The Preparation And Properties Of Thermally Conductive And Electrical Insulating Epoxy Composites

With the high integration and miniaturization of electronic devices,rapid and efficient dissipation of accumulated heat has become more and more crucial for the normal function of various high-performance devices.Due to the low thermal conductivity of most polymers??0.2 W·m-1·K-1?,various thermally conductive fillers are used to enhance their thermal conductivities.Compared to ceramic fillers,two-dimensional graphene has a higher thermal conductivity??5300 W·m-1·K-1?and is thus more efficient in improving thermal conductivity of polymers.However,its high electrical conductivity makes it impossible to prepare thermally conductive but electrically insulating polymer/graphene composites,because electrical conductivity is more sensitive to the content of graphene than thermal conductivity.To fully utilize the excellent thermal conductivity of graphene for electrically insulating polymer composites,various techniques have been developed to suppress its high electrical conductivity by constructing insulating nanoparticles or nanolayers on graphene surfaces.The contents of this subject consist of the following parts:1.Al₂O₃@Graphene hybrids were prepared using two different approaches.With the help of advantageous supercritical CO₂?SC CO₂?fluid,Al?NO3?3 hydrolyzes to form aluminum hydroxide on graphene,which is subsequently converted to Al₂O₃ nanoparticles by calcinating at 600?.However,the separated nanoparticles generally lead to loose and porous structures which will decrease the thermal conductivity of the hybrids.Alternatively,in a formic acid/ammonium formate buffer solution,the amount of ionized hydroxyl ions is moderate and stable,which makes Al₂?SO₄?₃ slowly nucleate and hydrolyze on graphene surfaces to form aluminum hydroxide nanolayers,which are then converted to Al₂O₃ nanolayers by the calcination at 600?.Both the Al₂O₃@Graphene hybrids exhibit significantly improved thermal stability because the thermally stable coating of Al₂O₃ acts as an insulator and a mass transport barrier,thereby reducing the decomposition rate and delaying the escape of volatile products released as graphene decompose.It is expected that the presence of the decorated Al₂O₃ can greatly suppress the electrical conductivity of the epoxy composites by preventing the direct contact of graphene while both the thermally conductive Al₂O₃ and graphene components can afford the effective phonon transfer in the epoxy matrix and thus benefit the enhancement in thermal conductivity of epoxy.2.The interfacial interactions are improved by the coated Al₂O₃ nanolayer on Graphene and a better filler dispersion is thus achieved in the epoxy composites filled with both Al₂O₃@Graphene hybrids.Importantly,both high thermal conductivity and electrical insulation are simultaneously realized by utmost utilizing the extraordinary thermal conductance of Graphene while greatly suppressing their high electrical conductance by coating the Al₂O₃ components.The Al₂O₃@Graphene hybrids endow epoxy with balanced the thermal conductivity and electrical insulating performances.