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Synthesizing the lotus leaf effect by adsorption of silica spheres on alumina surfaces . When a liquid droplet is placed on a solid surface, the degree of wetting depends on the balance between the energy necessary for the enlargement of the surface (i.e., spreading of the droplet) and the gain of energy due to adsorption of the liquid on the surface [1]. The equilibrium wetting depends on two main factors: the set of surface tensions between the solid surface, liquid droplet, and the surrounding atmosphere; and the roughness of the surface. The contact angle of the liquid droplet on the solid surface indicates the degree of wetting. Flat alumina substrates were dip-coated in a dilute silica suspension and made hydrophobic by attaching fluorosilanes. These surfaces show very high hydrophobicity (internal contact angle for water up to 166). The surface coverage depends on the concentration of the silica suspension and influences contact angle significantly, in accordance with a model developed for a coating of silica spheres. 
1] W Barthlott and C Neinhuis. Purity of the Sacred Lotus, or escape from contamination in biological surfaces. Ann. Botany, 79, (1997) 667. Return to the RISE 2000 project list |
