Evaporation of gelled sessile drops

Gelation occurs during the evaporation of many complex biological fluids. Further evaporation of solvent from the gel leads to a variety of patterning behaviours. During evaporation, flow drives solid particles to the contact line, where compaction leads to the formation of a gel front, which propagates into the bulk. An assortment of complex phenomena is involved in the formation and fracture of the gel front, however, the dynamics of fully-gelled droplets is not understood. Hence, we consider the problem of a drop with an already present solid network undergoing evaporation. A model is derived for the drying of a fully-gelled drop from the governing equations of nonlinear poroelasticity alongside the lubrication approximation. Poroelastic free surface profiles show good agreement with experiments. The evolution of the mechanical properties of the gel obtained from the fluid/solid dynamics can be fed into a fracture model to simulate a variety of crack morphologies also seen in experiments.