Fluorinated Titania Nanoparticle-Induced Piezoelectric Phase Transition of Poly(vinylidene fluoride).

We prepared F-coated rutile titanium dioxide nanoparticles (r-TiO2 NPs) via simple thermal annealing of titania NPs in poly(vinylidene fluoride) (PVDF) and demonstrated that the F-coated r-TiO2 NP-doped composite film could efficiently induce piezoelectric phase transition of non-electroactive PVDF due to highly electronegative F bonds on the surface of these NPs. In the case of a 2.0 wt % composite film, 99.20% of the non-electroactive PVDF was transformed into the electroactive phase. Additionally, utilizing the F-coated r-TiO2 NPs for a piezoelectric device led to an enhancement of the piezoelectric performance. With the 5.0 wt % composite film, the resulting piezoelectric device exhibited voltage generation of 355 mV, whereas a device with the innate r-TiO2 NPs exhibited voltage generation of only 137 mV. Furthermore, because of optical inactivity of F-coated r-TiO2 NPs, the piezoelectric films exhibited high stability under 64 h of photoirradiation at an intensity of 0.1 W/cm2. These results indicate that the F-coated r-TiO2 NP-doped composite films could be useful for various applications, including outdoor energy-harvesting, self-powered wearable devices, and portable sensors.