Preparation And Vertical Heat Dissipation Performance Of Vertical Graphene And Its Polyimide Based Composite Films

With the development of 5G,big data,artificial intelligence and other technologies,high-performance electronic components such as light-emitting diodes（LEDs）and computer chips are improving towards integration,miniaturization and intelligence,which result in concentration of the heat.The high heat directly affects the service life and performance of electronic devices.Therefore,to ensure the efficiency,reliability,safety,durability and stability of electronic devices,it is urgent to develop efficient thermal management materials.Because of its excellent thermal conductivity,graphene nanomaterials have gained the favor of researchers in the related fields.Its appearance has greatly promoted the application range of heat dissipation materials.Based on three-dimensional（3D）vertical graphene nanosheets（VGNs）with unique directional distribution,a series of composites with excellent vertical thermal conductivity were prepared in this paper.The main contents and results are drawn as follows:Firstly,the VGNs/CF composite films were prepared on a roughened stainless steel substrate using glucose as the carbon precursor and carbon fiber（CF）as the thermally conductive filler by thermochemical growth method in a tube furnace.The composite films were characterized by XRD,Raman,FT-IR,XPS,SEM and TEM for the physical phase,elemental and microscopic morph ology.The thermal performance of the films was tested by infrared thermography and laser flash method.When the concentrations of glucose and CF were set as 0.4 g/m L and 1.0 mg/m L,the surface morphology and heat dissipation performance of the composite film after being heated at 850°C for 3 h the best.The vertical thermal conductivity of VGNs/CF composite film could reach 17.7 W·m^-1·K^-1,which was 22.1%and 27.6%higher than that of the blank RSS substrate and the pure VGNs films,respectively.On the basis of the VGNs/CF composite films,the PI@VGNs/CF composite films were obtained by composition of VGNs/CF structure and polyamide acid（PAA）,followed by imimization and peeling off from the stainless steel substrate.The structural characterization and performance testing of the PI@VGNs/CF composite films were carried out.With the increase of CF concentration,the light transmittance of the composite films became weak,the tensile strength and thermal stability showed a trend of first increasing and then decreasing and the elongation at break also changes.When the CF concentration was 5 mg/m L,the tensile strength and elongation at break of PI@VGNs/CF composite films were the largest,which were improved greatly compared with those of pure PI firm and PI@VGNs composite film.It is worth noting that the vertical thermal conductivity of PI@VGNs composite film is0.34 W·m^-1·K^-1,which is increased by 55.2%and 55.9%compared with that of the pure PI film and PI@VGNs/CF composite film,respectively.This shows that compared to CF,the directional vertical arrangement structure of VGNs plays a leading role in improving the vertical heat dissipation perfo rmance of PI composite film.With the further development of materials modification technology,the multi-component cooperative modification of thermal conductive fillers usually has a significant effect on the heat dissipation performance of polymer compo sites.Therefore,the PI@VGNs/Al₂O₃ composite film was obtained by introducing Al ₂O₃particles into the structure of PI@VGNs composite film.The performance test results showed that the tensile strength and elongation at break of PI@VGNs/Al₂O₃composite film were improved compared with the pure PI and PI@VGNs composite films,which proved that the small amount addition of Al₂O₃ particles could effectively improve the rigidity and toughness of the composite films.With the increase of Al₂O₃ concentration,the light transmittance of the composite films deteriorated,the tensile strength and elongation at break decreased.At the Al₂O₃concentration of 0.2 mg/m L,the tensile strength and elongation at break of the PI@VGNs/Al₂O₃ composite films reached the maximum,and its vertical thermal conductivity reached 0.49 W·m^-1·K^-1,which was 122.7%and 44.1%higher than that of the pure PI film and PI@VGNs composite film,respectively.The PI@VGNs/Al₂O₃composite films shows good heat dissipation performance and thermal stability,which can be used as a chip surface heat dissipation material to improve the heat dissipation performance and service life of electronic components.