Dielectric barrier micro-discharges: mechanism for the charging of piezoelectric polymer foams

Dielectric barrier micro-discharges within the voids of cellular polymers are shown to be responsible for the charging of cellular space-charge electrets and also for the large piezoelectricity in these materials. Above the threshold voltage for breakdown in the voids, the micro-discharges are evidenced by light emission from the polymer, as well as by hysteresis loops in the dielectric and electromechanical properties versus applied voltage. Although cellular space-charge electrets are based on nonpolar dielectrics, the hysteresis in displacement and mechanical strain demonstrate close similarities to ferroelectric materials. The monitoring of the light emission during breakdown provides a quick and easy check for the suitability of cellular space-charge electrets for piezoelectric applications. It also allows for the visualisation of micro-pores in foams in a non-destructive way.