(ORDO NEWS) — The temperature-sensitive structure folds and unfolds like mimosa leaves. As a result, in the heat it exhibits cooling properties, and in the cold – warming.
Global climate change is exacerbating many extreme weather events. Heat waves and cold waves are no longer a rarity, leading to a painful increase in the cost of energy for air conditioning and space heating.
Materials for passive heating or cooling help to reduce such costs. In the simplest version, it can be white paint that reflects part of the sun’s rays. Other coatings, on the contrary, dissipate excess energy, giving it to the environment.
It has not yet been possible to combine these two possibilities, although in different seasons cooling and warming are required. The idea of an unusual structure that is capable of both at the same time was suggested to Chinese scientists by mimosa.
It is not for nothing that the name of this plant has become synonymous with bashful impatience: when touched, the leaves curl up.
Rujun Ma decided to use the same roll-up elements to change from a cooling cover to a warm one, and vice versa. The results of this work are presented in an article published in the journal PNAS .
The basis of the structure was the elements that change shape. They are made up of two layers: a layer of a transparent polymer that is resistant to heating and cooling, and a layer of polymers that contract or expand when the temperature changes.
This allows the elements to collapse or unfold depending on the temperature. Next, scientists added layers to them, designed to perform a useful task – to absorb or dissipate energy.
As a result, the entire multilayer structure collapses in the cold, leaving a dark heating layer on the surface. And as the temperature rises, it unfolds, revealing more and more reflective layer, which absorbs visible radiation and gives it in the infrared range.
This allows you to effectively cool and not heat up either the air or neighboring areas covered with a new material – “mimosa”, which does not absorb such photons.
Of course, the development was only the first step towards the creation of full-fledged industrial solutions. However, the prototype already obtained by Chinese scientists in the “warming mode” absorbs up to 73 percent of the energy of the incident sunlight, and in the “cooling mode” – only 35 percent.
At the same time, the structure endured 500 folding and unfolding cycles without any visible damage and almost without delamination. It is possible that the mass appearance of such coatings is closer than it seems.
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