Order-induced period doubling during surface-directed spinodal decomposition

We present first experimental evidence for period doubling as an alternative mode of coarsening during surface-directed spinodal decomposition in a binary mixture. The system under consideration is a symmetric blend of deuterated polystyrene (dPS) and partially brominated polystyrene (PBr_xS). We compare the surface domain coarsening of a thin film of a critical mixture with that of a multilayered structure of near-binodal compositions. While the former is found to coarsen monotonically via diffusion, leading to self-similar composition vs. depth profiles, the latter grows by dissolution of one of the layers feeding the adjacent domains of the respective phase. The results compare well with cell-dynamical simulations.