(181aj) Uniaxial Compression of PVDF: A New Approach to Form Isotropic ? Phase Thick Sheets

Piezoelectric materials generate an electric charge when they are deformed or vice-versa. Ceramics such as lead zirconate titanate (PZT) and quartz were used to be the only option for piezoelectric applications. But, demands for lightweight and flexible piezoelectric materials in areas like electronic devices, defence, and biomedical etc. have led to the development of alternate materials.

Polyvinylidene fluoride (PVDF) is a well known piezoelectric polymer and is widely used. There are various techniques for producing piezoelectric PVDF film and currently the most preferred technique is stretching PVDF films rich

in α (non-electroactive) phase followed by electrical poling. All the known techniques have some disadvantages like low value of piezoelectric constant and/or non-uniformity across the surface. Thick piezoelectric films are required for certain applications but making such PVDF films using conventional stretching is not possible.

So, isothermal unaxial compresssion of molded PVDF having α crystalline phase was done. This converted αinto β phase efficiently. To orient those β crystallites, corona triode poling was done at elevated temperatures. The effect of compression ratio and temperature was studied using FTIR and Raman spectroscopy and it was found that the content of β phase obtained at optimum conditions was more than 80%. Morphology was studied using cross-polarisation microscopy and small angle X-ray scattering (SAXS). Piezoelectric coefficient d₃₃ was measured using d₃₃_meter. PVDF films produced by this method are isotropic (in plane) as opposed to non-isotropic in uniaxial stretching.