Characterization of the Mechanical and Ferroelectric Properties of Plasticized Poly

This study examined the piezoelectric and ferroelectric properties of both unoriented and uniaxially oriented (draw ratio 3.9:1) films of poly(vinylidene fluoride) doped with a low molecular weight plasticizer tricresyl phosphate. The films were prepared by quenching from the melt and slow -cooling from the melt. Two different concentrations of dopant were used (5% and 10% by weight) in the film preparations and compared with the undoped films. In addition, a study of the piezoelectric and ferroelectric properties was initiated on unoriented films of a copolymer of poly(vinylidene fluoride -trifluoroethylene) doped with plasticizer at the same two levels of concentration. Again, films were prepared by quenching and slow-cooling from the melt. It was found that the addition of dopant to these films lowered the crystallinity, decreased the dynamic mechanical modulus, lowered the glass transition temperature and melting point, and decreased the heat of fusion. Increases were observed in pyroelectric strain coefficient, p _{rm y}, for the oriented films of doped PVF_2. Changes in piezoelectric coefficient, d_{31}, were observed for both the oriented PVF _2 and unoriented copolymer at the lowest dopant concentrations. The highest dopant concentrations showed a decrease in piezoelectric activity since the films were greatly effected by changes in dynamic mechanical modulus and percent crystallinity. Since it is known that the piezoelectric response of semi-crystalline polymers originates in the crystalline regions, both wide angle X-ray diffraction techniques and differential scanning calorimetry measurements were used to characterize the crystal structure and morphology of these films. These characterization studies enabled insight into the structure-property relationship of the piezoelectric response of the doped films. The most noted result was observed for the copolymer films doped 5% which showed an increase in the piezoelectric strain coefficient d _{31} despite a decrease in both crystallinity and remanent polarization. Films doped 10% with T.C.P. showed a significant decrease in piezoelectric response due to the reduced crystallinity.