Figure 11.

Guiding cracks in drying colloidal dispersions. (a) Colloidal silica (Levasil 30) is dried in a Hele–Shaw cell with a set of small openings on the sides to allow evaporation. Subsequent images show how drying proceeds in 1-hour steps. The initially liquid dispersion (milky off-white) dries into a darker solid deposit (translucent, on black background). The larger right-hand panel shows how cracks, which appear at the end of drying, lie perpendicular to the superimposed drying profiles (black lines). (b) The angle between a crack and the outward-pointing normal of the drying front profile, when it had been at that same point, shows a distribution that is sharply peaked around 0° (mean of 463 measurements is 1±1° and standard deviation 13±1°). (c) Another experiment, where one side of the cell was sealed after 5 h. In this case the front positions are shown in 4-hour steps, and one can see how the cracks bend to follow the memory of the drying. Videos of the drying process for both experiments are provided in the electronic supplementary material.