Ultrahydrophobicity
![A drop on a lotus surface.](/Images/godic/202501/19/DropConnectionAngel3057.jpg")
![A liquid droplet rests on a solid surface and is surrounded by gas. The contact angle, θC, is the angle formed by a liquid at the three phase boundary where the liquid, gas, and solid intersect.](/Images/godic/202501/19/Contact_angle.svg3057.png")
![A droplet resting on a solid surface and surrounded by a gas forms a characteristic contact angle θ. If the solid surface is rough, and the liquid is in intimate contact with the solid asperities, the droplet is in the Wenzel state. If the liquid rests on the tops of the asperities, it is in the Cassie-Baxter state.](/Images/godic/202501/19/Contact_angle_microstates.svg3057.png")
![Sample hydrophobic surface composed of square pillars. Λ = 4x/y2](/Images/godic/202501/19/Pillars_showing_unit_cell_perimter_per_area3057.png")
Ultrahydrophobic (or Superhydrophobic) surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet exceeds 150° and the roll-off angle/contact angle hysteresis is less than 10°. This is also referred to as the Lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet impacting on these kind of surfaces can fully rebound like an elastic ball, or pancake.