How Robust Is the Ring Stain for Evaporating Suspension Droplets?

Abstract

The ring stain is commonly seen when droplets containing particles, such as coffee, are left to dry on a surface: a pinned contact line leads to outward radial flow, which is enhanced by the diverging evaporative flux at the contact line. As shown by Deegan et al. (1997)

Controlling and characterising the deposits from polymer droplets containing microparticles and salt

“…The deposit shapes are more usefully quantified using surface profile data giving the height of the deposit h(r) as a function of distance from the droplet centre r. As we have shown previously [3], robust ring-stains are observed over a range of experimental conditions, and here we confirm this result, finding clear ring-stains for all particle droplets without PEO, c 0 = 0%, as evidenced by the c 0 = 0% curve in fig. 7 for 0.5 μm particles.…”

“…These two requirements lead to an outward flow to replenish solvent loss at the contact line, which sweeps suspended material to the contact line where it is deposited as a ring-stain. The size and shape of the deposit is robust over a range of experimental parameters and follows simple power-law predictions [3]. One of the aims of ongoing research into drying sessile droplets is to control and Contribution to the Topical Issue "Wetting and Drying: Physics and Pattern Formation", edited by Duyang Zang, Ludovic Pauchard and Wei Shen. a e-mail: david.fairhurst@ntu.ac.uk prevent the formation of the coffee ring-stain as many commercial processes require a uniform deposit.…”