Relationship Between Fracture Toughness and Domain Size of Liquid-Crystalline Epoxy Resins Having Polydomain Structure

A liquid-crystalline (LC) epoxy resin was cured at different temperatures and some types of curing systems having different phase structures (isotropic or polydomain, which have a microscopically ordered LC network structure) were obtained. The diameters of each domain in the polydomain system changed from the small to the larger size. The diameters of the LC domains were evaluated using a polarized optical microscope and the polarized microscopy FTIR mapping method. These systems were used to investigate the relationship between the network arrangement and mechanical properties. The fracture toughness of the cured systems was related to the enlargement of the ordered area in the network structures. With the toughness improvement, the meandering cracks were observed at the fracture surfaces. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 156-165, 2009