Printing Of High-? Crystalline PVDF Piezoelectric Thin Films In Near Electric Field

Because of its excellent piezoelectric and thermoelectric properties,low cost,good flexibility and high chemical stability,piezoelectric polymers are widely used to fabricate electronic components such as high precision sensors and actuators.PVDF piezoelectric thin films with high?crystals have the characteristics of wide frequency response,high mechanical strength and high electromechanical conversion sensitivity,so they have high research and application value.In order to find a way to further promote the formation and transformation of PVDF piezoelectric?phase,the near-electric-field printing method is used to prepare PVDF piezoelectric thin films.The effects of PVDF concentration,MWCNTs,graphene(GR)and electric field distribution on the?phase transformation of PVDF piezoelectric films were investigated.The results show that:(1)When the concentration of PVDF in printing solution is in the range of 12wt%-16wt%,the crystallinity,the relative content of?phase F(?)and the total content of?phase of PVDF piezoelectric film increase obviously with the increase of the concentration of PVDF.When the concentration of PVDF ranges from 16wt%to 22wt%,the crystallinity,F(?)and the total content of?phase of PVDF piezoelectric films tend to be stable.At this time,the concentration is no longer the main factor affecting.When the concentration of PVDF is higher than22wt%,due to the excessive viscosity of the printing liquid,the normal filament can not be produced and the printing can not proceed smoothly.(2)Because GR has lamellar structure,it will not entangle with each other as MWCNTs due to the increase of concentration.GR has a larger specific surface area than MWCNTs,and can more easily reduce the barrier that guides the crystallization of PVDF molecules on its surface.Moreover,the accumulation of charges on the surface of layered GR results in weak electric field between adjacent graphene sheets,promotes the orderly orientation growth of PVDF molecular chains,and makes the transformation of?phase easier to occur.Its effect is better than that of MWCNTs.(3)Using COMSOL Multiphysics 5.3a,five simplified near-electric-field printing models were established.Three different electric-field action modes,model 1,model 2 and model 5,were selected according to the actual printing situation.The electric-field intensity corresponding to model 5 was stronger and the distribution was the most uniform,with the highest value being 6.31×10~5 V/m and the minimum value being 5.11×10~5 V/m.(4)Under the synergistic action of optimum uniform electric field and adding GR,the crystallinity of PVDF/GR piezoelectric films is 58.53%,F(?)is88.13%,and the total content of?phase is 51.58%,which is higher than the total content of?phase of PVDF/GR piezoelectric films under non-uniform electric field(47.27%),and the voltage sensitivity and output voltage Vp-p value of PVDF/GR piezoelectric films are the best,and the frequency sensitivity is better.