Optimizing the piezoelectric response of poly(vinylidene fluoride-co-trifluoroethylene) electrospun mats: effects of copolymer composition, microstructure and thermal treatments

Electrospun piezoelectric polymers have attracted enormous interest in recent decades due to their flexibility, lightweight, and good piezoelectric response. This work investigates structure-property relationships in a series of electrospun poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) copolymers to find the conditions to maximize the piezoelectric charge coefficient, d33. Nanofibrous mats of PVDF-TrFE at different molar fraction compositions are annealed and/or poled at their respective Curie Temperatures and then characterized using DSC, WAXD, FT-IR, and piezometry. The data collected for the as-spun, annealed, and/or polarized samples are initially analyzed individually, followed by an evaluation of property interrelations. The results show a positive correlation between the d33 and the crystallinity degree and the crystallite size, while a negative correlation with the FT-IR absorbances associated with gauche defects is found. Interestingly, a linear combination of these three properties proves a good predictor of the d33 value. Notably, during this investigation, we measured d33 as high as 37.1, 42.7 and 34.7 pC N-1, for the 70:30, 75:25, 80:20 molar fractions, respectively, ranking among the highest reported for nanofibrous PVDF-TrFE mats. This outstanding result is obtained thanks to the synergic effect of annealing and poling treatments.