  Crack patterns in a layer of laponite gel allowed to dry in a static electric
field are studied. Crack patterns in natural and synthetic clays have been
studied extensively with interesting results. 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.
