Study On The Preparation And Thermal Conductivity Of Graphene-based Films By Moderate Process

Nowadays,people are increasingly dependent on small-sized,versatile electronic products for convenience and comfort.In order to remove the excessive heat generated by electrical components in a timely manner,the use of carbon-based film materials with high thermal conductivity in thermal management is an important approach.Although the diamond film has high thermal conductivity,it is hard and fragile,making it difficult to process.Furthermore,the synthesis of diamond film requires high temperature and this process is costly.Besides,the raw materials of graphite film with high thermal conductivity is expensive,and the technology is subjected to foreign countries.At the same time,the temperature is very high during the production.At present,graphene is the two-dimensional material with the highest thermal conductivity,and its macroscopic film is the most promising heat transfer material in the field of thermal management.The oxidation-reduction method makes low-cost and large-scale preparation of graphene films feasible,but the thermal conductivity of films is greatly affected by the heat reduction temperature and the structural integrity of graphene sheets.Previous studies have focused on high temperature thermal reduction and macro-molecular nitrogen-containing organic polymers to repair graphene defects,which cause problems such as harsh operating condition,high cost,and pollution of nitrogen compounds.Therefore,in order to overcome these disadvantages,this paper proposes a new idea of“moderate process thermal reduction”and“green small-molecule without N and other hetero atom organic compounds to repair graphene defects”to prepare graphene film materials with high thermal conductivity.In the preparation of graphene oxide(GO)film,the“two-step”modified Hummers method was used to prepare GO water dispersion,and the GO film was obtained by vacuum filtration.It demonstrated that GO nanosheet has a single-layer structure with a large number of oxygen-containing functional groups,mainly composed of-C-O groups.The ratio of carbon-oxide atomic(C/O)and interlayer spacing of the GO film are 3.03 and 0.804 nm,respectively.Most of the oxygen-containing functional groups in the GO can be removed during thermal decomposition above 400~oC.In terms of moderate thermal reduction,the effect of temperature(400~800 ~oC)on the thermal conductivity of reduced graphene oxide(RGO)films was systematically investigated.With the increase of temperature,the metallic luster of RGO film becomes more obvious,and the oxygen content of RGO film is lower,and the interlayer spacing of RGO film is smaller.When thermally reduced at 600 ~oC,RGO600 film has the best overall morphology,the least defects,and the largest sp~2 hybrid carbon crystallite size(L_a=18.14nm).Therefore,the in-plane thermal conductivity of RGO600 film reaches a maximum of 703 W/(m·K).As for defect repair,the“glucose”was selected as the defect repair agent to enhance the thermal conductivity of graphene films under moderate process conditions.Graphene oxide-glucose(GO-glu)composite film was prepared by the evaporation solvent method,which could control the amount of glucose,and the modified graphene(m-Gr)film was obtained by reduction at 600 ~oC.When the mass ratio of GO to glucose is 10:2,the m-Gr10-2film has the most flat surface and better layered structure.Also,the m-Gr10-2 film has the least defects and the largest sp~2 hybrid carbon crystallite size(L_a=18.31 nm).Therefore,the m-Gr10-2 film has the highest in-plane thermal conductivity of 1006 W/(m·K).