ESTEVES, Catarina, et
PNIPAAm polymer on cotton absorbs 3.4
liter water per kilogram of fabric
Fog-catching fabric could improve water
collection in deserts
A novel and affordable fabric may improve the efficiency of water
collection from fog, helping to provide freshwater in desert
Researchers from the Eindhoven University of Technology (EUT), in
the Netherlands, and Hong Kong Polytechnic University, China,
turned a cotton fabric into a water-collecting material by
coating it with a polymer called PNIPAAm.
The fabric switches between absorbing moisture directly from the
air when it is foggy and cold, and releasing it as water at warmer
temperatures, according to a paper to be published on 21 February
in Advanced Materials.
Every kilogramme of the sponge-like fabric can absorb around 3.4
litres of water from the air. When the ambient temperature
rises, the material's microstructure changes and the water is
released. These processes are repeatable, raising hopes the fabric
could act as an autonomous water-collecting device.
The team hopes the material could be used to harvest water in dry
coastal areas, such as the Namib Desert, in Namibia, where
rainfall is scarce but ocean air currents frequently bring
The temperature range within which the fabric collects, and then
releases, water is similar to the typical daytime highs and
night-time lows seen in deserts.
21 January 2013
Cotton with special coating collects water
from fogs in desert
Photo: TU Eindhoven/Bart van Overbeeke
Researchers TU/e together with researchers at the Hong Kong
Polytechnic University (PolyU), have developed a special treatment
for cotton fabric that allows the cotton to absorb exceptional
amounts of water from misty air: 340 % of its own weight. What
makes this 'coated cotton' so interesting is that the cotton
releases the collected water by itself, as it gets warmer. This
property makes of the coated cotton materials a potential solution
to provide water to the desert regions, for example for
agricultural purposes. The results of this research will be
published next month in the scientific journal Advanced Materials.
The researchers applied a coating of PNIPAAm, a polymer, to the
cotton fabric. At lower temperatures, this cotton has a
sponge-like structure at microscopic level. Up to a temperature of
34°C it is highly hydrophilic, in other words it absorbs water
strongly. Through this property the cotton can absorb 340 % of its
own weight of water from misty air – compared with only 18%
without the PNIPAAm coating.
Totally pure water
In contrast, once the temperature raises the material becomes
hydrophobic or water-repellant, and above 34°C the structure of
the PNIPAAm-coated cotton is completely closed. When these high
temperatures are reached the cotton has released all the absorbed
water, which is totally pure. The research shows that this cycle
can be repeated many times.
Inspiration from Nature
Beetles in desert areas can collect and drink water from fogs, by
capturing water droplets on their bodies, which roll into their
mouths. Similarly, some spiders capture humidity on their silk
network. This was the inspiration for this new coated-cotton
material, which collects and releases water from misty
environments simply as the temperature changes throughout the day.
This property implies that the material may potentially be
suitable for providing water in deserts or mountain regions, where
the air is often misty at night. According to TU/e researcher dr.
Catarina Esteves a further advantage is that the basic material –
cotton fabric – is cheap and can be easily and locally produced.
The polymer coating increases the cost slightly, but with the
current conditions the amount required is only about 12%. In
addition, the polymer used is not particularly costly.
Placed directly on the soil
Fine-mesh ‘fog harvesting nets’ are already being used in some
mountains and dry coastal areas, but these use a different
principle: they collect water from misty air, by droplets that
gradually form on the nets and fall to the ground or a suitable
recipient. But this system depends on a strong air flow, wind. The
coated cotton developed the research team can also work without
wind. In addition, cotton fibers coated with this polymer can be
laid directly where the water is needed, for example on cultivated
soil. The researchers are also considering completely different
applications such as camping tents that collect water at night, or
sportswear that keeps perspiring athletes dry.
The research was led by professor John Xin at PolyU and dr.
Catarina Esteves at TU/e. They now intend to investigate further
how they can optimize the quality of the new material. For example
they hope to increase the amount of water absorbed by the
coated-cotton. Moreover they also expect to be able to adjust the
temperature at which the material changes from water-collecting to
the water-releasing state, towards lower temperatures.
9 JAN 2013
Advanced Materials, Volume 25, Issue 8, pages 1150–1154,
February 25, 2013
Temperature-Triggered Collection and
Release of Water from Fogs by a Sponge-Like Cotton Fabric
Helen Yang, Haijin Zhu, Marco M. R. M. Hendrix, Niek J. H. G.
M. Lousberg, Gijsbertus de With, A. Catarina C.
Esteves, and John H. Xin
A sponge-like cotton fabric autonomously collects and releases
water from fogs triggered by typical day-and-night temperature
variations. The reversible switching between
results from structural changes of a temperature-responsive
polymer grafted on the very rough fabric-surface. This material
and concept presents a breakthrough into simple and versatile
solutions for collection, uni-directional flow, and purification
of water captured from the atmosphere.
APPARATUS FOR PRODUCING WATER
CHE JU HEE
The present invention relates to a water obtaining apparatus and,
more specifically, to a water obtaining apparatus capable of
easily obtaining water and being used even in a place difficult to
receive electricity by collecting fog with a simple configuration
and absorbing, storing, and discharging water. According to the
present invention, the water obtaining apparatus includes: a
support means; a fog collecting means connected to the support
means to be supported and having a mesh body woven from cotton
fabrics coated with a heating wire and poly-N- isopropyl
acrylamide (PNIPAAm); a weight sensor measuring the weight of the
fog collecting means; a temperature sensor measuring the
temperature of the fog collecting means; a power supply means
supplying power to the heating wire; a water collecting means
arranged under the fog collecting means and collecting water
discharged and falling from the fog collecting means; a filter
means filtering the water collected in the water collecting means;
a storing means storing the water passing through the filter
means; and a control means changing the temperature of the fog
collecting means by controlling the operation of the power supply
means according to the weight of the fog collecting means measured
by the weight sensor. The fog collecting means absorbs and stores
the water of the fog passing through the fog collecting means, and
power is supplied to the heating wire according to the control of
the control means. If the temperature of the fog collecting means
excesses the determined temperature, the fog collecting means
discharges the stored water.
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