The drying of isotropic and anisotropic colloids under confinement

Drying colloidal dispersions have been used extensively as examples of collective transport processes, particularly in fixed (sessile) drops. Much less attention, however, has been paid to the drying of droplets in the capillary liquid bridge configuration. Such confined drying is relevant in medical and industrial applications. We study the evaporation dynamics and deposition pattern of a colloidal dispersion containing particles of different shapes and sizes in restricted geometry. The effect of confinement spacing, particle size and shape, concentration, and the presence of an external field on the drying deposition pattern was investigated under ambient conditions. The drying deposition pattern of colloids containing nanoellipsoids results in a stick-slip pattern at high confinement spacing and a labyrinthine pattern at low confinement spacing. However, dispersions containing microparticles such as microellipsoids, cubes, and peanuts leave a uniform deposit at high confinement spacing and labyrinthine patterns at low confinement spacing after solvent evaporation. We measure the dependence, on concentration (C_s) and confinement spacing (h_c), of a characteristic length scale (Λ_c), which represents the spacing between the branched patterns, to elucidate the origin, and dependence on particle shape, of the labyrinthine patterns.