Quantitative nanomechanical characterization of the van der Waals interfaces between carbon nanotubes and epoxy

Interfacial interactions between carbon nanotubes (CNTs) and polymer matrices play a critical role in the bulk mechanical performance of CNT-reinforced polymer nanocomposites, but their mechanisms remain elusive after over a decade of research. Here we present an in situ electron microscopy nanomechanical study of the non-covalent van der Waals interfaces between individual CNTs and epoxy resins in conjunction with atomistic simulations. By pulling out individual double-walled CNTs from Epon 828 films inside a high resolution electron microscope, the nanomechanical measurements capture the shear lag effect on CNT-epoxy interfaces. The maximum pull-out load of CNT-epoxy interfaces is found to be about 44% higher than the recently reported value for CNT-poly(methyl methacrylate) (PMMA) interfaces that were characterized using the same experimental technique and the same batch of dispersed CNTs. The higher interfacial strength of CNT-epoxy interfaces is partially attributed to the forced molecular deformations of aromatic rings in epoxy chains in the vicinity of the binding interface, which is supported by molecular dynamics simulations of the CNT-polymer interfacial interactions. The research findings contribute to a better understanding of the local load transfer on the tube-polymer interface and the tube's reinforcing mechanism, and ultimately the optimal design and performance of nanotube-reinforced polymer nanocomposites.