| As a new type of material,flexible pyroelectric material has the advantages of corrosion resistance,oxidation resistance,flexibility,and has a good application prospect in many fields such as infrared thermal imaging system,infrared alarm system and pyroelectric detection system.Based on this,this thesis studies the preparation process of PVDF-based flexible pyroelectric thin films.The main research contents are as follows:1.The preparation of PVDF pyroelectric thin film was studied by a conventional three-step method.The first step was film formation,including casting method,hot pressing method and spin coating method,in this step the crystal structure of the film is mainly ? phase,and the subsequent stretching can increase the content of the ? phase,and then the thermal polarization makes the PVDF film has pyroelectric properties.The surface structure of the film was observed by SEM and the crystal structure of the film was studied by XRD and FTIR,it was verified that the ? phase content of the film can be improved by stretching and polarization.The pyroelectric coefficient of the film was tested by the built pyroelectric test platform,indicated that the larger of stretching ratio and polarization electric field,the better of pyroelectric performance.2.A casting-stretching composite process for preparing PVDF film is proposed.The process does not require high temperature stretching and high temperature polarization,but was stretched during film formation,and the prepared film directly has pyroelectric properties.According to the characterization analysis,the ? phase content of the film first becomes larger and then decreases with the increase of forming temperature,the residual polarization,dielectric constant and pyroelectric coefficient are also the same.PVDF film obtains the best pyroelectric performance at a solution concentration of 25%,a tensile rate of 20 cm/s,a tensile length of 15 cm,a film formation temperature of 80 °C.The test and analysis were carried out by the built dipole orientation measuring device,and it was proved that the dipole in the PVDF film prepared by the casting-stretching composite process has a certain component in the vertical direction.After that,the film-forming plate was subjected to hydrogen bonding treatment to obtain more excelent pyroelectric properties,and it was confirmed that the PVDF film prepared by the casting-stretching composite process directly has pyroelectric properties is due to hydrogen bond induction of the film-forming plate.3.Three simple and novel methods were explored to improve the pyroelectric properties of PVDF films:(1)The first method is to use a laminated structure to form a PVDF film into an electrode-film-electrode-film-electrode structure.The pyroelectric response is superimposed,so that the same film area can have a larger pyroelectric response.The test results verify this idea,but the response signal obtained is smaller than the sum of the two-layer membrane response signals.(2)The second method is to blend a non-ferroelectric phase which possess a high thermal expansion coefficient in the ferroelectric phase,this method improves the pyroelectric performance of the composite film by increasing the thermal expansion coefficient.The experimental results show that when the blend ratio of PMMA and P(VDF-TrFE)is less than 3:10,the pyroelectric response signal of the blended film is slightly increased,and the highest can be increased by 5%.(3)The third method is to incorporate PE particles with larger particle size into the PVDF film to increase the surface area of the film,increase the surface heat absorption rate and improve the pyroelectric performance.The experimental results show that when the mixing ratio of particles is less than 3:10,the pyroelectric response signal of the blended film can be increased by about 3.8%. |
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