The Study Of Molecular Simulation On The Interface Of Carbon Fiber/ Epoxy Resin

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. Studying in the interfacial micro-structure by traditional experiment methods is difficult and has its limitation. Therefore, the molecular simulation shows its particular advantages because it can visualize the micro-structure of materials to investigators so as to bring a lot of convenience. In this paper, the interfacial structure and interfacial energy between carbon fibers and epoxy resin were studied by molecular simulation.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 single epoxy molecular and carbon fibers were also built. The molecular dynamic simulation was applied that epoxy molecule was adsorbed on the surface of carbon fibers, and then the interaction energy of interface was calculated to study the effect of carbon fibers with different graft ratio of functional groups on the interaction energy of interface. The results showed that the main force to drive the epoxy molecule adsorbed on the carber fiber surface was the Vander Waals force. 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 best interaction engery can be achieved.Furthermore, the interfacial models of epoxy resin/carbon fiber composites mimicing the real situation were built and analyzed by the molecular dynamic simulation. The results indicated that the interface was relatively stable when the graft ratio of hydroxyl groups was 2.600 per nm2, and the lowest interaction energy of interface happened at the graft ratio with 23.400 per nm2. When the graft ratio of amino groups was 23.400 per nm2, there was the lowest interaction energy which was further lower than those at the other graft ratios. From the result of dynamic simulation on the interface models of carbon fibers and epoxy resins, interfacial shear models were constructed from optimum interface models. In the shear process, the relationship of interfacial shear energy and the graft ratio of functional groups was discussed. The results indicated that the graft ratio of functional groups can not be too big because of the effect of micro-mechanical interlocking and atomic level interactions on the interfacial shear energy so that the outstanding interfacial performance was difficult to be achieved. In summary, the final result demonstrates the stable interface structure exists at the graft ratio of 2.600 per nm2.