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Poly(vinylidene difluoride) (PVDF) based polymers, due to their multifunctional capabilities have attracted much attention in the field of high energy density capacitors, ferroelectric memory devices, sensors and actuators. Due to the superior mechanical property and easy processability, the copolymer, poly(vinylidinedifluoride – trifluoroethylene) [P(VDF-TrFE)] are extensively studied. These polymers, due to the presence of extra fluorine atom, which is bulky, adopt the least discomfort conformation, which is the phase, during crystallization. The beta phase is ferroelectric and as the temperature is increased a ferroelectric-paraelectric transition occurs at the Curie transition temperature. The melting temperature, crystallization temperature, Curie transition temperature, degree of crystallinity and hence the ferroelectric properties highly dependon several factors like conditions ofcrystallization, annealing, further processing by rolling/pressing of the sheets, etc. In this paper, we report studies on sheets of P(VDF-TrFE) (70/30 mol %) prepared by solution (DMF) cast method. After crystallization and annealing, these sheets were rolled to different times and further annealed. Morphology and microstructure of the rolled copolymer films were investigated using SEM. Differential Scanning Calorimetry and X-Ray diffraction methods were used to study the thermal characteristics and crystallinity of the sheets. FTIR spectroscopy was used to detect the local conformational structure by identifying the specific β-phase peaks. The ferroelectric nature of these films were identified from P-E loop measurements. These films were poled and made piezoelectric using a high electric field corona poling method. The piezoelectric coefficients were measured using a piezometer PM 300. The optimum conditions of casting and annealing temperature for obtaining maximum beta phase and crystallinity were arrived at by analysing the microstructure, XRD, DSC results and the poling results. An underwater acoustic sensor was also fabricated and its hydrostatic sensitivity is evaluated. The study reveals that these sensor materials are suitable for various large area sensors and sensors which need unconventional and conformal shapes.
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