Requirements of Super-Hydrophobic Surface Super hydrophobic surfaces with a water contact angle (CA) greater than 150o
_ Hysteresis H = Requirements of Super-Hydrophobic Surface Super hydrophobic surfaces with a low hysteresis receding contact angle advancing contact angle Small Hysteresis The contact angle hysteresis can be regarded as the force required to move a liquid droplet across a surface. Liquid droplet can roll off easily
Super-Hydrophobic Surfacefrom Nature Lotus Effect Self-Cleaning Adv. Mater. 2002, 14, 1857
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 Nature2004, 432, 36
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. 2002, 41, 1221
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= rcosΘ D. Quéré Soft Matter 2005, 1, 55
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
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.