| dc.description.abstract | As a part of a larger effort towards the fundamental understanding of mechanical
behaviors of polymers toughened by nanoparticles, this dissertation focuses on the
structure-property relationship of epoxies modified with nano-sized poly(ethylene-altpropylene)-
b-poly(ethylene oxide) (PEP-PEO) block copolymer (BCP) micelle particles.
The amphiphilic BCP toughener was incorporated into a liquid epoxy resin and selfassembled
into well-dispersed 15 nm spherical micelle particles. The nano-sized BCP, at
5 wt% loading, can significantly improve the fracture toughness of epoxy (ca. 180%
improvement) without reducing modulus at room temperature and exhibits only a slight
drop (ca. 5 �C) in glass transition temperature (Tg). The toughening mechanisms were
found to be BCP micelle nanoparticle cavitation, followed by matrix shear banding,
which mainly accounted for the observed remarkable toughening effect. The unexpected
?nano-cavitation? phenomenon cannot be predicted by existing physical models. The
plausible causes for the observed nano-scale cavitation and other mechanical behaviors
may include the unique structural characteristics of BCP micelles and the influence from
the surrounding epoxy network, which is significantly modified by the epoxy-miscible
PEO block. Other mechanisms, such as crack tip blunting, may also play a role in the toughening. Structure-property relationships of this nano-domain modified polymer are
discussed. In addition, other important factors, such as strain rate dependence and matrix
crosslink density effect on toughening, have been investigated. This BCP toughening
approach and conventional rubber toughening techniques are compared. Insights on the
decoupling of modulus, toughness, and Tg for designing high performance thermosetting
materials with desirable physical and mechanical properties are discussed. | en |
