Study On Design And Performances Of Three-Dimensional Thermally Conductive Graphene Based Polymer Composites

In recent years,with the rapid development of the emerging electronics industries,it has put forward higher requirements for the performance of materials.With the unique advantages,polymer composites play an important role in many fields.However,the low intrinsic thermal conductivity of polymers severely limits their further development in high-tech fields.Thus,on the basis of ensuring good comprehensive performances,maximizing the thermal conductivity of polymer composites has become the key to promoting the development of the electronics industries.So far,researchers have obtained many significant achievements in enhancing the thermal conductive performance of polymer composites.But,existing materials cannot fully meet the development requirements.In order to maximize the thermal conductive enhancement efficiency of fillers,graphene oxide with high thermal conductivity has been designed and constructed to 3D aligned heat conduction networks for polymer composites.And the effects of different skeleton structures on performances of polymer composites were also systematically studied.Firstly,in order to construct a highly oriented 3D thermally conductive framework,a unidirectionally oriented graphene-based aerogel was prepared by using interface self-assembly and unidirectional freezing casting technology.The aerogel acted as a thermally conductive skeleton,was introduced into polydimethylsiloxane（PDMS）to prepared polymer nanocomposites with low filler content.The results showed that the graphene-based aerogel combined‘soft’and‘hard’components,exhibiting unique mechanical properties;its polymer composites showed an anisotropic thermal conductivity,and the thermal conductivity of nanocomposites along the orientation direction was higher than that of pure PDMS increased by 448%at the skeleton content of 1 vol.%.The nanocomposites also exhibited promising applications as thermal interface materials in LED device.This strategy offers new insights into the design and fabrication of 3D multifunctional graphene aerogels.Secondly,in order to further improve the thermal conductivity of the polymer composites,a thermal conductive carbon nanotubes-based skeleton with long-range ordered microstructures was developed in alkaline conditions,assisted by a combined drying method.After the incorporation of the skeleton into polydimethylsiloxane resin,wood annual ring structured composites were prepared and they can exhibit a through-plane thermal conductivity enhancement of～744%at a low skeleton content of 6.0 vol.%.In addition,the excellent resilience of the composites is still maintained.The infrared thermal imaging results demonstrated that the polymer composites have high potential in thermal management applications.Thirdly,the effect of 3D skeletons on thermal conductivity of polymer composites can be affect by the density,pore size and orientation structures.In order to make up for the disadvantages of a single skeleton structure,a 3D radially aligned graphene skeleton was constructed by using radial freeze-casting,and was then introduced into the PDMS matrix with the second filler（MXene）to prepare a hybrid-filler polymer composite.The results show that compared with pure PDMS,the cross-plane and in-plane thermal conductivities of the composites were increased respectively by1420%and 1000%at 1.05 vol.%skeleton loading and 3.3 vol.%MXene loading,exhibiting significant anisotropy.The simulation results indicated the synergistic effect between graphene skeleton and MXene on improving thermal conductivity of polymer composites.In addition,the composites maintained good mechanical and electrical properties,which shows great potential applications in the fields of thermal management and sensing.Finally,the anisotropy of the 3D thermally conductive network could lead to a poor thermal conductivity in the direction perpendicular to the alignement of the network.Reducing the anisotropy of the skeleton can solve this problem.Inspired by the structure of spider webs in nature,a highly oriented 3D concentric-ring structured GO hydrogel was prepared by hydrothermal reaction in alkaline environment based on the characteristic of GO liquid crystals.With the help of radial freeze casting,the concentric ring structure was constructed into a 3D spider web-like graphene skeleton.The skeleton was introduced into paraffin wax to obtained phase change material（PCM）.The results showed that the graphene skeleton can hardly affect phase change behavior of paraffin wax.The PCM exhibited good thermal stability due to the role of3D graphene framework.In addition,the longitudinal and transverse thermal conductivity of the PCM can respectively reach 2.58 W·m^-1 K^-1 and 1.78 W·m^-1K^-1 at2.25 vol.%skeleton loading,which much higher than those of composites with unidirectional graphene network.The PCM also exhibited promising applications in battery thermal management.