Buckling of drying droplets of colloidal suspensions
Authors: N. Tsapis, E. R. Dufresne, S. S. Sinha, C. S. Riera, J.W. Hutchinson, L. Mahadevan, and D. A. Weitz
Physical Review Letters 94, 018302 (2005)
Soft matter keywords
buckling, elastic shell, drying, sol-gel, Leidenfrost effect
By Tom Kodger
Abstract from the original paper
Minute concentrations of suspended particles can dramatically alter the behavior of a drying droplet. After a period of isotropic shrinkage, similar to droplets of a pure liquid, these droplets suddenly buckle like an elastic shell. While linear elasticity is able to describe the morphology of the buckled droplets, it fails to predict the onset of buckling. Instead, we find that buckling is coincident with a stress-induced fluid to solid transition in a shell of particles at a droplet’s surface, occurring when attractive capillary forces overcome stabilizing electrostatic forces between particles.
Practical Application of Research
Rapidly dried droplets which contain suspended colloids are found in several industrial areas, and probably in your home office (unless you use a laser printer). Spray drying where fine powders are made by the evaporation of aerosols have been used in the manufacture of foodstuffs, pharmaceuticals, polymers, and detergents.
Capillarity at Work
The authors use a water droplet with suspended colloidal particles, with no added ions; therefore the capillary length l= √γ/ρ* g