Superhydrophobicity and the Lotus Effect

1. By: Derek McCurry Superhydrophobicity and the Lotus Effect

2. 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

3. 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 ˚ Ѳ Contact angle

4. 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

5. Examples • 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