PHASE-SEPARATION KINETICS AND MORPHOLOGY IN THE CRITICAL TO OFF-CRITICAL CROSSOVER REGION

Phase separation kinetics and morphology were studied for polystyrene/ poly(2-chlorostyrene) blends containing a small amount of di-n-butyl p hthalate over a wide composition range by using the time-resolved ligh t scattering technique and electron microscopy. Cocontinuous domains a nd isolated spherical domains (droplets) were observed to coexist in t he critical to off-critical crossover composition region: It was found that the phase-volume fraction was not the only factor determining th e crossover compositions. Two maxima corresponding to the scattering f rom cocontinuous domains and droplets respectively were observed in th e scattered light intensity profile. Because of a large difference in the coarsening rate between the two domain structures, only the maximu m corresponding to the cocontinuous domains was initially observed. Th e wavelengths at which the two maxima were located could be expressed by power functions of the phase separation time, and the exponent for each maximum had the same value as in the case where the corresponding domain structure existed separately. This indicated that the coarseni ng mechanisms of the cocontinuous domains and droplets were scarcely c hanged by coexistence with the other domain structure.