The effect of fumed silica (SiO2) particles on the phase behavior of poly(methyl methacrylate) (PMMA)/poly(styrene-co-acrylonitrile) (SAN) blends was studied by using small angle laser light scattering (SALLS) and dynamic rheology.The phase diagram of PMMA/SAN blends unfilled and filled with SiO2 particles was obtained.The results revealed that the influence of SiO2 particles on the phase separation behavior of the blend matrix was related to the components of PMMA/SAN blends.Comparing with the 60/40(W/W) PMMA/SAN blends

the addition of a small amount of SiO2 particles could increase the phase-separation temperature (Ts) and could hardly result in the changes of phase separation mechanism

namely

both filled and unfilled blends obeyed the spinodal decomposition mechanism.However

for 30/70 PMMA/SAN blends

the addition of SiO2 particles decreases Ts.This phenomenon was attributed to the component difference between the surface of SiO2 particles and the matrix of PMMA/SAN blends.