Comportamento relaxor de polímeros ferroelétricos submetidos a radiações eletromagnéticas

• Ano de defesa: 2008
• Autor(a) principal: Cezar Welter
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Ferroeletricidade; Polímeros ferroelétricos; Transição de fase; Polímeros fluorados; Física
• Link de acesso: http://hdl.handle.net/1843/ESCZ-7N4GFV

Electromagnetic radiation effects onto poly (vinylidene fluoride-trifluoroethylene), P(VDFTrFE) copolymers are studied. It is demonstrated that high energy (gamma radiation, E = 1250 keV ) and low energy (ultraviolet radiation, EUV = 4.88 eV ) ionizing radiation are able to induce a relaxor behavior to equimolar (PVDF-TrFE) ferroelectric copolymer. This is the first scientific report on the use of low energy radiation to induce and study the relaxor behavior in ferroelectric polymers. The experimental technics used to investigate the effects of radiations were: (1) xray diffractometry, to structurally characterize the crystalline phase and to find the relation between crystalline and amorphous phases; (2) differential scanning calorimetry, to analyze the thermal stability of ferro-paraelectric transition and the melting point;(3) thermo-dielectric spectroscopy, to qualify the electric dipoles interactions, that represent the ferroelectric domains of material and its interactions; (4) infrared and ultraviolet spectroscopy, to detect the included chemical changes; and (5) solvent dissolutions to confirm intermolecular chemicals modifications. We demonstrated that the mechanisms responsible for inducing the relaxor behavior under low and high energy radiation are distinct. In the case of gamma radiation, therelaxor behavior is a consequence of the decreasing correlation length between the ferroelectric domains (loss of cooperative ferroelectric effects), due three-dimensional reticulation. In the case of ultraviolet radiation, it is due to the formation of singlet, duplets, and triplets of double (C=C) bounds.