Influence of nanoparticle size and concentration on the electroactive phase content of PVDF in PVDF-CoFe2O4-based hybrid films

The synthesis and characterization of a new magnetoelectric polymer-oxide hybrid flexible class of materials were reported. It consists of ferrimagnetic and magnetostrictive cobalt ferrite (CoFe2O4) nanoparticles (NPs) dispersed into a ferroelectric and piezoelectric polyvinylidene fluoride beta-phase (-PVDF) film. 6-nm and 9-nm sized CoFe2O4 NPs were produced by forced hydrolysis in polyol. -PVDF films were obtained by drying a solution of PVDF/DMF at low temperature and by varying the amount and/or size of NPs inside them. The resulting composites were characterized by X-ray diffraction, transmission electron microscopy, infrared spectroscopy (attenuated total reflectance), differential scanning calorimetry and near-field microscopy (AFM). We clearly demonstrate that the presence of NPs leads to a decrease of the whole PVDF crystallinity within the hybrids but also that small variations of the size and amount of nanoparticles influenced the crystallization of the electroactive polar phase of PVDF. Higher percentages of polar PVDF phase were found in hybrid films processed at 80 degrees C and containing 9-nm CoFe2O4 NPs. [GRAPHICS] Self-standing films of neat beta-phase PVDF (left) and PVDF-CoFe2O4 (15 wt.%) hybrid (right).