Strain rate effect on toughening of nano-sized PEP-PEO block copolymer modified epoxy
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A bisphenol A-based epoxy was modified with an amphiphilic poly(ethylene-alt-propylene)-b-poly(ethylene oxide) (PEP-PEO) block copolymer as a toughening agent. PEP-PEO molecules self-assemble into spherical micelles in epoxy with an average diameter of 15 nm and give rise to 180% improvement in fracture resistance. The fracture and tensile behaviors of the PEP-PEO-modified epoxy were investigated at loading rates ranging from 0.51 to 508 mm min-1. The toughened epoxy exhibits mechanical properties that are significantly more rate dependent than the neat epoxy material. As expected, a higher test rate leads to a more brittle behavior of the material and a lower fracture toughness value. With careful systematic study of their micromechanical deformation processes, the observed strain rate dependence is explained. The implications of the current findings on nano-sized rubber toughening of epoxy are also discussed in detail. 2009 Acta Materialia Inc.