Influência das rotas de preparação na dinâmica de formação de fases cristalinas em filmes de fluoreto de polivinilideno (PVDF)

Abstract

Compounds based on polyvinylidene fluoride, or PVDF, have become one of the most attractive semicrystalline polymers in the industry due to their applicability, being able to be used in sensor devices, energy storage, and optical communications. PVDF polymers have advantages over other materials due to their light weight, good mechanical strength, and high temperature, chemicals, and abrasion stabilities. PVDF crystallizes in different crystalline phases: α, β, γ, and δ, and clusters between them. These crystalline phases, such as α and δ, are non-polar, without a great interest in the electronics industry. By the way, the β and γ phases have spontaneous polarity and can be used as ferroelectric devices. This work aims to investigate the influence of synthesis conditions on the formation of crystalline phases on PVDF films, goal the obtation of electroactive phases (fEA). PVDF films were prepared from the dissolution of the polymer in dimethylformamide (DMF) and subsequent removal of the solvent and polymerization at 50ºC and 90ºC, and at different times, 24h and 48h. In addition a thermal treatment in higher temperatures was performed to enhance the phase formation. The characterization by FTIR observe that the synthesis for 48 hours has major formation of electroactive phases (fEA) for both preparation temperatures, reaching relative concentrations greater than 80%. In addition, it was identified the fEA values have a direct relationship with the drying temperature and subsequent heat treatment. The optical microscopy analysis showed an increase in size of the spherulite area as a function of the fEA concentration values. The characterizations by fluorescence spectroscopy also demonstrate a relationship between the fluorescence intensity and relative amount of fEA. It was observed for all characterizations the fEA concentration around 80% marks the limit that the material has as optimized electroactive properties.