| Electronic devices have become an indispensable part of our daily life.Electronic devices are becoming miniaturized,integrated,high-frequency and multifunctional,and their power density and heat production per unit volume are increasing significantly.If the heat conduction system of the device is not perfect,the heat cannot be diffused out in time,and the working temperature of the electronic device will rise rapidly,affecting the service performance,reliability,safety and service life of the device.At present,most of the thermal interface materials studied are filled thermal conductivity composites,whose performance depends on the dispersion and interface interaction of the enhancement phase/functional phase.Chemical modification of thermal conductivity filler can greatly improve the agglomeration of nano-filler in the matrix,establish more effective thermal conductivity network,and improve the interface interaction between thermal conductivity filler and resin.Reduce the phonon scattering at the interface and improve the thermal conductivity of the thermal conductive composites.Due to the large specific surface area and high surface energy of inorganic fillers,it is inevitable that the filler is easy to agglomerate.Existing studies have shown that the thermal conductivity of composites is related to the dispersion state of the fillers when the content of the filler is fixed.The chemical modification of the thermal conductive packing particles will bring about the change of the dispersion state of the packing,the change of the interface thermal resistance and the change of the intrinsic thermal conductivity of the packing.These three aspects have been proved to have an impact on the thermal conductivity of composite materials,so it is difficult to study the influence of a single factor of interface thermal resistance on the thermal conductivity of composite materials.In this paper,Cu F/epoxy resin composites were prepared using mercaptoacetic acid and mercaptoethane to modify copper foam（Cu F）.The effects of interfacial chemical bond between filler and matrix resin and grafting density on thermal conductivity of epoxy resin composites were studied.In addition,by introducing a second thermal conductivity filler into the weak thermal conductivity cavity region of the copper foam composite,we also studied the network construction ability of different dimensions of the filler and the synergistic effect of the copper foam in the dominant thermal network and the secondary network of the second filler on the thermal conductivity of the composite.The main research contents of this paper are as follows:1.Copper foam/epoxy resin composites,thioglycolic acid modified copper foam/epoxy resin composites and mercaptoethane modified copper foam/epoxy resin composites with a filling capacity of 6.3 vol.%were prepared by vacuum impregnation method.The relationship between the types of surface modified molecules and the modification process with different graft densities on the thermal conductivity,mechanical properties and thermal management properties of the composites was studied.In the experiment,the density of covalent bond between copper foam and epoxy resin was determined by DSC test of the reaction enthalpy peak intensity.The results of FTIR and XPS showed that the mercaptogroup of mercaptoacetic acid could interact with copper,while the carboxyl group could form covalent bond with epoxy resin matrix.The thermal conductivity of thioglycolic modified copper foam/epoxy resin composites increased with the increase of graft density.When the grafting amount of thioglycolic acid was 0.45%,the thermal conductivity of copper foam/epoxy resin composites reached 1.696 W/m·K.At the same time,when there is no covalent bond interaction between copper foam and matrix resin,mercaptoethane modified copper foam/epoxy resin has little effect on thermal conductivity.Copper foam/epoxy resin composites modified by thioglycolic acid showed better thermal management performance in heat dissipation experiments.2.6.3 vol.%Cu F was used as the main thermal conductivity network,and spherical alumina（S-Al2O3）,hexagonal boron nitride（h-BN）,silver nanowires（Ag NWs）and multi-walled carbon nanotubes（MWCNT）were used as fillers to construct secondary networks in epoxy resin cavities.Four kinds of EP/Cu F/S-Al2O3,EP/Cu F/h-BN,EP/Cu F/Ag NWs and EP/Cu F/MWCNT composites with bi-scale interpenetrating structures were prepared by vacuum perfusion.The effects of microstructure formation of S-Al2O3,h-BN,Ag NWs and MWCNT in copper foam pores and the interaction of copper foam on thermal conductivity of copper foam/epoxy resin composites were investigated.The results show that the formation of the secondary network is closely related to the shape of the filler,and the thermal conductivity of the EP/Cu F/Ag NWs composite reaches 2.264 W/m·K under the same volume fraction（1vol.%）of the second filler.The ability of one-dimensional nano-filler Ag NWs and MWCNT to form secondary thermal conductivity network is better than that of two-dimensional micron h-BN and zero-dimensional micron S-Al2O3 at the same filling quantity.In addition,the formation of thermal conductivity path is related to the dispersion state of the fillers.For nano fillers Ag NWs and MWCNT,although the intrinsic thermal conductivity of MWCNT is higher than that of Ag NWs,the formation of secondary networks is seriously affected by the serious agglomeration phenomenon of MWCNT in the matrix resin,and the improvement of thermal conductivity of composites is limited.The thermal conductivity of EP/Cu F/2 vol.%Ag NWs composite is 2.536 W/m·K,which is 35%higher than that of EP/Cu F/2 vol.%MWCNT composite.In addition,the thermal conductivity of EP/Cu F/Ag NWs composites is higher than that of EP/Cu F/MWCNT composites under the same volume fraction load of the second filler,which may be due to the smaller thermal resistance of the metal-to-metal interface.The EP/Cu F/2 vol.%Ag NWs composites showed the best thermal management performance during both heating and cooling. |
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