Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 34: POSTERS Polymerphysics
CPP 34.2: Poster
Donnerstag, 28. Februar 2008, 17:00–19:30, Poster A
cellular polyethylene-naphthalate piezo- and ferroelectrets: foaming in supercritical carbon dioxide, structure improvement through inflation and stretching — •peng fang1, werner wirges1, reimund gerhard1, and larissa zirkel2 — 1Applied Condensed-Matter Physics, Institute of Physics, University of Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany — 2Institute of Polymer Materials, Friedrich-Alexander University Erlangen-Nürnberg, Martensstrasse 7, 91058 Erlangen, Germany
Cellular polymer films can be used as ferroelectrets in many transducer applications. Here, we propose a preparation process for cellular polyethylene-naphthalate (PEN) films with the following steps: (1) Foaming by means of supercritical carbon dioxide (CO2), (2) controlled inflation through gas diffusion and expansion, and (3) biaxial stretching. We demonstrate and describe the cellular structure that is formed under suitable processing conditions. For the foaming process, a PEN film is saturated with supercritical CO2 at room temperature for a few hours, at a pressure as high as 100 bar, where the temperature is very critical for controlling the sample density. Additional inflation can improve the cellular geometry. Stretching may be employed in order to achieve a cellular structure with lens-like voids. Piezoelectric coefficients of up to 140 pC/N demonstrate the suitability of such cellular PEN films for transducer applications. However, high electromechanical responses are found only on samples within the proper density range and with optimal cellular structures. Their piezoelectricity is partially stable at elevated temperatures as high as 100°C.