Phase equilibrium and mechanisms of crystallization in liquid–liquid phase separating system

The influence of liquid–liquid phase separation (LLPS) in a crystallizing system is examined, and the liquid–liquid tie lines are determined in the ternary system of butyl paraben, water and ethanol. Crystallization by evaporation in droplets (solution of butyl paraben in ethanol and water mixtures) of homogeneous solution and two-phase liquid mixtures on plates of different materials: glass, plastic, steel, and tin were investigated by microscopy. Different crystallization and liquid–liquid phase separation behaviour are observed depending on initial droplet composition and the surface material. This work reveals that crystallization in the LLPS solution of butyl paraben in ethanol–water mixtures starts in the butyl paraben rich phase as can be explained by a higher butyl paraben concentration, and a lower solid–liquid interfacial energy.