Study On The Preparation And Properties Of Modified Polyvinylidene Fluoride Piezoelectric Film

At present,high-performance piezoelectric polymer materials are widely used in sensing and control system components of satellite and other aerospace equipment.Compared with piezoelectric ceramics,piezoelectric polymer materials have many advantages,such as simple preparation process,light weight and soft material,etc.,and have a good application prospect in the field of aerospace.As the most typical piezoelectric polymer material,polyvinylidene fluoride(PVDF)possessing advantages like good processing performance,high dielectric constant,chemical resistance and other excellent properties,is widely used in the sensing field.However,the piezoelectric properties of PVDF films produced in China are poor,and there are few researches on the anti-electron radiation properties.The preparation process,composite material doping technology,piezoelectric properties,anti-electron radiation properties and other properties of PVDF film are comprehensively explored and optimized in this thesis.A relatively simple way and equipment are used to prepare polyvinylidene fluoride film with high voltage coefficient.Specific research contents are as follows:(1)We optimize the most suitable process conditions for the preparation of PVDF initial films and evaluate the effects of different experimental parameters on the properties of PVDF films.The experimental results show that the most suitable precursor solution concentration is13 wt%for the preparation of PVDF film based on the solution method.After heated at 90?for 3 h,the mechanical properties of PVDF films obtained by quenching are the best.The tensile strength and elastic modulus can reach 50.85 MPa and 1850 MPa,respectively.(2)In order to improve the mechanical properties and anti-radiation properties of PVDF thin films,the effects of different composite materials,including octaphenyl-caged polyhedral oligo siloxane(POSS),Fe(NO₃)₃·9H₂O,Tm Cl₃·6H₂O,carbon nanotubes(CNT),on the mechanical properties of PVDF thin films are studied.The experimental results show that CNT-PVDF thin film has the best doping effect,and the 1wt%CNT-doped PVDF thin films have the best mechanical properties.The tensile strength and elastic modulus of CNT-PVDF thin films reach 54.1 MPa and 1677 MPa,respectively.After 2×10¹⁵ e/cm² electron irradiation(40 ke V),the tensile strength and elastic modulus of the films decreased by 1.7%and 14.5%,respectively.(3)In order to improve the piezoelectric properties of PVDF films,we design the thermal stretching technology,the repeated folding and hot pressing technology,and six polarization methods to process PVDF films.The experimental results show that the most suitable heat treatment scheme is the repeated folding and hot pressing technology,and the most suitable polarization method is to place a copper sheet on both the upper and lower parts of PVDF film with an optimized polarization field intensity of 200 MV/m.The piezoelectric coefficients of pure PVDF films and composite CNT-PVDF films reached 6.5 p C/N and 11.5 p C/N respectively by using the hot pressing technology and the polarization method.