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In chemistry and materials science, ultrahydrophobic (or superhydrophobic) surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. [1] This is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant.
The lotus effect refers to self-cleaning properties that are a result of ultrahydrophobicity as exhibited by the leaves of Nelumbo, the lotus flower. [1] Dirt particles are picked up by water droplets due to the micro- and nanoscopic architecture on the surface, which minimizes the droplet's adhesion to that surface.
Superhydrophobic surfaces, such as the leaves of the lotus plant, are those that are extremely difficult to wet. The contact angles of a water droplet exceeds 150°. [ 6 ] This is referred to as the lotus effect , and is primarily a chemical property related to interfacial tension , rather than a chemical property.
The ultimate goal in developing superhydrophobic surfaces is to recreate the self-cleaning properties of the Lotus Leaf that has the inherent ability to repel all water in nature. The basis for superhydrophobic self-cleaning is the ability of these surfaces to prevent water from spreading out when in contact with the surface.
One example of a superhydrophobic surface in nature is the Lotus leaf. [12] Lotus leaves have a typical contact angle of θ ∼ 160 ∘ {\displaystyle \theta \sim 160^{\circ }} , ultra low water adhesion due to minimal contact areas, and a self cleaning property which is characterised by the Cassie-Baxter equation. [ 13 ]
A superhydrophobic coating is a thin surface layer that repels water. It is made from superhydrophobic (also known as ultrahydrophobic ) materials, and typically cause an almost imperceptibly thin layer of air to form on top of a surface.
Superhydrophobic surfaces have contact angles greater than 150°, showing almost no contact between the liquid drop and the surface. This is sometimes referred to as the "Lotus effect". The table describes varying contact angles and their corresponding solid/liquid and liquid/liquid interactions. [9]
This honey-spoon, at the Bonn University in 1994, was the first technical product to demonstrate the self-cleaning effect of superhydrophobic surfaces after the discovery of the lotus-effect in 1977 Hassallia byssoidea (biofilm and attached to the water droplet) is a terrestrial cyanobacterium forming extreme water-repellent biofilms on rocks.