STUDY OF EPOXY-RESIN FOR CRYOGENIC USE BY POSITRON-ANNIHILATION METHOD

The molecular state of epoxy resins for cryogenic use has been studied in terms of positron lifetime measurement. The addition of plasticize r increased the free volume in the epoxy and hence the ductility of th e epoxy at room temperature was increased. The fracture toughness at c ryogenic temperatures, however, decreased. The increase of molecular w eight between crosslinks decreased the free volume in the epoxy at roo m temperature and increased the fracture toughness slightly at cryogen ic temperature. Based on the data the molecular state model desired fo r cryogenic application was proposed and the nano-sized silica dispers ed epoxy was prepared by means of sol-gel method to follow the model. The cryogenic properties of the silica dispersed epoxy and the free vo lume evaluated by positron annihilation lifetime were also discussed.