(557g) Reshaping Drying Droplets Using Rod-Shaped Particles

Drying aqueous colloidal droplets on a superhydrophobic substrate suppresses coffee-ring formation by minimizing pinning and allowing three-dimensional self-assembly. We investigated the morphological behavior of these colloid-based suprastuctures obtained via evaporative assembly. Specifically, we monitored the evolution of curved shells formed as particles pack at the air-water interface during drying. We found that shells assembled with rod-shaped particles jam into stable suprastructures, whereas shells assembled with spherical particles experience a buckling. The competition of jamming and buckling phenomena in thin shells is driven by the difference in packing efficiency of spheres and rods, which in turn determines the pressure differential across the air water interface. We observed that particles of increasing aspect ratios form more permeable shells, allowing for better evaporation throughout the sol-gel transition of the shell compared to spherical particles. Our findings are of interest in the understanding of spray drying and encapsulation processes relevant in the pharmaceuticals, cosmetics and food industry.