Desiccation Cracks In Dispersion Of Ellipsoids: Effect Of Aspect Ratio And Applied Fields

Particulate films obtained by drying colloidal dispersions often displaying a network of cracks are ubiquitous. In particulate films, drying-induced internal stresses are accumulated as a result of the consolidation of particles during solvent evaporation and are released by the formation of cracks. The morphology of crack patterns can be controlled by externally applied fields, modulation of drying kinetics, or by exploiting the shape anisotropy of the colloids. Here, we explore the role of particle shape anisotropy and externally applied thermal and magnetic fields on the evolution of cracks by performing desiccation experiments, i.e., by drying colloidal-ellipsoid-laden sessile drops on solid substrates. We determine the critical aspect ratio (alpha(c)), where the cracks in the dried particulate deposit drastically change their orientation from a radial to circular pattern. It is observed that the drying of drops consisting of ellipsoids at an elevated temperature enhances the randomness in the particle arrangement and brings nontrivial modifications to the crack pattern. In addition, we show that the randomness in the particle arrangement due to the thermal field can be compensated by the application of an external magnetic field and the orientation of cracks can be completely restored.