Structural adhesives are increasingly used for bonding components within critical load bearing engineering structures such as aerospace and automotives. Typically these adhesives are based on epoxy polymers. Epoxies are inherently brittle due to their homogeneous microstructure and highly cross linked nature. Thus, there has been much research focused on improving the fracture toughness of epoxy polymers by incorporating a second minority phase at the nano-scale. These modifiers fall into one of two main categories: inorganic additives, e.g. silica [1,2], glass [3], alumina [4], nano-clays [5] and carbon nanotubes [6,7] or organic, usually rubber particles. Rubbery additives can be either core–shell rubber particles [8–10] or can form during curing via reaction induced phase separation mechanisms [11,12]. The primary energy dissipation mechanisms for rubber toughened epoxies are known to be both plastic void growth and shear band development [13]. It has also been shown that a combination of the above additives to create a hybrid material can provide synergistic toughening effects, e.g. carbon nanotubes and silica nanoparticles [14] or rubber with silica nanoparticles [15–17].
