Eliminating cracking during drying

When colloidal suspensions dry, stresses build up and cracks often occur - a phenomenon undesirable for important industries such as paint and ceramics. We demonstrate that the two viscoelastic moduli, $G'$ and $G''$, determine the cracking behavior. By adding emulsion droplets into colloidal suspensions, we systematically decrease the storage modulus, $G'$, and increase the importance of the loss modulus, $G''$, and effectively decrease the amount of cracks. At a critical droplet concentration, cracking disappears completely. Furthermore,adding droplets also varies the speed of air invasion and provides a powerful method to adjust drying rate. With the effective control over cracking and drying rate, our experiment may find important applications in many drying and cracking related industrial processes.