Biomedical Engineering Reference
In-Depth Information
(a)
Biomimicking of
structural color
(b)
(c)
Strucurally colored
silk fabrics
Figure 7.7
Biomimetics of structural colors
on silk fabrics. (a) The structure colors of
butterfly (
Papilio Ulysses
butterfly) and pea-
cock feather. (b) Fabrication of opal and
inverse opal on silk fabrics. Refer to [103]
for the details of fabrication. (c) Structurally
colored silk fabrics. Controlled colloidal
assembly: experimental modeling of general
crystallization and biomimicking of struc-
tural color. (Reprinted with permission from
Ref. [104].
©
2012 Wiley-VCH Verlag GmbH
& Co. KGaA, Weinheim. Patent approval is
pending [103].)
due to its wide applications in photonic crystals, cosmetics, and display technology
[98, 99]. In nature, the colorful feathers of many birds (i.e., peacock), the wings of
various butterflies and the shells of beetle are the excellent examples of structural
colors. It follows that the two-dimensional photonic-crystals in the cortex of different
colored barbules, are responsible for the coloration of peacock feather [100, 101],
while the multi-layer structures of wing scales produce the structural coloration of
some breeds of butterflies [102]. Compared with other coloring schemes, structural
color is longer lasting, brighter, and more deeply saturated.
During the last two decades, much effort has been devoted to mimicking natural
structural color. However, to obtain the dedicated structures with the structural
color as seen in animal kingdom (Figure 7.7a) remains to be a big challenge.
One of the approaches to acquire structural color is to adopt the nature structural
color materials as templates to replicate the nanostructures so as to obtain the
optical properties. Wang
et al
. examined the fine structure of the wing scale of
a
Morpho Peleides
butterfly and replicated the entire configuration by a uniform
Al
2
O
3
coating through a low-temperature atomic layer deposition (ALD) process
[105]. An inverted structure was achieved by removing the butterfly wing template
at high temperature, forming a polycrystalline Al
2
O
3
shell structure with precisely
controlled thickness. Other than the copy of the morphology of the structure,
the optical property, such as the existence of a photonic band gap (PBG), was
also inherited by the alumina replica. Other replicating methods have also been
employed to replicate the structures of natural photonic materials, including
conformal-evaporated-film-by-rotation technique, soft lithography technique, and
so on [106, 107].
Fabricating 3D colloidal crystals with a PBG lying in the visible range is
another option for mimicking natural structural color. Inspired by natural photonic
crystals (Figure 7.7), researchers have fabricated colloidal crystals with tunable
structural colors [108-110]. One of themost commonly used techniques to fabricate
colloidal crystals is the evaporation-induced self-assembly method, which enables
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