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Doctoral Thesis
DOI
10.11606/T.76.1999.tde-18062008-084814
Document
Author
Full name
Célio Wisniewski
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1999
Supervisor
Committee
Giacometti, José Alberto (President)
Ferreira, Guilherme Fontes Leal
Mastelaro, Valmor Roberto
Moreira, Roberto Luiz
Varela, Jose Arana
Title in Portuguese
Caracterização de polímeros ferroelétricos: metodologia e resultados
Keywords in Portuguese
Dielétricos
Ferroeletrecidade
Histerise
Polarização
Polímeros
Abstract in Portuguese
Neste trabalho, foram desenvolvidos e implementados três métodos experimentais, o método de corrente constante - CC (adaptado a partir do triodo de corona à corrente constante), o método de rampa de tensão - RT (adaptado a partir do método bipolar de medida de histerese elétrica) e o método para medida do coeficiente piroelémco pela técnica da temperatura oscilante (função senoidal). Os métodos foram empregados no estudo das polarizações elétricas apresentadas pelo PVDF, PVF, o copolímero P(VDF-TrFE) e a blenda P(VDF-TrFE) - PMMA. Verificou-se através de medidas de difratometia de raios-x, medida da polarização ferroelétrica (obtida pelos métodos CC e RT) e medida do coeficiente piroelétrico que parte da polarização elétrica relaxa após a remoção do campo elétrico e está associada a efeitos não hereditários. Foi estudada a dependência desta polarização com o campo elétrico aplicado (taxa de subida do campo e campo máximo), com o tempo de curto circuito que a amostra foi submetida entre processos de polarização consecutivos e o tipo de amostra. Foram determinados e comparados a polarização remanescente e o campo coercitivo dos materiais citados, obtidos pelos métodos CC e RT.
Title in English
Characterization of ferroeletric polymers: methodology and results
Keywords in English
Dieletrics
Ferroeletrecity
Hysterises
Polarization
Polymers
Abstract in English
In this work three experimental setups were developed, the constant current method (CC) (derived from the corona mode with constant current), the ramp voltage method (RT) (derived from the bipolar hysteresis measurements) and measurement of the pyroeletric coefficient employing a sinusoidal temperature variation. These methods were used to study the ferroelectric polarization in polymers such as PVDF, PVF, copolymer of P(VDF-TrFE) and P(VDF-TrFE) - PMMA blend. From x-ray, electric polarization and pyroelectric measurements it was found that part of the total polarization decays after removing the electric field. The dependence of such decaying polarization on the rate of increasing of the electric field, on the maximum field applied to the sample and the time interval of short-circuit between successive measurements was investigated. The value of the remanent polarization and the coercive field was determined for polymeric materials listed above and a comparison of the results obtained using the CC and RT method was performed.
 
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CelioWisniewski_D.pdf (3.93 Mbytes)
Publishing Date
2008-06-20
 
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