Constructing Network Structure To Fabricate Polymer Composites For Thermal Conduction And Microwave Absorption

Polymer composites have been widely used in electronic packaging due to their high performances,corrosion resistance,light weight and low cost.With the development of electronic technology,the new generation of electronic component has a higher power density which leads to electronic devices produce a lot of waste heat.Excessive residual heat would cause serious damage to the system,causing fire and other accidents.Using materials with high thermal conductivity can effectively dissipate excess heat and meet the thermal management requirements of equipment,which is very necessary for high-power systems.At the same time,with the increasing power density of electronic components,electromagnetic interference has attracted increasing attention.In order to improve the equipment's ability of anti-jamming,electronic packaging materials need to have a certain electromagnetic wave absorption'performance to protect electronic components.In general,the thermal conductivity,electrical conductivity and microwave absorption of polymer composites are relative low,which limits their further application in high-performance electronic systems.In order to solve these problems for the current industrial applications,it is a simple route to prepare function composites by adding high-performance fillers such as graphene,boron nitride and MXene into the polymer matrix.This processing strategy usually requires a high filling content to improve the performance of the material.However,the mechanical properties of the as-prepared composites will be significantly decreased due to the excessive filler content,which effect the application of the materials.The focus of this paper is constructing a continuous conductive network in a diversified system of composites to effectively improve the thermal conductance and microwave absorption performance,as well as maintain a certain mechanical strength to meet different application requirements.With different fabricate strategys basing on the advantages of composites,three dimensional networks are constructed by orderly arranging the fillers in the polymer matrix.Moreover,a further study of the relationships between conduction networks,the fillers' geometric morphology and distribution of the fillers is discussed.In addition,the relationships between the thermal conduction,microwave absorbing properties of the composites and the structure of the conduction networks are also studied in detail.The main results are presented as follows:1.Hexagonal boron nitride(h-BN)presents an excellent thermal conductivity and the outstanding insulating property for electronic packaging.However,a traditional method can enhance the thermal conductivity of composites by melt mixing fillers and polymers usually leading to composites with limited thermal conductivity.Here,we first prepared BN@PPS(Polyphenylene sulfide)core-shell structure particles and their composites with the 3D segregated architecture are presented.The composite achieves a high thermal conductivity of 4.15 W/(mK)containing 40 vol%BN,which is 16 times higher than that of PPS resin of?0.25 W/(mK)and 1.69 times higher than that PPS/BN blend composite with at the same BN loading of 2.45 W/(mK).The outstanding thermally conductive property of segregated architecture PPS/BN composite is attributed to the formation of BN flakes networks in the PPS matrices,which can provide effective thermal conductive pathway.This segregated architecture composite is an optimal material for insulating electronic packaging.2.The low value of thermal conductivity of boron nitride composite prepared by the conventional blending extrusion method is difficult to meet the heat dissipation requirements of the current electronic system,and the mechanical properties are degraded due to the high filling content of the filler,and the application is limited.Here,we report a facile method to fabricate annual ring-like structure BN/PEEK composites by rolling process and hot pressing.The composite presents a high thermal conductivity of 15.53 W/(mK)at 40 vol%loading,which is?5.1 times higher than that of the blend composite with the same content.This excellent thermally conductive property is ascribed to the lamellar thermal conductive pathway along the BN-rich phase.Meanwhile,the unique structure maintains a high mechanical performance.The composites exhibit enhanced compressive strength and flexural strength,increasing 135%and 134%respectively,compared to blend sample.Therefore,the annual ring-like structure composite is an optimal candidate for insulating electronic packaging.3.The three-dimensional conductive structure can effectively improve the electrical conductivity and enhance the conduction loss of the dielectric composite material for microwave absorption performance.Graphene is regarded as a two-dimensional material with high intrinsic conductivity to construct a conductive network.Here,we reported that the lightweight spongy bone-like graphene@silicon carbide(SiC)aerogels were fabricated by the directional freezecasting of graphene oxide(GO)coated SiC whiskers slurry and thermal reduction of GO@SiC aerogels.The unique hierarchically ordered structure of graphene@SiC aerogels is formed by graphene wrapped SiC whiskers,such a structure possesses great advantages including low density(72 mg/cm3)and high microwave absorption performance for aerogels.The minimum reflection loss of typical sample achieves-47.3 dB at 10.52 GHz with a thickness of 3 mm,and the effective bandwidth of reflection loss?-10 dB can reach 4.7 GHz.These results indicate that the novel graphene@SiC aerogels is an optimal material for high-performance microwave absorption application in aeronautics.4.As a new type of two-dimensional ceramic material,Mxene has an excellent electrical conductivity and microwave absorbing potential.Similar to graphene three-dimensional conductive structure,constructing a MXene network can effectively improve the electrical conductivity and the conduction loss of the dielectric composite,which can father enhance the mic rowave absorption performance.Here,we report that hierarchically structured cellulose aerogels with interconnected Mxene(Ti3C2Tx)networks are prepared via freeze-casting and chemical cross-linking processes.The individual MXene nanosheets are effectively combined together with cellulose to form.a conductive network by covalent cross-linking and hydrogen bond interaction.This unique structure of aerogel composites presents a low density(0.31 g cm-3)with excellent microwave absorption performance.The typical aerogel with its paraffin exhibits the minimum reflection loss(RL)of-43.4 dB at 11.2 GHz with a thickness of 2 mm and an effective absorption bandwidth of 4.5 GHz as a result of multiple reflection effects,conductive loss and polarization relaxation.These lightweight Ti3C2Tx MXene/cellulose aerogel composites are potential materials for high-performance microwave absorption applications in aeronautics.