High Piezoelectricity at Low Fields in Poly(vinylidene fluoride) via Thiourea Co-Crystallization

Abstract

Poly(vinylidene fluoride) (PVDF) has garnered extensive attention for flexible applications, yet its practical utilization is severely hampered by its limited piezoelectric response, the demand for high-voltage poling, and the difficulty in controlling the oriented amorphous fractions (OAFs). Herein, we demonstrate a thiourea (TU) cocrystallization strategy to efficiently regulate the phase evolution in PVDF toward superior piezoelectricity. PVDF/TU complexes are fabricated via electrospinning, followed by TU removal to obtain coalesced PVDF (c-PVDF). The c-PVDF film exhibits a high crystallinity of 61.8% and a dominant content of polar β/γ-crystal phases. More importantly, the c-PVDF film is capable of generating a substantial fraction of OAFs and distinct dipole orientation under moderate-to-low electric fields (<70 MV/m), far below conventional poling voltages. Systematic structural characterizations reveal that OAF content evolves nonmonotonically with poling field and plays a decisive role in piezoelectric performance. The optimized c-PVDF exhibits a high piezoelectric coefficient (d33) exceeding 70 pC/N at a poling field of only 55 MV/m, displaying low-field high-d33 characteristics compared to state-of-the-art PVDF-based piezoelectric materials. Furthermore, the poled c-PVDF film exhibits outstanding voltage outputs toward finger bending and airflow stimuli, demonstrating promising potential in flexible sensing. This work establishes an energy-efficient route toward high-performance piezoelectric PVDF, and provides mechanistic insights into OAF-governed piezoelectric enhancement, which will facilitate the rational design of high-performance electroactive polymer materials.