The role of electrospinning parameters for optimizing poly-vinylidene-fluoride nanofibers piezoelectricity

Several works in the last years demonstrated the strategic role of piezoelectricity in wide range of applications, ranging from flexible pressure sensors [https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.201504755] to energy harvesting [https://doi.org/10.1016/j.energy.2019.01.043]. Piezoelectricity is an intrinsic property of materials that are able to convert an electrical potential that they are subjected into a mechanical deformation. Poly-vinylidene-fluoride (PVDF) is one of the most attractive piezo-polymer due to its flexibility, transparency, lightweight, high chemical resistance due to the presence of C-F bonds, good resistance to mechanical deformation, biocompatibility, high thermal stability, low cost, and durability in the human body. Moreover, several studies investigated the enhancement of its piezoelectric features due to nanoconfinement [https://doi.org/10.1080/00150193.2018.1456304]. We investigate the role of electrospinning parameters on thefproperties of PVDF-piezoelectric nanofibers-NFs. 19wt% PVDF was dissolved in solvents (50:50wt% of Dimethylformamide:Acetone). In this works, the electrospinning parameters were selected to enhance solvents’ evaporation, nanofibers’ stretching, their alignment. A main focus was dedicated to: applied-electric field, (i.e. the ratio between applied voltage and working distance), and the collector used during nanofibers depositions, (planar versus drum-rotating collector). Fourier-Transformed-Infrared-Spectroscopy (FTIR) was implemented to investigate the presence of the piezoelectric β-phase and γ-phase . All samples show peaks at 532 cm⁻¹ and 761 cm⁻¹ belonging to the α-phase And larger peaks belonging to the β-phase at 510 cm⁻¹ and 840 cm⁻¹ . Peaks belonging to the β-phase at 445 cm⁻¹, 1274 cm⁻¹ and 1430 cm⁻¹ are present only in NFs, processed at low electric-field, confirming that higher electric-field can negatively affect the instauration of the β-phase. FTIR-results confirmed no correlation among the piezoelectricity and nanofibers’distribution. Ferroelectric hysteresis loop, and displacement loop demonstrated that the presence of β-phase peaks was related to piezoelectric properties.