Oppositely Charged Interfacial Janus Nanoparticles Induce the Formation of Highly Ferroelectric Poling-Free PVDF Films for Piezoelectric Energy Generation

Abstract

Poly(vinylidene fluoride) (PVDF) is widely used as a ferroelectric polymer due to its good flexibility and stability. However, its ferroelectricity requires enhancement through doping or modification processes, and the necessity for prepoling significantly limits its applications. In the present work, we propose an interfacial ion-dipole induction method for preparing high-ferroelectric PVDF films using oppositely charged single-chain Janus nanoparticles (OC-SJNPs). The SJNPs possess a positive end with quaternized amino groups that allow for uniform electrodeposition on the substrate surface. After hydrolysis, due to the nanoscale size, proton transfer occurs between carboxyl and amino groups, thus promoting the degree of ionization and the charge density of both ends. The negatively charged (−45 mV) end of OC-SJNPs exhibits strong dipole interaction with PVDF chains, leading to a high β-phase content of 90.8%, with a residual polarization strength of 10.6 μC/cm2, nearing the theoretical maximum of pure PVDF films. Additionally, the orientation of OC-SJNPs induces the alignment of PVDF dipoles, thus achieving high piezoelectric energy generation without prepoling. Another polar polymer, polyacrylonitrile (PAN) also demonstrated higher piezoelectric energy generation by using the proposed method. It not only successfully prepared high-ferroelectric and poling-free PVDF films as piezoelectric energy generators but also offers a universal and efficient approach for the preparation of polar polymer materials.