Universality of Viscoelastic Phase Separation in Dynamically Asymmetric Fluid Mixtures

We demonstrate here the possibility that strong dynamic asymmetry between two components of a fluid mixture generally leads to unusual phase separation (``viscoelastic phase separation''), which does not belong to the conventional classification of phase separation. In addition to polymer solutions, a mixture, one of whose components is close to its glass transition, transiently exhibits a morphology peculiar to viscoelastic phase separation, namely, a spongelike continuous pattern of the minority phase. This pattern is likely the morphology universal to elastic and viscoelastic phase separation in a dynamically asymmetric mixture containing a fluid as at least one of its components.