Fabrication Of PVDF Piezoelectric Thin Film By The Electric Poling Assisted 3D Printing Technology

In recent years,light and flexible piezoelectric sensors are urgently demanding in the fields of health mentoring and controlling of aerospace,tactile sensing of robots,manipulating of medical devices,and modern military equipment.The traditional piezoelectric sensors represented by silicon and ceramics are brittle and unable to withstand large deformation.It is difficult to meet the new requirements in the above fields.In this paper,using the electrical poling assisted 3D printing technology,the flexible PVDF piezoelectric thin film sensor was fabricated and its performance was tested.The external voltage and electric field distribution of the printed PVDF thin film were analyzed by comsol multi-physical field coupling software.The effect of printing voltage on the?to?phase transition in PVDF piezoelectric thin film was investigated,along with the effects of different solvent systems and different mass fractions on the crystallinity and?phase content of PVDF thin films.Different amount of multi wall cabon nanotubes(MWCNTs)and graphene(GR)were doped in the printing solvent,to explore its effect on the formation of PVDF crystal?phase and to study its formation mechanism.The following conclusions are obtained:(1)From the electric field simulation by Comsol Multiphysics,it is found that when the voltage of the external power supply is 6kV,the maximum electrical potential on the glass collection plate is152V and the maximum field strength is 6.8×10~5 V/m.At such field strength,the dipole can be induced by the electrical poling assisted 3D printing method without the occurrence of break down in the thin film,and the effective polarization of the film is also conducted at the same time.The experimental results match well with that simulation result.With the increase of the voltage,the content of?phase decreases,the?phase increases.It is obvious that the electric field can promote the transition from the?to?phase.(2)When the PVDF thin films are prepared by N-methyl pyrrolidone(NMP)solvent with the mass fraction of 12wt%~17wt%,the?phase content of the PVDF piezoelectric thin film increases first and then decreases with the increasing mass fraction of PVDF,and reaches their maximum at14wt%(46.31%);When the PVDF thin films are prepared by N,N-two methylformamide(DMF)solvent with the mass fraction of 13wt%to 17wt%,the corresponding diffraction peak representing the(110)crystal plane of the?phase is obviously enhanced with the increasing mass fraction of PVDF,except for the slightly reduced peak at the PVDF mass fraction of 16wt%.(3)The doping of multi wall carbon nanotubes(MWCNTs)affects?to?phase transition in PVDF piezoelectric thin film.After the doping,the transition effect of the?phase to?phase is obviously better than that in the absence of the Doping.Moreover,a small amount of MWCNTs can play the role as nucleating agent to improve the content of beta crystalline form.However,the doping of large amount of will MWCNTs reduces the crystallinity,but the extent of reduction is not great.The content of?phase in PVDF/MWCNTs piezoelectric thin film prepared by NMP and DMF is compared,and the obtained?phase content is not sensitive to the doping content in its range of0.02wt%~0.05wt%for both sovent.(4)The doping of graphene(GR)noticeably improves the crystallinity of the PVDF/GR piezoelectric film.When the mass fraction of GR is 0.05wt%,the crystallinity is increased by about1.51 times,with the content of?phase of 69.65%.The doping of GR has a much better effect than the doping of MWCNTs.(5)The feedback signal of the PVDF piezoelectric thin film sensor is consistent with the excitation signal.In the frequency range of the 10Hz~20Hz,the output voltage of the sensor feedback is almost unaffected by the excitation frequency;there are different feedback voltages for different excitation voltages,and the feedback voltage is enhanced with the increasing excitation voltage.