Confined-vapor driven solutal Marangoni effect controls nucleation mechanisms and crystalline morphologies in an evaporative crystallization*

The initiation of crystal nucleation near a contact line in evaporative crystallization is inevitable because the local concentration of suspended particles at the edge is for the most dramatically increased by coffee-ring effect. To control the crystalline pattern, the nucleation location should be handled. In this study, we showed that the nucleation site of the CTAB's crystallization could be controlled from the droplet edge to center by changing the evaporation boundary condition of multi-component droplets. In particular, we installed a confine chamber to capture the evaporated volatile vapors. In this experiment, we also tested different chain lengths of the surfactants (CTAB > TTAB > DTAB) where the gelation induced by micellization became predominant if the chain length decreased. Here, the gelation interrupted the nucleation control. During the talk, we will provide a regime map to distinguish a different crystallization process of cationic surfactants that are determined by three parameters: (1) the ethanol concentration in an ethanol-water mixture, (2) the confinement effect, and (3) the alkane chain length of the surfactants. We believe that the proposed idea has great potential to control the nucleation in the crystallization process and its crystalline morphology.