Spontaneous pinning of domain growth during spinodal decomposition of off-critical polymer mixtures

Abstract

Spinodal decomposition of off‐critical mixtures of poly(styrene–random–butadiene) copolymer with polyisoprene or polybutadiene was investigated as a function of the composition w of the mixtures and of the phase separation temperature T by time‐resolved light scattering. The coarsening behavior of the mixtures was characterized in terms of the time change of the maximum intensity I m and that of the magnitude of the scattering vector q m at which the intensity becomes maximum. It was found that the time changes of I m and q m for the off‐critical mixtures studied here are effectively pinned at a certain time defined here as the ‘‘pinning’’ time. This spontaneous pinning of the growth of the unmixing structure was found to occur earlier when w is biased toward 0 or 1 at a given T and when the phase separation temperature is raised at a given w, for these systems which seemingly have upper critical solution temperature behavior.