Direct preparation of β-crystalline poly(vinylidene fluoride) nanofibers by electrospinning and the use of non-polar silver nanoparticles coated poly (vinylidene fluoride) nanofibers as electrodes for piezoelectric sensor

A 96% beta-crystalline poly(vinylidene fluoride) nanofibers (PVDF NFs) were prepared by collecting electrospun NFs on a roller operated at 5000 rpm, followed by annealing at 150 degrees C. Dodecylamine functionalized non-polar silver nanoparticles (Ag NPs) were synthesized. The Ag NPs were brush coated on a PVDF NFs support and used as an electrode to demonstrate a piezoelectric sensor (PS). PVDF NFs was characterized with Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and field emission-scanning electron microscopy (FE-SEM). Changes in the absorbance of FTIR peak, 1275 cm(-1), revealed that the rise in roller speed from 0 to 5000 rpm, increased the beta-phase composition from 64 to 92% (rest was gamma-phase), decreased the lowest observed NFs diameter from 399 to 260 nm, and increased the orientation of NFs along the direction of rotation. The peaks relevant to beta-phase found in XRD patterns (20.8 degrees) and DSC thermograms (166 degrees C) were confirmed these findings. Annealing of NFs prepared at 5000 rpm (R5000) at 150 degrees C, increased the degree of crystallinity from 54.7 to 58.3% and the % of (3-phase from 92 to 96%, highest among all samples. The electrode was characterized using FE-SEM and energy dispersive X-ray spectroscopy (EDXS), which confirmed the Ag NPs coating (35-184 nm diameter). The static and dynamic load analyses were suggested that PS made using R5000 annealed at 150 degrees C was capable of sensing 0.3-500 N force. The voltage generated (400 mV) upon applying load on PS with a fingertip (similar to 3 N) can charge a 1 mu F capacitor in 0.8 s and also upon 10 x amplification a 4 V light emitting diode turned on to glow. Overall, the PS made with beta-crystalline R5000/150 and non-polar Ag NPs coated electrodes was found to be useful for force sensing and energy harvesting.