Preparation Of Graphene/Polyimide-derived Carbon Fiber Composites And Their Thermal Conductivity And Mechanical Properties

With the integration of electronic components and the improvement of power density,it is urgent to develop high-performance thermal management materials suitable for different fields.Graphene has great research and application prospects as a thermal management material due to its extremely high intrinsic thermal conductivity and excellent flexibility.However,the weak interfacial interaction between graphene sheets is not conducive to phonon transfer and energy dissipation,resulting in unsatisfactory thermal conductivity and mechanical properties of the composites,making it difficult to meet practical requir ements.Based on this,in this paper,graphene/polyimide-based composite films and composite aerogels with 3D covalent cross-linked structure were designed and synthesized,which were used as heat dissipation materials and thermal interface materials,resp ectively,and their thermal conductivity and mechanical properties were discussed.The main research contents and conclusions are as follows:（1）Preparation of graphene/polyimide-derived carbon fiber composite films and their thermal conductivity and mechanical properties.The surface-modified polyimide fibers（PDA@OPI）were uniformly blended with graphene oxide（GO）,assembled into films by a simple evaporation method,and then graphitized and machine-molded to construct G-g PDA@OPI composite films with 3D long-range interconnect structure.The PDA@OPI fibers are“welded”with the GO sheets through stable covalent bonds to form a three-dimensional heat transfer channel,which is also beneficial to the load transfer and stress dissipation of the composite m embrane.At the same time,the introduction of PI fibers not only provides an escape channel for the gas generated by the decomposition of oxygen-containing groups during heat treatment,thereby reducing the generation of defects,but also the enhanced int erfacial interaction between fibers and GO significantly promotes the synergistic graphitization effect between GO and PI fibers,and improves the degree of graphitization of the composite films.Therefore,the optimized composite films show excellent thermal conductivity and mechanical properties.Its thermal conductivity,tensile strength and ultimate strain rate reached 1028 W m^-1K^-1,78.5 MPa and 19.4%,respectively.At the same time,it also exhibits excellent flexibility and high resilience.（2）Preparation of graphene/polyimide-derived carbon fiber composite aerogels and their thermal conductivity and mechanical properties.The G-g PDA@OPI composite aerogel（S-GPA）with a"sandwich"structure was cleverly constructed using a"bidirectional evaporation-induced self-assembly"strategy.The formation mechanism is to control the evaporation process of water along the upper and lower surfaces of the precursor slurry,so that the surface solutes tend to be horizo ntally arranged,while the internal components are still in a randomly oriented hydrogel state.After freeze-drying and graphitization,the S-GPA aerogel with a dense surface and a3D porous network cavity was obtained,thereby constructing dual thermal co nduction channels in the horizontal and vertical directions in the system.In addition,the PDA@OPI fiber acts as a 1D reinforcement,which consolidates this 3D network structure through covalent interactions,which further promotes heat flow transfer and stress distribution.Therefore,the S-GPA thermal interface material has the advantages of light weight,high strength,and good thermal conductivity.The tensile and compressive moduli of S-GPA are 4.2 MPa and 81.7 KPa,respectively.When compressed by 50%,the in-plane and out-plane thermal conductivities of S-GPA can reach 72.1 W m^-1K^-1 and 14.5 W m^-1K^-1.This work not only provides an easy-to-control and low-cost technical route for the fabrication of multifunctional graphene thermally conductive film s,but also the proposed structural design and synthesis strategy of"bidirectional evaporation-induced self-assembly"provides an effective route for the preparation of high-performance graphene-based thermal interface materials,which is expected to acce lerate the research and application of graphene-based composites in the field of thermal management.