Multi-layer Assembly On Pitch-based Carbon Fiber Surface And Study On Interfacial Properties And Thermal Conductivity Of Their Composites

Structure/function integrated interphase of pitch-based carbon fiber composites has become a research hotspot recently.The interphase of their composites not only affects stress transfer between resin matrix and pitch-based carbon fiber（PCF）,acting as a"bridge",but also influences phonons transmission and loss between resin and PCF.So,the macro-mechanical properties and thermal conductivity of composites are directly determined by the structure and performance of interphase.However,ordinary covalent modification would damage intrinsic properties of PCF and the composites have upper interfacial thermal resistance.In view of these problems,a method of constructing three-layers assembly of perylene-diimide（PDI）/graphene（GN）/perylene-diimide on PCF surface was established.Meanwhile,the enhancement mechanism of interfacial properties and thermal conductivity of composites were proposed based on the design and control of multi-layer assembly of polycyclic aromatic compound/carbon nanoparticles,and the construction of structural/functional interphase was realized.（1）Amino terminated perylene-diimide molecules was designed and three kinds of suspensions-PDI_c-20 suspension（20 mg/ml）,GN stabilized suspension（0.2 mg/ml）and PDI_c-5 protonated suspension（5 mg/ml,p H≈9）were prepared.PCF-desized was impregnated with above suspensions in-turn,modifying by multi-layer assembly,and then PCF-GN,PCF-PDI,PCF-PDI/GN and PCF-PDI/GN/PDI were achieved to explore the effect of multi-layer assembly on the physical and chemical properties of PCFs.Compared with PCF-desized and PCF-GN,the surface chemical activity and specific surface area of PCF-PDI,PCF-PDI/GN,and PCF-PDI/GN/PDI were improved,owing to the construction of PDI nanowire assemblies,PDI/GN wrinkled nano-assemblies,and PDI/GN/PDI cicada-wing nano-assemblies.The mechanism of multi-layer assembly of polycyclic aromatic compound/carbon nanoparticles was proposed as follows:Under the action of dual non-covalent bonding ofπ-πstacking and hydrogen bonding,perylene-diimide and GN were promoted to be assembled on PCF surface layer by layer.（2）Epoxy resin was utilized as the matrix to achieve the unidirectional and bundled composites of PCF-desized/EP,PCF-GN/EP,PCF-PDI/EP,PCF-PDI/GN/EP and PCF-PDI/GN/PDI/EP and the interfacial properties and thermal conductivity of above composites were investigated.Compared with PCF-desized/EP composites,ILSS and TFBT strength of PCF-PDI/GN/PDI/EP composite had the greatest enhancement,which were increased by 29.49%and307.94%,respectively.Based on the microstructure,the change of carbon element and modulus of interphase,the enhancement mechanism of interphase was proposed as follows:PDI/GN/PDI three-layer assembly had the dual functions of crack inhibition by PDI assembly and interphase rigidity increase by PDI/GN assembly and promoted the enhancement of interfacial bonding strength.Meanwhile,PCF-PDI/GN/PDI/EP unidirectional composite had the highest thermal conductivity and the lowest thermal resistance,and the mechanisms of thermal conductivity were put forward as follows:PDI/GN/PDI tri-layer assembly not only improved the interfacial compatibility between PCF and EP,which reduced the interfacial thermal resistance of composites,but also formed the thermal conductivity pathways to promote the effective transfer of phonons.