Previously developed nano-epoxy matrices with reduced viscosity showed both substantially enhanced mechanical properties and interfacial adhesion with ultra-high molecular weight polyethylene ( UHMWPE) fibers vis-a-vis pure epoxy. In this work, mechanisms for the improvement in the interfacial adhesion were investigated. Atomic Force Microscopy and Energy Dispersive X-ray with Scanning Electron Microscopy analyses indicated that improved performance of the UHMWPE fiber composites with the nano-epoxy containing reactive graphitic nanofibers (r-GNFs) is attributed to mechanical interlocking and a diffusion mechanism. The nano-epoxy with the 'liquid nano-reinforcement' resulting in reduced viscosity provided better wettability, diffusion capability and reinforcing effect, which produced an effective improvement in the adhesion properties. (C) Koninklijke Brill NV, Leiden, 2009