Preparation And Thermal Management Performance Of High Thermal Conductivity Flexible Composite Materials Based On Boron Nitride Nanosheet

With the booming trend of high-power,high-capacity,high-integration and high-frequency of next-generation electronics,numerous thermal heat was generated during the operation of such devices.And with the accumulation of thermal heat,the temperature of the device will also rise to a higher temperature.Namely,thermal management of modern electronics has become more and more crucial,making it one of the most key concerns.In order to improve the reliability of electronic devices,as well as to prolong their working time,effective method to dissipate this thermal heat has to be provided.To date,thermal dissipation of electronic devices is mainly acquired by combining highly thermal conductive nanomaterials with polymer substrates,i.e.,nanocomposites with both high thermal conductivity and excellent mechanical properties.The common-used highly thermal conductive nanomaterials includes carbon materials（such as carbon nanotubes,graphene,etc.）,ceramics,and metals.Among them,boron nitride（BN）has been widely used as the thermally conductive fillers due to its large energy bandgap,good oxidation resistance,excellent thermal conductivity and thermal stability,chemical inertness and remarkable mechanical properties.As interfacial materials between electronic devices and the surrounding environments,the highly thermal conductive nanocomposites usually have the characteristics of high thermal conductivity,flexibility,and ease to process,besides the high thermal conductivity.Most importantly,complete and efficient thermal conductive pathways must be formed in the as-fabricated nanocomposites.In this thesis,starting with the exfoliation of boron nitride nanosheets（BNNSs）,highly thermal conductive nanocomposites have been fabricated using polymer as substrates,by constructing the stable thermal conductive networks.Furthermore,the relative properties,as well as the potential applications,have been studied.First,BNNSs/Thermoplastic polyurethanes（TPU）composite films with high thermal conductivity were prepared through the air-water interface method.In this case,a thin film with uniform thickness can be generated on the water surface through the synergistic effect of both surface tension gradient and buoyancy,leading to the overlap of BNNSs in the in-plane direction,forming the thermal conductive networks,to ensure a rapid thermal transmission.In addition to the high thermal conductivity,the film also has excellent electrical insulation and flexibility.And this nanocomposite has potential for the thermal management of electronics with irregularly shapes and surfaces.Second,nanocomposite film based on NaNbO₃:Pr³⁺（NNOP）/BNNSs/Polydimethylsiloxane（PDMS）has been prepared.The sample with excellent flexibility can be folded,curled,twisted and stretched.Moreover,due to the construction of the three-dimensional thermal conductive networks by BNNSs,the thermal heat can be transmitted in the composite fast,ensuring the thermal heat transmitting to the NNOP in a very short time,to excite the thermoluminescence rapidly.The results show that under the same thermal stimulus,the luminescence from the sample occurred earlier（26 s）compared to that without BNNSs（59 s）.Due to its excellent electrical insulation,high thermal conductivity,and fast thermoluminescence,the composite is hoped to be used for safety monitoring of modern devices and equipment.