Block Copolymer and Nanosilica-Modified Epoxy Nanocomposites

The effects of nanoscale silica particle additives on the tensile properties of neat and poly(ethylene-alt-propylene)-b-poly(ethylene oxide) block copolymer (BCP)-modified epoxies were evaluated. Nanosilica and BCP modifiers were dispersed both individually and together in epoxy formulations. The nanosilica formed a stable dispersion, and BCP modifiers formed well-dispersed spherical micelle nanostructures in the matrix. When both additives were used, BCP micelles were observed to adsorb on nanosilica surfaces, resulting in limited aggregation of nanosilica particles. Tensile tests on bulk specimens showed that the addition of nanosilica to both neat and BCP-modified epoxy formulations increased the modulus of the composites. Compact tension tests also revealed increases in the critical stress intensity factor, KIc, and critical strain energy release rate, GIc, in both the block copolymer and nanosilica-modified epoxies. Combining both additives in the epoxy enhanced toughness beyond that obtained with the individually modified formulations. Increasing nanosilica loading up to 25 wt % produced a monotonic increase in the modulus and GIc. The nanocomposite with 25 wt % nanosilica reached an optimal level of toughness at low BCP concentrations (ca. 4 wt %). Scanning electron micrographs obtained from fracture surfaces revealed topological features indicative of micelle cavitation and nanosilica debonding, toughening mechanisms that operate in concert.