Effect of thermal treatment on dielectric and acoustic properties of P(VDF/TRFE) film

Electroactive polymer films are widely applied in electroacoustic transducers and their properties can be tuned by matching the conditions of thermal treatment to the requirements of various devices. As the dielectric properties determine the piezoelectric response of the film we studied the effect of annealing at various temperatures on the dielectric dispersion of P(VDF/TrFE)(75/25) copolymer film. The most effective thermal treatment (in TC range) results in an increase in dielectric permittivity value and shifts the β-relaxation and piezoelectric resonance towards higher frequencies. The effect is related to the reduction of compensating charges piled up at the crystalline phase of the semicrystalline polymer. The heterogeneity of P(VDF/TrFE)(75/25) film annealed at temperatures in the TC range is also reflected in a complex acoustic response studied in one-side clamped conditions. Moreover, the room temperature sound velocity of the annealed copolymer film is considerably higher than that of non-annealed film.