Electric-field-induced crack patterns: Experiments and simulation

Abstract

We report a study of crack patterns formed in laponite gel drying in an electric field. The sample dries in a circular petri dish and the field is radial, acting inward or outward. A system of radial cracks forms in the setup with the center terminal positive, while predominantly cross-radial cracks form when the center is at a negative potential. The laponite accumulates near the negative terminal making the layer thicker at this end. A spring model on a square lattice is used to simulate the desiccation crack formation, with an additional radial force acting due to the electric field. With the radial force acting outward, radial cracks form and for the reversed field cross-radial cracks form. This conforms to the observation that laponite platelets become effectively positive due to overcharging and are attracted towards the negative terminal.

Crack Formation under an Electric Field in Droplets of Laponite Gel: Memory Effect and Scaling Relations

“…It is instructive to compare the experimental results presented here with the earlier work on larger circular systems in a radial electric field [17]. Several observations are similar e.g.…”

“…However, the appearance of cross-radial cracks for the CN configuration [17] is not seen here. The droplet may be too small for significant field gradients to develop.…”

“…Another area where considerable research is going on is the study of dessication crack patterns on layers of clay or other granular material [10,11,12,13,14]. Here a host of remarkable phenomena such as memory effects [15], magnetic [16] and electric field effects in DC [17] and AC [18] have been observed.…”

Dynamical scaling of fragment distribution in drying paste

“…The last term, σ dry , represents the drying part, since drying causes inner stress to increase with time. In previous works [19][20][21][22][23], a linear or exponential function of time has been used for σ dry . In this paper, we use a linear function that is the first order of the function presented in previous works; σ dry is then described by…”

“…(2)-(9) and (15) are discretized by using Eqs. (19)- (23), which are taken as the basic equations of the computational model. In the present model, we use the local average stress criterion in SPH to examine the nucleation of the crack.…”