Regensburg 2004 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 13: SYMPOSIUM: Understanding and Controlling Complex Structures: From Synthetic Polymers to Biomaterials I

CPP 13.9: Talk

Tuesday, March 9, 2004, 12:15–12:30, H 37

Structural modifications and electromechanical properties of inflated cellular polypropylene films — •Michael Wegener, Enis Tuncer, Werner Wirges, and Reimund Gerhard-Multhaupt — University of Potsdam, Department of Physics, Am Neuen Palais 10, D-14469 Potsdam

Voided space-charge electrets with internal charge layers show significant piezoelectrical properties. In such materials, e.g. cellular polypropylene, the piezoelectric coefficient strongly depends on the cell-size and -shape distributions. The electrically charged cells represent macroscopic dipoles. The typically air-filled cells can be deformed very easily by a mechanical stress or an electrical field, which represents the direct and inverse piezoelectric effects, respectively. By means of controlled inflation, cell sizes and shapes can be varied over a rather large range. This is achieved by altering pressure and temperature. Here, we describe various inflation procedures with several different pressures, temperatures and treatment times. After optimization the procedure yields high piezoelectric coefficients that may be due to the low elastic moduli of the inflated samples. The results are discussed with respect to the observed micro-structure of cellular films (as seen in SEM cross-sections), and are compared to the finite element analysis. The comparison to numerical simulations explains the micro-structural changes during the inflation process.