Study On The Construction And Thermal Conduction Of Conjugated Small Molecule Modified Graphene/Copper Interfacial Composites

The rapid development of modern technology has put forward higher requirements on the thermal conductivity of electronic devices.Traditional thermal conductive technology can no longer meet the thermal conductivity requirements of high-power density and high integration electronic devices.Therefore,it is urgent to develop materials with high thermal conductivity to improve the thermal conductance of electronic devices.Graphene is a single-atomic two-dimensional allotrope of carbon with extremely high carrier mobility and thermal conductivity.Graphene-related materials,including reduced graphene oxide,few-layer graphene,multilayer graphene and graphene nanosheets,represent the most advanced materials developed for heat conduction applications.In some applications,one desires to benefit from increasing both thermal and electrical conductivity,the combination of graphene and metal is promising applications.However,the interfacial thermal resistance between graphene and Cu even other metals hinders the thermal transport across the graphene-metal interface.Therefore,the reduction of the interfacial thermal resistance becomes the key to give full play to the thermal conductivity of graphene/Cu or graphene/metal composites.In graphene/copper composites,electrons are the main energy carrier in metal copper,and phonons are the main heat fluxers in graphene materials,so both phonons and electrons are involved in energy transfer.However,current studies mainly discuss the contribution of phonons to heat transfer in graphene/copper composites,neglecting electron transfer.A physical adsorption interface with charge transfer or a chemisorption interface with orbital hybridization can be formed between the metal and graphene.Compared with the physical adsorption interface,the chemisorption interface has a stronger bond with graphene and is easier to form real electrical contact.This study is devoted to the design of molecular junction chemical links between graphene and copper particles and form delocalized conjugate?bonds and construct electron thermal conduction paths.Through organic conjugated small molecule,as a bridge between them,the coupling between nanoparticles is formed,and the synergistic effect of phonon heat transfer and electron heat transfer is realized to reduce the interface thermal resistance,so as to improve the thermal conductivity of graphene/copper composites.It is expected to promote the application of graphene/metal composites in the field of next-generation thermal interface materials.To this end,this paper carries out the following research:(1)A novel electron heat conduction pathway of modified graphene/copper matrix composites is proposed and constructed:The functionalized graphene(FGr),diazotized with 4-ethynylaniline,and copper are connected to a p-orbital conjugated organic molecule by pulsed electrodeposition.The delocalized?-?bond at the graphene/copper interface is successfully established,and a new electron heat conduction path is constructed.The thermal diffusion coefficient of the prepared FGr/Cu composite is as high as 1.444 cm~2 s^-1 at 100?,corresponding to the thermal conductivity of 497 W m^-1 K^-1,which is higher than the reported value of phonon-only thermal conductivity path.The thermal conductivity of FGr/Cu composite is 1.61 and 1.31 times higher than that of Cu at 100?and 150?respectively,and the thermal conductivity of FGr/Cu composite remains excellent and stable even at high temperature.(2)Electron tunneling heat transfer of modified graphene/copper matrix composites was further constructed.Explain the thermal properties of graphene/copper composites formed by introducing organic conjugated small molecule containing sulfur chemically linked molecules between graphene and copper from the perspective of heat conduction and thermal radiation.While the thiophenol molecular junction(TP-Gr)is introduced on the graphene surface,and the electrochemical deposition technique deposits copper particles on the substrate,the S-Cu bond is formed between thiophenol anchor groups and copper in the molecular junction.The highly delocalized aryl properties of thiol phenyl groups facilitate electron tunneling,thereby reducing the thermal contact resistance between the copper particles and graphene,which is helpful to the electron heat transfer in the TP-Gr/Cu composites.Compared with the blank sample of Cu matrix,the thermal conductivity of TP-Gr/Cu composite increases by42.6%to 500.6 W m^-1 K^-1.In thermal radiation,the heat is absorbed to activate the molecular vibration of TP-Gr The surface molecular/lattice motion acts as a micro cooling fan,leading to the good heat dissipation of TP-Gr/Cu composite coating.(3)Select and optimize appropriate organic conjugated small molecule chemical connections to construct the delocalized conjugate system in modified graphene,that is,design and construct the electron heat transfer of the delocalized p-?conjugate system:by conjugating non-equivalent sp~2 orbital of aniline group with delocalized large?bond on graphene,a delocalized p-?conjugate system is established and a new electron heat conduction path is constructed.The results suggest that the thermal conductivity of the copper matrix composite(PA-Gr-Cu)deposited by aniline-functionalized graphene(PA-Gr)is 506 W m^-1 K^-1,which is 30.8%and 44.2%higher than that of the graphene-Copper composite(Gr-Cu)and copper(Cu)respectively.When heating at the same heat source,the heat source temperature rises from 30?to210?in 5 minutes,and the surface temperature of PA-Gr-Cu grows rapidly to 198?,while that of Gr-Cu and Cu only increases to 88?and 59?respectively.The results show that aniline with a pair of lone electrons in N atoms,as the intermediate bridging molecule,has an advantage in the heat conduction of the delocalized p-?conjugated system between graphene and copper.(4)The effect of substituent electronic effect of chemically linked conjugated small molecules between graphene and copper on thermal conductivity of modified graphene/copper composites is discussed.That is,chemical covalent grafting on graphene contains both the benzoic acid molecular junction(BA-Gr),which contains the electron-absorbing substituent group,and the phenol molecular junction(PH-Gr),which contains the electron-donating substituents;and-COOH and-OH in the molecular junction combine with copper ions to form complexes.By pulsed electrochemical deposition,copper ions in these complexes are reduced to copper particles,which nucleate and grow on the copper matrix,and then uniformly deposit into dense modified graphene/copper composites that contains molecular junction.Compared with blank sample Cu matrix,the thermal conductivity of Gr/Cu composites only increases by 10.2%,BA-Gr/Cu composites increases by 29.1%to 453 W m^-1 K^-1,and PH-Gr/Cu composites increases by 44.7%up to 508 W m^-1 K^-1.The results suggest that at room temperature,compared with the unmodified graphene samples,the modified graphene can significantly increase the thermal conductivity of graphene/copper composite material due to the introduction of oxygen-containing molecular junctions;and compared with the molecular junctions containing electron-withdrawing substituents,the molecular junctions containing electron-donating substituents increase the electron density of graphene,which lead to electron doping and increase of the electron mobility in composite materials,and more significant contribution of electron heat transfer as well as a higher thermal conductivity of the composite.