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4.5 Fabrication of Hydrophobic and Hydrophilic
Surface
Learning from nature is not a new thing, as we have been copying
natural designs and concepts for a long time in order to impart
efficiency to our laboratory-made products and technology. The key
aspect of natural design is that it does not use its full resources in
designing the 'best' and versatile product in the whole range, but
creates one 'best' suited for a particular function. For example, the
anti-reflection property of the moth-eye is suited only in the visible
spectrum which will be useful for the insect. The same design may
not suit a broadband spanning UV-VIS and IR. In short, nature gives
you the best of essentials only and doesn't provide for extravaganza.
However, laboratory techniques, while copying from natural designs
always want to impart that 'extra' bit to claim the top spot even if
the design is not the most efficient overall. However, the attempts
are wonderful and in certain cases we could copy natural designs
in the laboratory for the intended functions. Such experiments are
gaining popularity in technologies related to optical device designs,
micro-electro mechanical system (MEMS), micro-fluidics, textile,
adhesive tapes, Velcro, and so on. While trying to mimic the lotus leaf
for hydrophobic functionality below, we discuss some biomimetic
materials that demonstrate hydrophobic or hydrophilic properties
and have structures similar to their natural counterparts.
4.5.1 Hydrophilic Surface
Following the conical burls on the cornea of a moth eye or the bumps
present in lotus leaf, Lo
et al. [58] produced conical tip structures
using silicon in a complex plasma. The silicon nanotips (SiNTs)
demonstrated efficient anti-reflection and switchable (hydrophilic-
hydrophobic) wetting properties. The fabrication of the SiNTs is
described in this topic in Chapter 2 and hence would not be repeated.
The readers are suggested to go through the relevant part of Chapter
2 to understand the plasma mechanism for the synthesis of the SiNTs.
Lo et al. elaborately discussed the wetting properties of the SiNTs,
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