Preparation And Properties Of Graphene/Polyimide Composites With High Dielectric Constant

Graphene has attracted the attention of many researchers and became a new hotspot due to its outstanding physical and chemical performance since it was found.As a unqiue two-dimension layer reinforcing nanofiller and with excellent optical,electrical and mechanical property,graphene can significantly improve the mechanical,thermal and dielectric properties of the polymer matrix composites.In particular,graphene/polyimide composites have play a unique charm in film capacitor,super-large-scale integration and electrode material as a new type of high strength,lightweight high-performance dielectric materials.Graphene layers are very easy to aggregate on account of the Vander Waals force and ?-? stacking,which lead to poor dispersion especially when they are applied in polymer composites.To improve the dispersibilities of graphene sheets in the polymer matrix,one strategy is to use graphene oxide as a precursor to enhance compatibility with polymers.Then we can prepare grapheme/polyimide composites through in situ controllable reduction of grapheme oxide.A few reducing agents have been used for in situ chemical reduction of GO in polymer matrix,although there are mang reducing agents suitable for the reduction of graphene oxide.The reducing agents used in this reducing method should have no effect on the properties of the graphene/polymer composites.In addition,the reducing agents are easy to decompose and keep little decomposition product in the polymer matix.The main contents of the article are summarized below:1.We applied the modified Hummers method and ultrasonic exfoliation to prapare graphene oxide,and then we used 1,4-diiodobutane as the reducing agent to prepared reduced graphene oxide.We characterized graphene by fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),UV-visible spectra(UV-vis)and Transmisson Electron Microscope(TEM).Results showed that the C/O ratio of RGO nanosheet surface could be tailored by adjusting the ratio of graphene oxide(GO)and reducing agent.We determined the feasibility of controllable reduction of graphene oxide through this phase of work.2.The in situ controllable reduction strategy was applied to the fabrication of high dielectric constant graphene/polyimide composites.The reduction extents of RGO in polymer matrix can be readily manipulated just through al tering the addition of the reducing agent.The dielectric constants of gaphene/polyimidecomposites were significantly enhanced with the increasing of the reduction extent of RGO.A high dielectric constant of 75 was obtained when the G/D was 1:8 at the frequency of 10 Hz,which was almost 25 times higher than that of the pure PI films.Meanwhile,the tensile strength and tensile modulus of RGO/PI were also increased by about 29% and 15% as compared with that of GO/PI.Moreover,although the oxygen-containing groups of GO sheets were labile under high temperature,the thermal stability of the GO/PI and RGO/PI composites were still comparable to that of pure PI.From the analysis results,1,4-diiodobutane have no bad effect on the properties of graphene/polyimide composites during the reduction of graphene oxide.3.Quaternary ammonium(Tetrabutylammonium bromide and Tetrabutylammonium Iodide)can be served as the reducing agent for the fabrication of high dielectric graphene/polyimide composites via the in-situ chemical reduction of graphene oxide.As a surfactant,Quaternary ammonium can make graphene oxide dispersed more evenly in polymer matrix.Simultaneously,it can inserted into graphene layers and prevent the restacking of reduced graphene oxide.The results showed that the dielectric constant of graphene/polyimide composites was nearly 40 times as compared with that of graphene oxide/polyimide compared with pure PI films.The thermo stabilities and mechanical properties of graphene/polyimide composites were also improved simultaneously.Moreover,the quaternary ammonium surfactants would not remain in the composites,which can be decomposed after the RGO/PI composite materials was produced under high temperature.