Environmental Engineering Reference
In-Depth Information
known as pummelo). This Southeast Asian native fruit grows 10-15 m above the
ground and is the largest fruit of the Citrus genus (15-25 cm diameter). Once
ripened, it falls to the ground, quickly dissipating the kinetic energy (*90 J) to
resist outstanding deceleration forces without being visibly damaged. The 2 cm
thick pummelo's peel, with its alveolar structure, is acknowledged for this ability.
Metal foams have already been produced by emulating the peel's microstructure,
which reasonably reproduce the impact resistance properties of the pummelo fruit
(Fischer et al.
2010
). Applications of pummelo-like foams could range from low
weight package filling to protective coating for electronic devices or safety coating
(helmets).
3.3.2 Optical Properties
The ability to manage light (visible and nonvisible) is important for many
organisms in the most varied contexts. For example, by adequately absorbing and
reflecting light, organisms can send visual signals, which may serve to attract
individuals from the same species or to keep potentially harmful species at bay.
The handling of infrared, visible, and ultraviolet radiation may also be critical to
optimize thermoregulation, enhance photosynthesis or aid in navigation. A number
of examples are described next that are especially relevant to develop new
materials with impact in the aesthetics of facades and building envelopes.
Structural color. Living organisms, from flowers and fruits to birds, fishes and
butterflies, display a diversity of colors that has long marveled people and artists,
who thrive to capture them in their works. In many cases, color is imparted by the
presence of pigments, i.e., molecules capable of selectively absorbing visible
wavelengths, inducing the perception of color. However, research on the micro-
structure of hair-like setae of polychaete worms (Parker et al.
2001
), butterfly wing
scales (Kinoshita et al.
2002
), beetle cuticle (Seago et al.
2009
), bird feathers
(Stavenga et al.
2011
) and fruit peals (Vignolini et al.
2012
) has revealed that in
several situations bright and vivid colors have a structural component (Prum et al.
2006
; Ingram and Parker
2008
). This so-called structural color (Fig.
3.3
) is gen-
erated as a result of the interaction of the micro- and nano-structure of scales,
feathers, cuticles, petals or fruit peels with the incident light (Vukusic and Sambles
2003
; Eadie and Ghosh
2011
). This effect is based on the principle that physical
features with a size comparable to the wavelength of incident light can interfere
with it via multilayer interference, diffraction or scattering mechanisms (Prum
et al.
2006
).
Thus, structural color allows a precise control over the way light is reflected,
propagated or transmitted from a surface. This feature may present a significant
advantage in vital processes such as camouflage, long distance signaling and
thermoregulation (Vukusic
2006
). Structural coloring is more brilliant and intense
than pigment-induced color, it may possess iridescence properties or only be
visible at certain angles, and is less prone to bleaching. These characteristics have
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