Investigation of phase separation in a partially miscible polymer blend by rheology

The phase boundary and phase-separation dynamics of a binary poly(styrene-co-maleic anhydride)/poly(methyl methacrylate) blend have been investigated by rheological measurements and light scattering. The phase diagram was experimentally established by rheology, in which the binodal line was obtained by dynamic temperature ramps and the spinodal temperatures were quantitatively estimated on the basis of the theory developed by Ajji et al. The phase-separation dynamics from rheological viewpoints have been further investigated on the basis of the obtained phase diagram. Rheological measurements can sensitively detect the rather early stages of phase separation compared with light scattering techniques. It was found that the dynamic storage modulus initially increases over time and subsequently decreases during nucleation and growth; on the other hand, it always decreased over time during spinodal decomposition. Compared with light scattering techniques, rheological measurements were found to be relatively reliable for probing phase-separation mechanisms.