films Appl. Phys. Lett. 99, 142904 (2011) Tunable temperature dependence of electrocaloric effect in ferroelectric relaxor poly(vinylidene fluoridetrifluoroethylene-chlorofluoroethylene terpolymer Appl. Phys. Lett. 99, 052907 (2011) Beneficial and detrimental fatigue effects of dielectric barrier discharges on the piezoelectricity of polypropylene ferroelectrets J. Appl. Phys. 110, 024108 (2011) Energy harvesting by nonlinear capacitance variation for a relaxor ferroelectric poly(vinylidene fluoridetrifluoroethylene-chlorofluoroethylene) terpolymer Appl. Phys. Lett. 98, 222901 (2011) Photocrosslinking of ferroelectric polymers and its application in three-dimensional memory arrays Appl. Phys. Lett. 98, 183302 (2011) Additional information on J. Appl. Phys. We describe the concept, the fabrication, and the most relevant properties of a piezoelectric-polymer system: Two fluoroethylenepropylene ͑FEP͒ films with good electret properties are laminated around a specifically designed and prepared polytetrafluoroethylene ͑PTFE͒ template at 300°C. After removing the PTFE template, a two-layer FEP film with open tubular channels is obtained. For electric charging, the two-layer FEP system is subjected to a high electric field. The resulting dielectric barrier discharges inside the tubular channels yield a ferroelectret with high piezoelectricity. d 33 coefficients of up to 160 pC/N have already been achieved on the ferroelectret films. After charging at suitable elevated temperatures, the piezoelectricity is stable at temperatures of at least 130°C. Advantages of the transducer films include ease of fabrication at laboratory or industrial scales, a wide range of possible geometrical and processing parameters, straightforward control of the uniformity of the polymer system, flexibility, and versatility of the soft ferroelectrets, and a large potential for device applications e.g., in the areas of biomedicine, communications, production engineering, sensor systems, environmental monitoring, etc.

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Section: Sample Preparationmentioning

confidence: 99%

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

Altafim¹,

Qiu²,

Wirges³

et al. 2009

Journal of Applied Physics

144

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“…

The piezoelectric properties of ferroelectrets are based on the quasi-permanent internal electric charging of the cellular structure with charge layers of opposite polarity on void surfaces that face each other.

…”

mentioning

confidence: 99%

“…[3±10] Furthermore, piezoelectric cellular PP films are already implemented in several applications. [2] There is, however, an essential requirement that PP ferroelectrets do not meet: The thermal stability of the currently available piezoelectric cellular PP films is limited to around 60 to 70 C, depending on the chosen annealing treatment. [11,12] Here, more stable materials are clearly needed for most applications.…”

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confidence: 99%

Piezoelectric Polyethylene Terephthalate (PETP) Foams – Specifically Designed and Prepared Ferroelectret Films

2005

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Detailed knowledge about the essential properties required for piezoelectric polymer-electret foams (or ferroelectrets) [1,2] is exploited in the design and the preparation of cellular polyethylene terephthalate (PETP) electret films with piezoelectric properties. The relevant relationships between structural, elastic and piezoelectric properties had been established previously for polypropylene (PP) ferroelectrets and could be successfully employed in the present demonstration of the novel ferroelectret polymer PETP.The piezoelectric properties of ferroelectrets are based on the quasi-permanent internal electric charging of the cellular structure with charge layers of opposite polarity on void surfaces that face each other. Due to the bipolar charging, the centrosymmetry of the polymer foam is broken and macroscopic electric dipoles are formed. In addition, the voids must deform and the effective dipole moments change under mechanical stress. So far, because of the availability of highquality cellular PP films, PP has been the ºworkhorseº of ferroelectret research and development.In PP, the combination of a relatively soft structure (low elastic stiffness) with internally trapped bipolar charges yields a high piezoelectric coefficient in the film-thickness direction. Typically, PP ferroelectret films show direct and inverse piezoelectric d 33 coefficients of several hundred pC/N (or pm/V). For cellular PP films, the preparation, the optimization of the cellular structure by means of controlled inflation, the electrical charging through internal micro-plasma discharges, and the charge storage in deep traps are well understood. [3±10] Furthermore, piezoelectric cellular PP films are already implemented in several applications. [2] There is, however, an essential requirement that PP ferroelectrets do not meet: The thermal stability of the currently available piezoelectric cellular PP films is limited to around 60 to 70 C, depending on the chosen annealing treatment. [11,12] Here, more stable materials are clearly needed for most applications. Furthermore, the ferroelectret concept should be confirmed with independently developed polymer foams that exhibit similar piezoelectric behavior.Here, we investigate PETP films that are already produced in industry on a large scale and that offer chances to prepare ferroelectret films of high quality and to achieve slightly better thermal (and temporal) stabilities than the existing PP ferroelectrets.Recently, the dependence of the piezoelectric response on the elastic stiffness and on the void structure was established for cellular PP films. [7,13] In summary, the inversely U-shaped behavior schematically shown in Figure 1 is observed. Films with small (or low) voids are relatively stiff and therefore show only low piezoelectricity. The controlled increase of the void height by means of inflation [7±9] decreases the elastic stiffness and increases the piezoelectric activity until an optimal foam structure is obtained. For cellular PP films, a minimal elastic COMMUNICATI...

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“…Over the last ten years, electrically charged polymer foams were discovered and investigated as strongly piezoelectric transducer materials (see for example two recent reviews [1,2] and the references therein). The piezoelectricity of the socalled ferroelectret [1] films stems from the bipolar internal charging of their cellular voids combined with the alternation of relatively hard polymer layers and relatively soft air-filled voids.…”

Section: Introductionmentioning

confidence: 99%

“…[1,2] With piezoelectric coefficients of up to several hundred pC N -1 (or pm V -1 ), PP ferroelectrets exhibit very high piezoelectricity for a soft polymer material. [3][4][5] Their industrial applications are, however, still relatively scarce because of several limitations, the most severe of which is a low thermal stability.…”

Section: Introductionmentioning

confidence: 99%

Optimized Preparation of Elastically Soft, Highly Piezoelectric, Cellular Ferroelectrets from Nonvoided Poly(ethylene Terephthalate) Films

Wirges

Wegener

Voronina

et al. 2007

Adv Funct Materials

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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 poly(ethylene terephthalate) (PETP) films by means of foaming with CO2, biaxial mechanical stretching, controlled void inflation, and bipolar electric charging. The nonvoided PETP films were 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 inflation in a pressure chamber. Bipolar electric charging of the internal voids was achieved through the application of high electric fields in an SF6 atmosphere. The new optimized PETP ferroelectrets exhibit quite large piezoelectric coefficients up to almost 500 pC N–1, for which unusually low elastic stiffnesses of only around 0.3 MPa are essential. The PETP‐foam ferroelectrets possess unclamped thickness‐extension resonance frequencies between approximately 120 and 250 kHz, and are thus highly suitable for several established as well as novel ultrasonic‐transducer applications.

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Microstorms in Cellular Polymers: A Route to Soft Piezoelectric Transducer Materials with Engineered Macroscopic Dipoles

Cited by 180 publications

References 46 publications

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

Piezoelectric Polyethylene Terephthalate (PETP) Foams – Specifically Designed and Prepared Ferroelectret Films

Optimized Preparation of Elastically Soft, Highly Piezoelectric, Cellular Ferroelectrets from Nonvoided Poly(ethylene Terephthalate) Films

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