Preparation Of Thermally Managed Boron Nitride/Polymer Composites By Magnetic Regulation

Thermal management materials with diverse thermal function play increasing significant role in aerospace,5G,AI,soft wearable electronics and renewable energy field.For microminiaturization of high power electronics,exhausted heat must be dissipated efficiently to ensure their performance and reliability;for energy equipment,it is necessary to maintain temperature in a proper range when the heat source or ambient temperature change sharply.Therefore,materials with high thermal conductivity and/or high reversible jump of thermal conductivity are urgently needed to address above issues.Born nitride?h-BN?is commonly used to prepare thermal functional materials owing to its superior anisotropic thermal conductivity.The thermal performance of BN composites are determined by plan size,thickness and orientation,which is a challenge for preparing high performance BN composites.To fully develop the potential of the anisotropic thermal properties of BN,this study focus on the preparation of nano sheet BN and BN orientation suing magnetic field.The main results are followed:1.magetic oriented boron nitride / epoxy composite.First,large size and thin BNNs were prepared by using proper power of sonification and surface tension of exfoliating solution to ensure the intrinsic thermal properties of BN.Afterwards,magnetically responsive boron nitride?m-BNNSs?were fabricated by using in-situ co-precipitation method.Composites with various orientation and assemble state of BN were achieved by adjusting the strength and direction of magnetic field.The cthermal conductivities of composites strongly dependent on orientation condition.The thermal conductivity of well-oriented mBNNSs / epoxy resin composite is 15.18 W·m^-1·K^-1 with 30 wt% m-BNNSs,⁴ times higher than that of random composite,3.55 W·m^-1·K^-1.2.Boron nitride / organic phase change composites with reversible thermal conductivities.1)For m-BNNSs/polyethylene glycol modified polyethylene glycol composite, in solid state,the thermal conductivity reached at 3.17 W·m^-1·K^-1 when m-BN are oriented and assembled parallel to the heat flow direction;in the liquid state,the thermal conductivity fall to 0.49 W·m^-1·K^-1when m-BNNSs oriented and assembled perpendicular to the heat flow direction.The ration of thermal conductivity of solid and liquid was 6.5 times,which satisfies the requirements of circumstance with harsh temperature variation.2)For m-BNNSs/dodecyl triethoxysilane modified araffin wax composite,the compatibility was significantly improved.The composite with good orientated skeleton of m-BNNSs can not only effectively improve thermal conductivity jump,but also helpful maintain the shape stability when the temperature above the phase change point.