1. Requirements of Super-Hydrophobic Surface
Super hydrophobic surfaces with a water contact angle (CA) greater than 150o

2. Super hydrophobic surfaces with a low hysteresis
Requirements of Super-Hydrophobic Surface
Super hydrophobic surfaces with a low hysteresis
advancing contact angle
receding contact angle
Hysteresis H = _
The contact angle hysteresis can be regarded as the force required to move a liquid droplet across a surface.
Small Hysteresis
Liquid droplet can roll off easily

3. Super-Hydrophobic Surface from Nature
Lotus Effect
Self-Cleaning
Adv. Mater , 14, 1857

4. Water-Repellent Legs of Water Striders
20 μm
200 nm
SEM images of a leg showing numerous oriented spindly microseta and nanoscale grooved structures on a seta
L. Jiang Nature 2004, 432, 36

5. Artificial Super-Hydrophobic Surface
Super Hydrophobic Surface of Aligned Polyacrylonitrile Nanofibers
Transformation of a Simple Plastic into a Superhydrophobic Surface
30℃
60℃
Science 2003, 299, 1377
Angew. Chem. Int. Ed , 41, 1221

6. Two Models of Hydrophobicity (1)
R. N. Wenzel, 1936
Θw：CA on the rough surface
Θ ：CA on the smooth surface
r ：roughness factor (r ＞1)
cosΘw= r cosΘ
D. Quéré Soft Matter 2005, 1, 55

7. Two Models of Hydrophobicity (2)
A. B. D. Cassie, 1948
ΘC：CA on the rough surface
Θ ：CA on the smooth surface
f1：fraction of solid
f2：fraction of air (f1+f2 = 1)
cosΘc= f1cosΘ – f2
D. Quéré Soft Matter 2005, 1, 55

8. Create a rough surface (e.g., with a fractal structure)
Conventionally, super-hydrophobic surfaces have been produced mainly in two ways:
Create a rough surface (e.g., with a fractal structure)
Modify the surface with materials of low surface free energy, such as fluorinated or silicon compounds.