In-Situ Observation of DL-Alanine Crystallization from a Laser-Trapped Dense Liquid Droplet as a Heterogeneous Nucleation Site

Nucleation from an aqueous solution is an important step in crystallization which controls the physicochemical properties of crystalline materials. Although dense liquid droplets are considered as a precursor of a crystal in the two-step nucleation model, their actual role is unclear. Our in-situ microscopic observations of the crystallization of DL-alanine from a dense liquid droplet trapped by laser tweezers show that liquid droplets play the role of a substrate, facilitating heterogeneous nucleation, rather than a precursor of a crystal.