Droplets with particles in them can leave complex stains when they dry — just look at coffee rings and whiskey marks! Here, researchers look at the patterns left on glass by small droplets that evaporated and left behind their nanoparticles. As evaporation takes place, the droplet’s shape changes, adding stress to the growing layer of nanoparticle residue. Cracking is one way to relieve that stress. Another method is delamination — peeling up from the surface. On the leftmost drop, the outer rim of nanoparticles delaminated — as seen from the circular fringes — which released stress without cracking. The rightmost drop, which had a smaller contact angle with the surface, couldn’t delaminate and instead cracked throughout. (Image credit: M. Ibrahim et al.)
Drying Cracks
