Preparation Of Shell-like Structural Nanofiber/Graphene Composite Films With High Thermal Conductivity

With the rapid upgrading of electronic products,the heat dissipation problem of electronic components has attracted more and more attention.Among them,the thermal interface materials(TIMs)that play the role of heat transfer connection are one kind the key materials to solve the heat dissipation problem.The polymer/graphene thermally conductive composites combining the advantages of polymer materials such as good sealing,easy processing,low cost,and graphene's phonon-electron cooperative heat conduction,have been regarded as one of the ideal alternatives for advanced TIMs.In contrast,the shell-like layered polymer nanofiber/graphene composite film has attracted wide attention due to its light-weight,ultra-thin,high in-plane thermal conductivity,and simple preparation process,that showing considerable industrial application prospects.At present,the related researches still exist the following problems: high interface thermal resistance between polymer nanofiber and graphene;low-content construction of high-efficiency phonon transmission channels in layered structures;large-scale preparation of highly oriented layered structures.Based on these questions,this article carries out the following three researches:Aiming at the problem of interfacial thermal resistance,biomass polydopamine(PDA)is used to modify graphene nanosheets(GNS)in order to reduce the interfacial thermal resistance between graphene and cellulose nanofibers(CNF).Studies have found that the strong hydrogen bonding between PDA and carboxyl CNF can effectively reduce the interface thermal resistance between GNS and CNF.By adjusting the amount of PDA grafting,the contradiction between the improvement of interface thermal resistance and the introduction of heat insulation layer caused by PDA modification can be effectively balanced.When the ratio of PDA:GNS is 1:30,the thermal conductivity of 10 wt% CNF/GNS@PDA composite film is 13.47 W m-1 K-1,which is 23.4% higher than that of unmodified CNF/GNS composite film.At the same time,at a higher loading of GNS(50 wt%),PDA modification affects the direct contact of GNS,which is not conducive to the improvement of thermal conductivity.Aiming at the low-content construction of the phonon transmission path,a layered stacking strategy is adopted to concentrate the graphene content in the local layer structure,reduce the content of GNS in the entire film,and improve the overall phonon transmission efficiency.Studies have shown that the alternating layered structure GNS@CNF film prepared by alternating suction filtration of CNF solution and CNF/GNS solution exhibits the best thermal conductivity in a 5-layer alternating structure,and the thermal conductivity can reach 33.55 W m-1 K-1 with the GNS content of 25 wt%,the thermal conductivity of the homogeneous CNF/GNS film is improved by 44.6%.Further increase the GNS content(45 wt%),and the thermal conductivity of the layered structure composite film can be increased to 50.98 W m-1 K-1.Finally,the GNS@aramid nanofiber(ANF)composite film was prepared by the method of doctor-blading-sol-gel-evaporation film.Studies have shown that the combination of the shear force generated by solution scraping and the self-limiting effect of GNS during the self-assembly process of gel evaporation can realize the highly oriented dense stacking of GNS in the ANF matrix.Therefore,the obtained GNS@ANF composite film has a higher in-plane heat transfer function,and the thermal conductivity is 50.68 W m-1 K-1 with the GNS content of 50 wt%.Simultaneously,the preparation process of the doctor-blading-sol-gel-evaporation film is simple and not limited by the size of the machine,which is conducive to large-scale preparation.