| The interfacial thermal resistance between inorganic filler and polymer matrix is the key factor to hinder the thermal conductivity of polymer composites.In this thesis,by using graphite carbon nanoparticles(GCPs)and graphene oxide(GO)and multilayer graphene(MLG)as thermal conductive filler,the benzoxazine resins and epoxy resin as polymer matrix,the graphitic nanocarbon based thermal conductive polymer composites are prepared.The effects of GCPs graphitization level of GCPs,alkyl functionalization of GO as well as epoxy impregnation of MLG paper,on the thermal conductivity of the polymer composites,are systematically investigated.Combining the effective medium theory,the interface thermal resistance between filler and matrix is estimated to explaining the limited performance of polymer composite.The main contributions are summarized as follows.The tunable lattice thermal conductivity of GCPs and their polymer composites are investigated by controlling the carbonizing temperature from 700 °C to 1300 °C.Transmission electron microscopy(TEM),X-ray diffraction(XRD)and Raman spectra confirm that both the in-plane(La)and out-of-plane(Lc)coherence lengths of GCPs increase with carbonization temperature in the range of 700 °C to 1300 °C.The intrinsic TC of GCPs film is directly extracted from the dependence of the Raman G peak frequency on the excitation laser power(δω/δP)and the first order temperature coefficient(χG).It is found that the in-plane lattice TC increases exponentially with both of the increasing La and decreasing defect concentration.The GCPs are then used as highly processible fillers to fabricate thermoset composites based on reactive benzoxazine(BA-a).The total TC of the poly(BA-a)/GCPs are found increase monotonically from 0.27 W?m-1?K-1 to 0.34 W?m-1?K-1 with the increasing graphitization levels of GCPs,and a clear signature of thermal percolation threshold at 6% GCPs loadings is also observed.Alkylated graphene,C4-G and C16-G,are prepared via nucleophilic addition reaction of the carboxyl and epoxide group on the graphene oxide(GO)with the bromobutane and hexadecane,respectively.TEM,atomic force microscope(AFM),Raman spectroscopy,Fourier transform infrared spectroscopy(FT-IR),and fluorescence spectra confirm that the alkylation is accompanied by reduction reaction of GO.The thermal conductivity of alkylated graphene are evaluated by the dependence of the Raman G peak frequency on the excitation laser power,δω/δP.Alkylated graphene/epoxy resin composites are prepared by solution blending and thermal curing process,and the TC are determined by the transient hot-wire method.The TC enhancement factor of epoxy composite resins filling with GO,C4-G and C16-G,are calculated to be 6%,12% and 19%,respectively.Effective medium approximation(EMA)model calculation shows that,compared with GO,the interfacial thermal resistance(Rb)values of epoxy composite resin filling with C4-G and C16-G decreases by 7.6% and 3.1%,respectively.In addition,the thermal conductivity of the composite are found increases with temperature from room temperature to 90 °C.The graphene paper with a thickness of 100 m and a size of 50 mm has been prepared via solution filtration self-assembly method by using the 5 nm-thick multi-layer graphene(MLG)as building blocks.The δω/δP and the first order temperature coefficient of G phonon frequency of MLG paper,which are obtained by the temperature dependent and heating power dependent Raman speactra,are-0.019 cm-1?K-1 and-0.1125 cm-1?m?W-1,and hence the TC is calculated to be 167.47 W?m-1?K-1.The graphene paper is impregnated with epoxy resin solution,and finally the adsorption weight of epoxy resin is estimated to be 10%~30% against with graphene paper.When the adsorption weight of epoxy resin increases,the TC value of the graphene paper decreases rapidly.Only the TC values of 35.51 W?m-1?K-1 of MLG paper is presented when absorbing 30% of epoxy resin.The interfacial thermal resistance between MLG and adsorption epoxy resin extracted by EMA model is 1×10-13 m2?K?W-1. |
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