Observation and Analysis of Liquid-liquid Phase Separation and Crystallization Processes of Water/Ethanol/Butylparaben by an Evaporation Technique

Liquid-liquid phase separation (LLPS) that occurs during crystallization is problematic because it has various adverse effects. In this study, water/ethanol/butylparaben solutions were evaporated and the phase change process was observed under an optical microscope to investigate the effects of initial composition and evaporation rate on the solution morphology. It was found that LLPS could be avoided by selecting an initial composition such that the evaporation path does not pass through the LLPS region. It was also found that the probability of LLPS occurrence, the size of the dispersed phase, and the final morphology of the crystals differ depending on how the evaporation path crosses the LLPS region. Furthermore, when the evaporation pathway passed near the boundary of the LLPS region, if the evaporation rate was high, even if LLPS occurred, the crystals returned to one phase during crystallization and crystallization could be carried out as usual. Thus, we obtained non-equilibrium-specific findings that are not indicated by the phase diagram alone.