Colorful films could help buildings, cars keep their cool

Date:
March 27, 2023
Source:
American Chemical Society
Summary:
The cold blast of an air conditioner can be a relief as
temperatures soar, but 'A/C' units require large amounts of
energy and can leak greenhouse gases. Today, scientists report
an eco-friendly alternative - - a plant-based film that cools
when exposed to sunlight and comes in many textures and bright,
iridescent colors. The material could someday keep buildings,
cars and other structures cool without requiring power.


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FULL STORY ==========================================================================
The cold blast of an air conditioner can be a welcome relief as
temperatures soar, but "A/C" units require large amounts of energy
and can leak potent greenhouse gases. Today, scientists report an
eco-friendly alternative -- a plant-based film that gets cooler when
exposed to sunlight and comes in a variety of textures and bright,
iridescent colors. The material could someday keep buildings, cars and
other structures cool without requiring external power.


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The researchers will present their results at the spring meeting of the American Chemical Society (ACS).

"To make materials that remain cooler than the air around them during the
day, you need something that reflects a lot of solar light and doesn't
absorb it, which would transform energy from the light into heat," says
Silvia Vignolini, Ph.D., the project's principal investigator. "There are
only a few materials that have this property, and adding color pigments
would typically undo their cooling effects," Vignolini adds.

Passive daytime radiative cooling (PDRC) is the ability of a surface
to emit its own heat into space without it being absorbed by the air or atmosphere. The result is a surface that, without using any electrical
power, can become several degrees colder than the air around it. When
used on buildings or other structures, materials that promote this effect
can help limit the use of air conditioning and other power-intensive
cooling methods.

Some paints and films currently in development can achieve PDRC, but
most of them are white or have a mirrored finish, says Qingchen Shen,
Ph.D., who is presenting the work at the meeting. Both Vignolini and Shen
are at Cambridge University (U.K.). But a building owner who wanted to
use a blue-colored PDRC paint would be out of luck -- colored pigments,
by definition, absorb specific wavelengths of sunlight and only reflect
the colors we see, causing undesirable warming effects in the process.

But there's a way to achieve color without the use of pigments. Soap
bubbles, for example, show a prism of different colors on their
surfaces. These colors result from the way light interacts with differing thicknesses of the bubble's film, a phenomenon called structural
color. Part of Vignolini's research focuses on identifying the causes
behind different types of structural colors in nature. In one case,
her group found that cellulose nanocrystals (CNCs), which are derived
from the cellulose found in plants, could be made into iridescent,
colorful films without any added pigment.

As it turns out, cellulose is also one of the few naturally occurring
materials that can promote PDRC. Vignolini learned this after hearing
a talk from the first researchers to have created a cooling film
material. "I thought wow, this is really amazing, and I never really
thought cellulose could do this." In recent work, Shen and Vignolini
layered colorful CNC materials with a white- colored material made from
ethyl cellulose, producing a colorful bi-layered PDRC film. They made
films with vibrant blue, green and red colors that, when placed under
sunlight, were an average of nearly 40 F cooler than the surrounding
air. A square meter of the film generated over 120 Watts of cooling
power, rivaling many types of residential air conditioners. The most challenging aspect of this research, Shen says, was finding a way to
make the two layers stick together -- on their own, the CNC films were
brittle, and the ethyl cellulose layer had to be plasma-treated to get
good adhesion. The result, however, was films that were robust and could
be prepared several meters at a time in a standard manufacturing line.

Since creating these first films, the researchers have been improving
their aesthetic appearance. Using a method modified from approaches
previously explored by the group, they're making cellulose-based cooling
films that are glittery and colorful. They've also adjusted the ethyl
cellulose film to have different textures, like the differences between
types of wood finishes used in architecture and interior design, says
Shen. These changes would give people more options when incorporating
PDRC effects in their homes, businesses, cars and other structures.

The researchers now plan to find ways they can make their films even
more functional. According to Shen, CNC materials can be used as sensors
to detect environmental pollutants or weather changes, which could be
useful if combined with the cooling power of their CNC-ethyl cellulose
films. For example, a cobalt-colored PDRC on a building fac,ade in a
car-dense, urban area could someday keep the building cool and incorporate detectors that would alert officials to higher levels of smog-causing
molecules in the air.

The researchers acknowledge support and funding from Purdue University,
the American Society of Mechanical Engineers, the European Research
Council, the Engineering and Physical Sciences Research Council, the Biotechnology and Biological Sciences Research Council, the European
Union and Shanghai Jiao Tong University.

* RELATED_TOPICS
o Matter_&_Energy
# Civil_Engineering # Engineering_and_Construction #
Materials_Science # Thermodynamics
o Earth_&_Climate
# Air_Quality # Environmental_Science # Air_Pollution
# Pollution
* RELATED_TERMS
o Alternative_fuel_vehicle o Greenhouse_gas o
Climate_change_mitigation o Nuclear_power_plant o
Energy_development o Greenhouse_effect o Wind_power o
Attribution_of_recent_climate_change

========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


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Link to news story: https://www.sciencedaily.com/releases/2023/03/230327114920.htm

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