The effect of morphology on the optical properties of transparent epoxy/montmorillonite composites

Three kinds of epoxy-based transparent nanocomposites were prepared by the reaction of alkylammonium-exchanged montmorillonite (AMT) with diglycidyl ether of bisphenol A (DGEBA) and triethylamine as the curing agent. The morphology of these composites was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The effect of morphology on the optical transparency of epoxy/AMT composites (Ep/AMT) was investigated. The light transmittance of Ep/AMT depended greatly on the exfoliation degree (ED) of AMT in the epoxy matrix, and the transmittance of the composites with higher ED was notably higher than that with lower ED under the same AMT content. The light transmittance of composites prepared with different amounts of curing agent was also studied. Results suggested that the composites prepared with insufficient curing agent were more transparent than those prepared with stoichiometric and higher contents of curing agent because insufficient curing agent was benefitial to the exfoliation of AMT. An equation describes the relationship of the light transmittance of nanocomposites with the concentration, particle size and basal spacing of AMT as well as the wavelength. Theoretical analysis suggested that the effect of morphology on the transparence mainly comes from the changes of the particle size and basal spacing of AMT, and that the effect of the former is more significant than that of the latter (C) 2003 Society of Chemical Industry.