Structure And Performance Of Thermal Conductive Asphalt-based Composites

High-level integration and miniaturization of microelectronic components have been accompanied by rapidly increasing heat power densities.Heat dissipation has become a crucial factor determining the performance,reliability and lifetime of microelectronic components.Thermal interface materials(TIMs),filling between heat source and heat sink,play a vital role in reducing the thermal contact resistance and promoting the heat dissipation,ensuring a suitable working temperature range for highly integrated electronic devices.Therefore,developing high-performance TIMs with low cost has become an urgent task for the electronic industry.Asphalts are a class of potential matrix materials for TIMs due to their excellent adhesiveness and sealability,good workability and low cost.But the low thermal conductivity,weak mechanical properties and poor heat resistance of asphalts can not meet the demand of high-performance TIMs.In this dissertation,asphalts were chosen as the low-cost TIMs matrix,thermal conductive fillers were compounded to construct the thermal conductive pathways within for improving the thermal conductive properties of asphalts.Meanwhile,the mechanical properties and thermal resistance of the asphalt-based composites were also enhanced.The major works and achievements of this dissertation are as follows:Firstly,asphalt/styrene-butadiene-styrene tri-block copolymer(SBS)/alumina composites with spherical alumina micro-particles selectively distributed in SBS(asphalt/SBS/sd-Al₂O₃)were fabricated through pre-dispersion of silane modified alumina micro-particles in SBS,followed by compounding with asphalts.The continuous network of SBS/m Al₂O₃ phase formed the thermal conductive networks within the asphalt/SBS/sd-Al₂O₃ composites,leading to the enhancement in thermal conductivity,modulus,tensile strength and softening point.Additionally,the cost of asphalt/SBS blend used in this work is?1/5 the cost of epoxy and?1/6 that of silicone rubber,which are widely used in TIMs.Thus,the asphalt/SBS matrix has remarkable advantages in reduced costs for the manufacture of TIMs.Secondly,the high-power electron beam(EB)irradiation,with high efficiency,non-pollution and good controllability,was applied to asphalt/SBS/sd-Al₂O₃ composites to further improve their mechanical and heat-resistant properties.SBS molecules were crosslinked and grafted with asphalt under EB irradiation,which improved the mechanical properties of SBS rich phase and enhanced the interfacial interaction between SBS-rich phase and asphaltene-rich phase.After EB irradiation,the thermal conductivities of the asphalt/SBS/sd-Al₂O₃composites almost remained the same,while their tensile strengths,modulus and softening points were significantly improved.Thirdly,graphite nanoplatelets(GNPs)were simultaneously in-situ exfoliated and non-covalent functionalized by shearing natural graphite(NG)in SBS/NMP solution.The SBS/GNP nanocomposites were obtained by a co-precipitation process.And the asphalt/SBS/GNP nanocomposites(asphalt/SBS/sd-GNP)with GNPs selectively distributed in SBS(asphalt/SBS/sd-GNP)were fabricated by blending SBS/GNP nanocomposites with asphalts.The SBS/GNP nanocomposites with well dispersed GNPs and reduced thermal resistance have formed efficient thermal conductive pathways within asphalt/SBS/sd-GNP composites,leading to improved thermal conductivity.More importantly,nano-sized GNPs are easier to form high-efficiency thermal conductive pathways than spherical alumina micro-particles.Therefore,the filler thermal conductive enhancement(?)value of asphalt/SBS/sd-GNP composite with 2.9 vol%filler loading reached up to 30.7%,which is much higher than that of asphalt/SBS/sd-Al₂O₃ composite with 30 vol%filler loading.Finally,a facile,efficient and environment-friendly three-roll milling method was adopted to in-situ exfoliate NG in asphalts to fabricate asphalt/GNP nanocomposites.The GNPs are well-dispersed in asphalt matrix and easier to form well-connected thermal conductive networks in asphalt/GNP nanocomposites.At 25 vol%loading,the thermal conductivity of asphalt/GNP nanocomposite reached up to 1.95 W·m^-1·K^-1,which is 114%higher than that of the asphalt/commercial GNP(c-GNP)composites prepared by simply melt-blending c-GNPs with asphalts.Moreover,the well-dispersed GNPs have excellent interfacial adhesion with asphalts,which enhanced the modulus,tensile strength and softening point of asphalt/GNP nanocomposites.