Biomedical Engineering Reference
In-Depth Information
superhydrophobic coating. In order to achieve superhydrophobic behavior with
limited light scattering, they optimized the level of surface roughness by con-
trolling the placement and level of aggregation of differently sized nanoparticles
within the multilayer thin film. It follows that optical transmission levels above 90%
throughout most of the visible region of the spectrum were achieved in optimized
coatings [
13
].
As an important aspect, some experimental studies show that antireflective super-
hydrophobic coatings on uneven solar cell surfaces can increase the performance of
solar cells. Prevo et al. assembled silica nanoparticles into antireflective coatings on
the rough uneven surfaces of polycrystalline silicon solar cells by controlling the
evaporation process.
The nanocoatings reduce the reflectance of the solar cells by approximately 10%
across the UV to near IR range, providing a 17% increase in the output power.
Furthermore, the superhydrophobic coating can help to decrease water uptake which
improve maintenance of the performance in the antireflective properties [
189
].
9.5.2
Structural Color and Iridescence
The vivid color and special wetting features of butterfly wings have attracted in-
creasing attention, because of their potential applications in the external decoration
of architectures, where both esthetic and self-cleaning are required. Gu et al. [
190
]
have presented uniform inverse opal film to mimic the colored superhydrophobic
property of butterfly wings by a convenient dipping method shown in Fig.
9.11
.To
exhibit both structural color and superhydrophobicity, colloidal particles with two
different sizes were utilized to deposit on glass in a long-range order structure.
Iridescence is generally known as the change in color with different observation
angles or lamp flounce, and there are rare studies reporting on artificial superhy-
drophobic surfaces endowed with such vivid color. Wu et al. employed lithography
to fabricate regular micro-needle arrays and further implanted nanometal protru-
sions on its surface via electroless plating to achieve hierarchical structure. The
as-prepared sample exhibited both the superhydrophobic ability and iridescence
feature [
16
]. Alternatively, optical feature can be imparted to the superhydrophobic
materials by the inclusion of quantum dots or organic dyes. Hong et al. demonstrated
multifunction thin films by incorporating CdSe@ZnS quantum dots (QD) and or-
ganic dye into the polystyrene (PS) cores of charged block copolymer micelles [
15
].
9.5.3
Air-Retaining Property and Fluidic Drag Reduction
and Water Support Force
Whereas large amount of superhydrophobic materials have been functionalized in
the ambient state, little attention was given to their air-retaining feature when they
