Preparation And Characterization Of Polyimide/Inorganic Nanocomposites

In recent years, researches on organic-inorganic nanocomposites haveattracted great interest since they frequently exhibit unexpected propertiessynergistically derived from two components, which combine the advantages of theinorganic materials (rigidity, high thermal stability) and the organic polymer (flexibility,dielectric, ductility, and processability). Among the organic materials, high-performancepolymers of the polyimide (PI) type are already widely used in microelectronicindustries because of their outstanding characteristics, such as excellent good chemicaland mechanical properties as well as low dielectric constant. Possessing very highdielectric constant, barium titanate (BaTiO₃) based ceramic has been widely utilized ascapacitors and piezoelectric transducers. But the nano-SiO₂ is currently to apply one ofthe most extensive nano-materials, its special surface effect, the effect of the quantumsize and volume effect etc, which has pay attention to researchers at many sciencematerials and becoming gradually the hotspot of material science research.Therefore,the preparation and application of the composites based on polyimide have become aquickly expansive area. So it can be expected to obtain better materials from the thecomposites material of polyimide polymer and silica, barium titanate and silica-bariumtitanate. In this thesis, our research is mainly focused on the following four parts:1. Barium titanate (BaTiO₃) nanoparticles coated with polyimide had beensynthesized by a dispersion polymerization method. The structures of polyimide-bariumtitanate nanocomposite were investigated by using XRD, FT-IR and TEM. The TEMimage indicates that they were all spherical with smooth surfaces, the nanocompositeparticles were dispersed homogeneously and the size of them were about 50～60nm. TheBaTiO₃ particles kept up the cubic form of crystalline in preparing composite process.The FT-IR indicated the chemical bond formed between the inorganic phases and thepolymer matrix. And the functional groups of the APTES provided a link between theinorganic domains and the polymer matrix in preparing composite process andintensively increased the interaction between the inorganic particles and the polymermatrix. In addition, the BaTiO₃ particles were dispersed homogeneously throughout thepolyimide matrix and there was no obvious aggregation of BaTiO₃ particles in the composite. Moreover, it was found that the content of BaTiO₃ influenced on the thermalproperties of the nanocomposite materials. With the increasing of BaTiO₃ content, thethermal stability of the nanocomposite grew higher. At the same time, we discovered theelectric conductivity rate of nanocomposites has much to do with the content ofinorganic particles, the dissimilarity content of inorganic particles present differentelectric conductivity rate.2. Silicon dioxide (SiO₂) nanocomposite spherical particles coated with polyimidehad been synthesized by a dispersion polymerization method. The chemical structure ofpolyimide-silicon dioxide nanocomposite spherical particles was investigated by usingFT-IR. And the surface morphology characterization was performed with SEM. TheTEM showed that SiO₂ was surface-coated with polyimide and the polyimide thicknesswas about 20 nm. Moreover, the particles were homogeneous distribution andinterconnected very fine, no obvious aggregation of SiO₂ particles in the composite. Inaddition, it turned out that the polyimide/SiO₂ nanoparticles were core-shell structure.The content of SiO₂ is higher and the decomposition temperature of nanocomposite ishigher. The doping of SiO₂ particles improved the thermal stability obviously.At thesame time, it was found that the content of SiO₂ influenced on the electric conductivityrate of nanocomposites3. On the base of preparation silica-barium titanate nanocomposites by sol-gelprocess, the silica-barium titanate nanocomposites coated with polyimide had beensynthesized successfully by a dispersion polymerization method. The conformation,structure and size of silica-barium titanate nanocomposites coated with polyimide wereinvestigated by using FT-IR, EDAX, XRD, TEM, SEM and TGA. The results indicatethat there is a thin layer polymer of silica-barium titanate nanocomposites surface, thepolymer thickness is about 10 nm. In addition, the chemical bond is formed between theinorganic phases and the polymer matrix and the crystal structure of BaTiO₃ is stable inpreparing composite process. TGA results suggested that the thermal stability wasimproved, which suggested the successful incorporation of the inorganic moiety(SiO₂-BaTiO₃) in the nanocomposite materials. The enhanced thermal stability ofpolyimide in the nanocomposites was due to the formation of network of polyimide andthe inorganic moieties, which limited these segmental movements of the PI. As well aswe discovered the electric conductivity rate of nanocomposites has much to do with thecontent of inorganic particles. 4. We gained composite hydrogel after three different composites were dispersed inthe gelatin aqueous solution and has studied the particles influence of the electricperformance of the colloid.we discovered the electric conductivity rate ofnanocomposites has much to do with the content of inorganic particles, the dissimilaritycontent of inorganic particles present different electric conductivity rate. At the sametime, the results show that the PI/BaTiO₃ nanocomposites may improve the conductivityelectric performance of the colloid.