Preparation Of Graphene Three-dimensional Heat Transfer Skeleton And Phase Change Composites

The rapid development of the electronic field requires high-efficient thermal management capabilities for electronic devices.For this reason,phase change materials（PCM）with thermal energy control show broad application prospects.However,the disadvantages of PCM,such as low intrinsic thermal conductivity,easy leakage,and poor shape stability,limit its application range.The introduction of three-dimensional（3D）thermal conductive skeletons has been widely recognized as an effective solution to the above-mentioned problems of PCMs.But the improvement of thermal conductivity of PCMs still faces challenges due to the high interfacial thermal resistance between fillers caused by physical contact in the 3D skeletons.In this respect,two methods for reducing interfacial thermal resistance were used in this paper,using graphene nanoplatelets（GNP）as thermally conductive fillers and polyethylene glycol（PEG）as phase-change matrix to prepare phase-change composites with excellent thermal conductivity.The main work are as follows:（1）A high-temperature“carbon-welding”strategy was adopted to reduce the inter-filler interfacial thermal resistance in the 3D graphene skeleton by realizing lattice connections between the contacting GNP.The 3D thermally conductive network was formed by the unidirectional assembly of GNP with the assistance of polyamide acid（PAA）by ice-template method.Adjacent GNP are welded by carbonized polyimide（PI）using imidization and high temperature carbonization treatments.PI carbides have a similar lattice structure to graphene,which can significantly reduce phonon scattering and interfacial thermal resistance in the contact area.After PEG impregnation,phase change composites with efficient thermal conduction pathways were obtained.The phase change composite has the maximum thermal conductivity(7.032 W m^-1K^-1)at～11.6 vol%GNP loading,which is more than twice that of the uncarbonized skeleton composite.In addition,the existence of the 3D graphene skeleton can effectively avoid leakage during the solid-liquid phase transition process,and significantly improve the shape stability of PCM.Meanwhile,the graphene skeleton can confer excellent photothermal conversion performance to the phase change material.（2）The strategy of bridging 2D GNPs with 1D silver nanowires（AgNW）was adopted to reduce the interfacial thermal resistance between GNP in 3D oriented skeleton structures,and to prepare directional thermal conduction paths to obtain highly thermal conductive phase change composites.Due to the high aspect ratio and high intrinsic thermal conductivity of AgNW and GNP,combined with the directional freezing process to form a 3D vertically oriented GNP-AgNW skeleton,the thermal conductivity of PCM can be significantly improved.When the filler content is less than15 wt%,the thermal conductivity of the phase change composites can reach 7.239 W m^-1K^-1,which realizes the preparation of high thermal conductivity phase change composites with lower filler content.The 3D skeleton encapsulates the PCM to solve the leakage problem,which can improve the shape stability during the melting/solidification process and effectively prevent the leakage of organic PCM during the solid-liquid phase transition.In addition,the existence of graphene and silver nanowires endows PCM with excellent photothermal conversion properties,expanding their application prospects in the fields of thermal management of electronic devices and energy storage.