Molecular dynamics investigation of polyvinylidene difluoride dipole movement in electromechanical stretching: A key impact on the polymer’s piezoelectric phenomenon

Abstract

The transition from $\alpha$$\alpha$-phase to $\beta$$\beta$-phase is critical for the piezoelectric functionality of polyvinylidene difluoride (PVDF), with the dynamical behaviors of polymer molecular during this transition playing the key role in determining the piezoelectric performance. A molecular dynamics simulation was used to investigate the effects of the duration and direction of an applied electric field during external stretching on enhancing the $\beta$$\beta$-phase content in PVDF. A simulation scheme, aligned with the electrospinning process, was designed, and phase transition simulations were conducted. The results show that mechanically stretched PVDF fibers form a disorder structure $\beta$$\beta$ phase lacking piezoelectric properties due to internal dipole cancellation. However, applying an electric field perpendicular to the stretching direction during stretching aids in dipole alignment, creating overall polarity. When an electric field with varying direction is applied during stretching, polymer’s polarity direction shifts rapidly, with the electric field strength playing a positive role in the process. The variation in electric field direction is crucial in differentiating the piezoelectric coefficients of near-field and far-field electrospun films. This work provides a theoretical foundation for optimizing nanofibrous fabrication processes for high-performance piezoelectric applications.