The Research On The Preparation And Thermal Conductivity Of Three-dimensional Graphene/polystyrene Composites

The heat generated by electronic devices increases dramatically as electronic devices are developing toward to integration and miniaturization.In order to ensure the normal operation of electronic devices,it is an urgent problem to speed up the heat transfer between electronic devices.At present,thermal interface materials play an important role in electronic packaging.However,the thermal conductivity of polymer in thermal interface materials is very low,which is not conducive to heat transfer between solid interfaces.Relevant scholars have found that adding fillers with high thermal conductivity(such as metal particles,ceramic particles and carbon materials)can effectively improve the thermal conductivity of the polymer.In recent years,graphene has been widely used to improve the thermal conductivity of polymer due to its high thermal conductivity.The construction of interconnected graphene heat channels has always been an effective method to improve the thermal conductivity of graphene/polymer composites.The key to improve the thermal conductivity of graphene/polymer composites is that enhancing interfacial binding between graphene and polymer and between adjacent graphene.In order to construct interconnected graphene heat channels,in this paper,we used reduced graphene oxide(rGO)as thermal conducting filler and polystyrene(PS)microspheres as polymer matrix to prepare three-dimensional(3D)reduced graphene oxide/polystyrene(PS/rGO)composites by electrostatic adsorption method.The influence of graphene distribution on the thermal conductivity of PS/rGO composites was studiedbycontrastingthe thermal conductivity of PS/rGO composites preparaed with solution blending and electrostatic adsorption.Then,the effects of rGO content and reduction degree on the thermal conductivity of 3D PS/rGO composites were alsostudied.This result showed that when the content of rGO was 2.39vol%,the thermal conductivity of PS/rGO composite reached the maximum(0.28W/(m·K)),which was equivalent to 1.75 times of pure PS.In addition,with the increase of rGO reduction degree,the thermal conductivity of PS/rGO composites increases gradually.When the C:O is 18.23,the thermal conductivity of the composites reached the maximum(0.33W/(m·K)).To sum up,with the increase of rGO reduction,the thermal conductivity of the composite was improved,but the effect was not significant.The reason why the thermal conductivity of composites can not be improved dramatically isthat the interface bond strength between adjacent rGO was not high and there is interfacial scattering.In order to enhance the interfacial bonding strength between 3D rGO,silver nanoparticles(AgNPs)and p-phenylenediamine(PPD)were used to modify the surface of rGO,respectively.Then,we prepared the 3D graphene/polystyrene(PS/rGO-AgNPs)composites and the 3D graphene/polystyrene(PS/rGO-PPD)composites modified by silver nanoparticles and amino group,respectively.The results showed that the thermal conductivity of PS/rGO-AgNPs composites first increases then decreases with the increase of silver.When the silver content was 2.39vol%,thermal conductivity of PS/rGO-AgNPscomposite reached its maxmum(0.54W/(m·K)),equivalent to about 3.4 times of pure PS.This means that AgNPs can be used as a bonding in the process of hot pressing to sinter and connect adjacent rGO,and reduce the interface thermal resistance between adjacent rGO.Therefore,the thermal conductivity of PS/rGO-AgNPs composite can be improved.For amination of PS/rGO-PPDcomposite,the thermal conductivity of PS/rGO-PPD composite showed a trend of increasesfirstdecreases after along with the increase of PPD.The thermal conductivity of PS/rGO-PPD composite reached its maxmum(0.47W/(m·K))under the appropriate PPD content,equivalent to 2.9 times of pure PS.This means that the appropriate content of PPD can modify rGO,and connect adjacent rGOby covalent bonds.Thus,the interface thermal resistance between adjacent rGO can be reduced,and thermal conductivity of PS/rGO-PPD composites was improved.