Regensburg 2007 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 31: New Materials

CPP 31.1: Talk

Friday, March 30, 2007, 10:30–10:45, H40

Piezoelectric properties of polyester ferroelectrets made from polyethylene terephthalate — •Olena Voronina, Michael Wegener, Werner Wirges, and Reimund Gerhard — University of Potsdam, Institute of Physics, 14469 Potsdam, Germany

Ferroelectrets are cellular polymer foams with macroscopic electric dipoles that are formed by charges trapped on the internal void surfaces. The piezoelectricity of ferroelectrets arises from changes of the void heights (and thus of the dipole sizes) when mechanical or electrical stress is applied. Ferroelectrets are usually relatively soft in the thickness direction which leads to high piezoelectric activities with coefficients up to hundreds of pC/N [1].

Here, we describe the preparation and the resulting properties of new polyethylene-terephthalate (PETP) ferroelectrets [2]. An optimized sequence of steps for preparation is described. It includes foaming of commercial PETP films in supercritical CO2 accompanied by a heat treatment as well as biaxial stretching and electric charging. The optimized PETP ferroelectrets exhibit piezoelectric thickness coefficients up to 500 pC/N for which the low elastic stiffness of only around 0.3 MPa is essential. The PETP ferroelectrets show unclamped thickness-extension resonance frequencies between approximately 120 and 250 kHz, and are thus particularly suitable for ultrasonic-transducer applications.

[1] M. Wegener and S. Bauer, ChemPhysChem 6, 1014-1025 (2005).

[2] W. Wirges, M. Wegener, O. Voronina, L. Zirkel and R. Gerhard-Multhaupt, Advanced Functional Materials, in press