The buckling and invagination process during consolidation of colloidal droplets

Drying a droplet of colloidal dispersion can result in complex pattern formation due to both development and deformation of a skin at the drop surface. The present study focuses on the drying process of droplets of colloidal dispersions in a confined geometry where direct observations of the skin thickness are allowed. During the drying process, a buckling process is followed by a single depression growth inside the drop. The deformation of the droplet is found to be generic and is studied for various colloidal dispersions. The final shape can be partly explained by simple energy analysis based on the competition between bending and stretching deformations. Particularly, the final shape enables us to determine precisely the critical thickness of the shell for buckling. This study allows us to validate theory in 2D droplets and apply it to the case of 3D droplets where the thickness is not accessible by direct observation.