The Construction Of Three-dimentional Filler Network For Thermally Conductive Rubber Composites

With the development of electronic devices towards high loss of power,miniaturization and integration,its energy density is greatly improved,which brings increasinglly serious heat dissipation problems.Failure of thermal management will lead to equipment jam,circuit damage,buried serious safety hazards.The design and preparation of high-performance cooling materials to ensure the reliable operation of electronic components has become one of the major bottlenecks in the future development of electronic technology.Thermally conductive rubber composite is a key component,which plays an irreplaceable role in aerospace,electronics,military equipment,communications,LED lighting and other fields.Traditional processing strategy,limited by high product density,processing difficulty,low enhancement efficiency of thermal conductivity,low mechanical strength and other shortcomings,has been difficult to meet the development needs of the electronics industry.Therefore,it is urgent to develop new and effective preparation methods and design concepts to provide theoretical support and technical guidance for the development of new thermal rubber composites.Herein,based on the analysis and summary of the application,present research,and development trend of thermally conductive polymer composite materials,aimimg at acquiring high thermal conductivity,high flexibility and versatility,three-dimensional filler network structure was construct to implement a variety of different types of high thermally conductive rubber composite materials preparation.The main innovative research contents and results are summarized as follows:1.A novel and cost-effective foaming route to construct the three-dimensional(3D)interconnected boron nitride(BN)network was proposed.Owing to the inspiration of jelly,curdlan an esculent polysaccharide with unique gelling behavior,is employed as gelling agent to stabilize and immobilize the bubble-templated network.The results show that the thermal conductivity of the polydimethylsiloxane(PDMS)composites containing this 3D BN thermal conductive network reaches 1.58 W/(m·K)at a low BN loading of 25.4wt%,which is 749%higher than that of neat PDMS.Moreover,the density of this composite is about 1.27 g/cm3,which is 40%?50%lower than that of commercial silicone pad products with thermal conductivity of 1.5 W/(m·K).Meanwhile,the composites are also highly electrically insulating with a volume electrical resistivity over 1015 ?·cm.The superior performance of the as-obtained composites demonstrates a promising prospect to tackle thermal management problems in a variety of emerging electronic devices.2.3D connected graphene nanoplates(GNP)foam was prepared by using GO as gelling agent,combining with aqueous phase foaming technology and hot air drying.After heat treatment at 1500? and vacuum impregnation,silicone rubber composites(3D T-rGO-GNP-PDMS)was prepared.The microstructure of 3D graphene foam and composites was studied by scanning electron microscope.It is found that high temperature heat treatment can greatly improve the thermal conductivity and electromagnetic shielding efficiency(EMI SE)of the composites.33D T-rGO-GNP-PDMS has extremely high EMI SE and thermal conductivity.When its thickness is 1 mm,EMI SE is up to over 70 dB,which is at the forefront of the reported values in recent years,indicating that the foam-templated 3D graphene framework has an ext emely obvious electromagnetic shielding advantage.At graphene content loadings of 18.1 wt%,its thermal conductivity reached more than 3 W/(m·K),which also has obvious advantages compared with the ice template method and 3D hot pressing method reported in recent years.3.The problems of the poor flexibility and low out-plane thermal conductivty of the heat-dissipation films remain outstanding,significantly restricting their large-scale application.A novel GO-assisted gelation method combined with facile hot compression to fabricate the highly flexible rGO-BN-NR composite films with an outstanding heat dissipating performance was developed.The as-prepared films,at a BN loading of 250 phr,demonstrated both superior in-plane thermal conductivty(16 W/(m·K))and impressive elongation at break(113%).In addition,the composite films also exhibited excellent flame-retardant ability and pronounced antistatic performance.More importantly,to accommodate the applied characteristics of thermal interface materials,the orienting direction of the composites can be easily transferred to achieve a high vertical thermal conductivty.The strong cooling capability of the rGO-BN-NR composite films was directly certified by thermal infrared imaging and finite element simulation,indicating a broad and bright application for thermal management in a variety of emerging electronic devices.4.Restricted by traditional processing approaches,it remains challenging to fabricate high-performance rubber nanocomposites with both good mechanical strength and high thermal conductivity.We develop a novel GO-assisted gelation method to construct a 3D interconnected rGO@Al2O3 hybrid fillers network as efficient heat transfer path in natural rubber nanocomposite acquiring desirable performance.The as-prepared rubber nanocomposite,at a filler loading of 18.0 vol%,exhibits not only a largely increased tensile strength(25.6 MPa)but also a high thermal conductivity(0.514 W/(m·K)).Owing to the construction of a highly interconnected filler network,the resulting 3D rGO@Al2O3-NR shows apparently higher thermal conductivity than the nanocomposites prepared by conventional method at the same filler content.Moreover,we.can easily control electrical resistance by adjusting the mass ratio of GO to Al2O3,making the nanocomposites satisfy the use requirement of electrical insulation.5.To solve the problem that graphene is not good for the electrical insulation of composites,a micro-nano multi-scale hybrid filler network was constructed to prepare thermally conductive and electrically insulting silicone rubber composites.The graphene hybrid filler(GO@Al2O3)coated with nano-alumina and micron alumina(m-Al2O3)were compounded and filled into liquid silicone rubber.It is found that when GO:Al2O3=1:5(mass ratio),the composites changed into electrical insulation state.Combining with the HS upper and lower bound model,the synergistic effect of thermal conductivity between GO@Al2O3 and m-Al2O3 is deeply studied.It is found that at high GO@Al2O3 content,a very small amount of GO@Al2O3 can play the role of"thermal bridge",greatly improve the interconnectivity of thermally conductive network,and thus greatly improve the thermal conductivity.