Nucleation of the Electroactive γ Phase and Enhancement of the Optical Transparency in Low Filler Content Poly(vinylidene)/Clay Nanocomposites

Poly(vinylidene fluoride), PVDF, based nanocomposites with different clay structures have been processed by solvent casting and melt crystallization. Depending on the melting temperature of the polymer, the nanocomposite recrystalises in the electroactive gamma or nonelectroactive alpha phase of the polymer. This fact is related to the thermal behavior of the clay. For montmorillonite clay, the full crystallization of the electroactive gamma phase occurs for day contents lower than 0.5 wt %, allowing the nanocomposites to maintain the mechanical properties of the polymer matrix The electroactivity of the material has been proven by measuring the piezoelectric d(33) response of the material. The obtained value of d(33) is - 7 pC/N, lower than in beta-PVDF obtained by mechanical stretching but still among the largest coefficients obtained for polymers. Further, the optical transmittance in the visible range is strongly enhanced with respect to the transmittance of the pure polymer. Finally, it is demonstrated that the nucleation of the gamma phase can be also obtained in other clays, such as in kaolinite and laponite.