Plasticizing and Reinforcing Features of Siloxane Domains in Amine-Cured Epoxy/Silica Hybrids

Organic/inorganic hybrid materials comprising an amine-epoxide network and siloxane domains are produced by the sol/gel method. The presence of both plasticizing flexible linear siloxane sequences and reinforcing nanosized silica particles and branched silsesquioxanes (SSQO) structures is confirmed by Si-29 NMR and SAXS analysis. The hybrids display simultaneously a monotonical reduction in Tg and an increase in rubbery plateau modulus with increasing siloxane content. At the same time, nanoindentation tests reveal an improved resistance to plastic deformation. The effect of siloxane content on the values of the rubbery plateau modulus is evaluated through the EBM model for blends and composites exhibiting the characteristic co-continuity of the two constituent phases.