Study of Interaction between Epoxy Molecules and Carbon Fiber Surface with Molecular Simulation
|School||Harbin Institute of Technology|
|Course||Polymer Chemistry and Physics|
|Keywords||molecular simulation carbon fiber interfacial interaction energy graft ratio interface shear|
Interface is an important micro-structure to connect fibers and polymer matrices in composite materials. It makes a vital role to decide the mechinical properties of composites. In this paper, the interfacial structure and interfacial interaction energy between carbon fibers and epoxy molecules were studied by molecular simulation, and the shear behavior between carbon fibers and epoxy molecules were studied with modified shear model.Firstly, the surface structure of carbon fibers was designed from cleaved graphite layer on the molecule level. The carbon fiber models were built with the different graft ratio of hydroxyl groups and amino groups, and the interfacial models between the epoxy molecules and carbon fibers were also built.The molecular dynamic simulation was applied that epoxy molecules was adsorbed on the surface of carbon fibers, and then the change of energy was calculated to study the elements of interfacial energy. The results showed that the interfacial energy comprised the interaction of epoxy molecules /carbon atoms of the fiber surface and the interaction of epoxy molecules /the functional group grafted on fiber surface. They codetermined the value of interfacial energy. The two parts of interaction energy changed with graft ratio of functional group contrarily. The optimized graft ratio exited when interaction energy was lowest.Based on the interaction energy comparisons between the different interfacial models, the functional groups took the main role on the interfacial intensity. Besides, the optimized graft ratio of different functional groups exists so that the lowest interaction engery can be achieved. The type and chain length of the functional group also have effect on the interfacial energy.Furthermore, the interfacial shear models of epoxy molecules/carbon fiber composites similar to the real situation were analyzed by the molecular dynamic simulation. In the shear process, the relationship of interfacial shear energy and the graft ratio of functional groups was discussed. The results of non-dynamic simulation under non-periodical boundary condition indicated that the shearing energy was highest when the graft ratio of amido groups was 1.300 and 2.600 per nm2, interface was relatively stable than those at the other graft ratio. From the result of sub-dynamic simulation under periodical boundary condition, the results proved that the fastest shear velocity was lowest when the graft ratio of amido groups was 2.600 and 3.900 per nm2, interface was relatively stable than those at the other graft ratio. In summary, the final result demonstrates the stable interface structure existed at the graft ratio of 2.600 per nm2.