Environmental Engineering Reference
In-Depth Information
Anti-icing. Icing is another climatic event capable of affecting vital infra-
structures of modern society. Ice may block roads, take down power cables, cause
the rupture of pipelines and promote pedestrian slip events. The aeronautics
industry has invested considerable resources on this problem, since the accumu-
lation of ice over the fuselage of aircrafts increases its weight, unbalances the flight
and increases drag, consequently reducing fuel efficiency and raising safety con-
cerns (Bahadur et al.
2011
). The ice formed when supercooled suspended drops
aggregate on airplane surfaces has been appointed as culprit on many plane crashes
over the years. Conventional solutions to create anti-icing surfaces are not sus-
tainable or reliable. On one hand, such surfaces depend on an energy intensive
heating system, while on the other, they depend on anti-cryogenic chemicals, such
as glycerol, which are toxic and require permanent replenishment. Researchers
have looked up to nature for inspiration and were rewarded with two potential
ideas. For example, superhydrophobic surfaces have been created using topo-
graphic features inspired on the defogging mosquito eyes, which also prevent ice
crystals nucleation, and on the water repellent hairs of buoyant insects (from order
Hemiptera). Assays on the behavior of droplets impacting on these surfaces at
supercooled conditions revealed that they can avoid ice formation down to -25 C
(Mishchenko et al.
2010
). The second strategy uses slippery liquid-infused porous
surfaces (SLIPS) inspired in carnivorous plants from the Nepenthes genus that
lower the nucleation temperature of supercooled water (Wilson et al.
2012
). These
plants attract insects to their pitcher cups, hampering their escape as a result of the
slippery inner surface (Kim et al.
2012
). The pitfall traps have a porous lining
permeated with an aqueous solution, which is incompatible with the oils sheathing
the insect's feet. The SLIPS systems consist of a microporous scaffold infused with
a lubricating fluid with which the liquid to repel (in this case water) is immiscible
(Wilson et al.
2012
). In nature, a structure is often multifunctional, and SLIPS
are no exception. Besides preventing ice formation, they are self-cleaning, anti-
corrosive, and anti-biofouling (i.e., they prevent the adhesion of organisms).
3.3.4 Anti-biocolonization Properties
The biological colonization of walls, tiles, flooring, and other building surfaces
(external and internal) by organisms like algae, bacteria and fungi can cause direct
and indirect damage (e.g., blackening, greening, fissuration) to materials and
elements of construction (Macedo et al.
2009
), even if some species (e.g., lichens,
mosses) can enhance the appearance and character of buildings and structural
monuments. Such biological and microbiological growths are usually dependent
on both the bioreceptivity of the underlying materials and on the environmental
conditions (e.g., humidity, temperature, solar exposure). While this type of
material decay and soiling can be partially alleviated by resorting to a planned
preventive maintenance, the development of anti-biocolonization materials could
constitute a valuable alternative to the construction industry.
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