In 125 MV m?1 is required to fully polarize

In order for the smart composite structure to generate responses due to an applied load, the PVDF material must be polarized to align the dipole moments of its crystalline structure. The crystalline structure of the PVDF film will determine the polarization properties of the film. There are four possible crystalline forms of the PVDF polymer: the alpha, beta, gamma, and delta phases 17. Only the beta, gamma, and delta phases can be polarized. However, the alpha phase can also be polarized by applying a large electric field, which will convert the alpha phase to the delta phase 17. The processing conditions of the PVDF film determine the dominant crystalline phase. When the PVDF film layers in the composite samples are melted and solidified, the dominate phase is the alpha crystalline phase 18. Since the alpha phase is the dominate phase upon solidification, an electric field must be applied to convert the alpha phase to the delta phase and to align the dipoles for the proposed smart composite structures. Existing research shows that an electric field of around 125 MV m?1 is required to fully polarize a predominately alpha phase PVDF film 19. However, a higher piezoelectric coefficient can be attained by polarizing a beta phase film since the beta crystal phase has a greater dipole moment than the delta phase 20. One of the most commonmeans mentioned in the literature to achieve a predominately beta phase PVDF film is to stretch the film mechanically to many times its original length 21. A second method to transition from an alpha phase film to a beta phase film is to apply a very high electric field on the order of 500 MV m?1 19. A third method mentioned in the literature to achieve a predominately beta phase PVDF film is to cure the film under high pressure 22. Finally, the copolymers of PVDF containing trifluoroethylene (TrFE) or tetrafluoroethylene can be added to the film to encourage the formation of the beta phase 23.During hot press pvdf film looses small amount of polarization because of high temperature. To conduct polarization measurements we need fully polarized film. So we used one method to increase its polarization.For that method we need equipment set up. The following figure shows the set up to increase polarization in pvdf film.Annealing involves heating a material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling. The heat treatment is necessary to increase the crystallinity of ferroelectric copolymer layers. Annealing process occurs in three stages. For example, sample has to annealed at 110°C. First stage the copolymer gets heated from 30°C temperature to 110°C in one hour. In the second stage the copolymer must stay for 2 hours at 110°C. In this stage recrystallization occurs. In the third stage the copolymer gets cooled from 110°C to 30°C in one hour. 5