Study On Dielectric And Piezoelectric Properties Of PVDF-based Polymer And Its Composites

With the rapid development of the electronics industry,people's lifestyles have undergone earth-shaking changes.As the basis of the modern electronics industry,electronic functional materials provide powerful support for the development of science and technology.Among them,PVDF-based polymers have outstanding performance in dielectric,ferroelectric,piezoelectric,pyroelectric and other electrical properties,and have received widespread attention.In recent years,the continuous integration and miniaturization of microelectronic devices have placed higher requirements on dielectric materials.Compared with ceramic dielectric materials,the low dielectric constant and poor temperature stability of PVDF-based polymers have become deficiencies that limit their further development.To deal with these problems,the method of combining PVDF-based polymers with ceramics is usually used to obtain optimized electrical properties.However,the addition of ceramic materials would damage the flexibility and reduce the breakdown strength of polymers to a certain extent,which is not conducive to the practical application of dielectrics.Considering the problems above,PVDF-based polymers were chosen as experimental objects.Different methods were used to optimize the electrical properties of PVDF-based polymers on the premise of retaining the flexibility of polymers.The dissertation is mainly divided into five chapters.Excluding the last chapter which offers conclusion,the main contents of the first four chapters are summarized as below:In Chapter 1,the dielectric materials and its electrical properties such as dielectric,ferroelectric,piezoelectric,etc.are reviewed.Then,the crystal structures of PVDF-based polymer are introduced.Finally,the current modification methods for PVDF-based polymer materials in terms of electrical properties are summarized.In Chapter 2,a new type of P(TFE-HFP-VDF)terpolymer which has very low dielectric loss,moderate dielectric constant and excellent temperature stability was studied.We discovered that P(TFE-HFP-VDF)terpolymer has a relaxor-like ferroelectric behavior for the first time,and revealed that the energy storage performance can be regulated by changing the size of the polar microdomains through heat treatment.This research has guiding significance for the design of high-performance energy storage dielectric materials.In Chapter 3,the all-organic composites of cyanoethyl pullulan(CEP)and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)[P(VDF-TrFE-CTFE)]were systematically studied.Evidence indicates that the blends are partially miscible.Then,a high-temperature thermal treatment(HTT)was conducted on the blended films to study the relationship between microstructure and dielectric properties.Experimental results suggest that the HTT process favors the incorporation of CTFE units into the crystalline phase and induces a less polar crystal structure of the terpolymer,while the addition of CEP would impede the inclusion of bulky CTFE monomer units into the crystalline phase of the terpolymer,leading to a more polar crystalline structure.Finally,by optimizing the composition of the blends and applying heat treatment,the dielectric energy storage performance of the blends can be improved in comparison with that of the terpolymer.In Chapter 4,the nylon 11/P(VDF-TrFE)copolymer nanocomposites were prepared by a modified solution method.Experimental results suggest that the incorporation of low-content nylon 11 nanoparticles could optimize the dielectric and piezoelectric properties of the copolymer.The structural changes of the copolymer after the introduction of nylon 11 nanoparticles were analyzed through structural characterization.We suppose that the improvement of the electrical properties of composite materials may be due to the reduction of crystal domain size and interface effect.