Polymer electrets

Piezoelectricity in polymer films is greatly increased by polarizing the film under a high d.c. field at high temperatures. This effect, the piezoelectricity of a polymer electret, has attracted the attention of many investigators from the scientific as well as industrial point of view, since the early work by Kocharyan and Pachadzhyan (1963,1966) on PMMA and PVC. 

Murayama.N. Piezoelectric and pyroelectric effects of polymer electrets. Microsymposium on Electrical Properties of Polymers, Tokyo (Jan. 1972). 

Van Turnhout J, "Thermally Stimulated Discharge of Polymer Electrets", PhD Thesis, Leiden, 1972 as book published by Elsevier, Amsterdam (1975). 

Table IV. Charge Storage/Lifetimes of Some Polymer Electrets...

Recent Advances in the Improvement of Polymer Electret Films... 

Electret materials are meanwhile used in a large number of modern high-tech applications including microphones, acoustic sensors, transducers, radiation and pollution dosimeters, power generators, filters, and many more. Additionally, electret technology is of great interest in the field of biomaterials, for instance in callus formation and wound healing [10, 11], When used in cellular or in multilayer sandwich structures, polymer electrets can exhibit piezoelectricity. Such materials are ferroelectrets, as they show typical features of ferroelectric materials such as piezo-and pyroelectricity [12-17],... 

Based on these results, our recent research on polymer electret materials focuses on the understanding of (1) the role of the chemical structure of the polymer, (2) the influence of additives, and (3) the variation of processing parameters on the electret performance. As schematically illustrated in Fig. 7, the objective of our research is to provide concepts and methods to improve substantially the electret performance of polymer materials. 

In this chapter we have presented concepts and methods to improve polymer electret materials. Corona charging was employed for film charging since this method possesses the advantages of being cost-effective, easy to perform, and applicable in short periods of time. 

Special thanks go to Prof. Gerhard M. Sessler and to Dr. Joachim Hillenbrand (Technical University of Darmstadt) for their continuous support and many fruitful discussions on the physics and characterization of our polymer electret materials. Additional thanks for performing the TSD measurements. 

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