Innovative material for energy-efficient architecture: Researchers at the Karlsruhe Institute of Technology (KIT) present a polymer-based material with special properties in the current issue of the journal Nature Communications . The material allows sunlight into the interior, ensures a more pleasant indoor climate and cleans itself like a lotus leaf. The new development could replace glass components in walls and roofs in the future. The research team successfully tested the material in outdoor tests on the KIT campus. ( DOI: 10.1038/s41467-024-48150-2 ).
As much natural light as possible in buildings is popular and saves energy costs. However, traditional glass roofs and walls also pose problems such as glare, lack of privacy and overheating. Alternative solutions such as coatings and light-scattering materials do not yet offer a comprehensive solution.
New material combines several functions
Researchers at the Institute of Microstructure Technology (IMT) and the Lighting Institute (LTI) of KIT have now developed a novel polymer-based metamaterial that combines various properties and could replace glass components in the construction sector in the future. The so-called Polymer-based Micro-Photonic Multi-Functional Metamaterial (PMMM) consists of microscopic pyramids made of silicone. These micropyramids measure around ten micrometers, which is about a tenth of the diameter of a hair. This nature gives the PMMM film several functions: light scattering, self-cleaning and radiative cooling while maintaining high transparency. “A key feature is the ability to efficiently radiate heat through the long-wave infrared transmission window of the Earth’s atmosphere, thereby releasing heat into the cold vastness of the universe. This enables passive radiative cooling without power consumption,” explains Bryce S. Richards, professor at IMT and LTI.
Cooling, translucent and anti-glare
In the laboratory and in open-air experiments under real outdoor conditions, the researchers tested the properties of the material and used modern spectrophotometry to measure light transmission, light scattering, reflection properties, self-cleaning ability and cooling performance. The result: In the tests, cooling of six degrees Celsius compared to the ambient temperature was achieved. There was also a high spectral transmittance, i.e. transparency of 95 percent. In comparison, glass typically has a transparency of 91 percent. At the same time, 73 percent of the incident sunlight is scattered by the micropyramid structure. This creates a blurry appearance. “When the material is used in roofs and walls, it enables bright and at the same time glare-free and visually protected interior spaces for working and living. In greenhouses, high light transmission could increase yields because the efficiency of photosynthesis is estimated to be nine percent higher than in greenhouses with glass roofs,” says Dr. Gan Huang, group leader at IMT. The micropyramids also give the PMMM film superhydrophobic properties, similar to a lotus leaf: water rolls off in the form of drops, removing dirt and dust from the surface. This self-cleaning function makes the material easy to care for and durable.
Potential for construction and urban development
“Our newly developed material has the potential to be used in a variety of areas and makes an important contribution to sustainable and energy-efficient architecture,” explains Richards. “The material can simultaneously ensure optimal use of sunlight indoors, provide passive cooling and reduce dependence on air conditioning. The solution can be scaled and seamlessly integrated into plans for green housing and urban development,” says Huang.
The Karlsruhe research team had already won first place in the Public Choice Award of the Helmholtz Best Scientific Image competition last year for its work.
Original publication
Gan Huang, Ashok R. Yengannagari, Kishin Matsumori, Prit Patel, Anurag Datla, Karina Trindade, Enkhlen Amarsanaa, Tonghan Zhao, Uwe Köhler, Dmitry Busko, Bryce S. Richards: Radiative cooling and indoor light management enabled by a transparent and self- cleaning polymer-based metamaterial, Nature Communications volume 15, Article number: 3798 (2024). DOI: 10.1038/s41467-024-48150-2
As “The Research University in the Helmholtz Association,” KIT creates and imparts knowledge for society and the environment. The aim is to make significant contributions to global challenges in the fields of energy, mobility and information. To this end, around 10,000 employees work together on a broad disciplinary basis in natural sciences, engineering, economics, humanities and social sciences. KIT prepares its 22,800 students for responsible tasks in society, business and science through research-oriented university studies. The innovation activity at KIT builds the bridge between knowledge and application for social benefit, economic prosperity and the preservation of our natural resources. KIT is one of the German universities of excellence.
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