The influence of hydrophilic SiO2 nanoparticles on the stability of co-continuous structure in poly(methyl methacrylate)/polystyrene (PMMA/PS) blends under quiescent melt annealing was investigated.It was found that the filled blends displayed broader co-continuous interval and less coarsened structure than those of unfilled blends after annealing.The result indicated that the morphological stability of co-continuous blends can be improved effectively by the addition of SiO2 nanoparticles.Rheological measurements showed that the viscosity and elasticity of filled PMMA/PS blends

which were associated with the destruction process of the co-continuous structure such as breakup or retraction

were enhanced significantly.The influence of the change in the viscoelasticity and interfacial tension of blends upon the addition of SiO2 nanoparticle was analyzed qualitatively based on two available theories describing the coarsening process of the co-continuous structure of polymer blends.It was proposed that the change in the viscoelastic properties of PMMA/PS blends instead of the interfacial tension plays a dominant role in the coarsening rate of the co-continuous structure during the quiescent annealing in melt state.