Research Of Conductor/polymer Gradient Composites

High permittivity composites have a significant future in electron and electricindustry. In this thesis, several conductor/polymer composites have been studied with anew idea that the concept of functionally gradient materials to be used in highpermittivity composites.Firstly, as an exploratory study, carbon nanotubes/cyanate ester (CE) resincomposites were researched. Novel permittivity gradient (ε-G) composites based onsurface treated multi-walled carbon nanotubes (eMCNTs)/CE resin were successfullydeveloped by the gravity sedimentation method. The composites consisting of originalmulti-walled carbon nanotubes (MCNTs) and CE resin, coded as MCNT/CE, were alsoprepared for comparison. Each composite was cut into three slices in the direction ofthickness for evaluating the difference of dielectric properties over a wide frequencyrange from1to109Hz between the whole composites and their slices. Results showthat the surface treatment of MCNTs is necessary to form ε-G composites because thegood dispersion of nanotubes in the resin matrix, and the attractive interfacial adhesionbetween nanotubes and the matrix are key aspects for guaranteeing the gradientdistribution of the concentration of nanotubes in the composites. Note that, twointeresting phenomena were discovered. First, the whole composites show differentconductive and dielectric properties from their slices, specifically, the percolation effectdoes not appear in either whole eMCNT/CE or MCNT/CE composite, while which canbe observed in their slices. In addition, the percolation threshold of eMCNT/CE slice isabout25%lower than that of MCNT/CE slice. Second, with regard to the wholecomposite and its slice with the same content of nanotubes, they have similar dielectricconstant, but the dielectric loss factor of the former is remarkably larger than that of thelatter; these differences in properties are attributed to the different space distribution ofthe concentration of nanotubes between the whole composites and slices. These attractive features of eMCNT/CE composites suggest that the method proposed herein isa new approach to develop high performance ε-G composites, especially those withhigh dielectric constant and extremely low dielectric loss for cutting-edge industries.By reason of exploratory research about carbon nanotubes/CE system gradientcomposites, the special dielectric properties of gradient composites were found. Tofurther research unique dielectric properties of gradient composites, summarize thecommon properties of conductor/polymer gradient composites, promote the applicationof it. MCNT/EP and eMCNT/EP system gradient composites were prepared used moreordinary epoxy (EP) resin by layer by layer casting method. The dielectric properties ofMCNT/EP and eMCNT/EP system were studied by the same way to MCNT/CE andeMCNT/CE system. The result shows that the conductor/polymer gradient compositesindeed can keep high dielectric constant and extremely low dielectric loss,simultaneously. In addition, the dielectric properties of these conductor/polymergradient composites subject to thickness of insulating top layer, permittivity can beenhanced with low dielectric loss by reducing the thickness of insulating top layerwithin a certain range. But, a critical value exists in the thickness, when the thickness isless than critical value, percolation effect appeared, both permittivity and dielectric lossincreased sharply. Finally, there are lower cost to prepare eMCNT/EP composites thaneMCNT/CE composites, while eMCNT/EP composites keep excellent dielectricproperties, and more conducive to practical application.