Preparation And Thermal Conductivity Of Graphene And Hexagonal Boron Nitride Nanosheets Thin Films

Graphene holds excellent physical and chemical properties,such as high carrier concentration,large specific surface area,good mechanical stretchability and ultra-high thermal conductivity,as the thinnest,advanced 2D material,and it is expected to be used in thermal interface materials.Hexagonal boron nitride nanosheets(BNNS),known as "white graphene",are metallic analogs of graphene.Although the thermal application based on graphene has been extensively studied,the conductive properties limit the use of graphene for some specific purpose.In contrast,BNNS is an electrical insulating material with a dielectric constant of 2-4.8.As a result,BNNS is particularly promising for heat transfer and dissipation applications in electronic packaging and high power electronics.However,The preparation of BNNS from exfoliation of hexagonal boron nitride(h-BN)has proven to be more challenging。The paper mainly includes three parts:(1)effect of Different Sizes of Graphene on Thermal Transport Performance of Graphene Paper;(2)we exfoliate BNNS from h-BN and prepared G-BNNS-G sandwich composite film,what’s more,we studied the thermal properties of G-BNNS-G film;(3)Independent BNNS thin film were prepared via filtration method,and studied the application of BNNS in PI.Furthermore test the thermal conductivity of BNNS film and BNNS/PI film.The results show that:(1)the higher the thickness is,the higher the thermal conductivity of the graphene film will be.The thermal conductivity of GNP-7 films with a thickness of 7 nm is as high as 149.2 W/mK,about seven times than that of GNP-3 and GNP-5.In addition,the thermal conductivity of GNP-7 after cold pressing has increased by 25%,namely 187.4 W/mK.(2)A method for preparing hexagonal boron nitride nanosheets by fused alkali and ultrasonic has been studied.This BNNS exfoliation method is simple、low price and access for raw material、low requirements for equipment,low toxicity to environment,advantages for the mass production、low the product cost,and more important,the yield is as high as 19%,which is higher than most of the liquid phase exfoliation method reported before.Meanwhile,the particle size of as-prepared BNNS with hydroxyl group was 0.5-2.5 um and the thickness was 0.5-7 nm.And then a sandwich film of graphene-boron nitride-graphene was prepared by simple vacuum suction method.The results show that the thermal conductivity of the sandwich film is 53.09 W/mK,which is higher than that of the neat graphene film(21.5 W/mK);(3)Thermal conductivity of the BNNS film in the horizontal direction is up to 58 W/mK.BNNS was added to the polyimide(PI)to form BNNS/PI.The out-plane thermal conductivity of the BNNS/PI composites was 0.441 W/mK,while the thermal conductivity in the horizontal direction was 2.946 W/mK.Which increased by 76%and 1078%,respectively in comparison to neat PI,indicating the anisotropy of BNNS.