Study On Preparation Of Resin-based Thermally Conductive Composites And Their Structure-properties Relationship

With the development of the current electronic devices toward the trend of miniaturization,multifunction,high integration and high power density,heat accumulation has become a critical issue that influences the performance,efficiency,and reliability of electronic devices.The application of high-performance thermally conductive materials as a thermal management strategy for keeping electronic devices cool is commonly employed to tackle this problem.Therefore,the preparation and development of high-performance thermally conductive materials has very important research significance and great market value.Polymer-based thermally conductive materials are most widely used in electronics devices for packaging and thermal management due to their excellent electrical insulation and mechanical properties,good thermal stability and processability,and low dielectric constants.However,limited by the low thermal conductivity of neat polymer matrix,the combination of highly thermally conductive fillers is usually employed to strengthen its thermal conductivity.In view of this,in this thesis,several high-performance epoxy resin-based thermally conductive composites were prepared based on the construction of different structural thermal conductivity networks through the microstructure design of fillers.The relationship between the microstructure of the filler and the thermal conductivity of the composites was investigated,and the mechanism of the influence of structurec of the composites on the thermal conductivity was elucidated by theoretical model analysis and finite element simulation.The specific results were summarized as follows:（1）Barium titanate coated commercial Cu particles（Cu@Ba Ti O₃）core-shell fillers were prepared by sol-gel process and then employed as thermal conductive fillers to reinforce epoxy matrix.The epoxy composites were fabricated by means of ball milling.The results indicate that due to the excellent thermal conductivity of Cu,thermal conductivity of the Cu@Ba Ti O₃/epoxy composites reaches 1.09 W/m·K at 10 vol%loading,achieving 580%elevation on neat epoxy matrix.Meanwhile,the Ba Ti O₃ insulating shell layer can hinder the formation of conductive pathways and effectively inhibit the deterioration of electrical insulation properties of composites caused by metallic Cu.Therefore,the composites retain high electrical insulation(7.9×10¹³Ω·cm).The Ba Ti O₃ coated on the surface of Cu particles promotes dispersion,enhances interfacial interactions,and restrict the electron transport while improves the phonon match between the stiff Cu（core）and the soft epoxy matrix.As a result,the thermal conductivity was enhanced and high electrical insulation was retained for epoxy composites.This strategy addresses the deterioration of insulation properties caused by filling with highly thermally conductive metal fillers,which will help to reduce the filler content.（2）Based on the work in the previous chapter,the shell material was optimized.Herein,we report the development and characterization of highly thermally conductive but electrically insulating Cu@Al₂O₃/epoxy composites.Insulating Al₂O₃ nanoshells can be facilely coated on the Cu surface by a solution-based synthesis process.Benefiting from the rich hydroxyl groups in surface of Al₂O₃,improved dispersion of the fillers,enhanced interfacial interactions and promoted phonon match were obtained between fillers and epoxy matrix.The Cu@Al₂O₃/epoxy composites exhibit a superior thermal conductivity of 1.32W/m·K at 10 vol%filler content,which is nearly 7 times higher than that of the epoxy resin.Simultaneously,the Cu@Al₂O₃/epoxy composites still retain a high electrical resistivity of2.3×10¹³Ω·cm,which is 6 orders of magnitude greater than that of Cu/epoxy composites without Al₂O₃ barrier layers,because the dense nanoscale insulating Al₂O₃ shell effectively inhibits the electron transfer inside the composites.In addition,the Cu@Al₂O₃/epoxy composites possess lower dielectric constant and dielectric loss,and better mechanical properties than those of Cu/epoxy composites.（3）In this work,a novel 3D CNNS/epoxy composite with high thermal conductivity was developed by introducing 3D CNNS skeleton fillers which can prepare by a facile and scalable strategy assisted by salt template.The interconnected porous structure of 3D CNNS skeleton was verified by optical microscopy and SEM.Benefiting from the continuous heat transfer pathways formed in the CNNS skeleton,a superior thermal conductivity of 1.27W/m·K was obtained on 3D CNNS/epoxy composites at a relatively low CNNS loading of17.0 wt%,which is 6.35 and 1.57 times higher than those of epoxy resin and convention CNNS/epoxy,respectively.With the aid of theoretical model analysis and finite element simulation,the pronounced enhancement effect of 3D CNNS skeleton on thermal conductivity performance of epoxy composites is found to be attributed to the continuous3D CNNS thermally conductive network,the reduced CNNS-CNNS interfacial thermal resistance,and the effective interfacial interactions between epoxy resin and CNNS in the3D CNNS/epoxy composites.In addition,the 3D CNNS/epoxy composites possess high electrical insulation and desirable mechanical strength.（4）Herein,a novel graphitic carbon nitride@nanodiamond（CN@ND）/epoxy composite with high thermal conductivity was developed by introducing nanohybrid CN@ND fillers prepared by a facile in-situ fabrication.Benefiting from the enhanced heat transfer pathways in“Point-Plane”structured CN@ND,20.0 wt%CN@ND/epoxy composites achieve a superior thermal conductivity of 1.06 W/m·K,which is 5.30 and 1.29 times higher than those of epoxy resin and CN/epoxy,respectively.With the aid of theoretical model analysis and finite element simulation,the pronounced enhancement effect of nanohybrid CN@ND on thermal conductivity of epoxy composites is found to be attributed to the improved thermally conductive network,enhanced heat flow intensity,and decreased filler-filler interfacial thermal resistance.In addition,the CN@ND/epoxy composites possess high electrical insulation and desirable mechanical strength.