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