Polarization and space charge analysis in thermally poled PVDF

Abstract

The spatial distribution of the polarization and space charge in thermally poled poly (vinylidene fluoride) is studied using the laser intensity modulation method. Injected space charge, localized near the electrode polymer interface, tends to prevent the formation of uniform polarization in the polymer bulk. The actual amount of charge existing in the poled specimen is determined using hysteresis measurements and thermally stimulated discharge current (TSDC) measurements. By using the peak cleaning technique and by measuring the pyroelectric current during the cooling of the specimen, the contribution of depolarization current and space charge detrapping to the TSDC measurement is considered. From hysteresis measurements a relaxation process was observed around 65°C which was related to the dipolar relaxation in the crystalline phase known as the αc relaxation. A significant increase of the TSDC at temperatures higher than 130°C was observed meaning that the dipolar charge and the space charge are very stable up to high temperature. In this temperature range, the pyroelectric current is significant. Two relaxation processes were identified for a polarizing temperature lower than 120°C. One is centred around the polarizing temperature and is related to space charge release. The second is related to dipole relaxation in the crystalline phase. The position of the last peak is determined by interaction between the dipoles and the internal electric field, resulting from the charge stored in the sample. We propose to call this as the αcρ interaction. The higher temperature of the dipolar peak was identified as 86°C with an activation energy of 0.52±0.04 eV.

TSDC spectroscopy of relaxational and interfacial phenomena

“…Individual polymers (such as polystyrene [228], polycaprolactone [229], polyoctenylene [230], polyvinylnaphthalene [231], unsaturated polyester resins [232,233]) and copolymers [234][235][236][237] as well as composites [238,239] were investigated by the TSDC and other relaxation techniques. Dipolar relaxation in amorphous [240,241], semi-crystalline [241] and liquid crystals [242] were investigated by the TSDC method, and the effects of polarisation and space charging were analysed for different systems [243][244][245]. Both TSDC and TSPC methods were applied to polymers [246].…”

Ferroelectric and magnetic studies on unpoled Poly (vinylidine Fluoride)/Fe3O4 magnetoelectric nanocomposite structures

“…This paper throws light on the fabrication of magnetoelectric PVDF/Fe 3 O 4 composite films and studies their ferroelectric and magnetic properties. The ferroelectric studies are commonly made on electrically or thermally poled samples to enhance the polarization effect [10]. But, the present work deals with the unpoled samples to understand the effect of nano Fe 3 O 4 on the inherent ferroelectric property of PVDF.…”

Enhancement of etch rate for preparation of nano-sized ion-track membranes of poly(vinylidene fluoride): Effect of pretreatment and high-LET beam irradiation

“…In line with this discussion, an apparently small pretreatment effect at À84°C can be due to the retarded oxidation in the temporarily-frozen rigid macromolecules below the glass transition temperature (T g ) of PVDF, À40 to À30°C. PVDF exhibited another transition related to a certain kind of relaxation slightly above the etching temperature of 80°C [19,20], which might be one of the reasons for the maximum pretreatment effect achieved at 120°C. Table 2 summarizes not only the irradiation conditions, but also the results of the etching of the PVDF films which were irradiated with various ions and then stored in air at 25°C.…”