Nanofiller Encapsulated Microparticles For Electrically Insulating And Thermally Conductive Epoxy Composites

With the development of the electronic and electrical industry toward the direction of high integration and high performance,the power per unit area of the device is continuously increasing,and the accompanying heat generation is also increasing.If electrical and electronic equipment is operated at a relatively high temperature for a long time,not only its own performance will be degraded,but also its internal components will accelerate aging,resulting in greatly reduced life or even direct failure.Therefore,thermal management is very important for electrical and electronic equipment.Polymer-based thermal insulation composite materials are increasingly studied and used in the industry due to their corrosion resistance,light weight,easy processing and excellent electrical insulation properties.However,due to the low intrinsic thermal conductivity of the polymer matrix,it is difficult to meet the industry's demand for properties of thermally conductive materials.In this paper,we start from the point of designing the structure of the thermally conductive filler.A kind of micro@nano multi-stage structure hybrid filler was designed to build a more efficient heat conduction path for the composite material to improve the thermal conductivity of the polymer,and to study the filler coating structure.The effect on the electrical properties and thermal stability of the composite was also been researched.Firstly,a high-efficiency thermally conductive hybrid filler,i.e.,Al₂O₃@BNNS that the surface of Al₂O₃ microspheres were encapsulated with BNNSs,and then adding this type of fillers into epoxy matrix to obtain economical high-TC composites which are suitable for large-scale industrial production.we chose the advanced thermally conductive filler,i.e.,relatively flexible thin BNNS to serve as highway for heat transfer,the traditional filler Al₂O₃ microspheres to act as foundations for supporting BNNS highway.The Al₂O₃@BNNS filler were prepared via the reaction of chemical group on the surface of those two fillers induced self-assembly.Inside the composite,due to the existence of massive Al₂O₃ microspheres,the percolation threshold for BNNS remarkably decline,even a few content of flexible BNNSs could also build a thermally conductive highway network.The prepared epoxy composite with 65 vol%Al₂O₃@BNNS hybrid filler loading possesses the thermal conductivity of 2.43 W m^-11 K^-1)at a low BNNS loading level of only 8.1vol%,which corresponds to a thermal conductivity enhancement of about 74%compared with that of 65 vol%pure Al₂O₃ filler composite.Furthermore,the Al₂O₃@BNNS/epoxy composite maintain the excellent electrically insulating property.In addition,a new kind of hybrid filler??m@nm-Al₂O₃?with a special shape of“strawberry type”was prepared by surface modification and self-assembly of micron-sized alumina and nano-sized alumina fillers,and further a high thermal conductivity insulating epoxy composite material is prepared by introducing epoxy matrix.The results show that the?m@nm-Al₂O₃ hybrid filler could improve condition of the uneven distribution of nano-sized fillers in composites,and achieve the purpose of filling micro-alumina due to large size.The material has a significant improvement in thermal conductivity.In the 65 Vol%filling system,when the micron-sized alumina and nano-alumina have a volume ratio of 4:1,the?m@nm-Al₂O₃/Epoxy composite reaches the maximum relative thermal conductivity.The increase rate is 12.1%,16.2%and 21.5%higher than that of the random-?m@nm-Al₂O₃/Epoxy,?m-Al₂O₃/Epoxy and nm-Al₂O₃/Epoxy composites,respectively.In the case of 70 Vol%filling system,when the volume ratio of the two fillers is 5:1,the maximum relative thermal conductivity is achieved,and the thermal conductivity is increased by 12.3%,18.6%,and23.0%,respectively,compared with the above three sets of the same filling;in addition,?m@nm-Al₂O₃/Epoxy composites maintain good thermal insulation properties while maintaining good electrical insulation properties and thermal stability.They can be widely used in thermal management of electronic packaging and electrical equipment,and are suitable for most working conditions.