From induction to optimization: synergistic strategy of polar-modified MoS₂ and thermal stretching for high-efficiency PVDF self-polarization

Circumventing the intricate high-voltage poling process is a pivotal challenge for advancing the practical application of poly(vinylidene fluoride) (PVDF)-based flexible piezoelectric devices. This study employs a synergistic strategy that combines molybdenum disulfide modified with polar compounds (P-MoS₂) as β-crystal inducer with thermal stretching to successfully fabricate high-performance self-polarized PVDF composite films. The results demonstrate that the P-MoS₂ significantly enhances the β-phase crystal content of PVDF via strong interfacial interactions and charge-induction effects, while simultaneously achieving initial dipole alignment. This results in simultaneous improvements in piezoelectric output and dielectric constant. A more significant discovery is that, after controlled thermal stretching of the aforementioned self-polarized films, the piezoelectric and dielectric properties of the material exhibit distinct evolutionary trajectories: as the degree of stretching increases, both the β-crystal content and piezoelectric output voltage show a continuous monotonic rise, while the dielectric constant exhibits a non-monotonic change of first increasing and then decreasing. This “performance decoupling” phenomenon reveals a dynamic shift in the dominant physical mechanisms within the material where the sustained enhancement of piezoelectric output primarily stems from the extreme optimization of β-crystal macroscopic orientation achieved through thermal stretching. Conversely, the evolution of the dielectric constant arises from the interplay between two competing mechanisms: the initial interface polarization strengthened by improved filler dispersion and the subsequent highly oriented crystal structure that severely restricts polymer chain segment mobility while suppressing dipole switching polarization. This work not only demonstrates the tremendous potential of a synergistic strategy combining chemical modification and physical stretching for achieving highly efficient self-polarization, but more importantly, elucidates the inconsistent performance evolution. By revealing the competition among multiple mechanisms within self-polarizing materials, it provides crucial theoretical and experimental foundations for designing new-generation of high-performance flexible piezoelectric materials that require no high-voltage polarization.