Nano-Toughening of Epoxy Using Self-Assembled Block Copolymer Micelles
J. Liu, H-J Sue, Z.J. Thompson, F.S. Bates, M. Dettloff, G. Jacob
Texas A&M University, US
Keywords: epoxy, block copolymer, nanoparticle, toughening mechanism, nanocomposite
Abstract:Nanotechnologies present tremendous potentials for the polymer industry. Among the many possibilities, polymer nanocomposites that contain either inorganic nanoparticles or organic nano-domains, or both, exhibit many promising properties that are suitable for various engineering and microelectronic applications. However, fundamental knowledge on the nano-scale phenomena is still lacking. Significant efforts are still needed. In this presentation, focuses will be placed on our recent findings on epoxies toughened with nano-sized block copolymer micelle particles. An amphiphilic PEO-PEP block copolymer toughener was incorporated into a liquid epoxy resin and self-assembled into well-dispersed 15 nm spherical micelle particles. The nano-sized block copolymer at 5 wt% loading can significantly improve the fracture toughness of epoxy without causing reduction in modulus at room temperature and exhibits only a slight drop in glass transition temperature. The toughening mechanisms were investigated and found that the block copolymer micelle particles could cavitate to induce matrix shear banding, which mainly accounted for the observed remarkable toughening effect. The nano-cavitation of the 15 nm particles is believed to be the first reported in polymer toughening, which is far below the lower limit predicted by any existing physical models. A discussion is given on the unique nano-scale modification and toughening effects responsible for the attractive mechanical property improvements and other interesting phenomena (for instance, an enhanced strain rate effect). In addition, new results in toughening brittle nanocomposites containing inorganic nanoplatelets will be reported. Implication of the present findings for designing toughened polymers/nanocomposites will also be discussed.