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Piezoelectric activity and thermal stability of cellular fluorocarbon films

Two methods for preparing piezoelectric fluorocarbon polymers with cellular structure (ferroelectrets) are introduced. Piezoelectric activity of laminated fluorocarbon films made from polytetrafluoroethylene (PTFE) and fluoroethylenepropylene (FEP) is characterized by quasistatic measurement of piezoelectric d33 coefficient, while the thermal stability of d33 is investigated by their isothermal decay. The results show that the quasistatic d33-coefficients between 500 and 2200 pC/N are obtained for such fluorocarbon films; d33-coefficients are relatively independent of the static pressure in the range of 20 kPa; comparing to cellular polypropylene (PP) film the new fluorocarbon films show not only higher values of d33, but also much better thermal stability; moreover, thermal stability of the fluorocarbon film can be further improved by the process of pre-ageing.