Mutual diffusion diagram of liquid-liquid interfaces for morphological control of NaCl crystals

Liquid-liquid interfacial crystallization requires mutual diffusion between two liquids to drive the crystallization. Understanding mass transfer between two liquids is important for achieving sophisticated morphological control. In this work, the effect of mutual diffusion on crystal morphology was examined by calculating the solute concentration near the interface. NaCl crystals were prepared with various organic solvents. The crystal shape, amount of precipitation, and particle size were evaluated. The diffusion rate in each organic solvent was measured from the time evolution of the surface area and the volume of the droplet. The solute concentration and the supersaturation ratio near the interface were calculated by Fick's law. The change in crystal morphology revealed that either nucleation or crystal growth preferentially occurred depending on the organic solvent. The magnitude of the water diffusion rate affected the crystal morphology. The dependence of the crystal morphology on the organic solvent was also determined by the diffusion coefficient and the mutual solubility. These results provide new insight into our understanding of the mutual diffusion at liquid-liquid interfaces and the development of crystal morphology control.