الفهرس 
Introduction and Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
The thesis deals with the study of the pyro-, piezoelectricity and the thermally stimulated depolarization current (TSDC) of some electrets formed from poly (vinylidene fluoride–trifluroethylene) P(VDF-TrFE) doped with three different types of dyes, Crystal violet (CV), Coumarin 2 (C2) and N,NDimethyl- 4-nitro-4-stilbenamine (DANS). The other copolymer Styrene- Acrylonitrile (SAN) has been doped with two dyes, 4N, N-dimethylamino-4’-Nmethyl- stilbazoliumtosylate (DAST) and (DANS). The films were prepared by two different methods: casting and spin coating techniques. The two wellknown thermal poling and corona charging techniques have been applied during electrets formation. Infra-red spectroscopy, wide angle X-ray diffraction and UV/vis spectroscopy investigations were carried out to specify the morphology and microstructure of the specimens. It was required to recognize the influence of the applied stress at high temperature on the morphology and the microstructure of the investigated materials. The dependence of morphological structures for a great extent on the different types of dyes was observed. H- and J- aggregates were observed in the CV and C2 doped P(VDF-TrFE) copolymer, respectively, while those doped with DANS show lamella structure. Tree-like structure was found in pure SAN and DAST-SAN films. The application of pressure induced crystals in case of DANS doped- SAN copolymer. Wide angle X-ray diffraction scans confirm the phase transformation during the amorphous phase; this multiphase structure reflects the pyro- and piezo response in these materials. TSDC spectra of thermal poled and corona charged electrets were recorded. The influence of the experimental parameters, i.e, poling field (Ep), poling temperature (Tp) and poling time (tp) configuration on the TSDC spectra of the investigated specimen was determined. Continuous complex spectrums were 13 observed. Relaxation peaks were observed in the motion of the space charge and to the molecular dipole orientation occurred in the neighbourhood of the glasstransition temperature, Tg. The activation energy Ea was calculated using Arrhenius relationship. TSDC measurements revealed that, the ferroelectric to paraelectric transition peak has been taken place in the C2 and DANS doped P(VDF-TrFE) copolymer. TSDC measurements of DAST doped- SAN showed two peaks, the first peak could be due to the disorientation of DAST dipole, and the second was attributed to the molecular dipole orientation occurred in the neighborhood of the glass-transition Tg (390K). . The pyroelectricity observed in the investigated material can be accounted for by two processes: (i) The charge injected in the specimen is trapped in non-cento symmetrical sites and (ii) the electric field created by the space charge in the specimens produces an orientation of the dipoles (either dipoles created during the injection process or intrinsic dipoles) of the materials. On the other hand, the piezoelectricity, as a result of the stress is applied along the film length, and the current of piezoelectricity was measured along the direction perpendicular to the sample and stress direction, the piezoelectric coefficients, d33 were calculated for the investigated materials. The magnitude of d33 coefficient depends on the morphology, microstructure of the specimens and measuring temperature. The study revealed that the dye doped copolymers has a detectable change in their pyro-and piezoelectric activities comparing with pure material. Kohlrausch-Williams-Watts stretched function is applied to estimate the relaxation time of piezoelectric current.