Evaporation-driven self-assembly in the mixtures of micro and nanoparticles

We report experimental studies on the self-assembly of silica microspheres and Laponite nanoplatelets (NPs) in evaporating sessile droplets and in thin films, respectively. A ring-like stain of the silica microspheres with positional order is observed after the evaporation of sessile droplets due to the coffee-ring effect. This effect is suppressed in the binary mixtures of silica microspheres and Laponite NPs. A depletion zone has been observed in the mixtures during the sessile droplet evaporation, the width of which can be tuned by varying the compositions. We demonstrate a simple method for preparing core-shell particles by evaporating thin films of binary mixtures in which the Laponite NPs self-assemble to form a crystalline shell on the amorphous silica microspheres. We present a possible orientation of the Laponite NPs in the shell.