Abstract
Researches are underway to create functional particles with high added value through crystallization processes using concentrated seawater after salt production, such as bittern, as a raw material. To produce highly functional particles through the crystallization process, it is necessary to develop a crystallization field that is different from the usual one. Crystallization methods utilizing the liquid-liquid phase separation (LLPS) phenomenon that occurs during anti-solvent crystallization have garnered attention. The control of crystal properties using LLPS is promising not only for organic compounds but also for inorganic compounds such as seawater resources. To achieve the desired crystal particles in such processes, it is necessary to design the process considering mass transfer across the solution/anti-solvent interface. However, the molecular level mechanisms of mass transfer at the interface in LLPS systems remain largely unexplored. Herein, we used molecular dynamics simulations to investigate solvent diffusion and the resulting changes in solution structure in the typical LLPS system of water (anti-solvent)-ethanol (good-solvent)-butylparaben (solute). The results indicated that the presence of butylparaben as the solute in the miscible water-ethanol system alters the diffusion behavior of both solvents. At the interface between the butylparaben-ethanol solution and water, a strongly localized solvent layer was observed. Furthermore, compared to previous studies, it was found that the formation and time dependent changes of the liquid-liquid interface and its structure vary depending on whether the system is miscible, immiscible, or undergoes LLPS. In other words, even in the same antisolvent crystallization process, the changes in supersaturation vary by system, suggesting that these variations can affect the morphology of the precipitated crystals.
