Desiccation crack patterns in drying laponite gel formed in an electrostatic field

Desiccation cracks form interesting patterns in natural and synthetic clays. Clay platelets, having a net negative surface charge in aqueous solution, are affected by an electric field. We report observation of cracks forming in a radial external electric field. The cracks start radially from whichever electrode is positive, whether it is the central or outer electrode. The same geometry without the field does not produce the characteristic radial pattern. The non-uniform nature of the field due to the radial arrangement is a crucial factor, we find that the uniform field produced in rectangular geometry does not show any distinctive feature. SEM images of the films show that the arrangement of the clay nano-platelets is quite different in samples dried with and without the external field. With no field, the particles are aligned linearly, presumably along defects on the substrate, but the electric field disrupts this alignment and produces a homogeneous disordered arrangement.