Network Domain Structure in Viscoelastic Phase Separation

By solving a viscoelastic model of polymer solutions in two dimensions, we demonstrate that polymer-rich regions can form a spongelike network in deeply quenched cases. In late stages the velocity field is suppressed because the network supports stress and is rigid. As a result the domain size grows as $t^{1/3}$. In an early stage the polymer-rich regions are shrunken due to desorption of solvent, whereas in late stages they are elastically expanded perpendicularly to the interface in regions with relatively small curvature. The viscoelastic stress then cancels the stress due to the surface tension and stabilizes the network structure for a long time.