Spreading- and evaporation-mediated 2D colloidal assemblies on fluid interfaces

Fluid interfaces exhibit remarkable capabilities and significant application prospects in fabricating twodimensional (2D) materials and colloidal assemblies. However, the efficient realization of the fluid-mediated self-assembly of colloidal particles has become challenging owing to the complex evolution of spatiotemporal processes and dynamic behaviors at fluid interfaces. In this study, we hypothesized that the superspreading of a volatile droplet directed the ultrafast self-assembly of colloidal particles on an insoluble fluid interface. To validate this hypothesis, employing high-speed and large-field microscopic observation experiments in tandem with theoretical analysis, the time evolution processes of droplet spreading, evaporation, dewetting, and particle assembly were captured, and the multi-scale dynamic behavior of volatile colloidal droplets on an immiscible liquid substrate was studied. Our findings revealed the power law of droplet spreading dynamics at the macroscale, evaporation-induced dewetting of the liquid film and aggregation of colloidal particles at the mesoscopic scale, and colloidal self-assembly under the action of capillary and DLVO forces at the microscopic scale. Moreover, we realized the ultrafast fabrication of 2D colloidal assemblies on liquid interfaces. This work presents a simple, robust, and efficient method for self-assembling and manufacturing 2D-ordered structures and materials based on a platform of fluid interfaces.