Enhanced dielectric properties of electrically poled poly(vinylidene fluoride) (PVDF) and polycarbonate (PC) multilayer films via interfacial polarization

Electrically poled poly(vinylidene fluoride) (PVDF) and polycarbonate (PC) multilayer films can be considered as a polymer electret, which stores quasi-permanent charges (i.e., ions) at PVDF/PC interfaces. In this study, the corresponding dielectric properties of electrically poled PVDF/PC multilayer films are investigated experimentally. First, the bipolar hysteresis loop becomes narrower for the poled PVDF/PC multilayer films upon increasing the poling time, because the impurity ions in PVDF are locked at the PVDF/PC interfaces. Second, asymmetric DC conductivity in poled PVDF/PC multilayer films is observed because of the pre-existing electric field in the electret layers. When the pre-existing field is in the same direction of the applied external field, enhanced DC conductivity is observed in the leakage current measurement. In contrast, if the pre-existing field is opposite to the applied external field, decreased DC conductivity is seen. More experimental evidence of polarized charge at the PVDF/PC interfaces in poled PVDF/PC multilayer films is also manifested by thermally stimulated depolarization current (TSDC) experiments.