Hard-to-soft transition-enhanced piezoelectricity in poly(vinylidene fluoride) via relaxor-like secondary crystals activated by high-power ultrasonication

• Published in: Materials horizons 2022-07, Vol.9 (7), p.1992-1998
• Main Authors: Rui, Guanchun, Allahyarov, Elshad, Li, Ruipeng, Taylor, Philip L, Zhu, Lei
• Format: Article
• Language: English
• Subjects: Broadband; Copolymers; Crystal structure; Crystals; Fluorides; Piezoelectricity; Polyvinylidene fluorides; Relaxors; Room temperature; Thermal stability; Ultrasonic processing; Vinylidene fluoride
• ISSN: 2051-6347; 2051-6355
• DOI: 10.1039/d2mh00442a

Although high piezoelectric coefficients have recently been observed in poly(vinylidene fluoride- -trifluoroethylene) [P(VDF-TrFE)] random copolymers, they have low Curie temperatures, which makes their piezoelectricity thermally unstable. It has been challenging to achieve high piezoelectric performance from the more thermally stable PVDF homopolymer. In this report, we describe how high-power ultrasonic processing was used to induce a hard-to-soft piezoelectric transition and improve the piezoelectric coefficient in neat PVDF. After high-power ultrasonication for 20 min, a uniaxially stretched and poled PVDF film exhibited a high of 50.2 ± 1.7 pm V at room temperature. Upon heating to 65 °C, the increased to a maximum value of 76.2 ± 1.2 pm V , and the high piezoelectric performance persisted up to 110 °C. The enhanced piezoelectricity was attributed to the relaxor-like secondary crystals in the oriented amorphous fraction, broken off from the primary crystals by ultrasonication, as suggested by differential scanning calorimetry and broadband dielectric spectroscopy studies.