B. Demir, T.R. Walsh
Keywords: carbon fiber, epoxy, composite, surface grafting
Summary:Due to their promising properties as light-weighting materials in, e.g. the aerospace industry, carbon fiber reinforced polymer (CFRP) composites are the subject of intense scrutiny. Of particular interest is the structure/property relationship arising from the polymer matrix interphase, which strongly influences the mechanical properties of the material. Investigating the molecular-level structural details of the polymer at the fiber-to-matrix interface using experimental techniques alone can be challenging. Here, molecular dynamics (MD) simulations can complement experiments, to bridge these knowledge gaps. Results obtained via MD simulations can be compared to experimental results, to enable advances in our search for composite materials with superior properties. Here, we investigate a well-studied epoxy polymer, EPON-862/DETDA, to create a CFRP composite model. To do this, a reliable in-situ cross-linking procedure is developed, which enables us to model the formation of epoxy cross-links in the presence of CF surface. We consider a surface-grafted molecule to functionalize the CF surface that was proposed and tested by our experimental partners. This grafted molecule can react with the EPON during the curing process. To systematically evaluate the effects of surface functionalization, we study four different systems: (1) the pure epoxy polymer, (2) epoxy CFRP with a bare graphene surface, (3) CFRP with a functionalized surface that is not reactive with EPON, and (4) CFRP with a functionalized surface, that can form covalent bonds with EPON. Our investigation has a twofold purpose. First, the effect of the presence of the CF surface on the mechanical properties of the CFRP is investigated. Second, the structure of the grafted molecule is investigated to elucidate its beneficial effect on the mechanical performance of the composite. Our findings provide a platform for the systematic and knowledge-based design and testing of CF surface treatments for generating new CFRPs with superior properties.