Air-breakdown charging mechanism of fibrous polytetrafluoroethylene films

Recently air-breakdown phenomena have gained increasing interest with respect to porous electrets for use as piezoelectric polymers. A strong discrepancy between porous (closed-porous) polypropylene and fibrous (open-porous) polytetrafluoroethylene (PTFE) has been recognized concerning the obtainable polarization and the related piezoelectric d33 coefficients. The present study aims to clarify the reasons for a poor charge separation ability of fibrous materials when exposed to electrical breakdown in its air voids. Therefore air-breakdown phenomenon of 91% fibrous PTFE films has been studied in detail, utilizing a corona triode for voltage application. At sufficient surface potential air breakdown sets in at an average field strength of 11.7MV∕m, which corresponds to the value expected by Paschen breakdown in air. For higher applied voltages and therewith higher electric-field strengths in the film, the current generated by such electrical breakdown limits the maximum obtainable surface potential. It wil...

[1]  H. Kawai,et al.  The Piezoelectricity of Poly (vinylidene Fluoride) , 1969 .

[2]  Graham Williams,et al.  Conference on Electrical Insulation and Dielectric Phenomena , 1982, IEEE Transactions on Electrical Insulation.

[3]  Jukka Lekkala,et al.  ElectroMechanical Film (EMFi) — a new multipurpose electret material , 2000 .

[4]  R. Gerhard-Multhaupt.  Voided polymer electrets - new materials, new challenges, new chances , 2002, Proceedings. 11th International Symposium on Electrets.

[5]  Michael Wegener,et al.  Understanding the role of the gas in the voids during corona charging of cellular electret films - a way to enhance their piezoelectricity , 2001 .

[6]  Werner Wirges,et al.  Thermally stable dynamic piezoelectricity in sandwich films of porous and nonporous amorphous fluoropolymer , 2001 .

[7]  J. Hillenbrand,et al.  Piezoelectricity of cellular and porous polymer electrets , 2002, Proceedings. 11th International Symposium on Electrets.

[8]  Werner Wirges,et al.  Controlled inflation of voids in cellular polymer ferroelectrets: Optimizing electromechanical transducer properties , 2004 .

[9]  Werner Wirges,et al.  Two-step inflation of cellular polypropylene films: void-thickness increase and enhanced electromechanical properties , 2004 .

[10]  J. Scheinbeim,et al.  Piezoelectric properties and ferroelectric hysteresis effects in uniaxially stretched nylon‐11 films , 1984 .

[11]  Bing Zhou,et al.  Study of porous dielectrics as electret materials , 1998 .

[12]  S. Bauer,et al.  Large piezoelectric effects in charged, heterogeneous fluoropolymer electrets , 2000 .

[13]  Gerhard M. Sessler,et al.  Piezoelectric d33 coefficient of cellular polypropylene subjected to expansion by pressure treatment , 2004 .

[14]  I. M. Ward,et al.  The measurement of the shear piezoelectric coefficients of polyvinylidene fluoride , 1986 .

[15]  David R. Smith,et al.  Reversing Light: Negative Refraction , 2004 .

[16]  M. Paajanen,et al.  Electromechanical modeling and properties of the electret film EMFI , 2001 .

[17]  Xiaoqing Zhang,et al.  Improvement of piezoelectric activity of cellular polymers using a double-expansion process , 2004 .

[18]  B. Gross,et al.  Measurement of potential buildup and decay, surface charge density, and charging currents of corona‐charged polymer foil electrets , 1976 .