Segregation in multicomponent ceramic colloids during drying of droplets.

Studies of drying of colloidal droplets focus on unary particle systems. We report here the drying of binary and ternary powder suspensions. When multicomponent ceramic suspensions are deposited in the form of small drops (5 microl), particle segregation can occur on drying so that the upper surface of the powder residue does not match that of the bulk composition. We show that the segregation effect and the shape of the droplet residues are both related to the participation of particles in two types of flow during drying; radial flow toward the rim where the three-phase boundary becomes locked by a pile up of particles and secondly, recirculation flows in the remaining liquid driven by Marangoni stresses. Methods to control both shape and segregation are described. The phenomenon described is general and independent of the method of preparing the drops but the motivation is to obtain uniform drop shape and composition in thick film ceramic libraries in combinatorial ink-jet printing.