"Delayed" phase separation in a gelatin/dextran mixture studied by small-angle light scattering, turbidity, confocal laser scanning microscopy, and polarimetry.
Small-angle light scattering, turbidity, and confocal laser scanning microscopy were used to study microstructure formation and evolution in a gelatin/dextran mixture. There was a time-delay of up to tens of minutes between reaching the quench temperature and the onset of phase separation, because demixing only occurred once a certain amount of ordering of the gelatin molecules, measured by polarimetry, was attained. The accompanying phenomenon of gelation retarded the development of the microstructure to different extents, depending on the quench temperature. At low temperatures, the structure was rapidly trapped in a nonequilibrium state with diffuse interfaces, characteristic of the early and intermediate stages of phase separation. At higher temperatures, coarsening continued for a certain amount of time before the structure was trapped. The duration of the coarsening period increased with increasing temperature and the interface between the phases became sharp, characteristic of the late stages of phase separation. Because the ordering process continued after the target quench temperature was reached, the effective quench depth continued to increase after the initial phase separation. At high quench temperatures, the system was able to respond to the thermodynamic requirements of the increasing effective quench depth by undergoing secondary phase separation to form a droplet morphology within the preexisting bicontinuous one.