The Design Of Boron Nitride Nanosheets Based Thermal Conductive Network And Its Application In Thermal Interfacial Materials

With the development of microelectronics industry,the integration of devices have rapidly increased,high-power devices have put forward higher requirements for heat dissipation materials and their internal heat dissipation package structure design.Polymer materials have broad application prospects in thermally conductive materials due to their good processability and interstitial properties;however,unlike ceramic and metal materials which contain regular crystal regions,the existence of a large number of amorphous regions inside them will cause phonon scattering which occur between different structural interfaces,so high thermal conductive fillers are filled to improve its thermal conductivity.However,a large number of studies have found that polymer-based thermally conductive composites also have some key issues that need to be resolved urgently.The first is that the phonon scattering at the two-phase interface will increase the interface thermal resistance;on the other hand,the dispersion state of the thermally conductive filler in the polymer matrix will affect the construction of the thermally conductive network.Disordered dispersion requires a high number of fillers to achieve the ideal Performance,which will inevitably affect the mechanical properties of composite materials while improving thermal conductivity.Therefore,exploring reasonable filler surface treatment methods to improve interface compatibility and building an orderly thermal network are key issues in thermal interface materials.In response to the above problems,this paper used h-BN as thermally conductive filler to prepare a stable suspension of boron nitride nanosheet(BNNS)through high-temperature hydrolysis of alkali solution and ultrasonication;The orientation method makes BNNS and nanocellulose(CNF)form a layered in-plane oriented thermally conductive network,and the good overlap of the thermally conductive filler in the in-plane direction facilitates the transfer of heat flow.This study found that with the increase of BNNS contents,when the filler content reaches to 70wt%,the in-plane thermal conductivity of the thermally conductive film is11.8W/(m·K),while still having good flexibility and mechanical strength.It is proved that the ordered orientation arrangement of BNNS is beneficial to the improvement of the thermal conductivity in the orientation direction.In order to use the prepared BNNS to construct a dual-oriented thermal conduction network that is more consistent with the heat transfer path from the heat source to TIM.In this study,magnetized BNNS particles(BNNS/Fe₃O₄@PDDA)were prepared based on electrostatic interaction and magnetic field-assisted alignment,vacuum filtration was also used to prepare a thermally conductive network with highly oriented in-plane and vertical directions inside the film.When the content of BNNS@Fe₃O₄ was 30wt%,the content of Fe₃O₄ was13wt%,the dual-oriented structure film composite material still has excellent flexibility,can be bent at will,the vertical thermal conductivity reaches 1.08W/(m·K),and the in-plane thermal conductivity reach to 6.17 W/(m·K),the overall heat dissipation efficiency is better than that of a single-plane oriented thermal film.the thermal conductivity of composite materials has been further improved from BNNS's multi-orientation thermal network construction.In order to further explore the orderly orientation processing method of BNNS and its potential application prospects in thermally conductive elastomers,this work chooses the ice template confined self-assembly method to prepare BNNS@PDA/Ag aerogels.PDMS was infiltrated to prepare a flexible thermally conductive pad with good mechanical strength.And the introduction of Ag nanoparticles to further enhance the density of the thermal network,increase the contact between the layers of the BNNS sheet and reduce the interface thermal resistance.When the content of BNNS@PDA was 19.6wt%of the total weight of the composites material and the content of Ag was 7wt%,BNNS@PDA/Ag-PDMS composites still has excellent flexibility,can be bent at will,and has vertical thermal conductivity of 3.23W/(m·K).Under a constant 20%compressive strain,the compressive stress of the composite is only relaxed by 11.7%.This research has made progress in the directional construction of BNNS's hybrid thermal network and the theoretical analysis of the application stability of thermally conductive pad.