Similarity of the signatures of the initial stages of phase separation in metastable and unstable polymer blends.

Time-resolved small angle neutron scattering was used to probe the initial stages of liquid-liquid phase separation in both critical and off-critical binary polymer blends, and the critical (q(c)) and most probable (q(m)) wave vectors were identified for several quench depths. For the critical blend, the Cahn-Hilliard-Cook theory provides a framework for analyzing the data and explains the observed decrease in q(m) with time. For the off-critical blend, q(m) is independent of quench time, regardless of whether the quench is metastable or unstable.