Crack formation in drying laponite

Natural clay and other granular materials form crack networks with typical patterns on desiccation. The present paper reviews a series of studies on crack patterns produced by drying laponite suspensions in different solvents, on different substrates. Laponite is a synthetic clay composed of nanosized platelets of uniform size and composition. The area covered by the cracks shows a scaling behavior with layer thickness. The salient features of the experimental observations can be reproduced by a computer simulation with a chain of springs modeling the clay. We review earlier work done on crack patterns in drying laponite, suspended in methanol as well as water. Experiments on a modification of the setup where the samples are allowed to dry in an electric field are also reviewed. We present new results done on a different geometrical arrangement of the electrodes. The crack patterns are again found to follow the symmetry of the field. Another new observation is that gelation starts earlier when suspensions with excess water are placed in an electric field.