Research On Preparation Method And Properties Of Thermal Management Materials Based.on Boron Nitride Nanosheets

With the rapid development of information technology represented by 5G and aerospace technology,the power density and heat generation of new devices and equipment are increasing exponentially,leading to a decrease in device performance,operating stability and service life.The use of highly thermally conductive materials for rapid heat transfer from heated components to low-temperature regions is an important approach to solve this problem.In this paper,based on thermal management materials,we prepared composites by growing silver nanoparticles on the surface of boron nitride nanosheets（BNNS）with polyvinyl alcohol（PVA）,and prepared large-area thermal conductive films as thermal conductive substrates by electrostatic spinning technique,after which the thermal conductive films were stacked and cut to prepare highly thermally conductive spacers,and finally tested the two-dimensional heat transfer properties of BNNS at the microscopic scale using Raman method.The main contents are as follows:（1）Large-area,deformable thermally conductive substrates were prepared by growing silver nanoparticles（Ag）on the surface of BNNS and mixing BNNS with PVA as composites,and using electrostatic spinning and hot pressing.With the assistance of electrostatic spinning and hot pressing,the boron nitride films have better in-plane alignment and dense filling,thus obtaining high in-plane thermal conductivity(32.3 Wm^-1K^-1)and tensile strength（25.7 MPa）for practical use while maintaining good electrical insulation.simulations by COMSOL confirm the great potential of this film as a flexible electronic device.Further,by printing the circuit on the experimentally prepared thermally conductive substrate and characterizing the heat dissipation capability of the sample compared with the commercial polyimide film as a thermally conductive substrate using infrared thermography,the results show that the prepared boron nitride thermally conductive substrate has a better heat dissipation effect,further verifying the application value of the experimentally prepared boron nitride thermally conductive film as a flexible electronic substrate.（2）BNNS-Ag/PVA thermally conductive spacers with high orientation were obtained by stacking and hot pressing the BNNS-Ag/PVA films prepared in the previous part of the work and cutting them in specific directions.The thermally conductive gasket samples have high thermal conductivity(15.1 Wm^-1K^-1),and it was demonstrated experimentally that the growth of silver nanoparticles on the surface of BNNS still enhances the thermal conductivity of the thermally conductive gasket sheets out-of-plane better.The same content of BNNS/PVA thermal conductive gaskets without orientation was prepared and the comparison of thermal conductivity also proved that the increase of orientation of the gaskets prepared by stack cutting process would have a greater improvement of the external thermal conductivity of the gaskets.The thermal conductivity of the BNNS-Ag/PVA composite was characterized by Photothermal technique,and the actual thermal conductivity of the three shim samples as thermal interface material（TIM）was tested using the T3ster test system for 1000 cycles.The results also showed that the gaskets have good stability for practical applications as well.（3）In order to investigate the two-dimensional heat transfer properties of BNNS at the microscopic scale,this experiment was conducted to test the two-dimensional in-plane thermal conductivity of BNNS in two-dimensional form and the contact thermal resistance with Si O₂substrate by using laser Raman thermal measurements.In this experiment,the laser spot size,the absorbed power of BNNS sample,the thickness of BNNS sample,and the characteristic peak Raman signal of BNNS sample versus temperature and power were tested,and the contact thermal resistance of BNNS with the substrate was calculated to be about 7.2×10^-7Km²/W,and the thermal conductivity of BNNS was 91.95 Wm^-1K^-1.