Requirements of Super-Hydrophobic Surface

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Requirements of Super-Hydrophobic Surface
Super hydrophobic surfaces with a water contact
angle (CA) greater than 150o
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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
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Super-Hydrophobic Surface from Nature
Lotus Effect
Self-Cleaning
Adv. Mater. 2002, 14, 1857
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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
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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
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Two Models of Hydrophobicity (1)
R. N. Wenzel, 1936
TwCA on the rough surface T CA on the smooth
surface r roughness factor (r gt1)
cosTw r cosT
D. Quéré Soft Matter 2005, 1, 55
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Two Models of Hydrophobicity (2)
A. B. D. Cassie, 1948
TCCA on the rough surface T CA on the smooth
surface f1fraction of solid f2fraction of air
(f1f2 1)
cosTc f1cosT f2
D. Quéré Soft Matter 2005, 1, 55
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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.