Viscoelastic phase separation in polymer blends.

In this paper, the dynamics and morphology of viscoelastic phase separation in polymer blends is investigated based on the two-fluid model in two dimensions. At critical composition, we have carefully checked the role of shear modulus, without taking account of bulk modulus. The results show that the higher shear modulus component tends to form a dispersed phase in the intermediate stage of phase separation, if the difference between the shear moduli of the components is large enough. This is opposite to the role of bulk modulus, that the higher bulk modulus component forms a networklike pattern without taking account of the shear modulus even if it is the minority phase. The morphological formation is determined by the competition of opposite effects of shear modulus and bulk modulus. For polymer blends at critical composition, the bulk modulus difference leads to a networklike pattern formed by the higher modulus component in the intermediate stage of phase separation. But if the difference between the shear moduli of the components is large enough, a co-continuous structure is observed, resulting from the competition between shear and bulk moduli. For off-critical composition, difference in bulk modulus also leads to a networklike pattern of the component with higher bulk modulus in the intermediate stage of phase separation, but phase inversion is observed rapidly. A small difference between the shear moduli of the components can support the networklike pattern to continue for longer time. But the networklike pattern does not occur for large difference between shear moduli.