Nano-scale characterization of fracture surfaces of blended epoxy resins related to fracture properties

The fracture surface morphologies of epoxy resins with different macromolecular structures created by blending two epoxy monomers with different molecular weights (Epikote 828 and Epikote 1001) were characterized using atomic force microscopy with different sampling intervals. A measured fracture surface parameter (roughness ratio, Sdr) was quantitatively analyzed from the topographic images and then correlated to the measured fracture energy, GIC. The fracture energy increased with the content of Epikote 1001 monomer, ϕ. The nano-scale surface roughness strongly depended on ϕ, meaning that each epoxy resin can be considered to have a different material structure in several nano-scales; heterogeneity, network or crosslink, which can be observed at higher resolution, 6 nm for 3 × 3 μm2 scanning area, and 2 nm for 1 × 1 μm2 scanning area. The fracture property is thus sensitive to the observed nano-structure whereas the glassy modulus is not. Therefore, the combination of the viscoelastic and fracture properties can be tailored by changing the network or crosslink structure by blending monomers with different molecular weights.