Wetting Properties of Natural and Plasma-Processed Biomimetic Surfaces - Biomimetic Architectures by Plasma Processing - page 125

the water droplets and the apex of the nanostructures rendering
them considerably super-hydrophobic. Water on such a super-
hydrophobic surface forms a spherical droplet, with very small
contact area and adhesive force with the surface. During the roll-
off at small values of (Fig. 4.9a), this spherical droplet will collect

dirt and other particles from the leaf surface finally leading to self-
cleaning.

a

Figure 4.10 (a) Picture of water droplets on a (lotus)

leaf. (b) Static CA measurement of a water droplet of 0.78
mm radius on the lotus leaf surface; the CA is 153°

Nelumbo nucifera

1°. (c)
Scanning electronic micrograph (SEM) image of the leaf surface
comprising of almost hemispherically topped papillae with
sizes 5-10 µm with surface density of 4.2 × 10 5 cm -2 (scale bar
10 µm). (d) High-magnification SEM image of a single papillose
depicting branch-like protrusions with sizes of about 150 nm
(scale bar 1 µm). Reprinted from Ref. [41], Copyright © 2008
WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

±

Barthlott et al. [35] also reported about the super-hydrophobici-
ty of lotus leaf in combination with a low hysteresis angle which can
lead to the self cleaning property discussed above (Eq. 4.10, Fig. 4.9).
The lotus leaves have a static CA of 162° and very low CAH which
leads to rolling of water over such a hydrophobic surface at

a

~ 4°.