Mechanisms And Applications Of Interfacial Effects On Thermal Conductivity In Al₂O₃/epoxy Composites

With the continuous upgrading of China’s power equipment,the preparation of composites with superior thermal properties has become the key to the upgrading and stable operation of power systems in order to accommodate the ever-serious heat generation problems in high-power equipment.In order to study the way of improving the thermal properties of alumina/epoxy composites,this paper has conducted a study on the overall and interfacial thermal properties of alumina and epoxy resin through a joint study and comparison of experiments and simulations,revealing the microscopic mechanism of the overall alumina/epoxy resin composite and its action at the interface,and providing guidance for improving the thermal properties of alumina/epoxy resin composites.Firstly,the alumina/epoxy composites were prepared and their properties were tested.The alumina/epoxy composites were prepared by modifying the alumina surface with different coupling agents and different modified alumina/epoxy composites were prepared.The thermal conductivity,glass transition temperature and dielectric constant of the composites were tested using a laser thermal conductivity meter,a comprehensive thermal analyser and a broadband dielectric spectrometer.The effects of the addition of alumina and different coupling agent modifications on the properties of the composites were measured and analysed comprehensively to provide an experimental basis for molecular dynamics simulations.Secondly,a composite model of epoxy resin encapsulated alumina nanoparticles with different coupling agent modifications was developed.The principles of molecular dynamics simulation are explored and the principles of thermal conductivity calculation represented by the RNEMD method are introduced.The thermal conductivity,glass transition temperature,coefficient of thermal expansion and relative dielectric constant of the composite model are simulated.By comparing with the experimental test results,the effects played by the addition of nanoparticles and the interfacial modification between filler and matrix on the thermal conductivity,glass transition temperature,thermal expansion coefficient and relative permittivity of the composite are analysed,and the results are analysed by molecular dynamics simulations for the microscopic mechanism.Finally,this paper analyses the alumina crystalline surfaces through the BFDH and AE model theories.The differences and similarities between the alumina crystalline surfaces are analysed through the BFDH model and the AE model,and the crystalline surfaces for stable contact between alumina and epoxy resin are determined.Based on the analysed crystalline surfaces,an alumina/epoxy resin interface model was established under different coupling agent modifications.The interfacial model was investigated from three perspectives:interfacial binding energy,relative density distribution and interfacial thermal resistance.The microscopic effects of bond lengths and groups of coupling agents on interfacial properties were summarised,and the best coupling agent for modification of alumina/epoxy composites was determined to be KH792 coupling agent.