Dynamics of phase-separated microdroplets near the contact line of evaporating all-aqueous drops†

Evaporation of multicomponent drops can induce liquid–liquid phase separation and spatial reconfiguration of phases. Here, we unveil several novel dynamics near the contact line of evaporating multicomponent drops containing polyethylene glycol and dextran. The interplay between background Marangoni flow and self-migration of nucleated microdroplets creates both unstable and stable equilibrium points. This leads to either continuous migration or stepwise advancement of microdroplets, influenced by random coalescence events. Tiny dextran microdroplets nucleating at the contact line can migrate toward the bulk only by growing in size with coalescence events. Our findings offer new insights into the fundamental understanding of evaporating multicomponent drops and factors influencing the spatial segregation of phases in evaporative liquid–liquid phase separation with implications in prebiotic biomolecular reactions to industrial applications.