Crystal–Liquid Interfacial Free Energy on Extremely Supersaturated Aqueous Solutions Using a Containerless Method

Crystal–liquid interfacial free energy (IFE) is a crucial parameter that elucidates the nucleation phenomenon and multiple crystallization pathways. In this article, we report the IFE of extremely supersaturated aqueous KH2PO4 (KDP) and NH4H2PO4 solutions using the electrostatic levitation technique. We measure the volume, concentration, and density of the levitated solution droplets as a function of time and supersaturation as well as their Raman spectra. We find that the IFE of the metastable KDP crystal is smaller than that of a stable KDP crystal, explaining the formation of a metastable KDP crystal in the highly supersaturated KDP solution prior to the formation of a stable KDP crystal. This result supports that the similar molecular structure of the H2PO4 anion cluster facilitates the formation of the metastable KDP crystal rather than the stable KDP crystal in a highly supersaturated solution.