Effect of Near-Electric-Field 3D Printing on the -Phase of PVDF Thin Films

High beta-phase polyvinylidene fluoride (PVDF) thin films have excellent piezoelectricity and flexibility. They are widely used in wearable devices, hydroacoustic ultrasound, and energy harvesting. The preparation of PVDF thin films by near-electric-field 3D printing can be customized in shape, and the high beta-phase can be obtained without stretching or polarization. In this work, the effects of polar solvent, printing voltage, and PVDF molecules on the beta-phase content of PVDF thin films prepared by near-electric-field 3D printing were analyzed. The results show that the polarity of the solvent affects the molecular chain conformation of PVDF, which is favorable for the generation of the beta-phase. With the increase of solvent polarity, the beta-phase content in PVDF films increased from 21.40% to 26.31%. The mutual motion of the collecting plate and the needle will produce stronger mechanical traction on the PVDF fibers, which is due to the smaller diameter of the PVDF fibers caused by the high printing voltage. The joint action of this tensile force and the strong electric field attraction promotes the beta-phase transition. When the printing voltage is 8 kV, the F(beta) value of PVDF film is increased by 47.37% over that without applied voltage. In addition, the interaction of small and large PVDF molecular weight will also result in mechanical deformation of the molecular chain and promote the beta-phase transition.