Structure and piezoelectric properties of microporous polyvinylidene fluoride films

A method to produce microporous polyvinylidene fluoride films characterized by a high content of a piezoactive crystalline phase and a developed relief surface is elaborated. The porous films are obtained in the process based on melt extrusion with subsequent isometric annealing and uniaxial extension. It is found that the samples have an oriented lamellar structure containing both $\alpha$- and $\beta$-modifications of the crystallites. The effect of temperature and degree of uniaxial extention of the annealed films on the characteristics of the porous samples, that is, the content of the piezoactive crystalline $\beta$-phase, overall porosity, breakdown voltage and the piezoelectric modulus is studied.