Invagination process induced by 2D desiccation of colloidal solutions

The drying process of a suspension of hard colloidal particles is investigated in a circular thin cell which ensures a two-dimensional radial drying. During solvent removal the concentration of particles accumulates to the liquid–gas interface and reaches the close packing concentration: a rigid skin forms. During the evaporation of water, the length of this rigid envelope keeps on decreasing till it stops shrinking. Then a buckling process occurs that leads to an inversion of the curvature. At this time and after a steady decrease, the envelope periphery starts to increase while its inner volume keeps decreasing. This deformation continues as the depressed region extends and invaginates inside the film. An experimental procedure coupling imaging of the skin formation and drying kinetics measurements provides a complete description of the successive mechanisms: drying process, formation of the rigid skin and invagination process.