Here we demonstrate the first evidence that phase separation in polymer solutions could be essentially different from that in binary liquid systems. This difference is likely to originate from the strong asymmetry in molecular dynamics between the two separated phases. When the rheological time of the polymer-rich phase is slower than the deformation time, the stress field can be strongly coupled with the concentration diffusion and the coarsening dynamics is dominated by the viscoelastic effect. This causes mechanically dominated pattern evolution. The dynamic symmetry should be considered in addition to the static, composition symmetry.

• Received 1 February 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.3158