Superhydrophobicity and the Lotus Effect
By: Derek McCurry
Lotus Effect
The Lotus effect refers to the very high water repellency exhibited by the leaves of the lotus plant
Allows for self-cleaning, where dirt particles are picked up by passing water droplets due to the architecture of the leaf surface which minimizes adhesion
Main purpose is for protection against pathogens (fungi/algae)
Pathogens
Dirt particles
Superhyrdrophobicity
The leaves of the lotus plant are superhydrophobic
Superhydrophobic simply means the surface is very difficult to wet due to the contact angle of the water droplet with the surface
Contact angle: ≥ 150˚
Roll-off angle: <10 ˚ Contact angle
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Thermodynamics
The free energy transfer of non-polar solvent to aqueous solvent is often used to quantify the hydrophobic effect
∆G = H - ∆ TS > O
Hydrophobic effect is entropy-driven at room temperature (H = zero)
Heat capacity change in transfer is positive, whereas it is negative for hydrophilic molecule
Cp > O
O < O
Nanotechnologists have developed surfaces that can remain dry and clean themselves similar to the lotus leaf including; Treatments Coatings Paints Roof tiles Fabrics
Flying insects Butterflies Dragonflies
Self-cleaning glass Protection against concrete corrosion Anti-snow sticking
Examples