Influence of the curing temperature on the structure of epoxy/rectorite nanocomposites studied by positrons

The epoxy-rectorite nanocomposites were prepared at different curing temperature ranged from 70 °C to 200 °C and the effects of curing temperature on microstructure of material have been studied by positron annihilation lifetime spectroscopy (PALS), and X-ray diffraction (XRD). The XRD patterns show that the intercalated structure existed in the samples cured at 70 °C and 90 °C, and the clay platelets were completely exfoliated while the curing temperature is higher than 110 °C. At low rectorite content the Ps is mainly formed and annihilated in the free volume of the epoxy matrix and the average size of the free volume is essentially unchanged with the curing temperature. With the increasing curing temperature from 70 °C to 110 °C, the dramatic increase in the intensity I2 of second lifetime component indicates the formation of interfacial layers between rectorite and epoxy matrix. The distributions of o-Ps lifetime and the free volume size have the narrowest distribution for the samples cured at temperature 110 °C and 140 °C, which imply the most homogeneous structure existed in the nanocomposites. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)