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shark skin is covered by placoid—a special type of scale made of
the same material as that of the shark's teeth. The small bump-like
rough surface reduces the friction with water and works as an anti-
drag surface when the shark glides through water, making them very
quick and efficient swimmers.
4.3.4 Pond Skater
A pond skater (
) can easily walk upon a water surface
without drowning or getting wet (Fig. 4.12a). Even a rain drop with
size greater than the Strider's size cannot drown it. Gao et al. [2]
reported about the special hierarchical structure of the Strider
legs, covered by large numbers of oriented tiny hairs (micro setae)
with nano-grooves, which are responsible for the water resistance.
According to their analysis, the leg does not penetrate the water
surface until a depression of 4.38 mm is formed. They mentioned
that the maximal supporting force of a single leg is 1.52 mN which is
approximately 15 times the total body weight of the insect and due
Gerris remigis
(
c
)
(
d
)
Figure 4.12
The super-hydrophobic water strider legs. (a) Photograph
of a water strider standing on the water surface. (b)
SEM image of the leg with oriented spindly setae and
the nanogrooves on a single seta [inset in (b). Reprinted
with permission from Ref. [52]. Copyright 2007 American
Chemical Society. (c) Photograph of a sandfish skink (
Scincus
scincus
). Reprinted from Ref. [12], © 2008 Baumgartner
et al. (d) SEM image of sandfish skink scale. Reprinted
from Ref. [53], with permission from SPIE, copyright 2011.
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