NOVEL SURFACE-MODES IN SPINODAL DECOMPOSITION

We study the spontaneous phase separation of a binary mixture in the p resence of a flat wall, focusing on the early stage of the demixing ki netics. Based on a Ginzburg-Landau type approach, we show the existenc e of novel unstable concentration waves with wave vectors (k) over rig ht arrow(parallel to) parallel to the wall, which are characterized by a surface dispersion relation omega(s)(k(parallel to)) and amplitudes (s) over bar decaying exponentially into the bulk. The surface modes are superimposed on the laterally averaged concentration profile and a re directly observable by experiment, if the wall right after a quench does not favor any of the two components of the mixture.