Field induced radial crack patterns in drying laponite gel

We present a study of crack patterns in a layer of laponite gel allowed to dry in a static electric field. Crack patterns in natural and synthetic clays have been studied extensively with interesting results. Since clay platelets have a surface charge in aqueous solution, it is natural to expect the cracking patterns to be affected by an electric field. This is the first report of such an observation in a radial electric field. The nano-sized disc-like laponite particles carry a quadrupole moment due to their charge distribution. The interaction of the quadrupole moment with the field gradient in a non-uniform field of radial symmetry is probably responsible for the characteristic pattern observed. The cracks start radially from the positive electrode. The same geometry with no field does not produce the characteristic pattern, neither does a uniform field with rectangular geometry. (C) 2007 Elsevier B.V. All rights reserved.