The Influence of Epoxy Functionalized Silica Nanoparticles on Stress Dispersion and Crack Resistance in Epoxy-Based Hybrids

The article presents synthesis, characterization, mechanical properties and fracture behavior of the epoxy polymers reinforced with either pristine or epoxy functionalized silica nanoparticles. The nanoscale silica is prepared and functionalized in situ via acidic hydrolysis and pre-organization of different alkoxysilane precursors into the epoxy monomers. It is demonstrated that epoxide functionalization of silica nanoparticles not only improves their distribution in the epoxy polymer, but simultaneously enhances the strength [>60%], Young's modulus [>85%] and tensile toughness [>56%] of the resulting hybrids, without adversely affecting their ductility [<7%], even at 15 phr silica loading. The atomic force micrographs of the 'stress fractured' hybrid surfaces reveal that stronger interfacial interactions lead to the effective dispersal of stress and offer efficient resistance to crack propagation. Furthermore, different types of fracture mechanisms are investigated and it is evidenced that crack deflection is the most likely mechanism contributing to the improved mechanical performance of these hybrid epoxy/silica polymers.