PVDF, Poly(vinylidene fluoride), is a polymer that has been studied for over four decades due to its good electromechanical properties, stability, and durability in various environments. Currently, PVDF is the only commercially available piezoelectric polymer. PVDF is a polymorph, which indicates the presence of several crystalline phases such as α, β, γ, and δ-phase. Oriented β-phase PVDF exhibits ferroelectric properties and displays the largest piezoelectricity amongst the four phases, which makes it the most desirable phase. Preparing oriented β-phase PVDF is a multi-step process, which is cost intensive, due to the time, labor and energy utilized. The main goal of this work is to prepare oriented β-phase PVDF using the electrospraying technique in a one step process. During the electrospraying process a polymer jet is ejected. This jet disintegrates into droplets due to overwhelming surface tension, resulting in a sprayed coating on the collector substrate. Because of the combination of jet ejection and the high voltage applied between the needle tip and the substrate, the droplets can be stretched and the polymer chains can be oriented. Both the stretching and the high electric field are required for the transformation of α-phase to the oriented β-phase. This study proposes that by using the electrospraying technique it is possible to transform the α-phase to the β-phase in a one step process starting from solution. This research focuses on the processing and characterization of electrosprayed PVDF as well as electrosprayed PVDF/carbon nanotubes (PVDF/CNT) nanocomposites. The specific tasks are to determine the changes to the PVDF phases due to the electrospraying technique, and to determine the changes in the PVDF morphology due to the addition of carbon nanotubes to the polymer matrix.PVDF with two different molecular weights were electrosprayed using different solvents and parameters. Initial observations after electrospraying were that, high boiling point solvents resulted in the spraying of the solution and forming films, whereas a low boiling point volatile solvent such as acetone resulted in the spinning of the solution thus forming non-woven fiber mats. The thermal and electrical properties of the electrosprayed PVDF and PVDF/CNT composites are measured using several characterization techniques, including Modulated Differential Scanning Calorimetry (MDSC), Dielectric spectroscopy, Thermally Stimulated Current (TSC), Fourier Transform Infrared Spectroscopy (FT-IR), and X-Ray Diffraction (XRD). MDSC results show that electrosprayed PVDF has a lower melting point temperature than that of PVDF commercially available pellets. In addition, electrosprayed PVDF/CNT nanocomposites show a linear increase in the percentage of crystallinity with the increase of CNT concentration in the composite. Dielectric spectroscopy results indicate that by increasing the CNT concentration in the composite, the dielectric constant and the polymer conductivity increase.From the four characterizing techniques used, two of them, FT-IR and XRD, show that it is possible to transform α-phase to β-phase PVDF in a one-step process using electrospraying. The other two techniques, TSC and dielectric spectroscopy, show α-phase for the electrosprayed samples without CNT, and some β-phase formation with samples electrosprayed with CNT. These last two techniques; TSC and dielectric spectroscopy have results that differ from the FT-IR and XRD techniques. This contradiction may be a result of the small amounts of β-phase in the sample, which cannot be detected using these techniques. Another reason may be due to the difference in the probing levels between these techniques. XRD and FT-IR probe at the molecular level, whereas TSC and dielectric probe at a much larger scale, which may make it hard to detect small amounts of β-phase.

Neste trabalho desenvolvemos um método de controle e aquisição de dados, particularmente aplicado a medidas de correntes termoestimuladas (TSC), mas que podem ser estendidas a sistemas semelhantes. O sistema automatizado de medidas TSC em plataforma GUI, foi implementado de modo a realizar o controle da temperatura de uma estufa, de forma que seja possível gerar rampas lineares com taxas programáveis, e também a leitura de sinais analógicos referentes ao sistema, como corrente e temperatura, e processar os sinais obtendo como resultado curvas gráficas (sinais processados em função do tempo). Os resultados são armazenados e podem ser exibidos, ou impressos e transferidos para o padrão de arquivo de entrada de outros aplicativos. Os dados são obtidos em tempo real e o sistema utiliza conceitos da tecnologia GUI, onde provemos um estudo desta, gerando janelas com interação orientada a eventos e uma interface gráfica com o usuário bastante interativa. O sistema faz uso de microcomputador padrão IBM PC AT e utiliza o MS-Windows 3.1 como plataforma GUI (\"GraphicsUser Interface\"). / A method for control and data acquisition using GUI environment, applied to thermal and electrical measurements was developed. The method was specifically applied to thermal stimulated current (TSC), but it can be extended to similar systems. The GUI - based automated TSC system maked possible the accurate control of the oven temperature, at different heating rates. This system performs the data acquisition of analogic signals (current and temperature, for instance), and those signals are processed generating functions of time and/or temperature (TSC curves, for example). Stored results can be displayed, printed, as well as transferred to files, which are compatible to standard applicative for data treatment. Data are obtained in real time and the system uses GUI concepts, which are extensively studied in this work, generating events oriented windows and a user-friendly graphical interface. The system configuration consists of an IBM PC AT microcomputer and the MS-Windows 3.1 is used as the GUI environment.

Neste trabalho desenvolvemos um método de controle e aquisição de dados, particularmente aplicado a medidas de correntes termoestimuladas (TSC), mas que podem ser estendidas a sistemas semelhantes. O sistema automatizado de medidas TSC em plataforma GUI, foi implementado de modo a realizar o controle da temperatura de uma estufa, de forma que seja possível gerar rampas lineares com taxas programáveis, e também a leitura de sinais analógicos referentes ao sistema, como corrente e temperatura, e processar os sinais obtendo como resultado curvas gráficas (sinais processados em função do tempo). Os resultados são armazenados e podem ser exibidos, ou impressos e transferidos para o padrão de arquivo de entrada de outros aplicativos. Os dados são obtidos em tempo real e o sistema utiliza conceitos da tecnologia GUI, onde provemos um estudo desta, gerando janelas com interação orientada a eventos e uma interface gráfica com o usuário bastante interativa. O sistema faz uso de microcomputador padrão IBM PC AT e utiliza o MS-Windows 3.1 como plataforma GUI (\"GraphicsUser Interface\"). / A method for control and data acquisition using GUI environment, applied to thermal and electrical measurements was developed. The method was specifically applied to thermal stimulated current (TSC), but it can be extended to similar systems. The GUI - based automated TSC system maked possible the accurate control of the oven temperature, at different heating rates. This system performs the data acquisition of analogic signals (current and temperature, for instance), and those signals are processed generating functions of time and/or temperature (TSC curves, for example). Stored results can be displayed, printed, as well as transferred to files, which are compatible to standard applicative for data treatment. Data are obtained in real time and the system uses GUI concepts, which are extensively studied in this work, generating events oriented windows and a user-friendly graphical interface. The system configuration consists of an IBM PC AT microcomputer and the MS-Windows 3.1 is used as the GUI environment.

No estudo do transporte e armazanamento de cargas elétricas, em filmes de Teflon FEP, utilizamos a Técnica de Pulso Térmico em conjunto com a Técnica de Corrente Termoestimulada em circuito aberto. Através das duas técnicas, pudemos acompanhar a evolução das cargas nas amostras (de 25 &#956m) submetidas ao Annealing e a descarga iônica em diferentes situações, comparando os resultados obtidos em amostras virgens com as amostras tratadas ou irradiadas. No caso das amostras irradiadas, verificamos que o contato era injetor de buracos e, posteriormente, sugerimos a dependência da mobilidade de buracos com o campo elétrico aplicado. Na tentativa de explicar os resultados obtidos, fizemos uso de alguns modelos teóricos de correntes limitadas por carga espacial. / The Heat Pulse and TSC (Thermo-Stimulated-Current) in open circuit techniques were used to study the transport and storage of injected charge in Teflon FEP films. Using these techniques it was possible to follow the evolution of the injected charge inside the samples. Virgin samples (as received), previously annealed samples and previously ionic bombarded samples were used. The results of treated samples were compared with the results of virgin samples. Aluminum evaporate contacts covering ionic bombarded surface show hole injection properties. Measurement of space charge limited currents shows a mobility dependent of the electrical field (&#956 &#945 E-1/2).

No estudo do transporte e armazanamento de cargas elétricas, em filmes de Teflon FEP, utilizamos a Técnica de Pulso Térmico em conjunto com a Técnica de Corrente Termoestimulada em circuito aberto. Através das duas técnicas, pudemos acompanhar a evolução das cargas nas amostras (de 25 &#956m) submetidas ao Annealing e a descarga iônica em diferentes situações, comparando os resultados obtidos em amostras virgens com as amostras tratadas ou irradiadas. No caso das amostras irradiadas, verificamos que o contato era injetor de buracos e, posteriormente, sugerimos a dependência da mobilidade de buracos com o campo elétrico aplicado. Na tentativa de explicar os resultados obtidos, fizemos uso de alguns modelos teóricos de correntes limitadas por carga espacial. / The Heat Pulse and TSC (Thermo-Stimulated-Current) in open circuit techniques were used to study the transport and storage of injected charge in Teflon FEP films. Using these techniques it was possible to follow the evolution of the injected charge inside the samples. Virgin samples (as received), previously annealed samples and previously ionic bombarded samples were used. The results of treated samples were compared with the results of virgin samples. Aluminum evaporate contacts covering ionic bombarded surface show hole injection properties. Measurement of space charge limited currents shows a mobility dependent of the electrical field (&#956 &#945 E-1/2).