Researchers at the Institute for Microstructure Technology (IMT) and the Light Technology Institute (LTI) at the Karlsruher Institut für Technologie in Germany have developed a novel polymer-based metamaterial that combines a range of useful properties and could replace glass components in construction in the future. The new polymer-based material allows sunlight to enter, maintains a more comfortable indoor climate without additional energy and cleans itself like a lotus leaf. The new development could replace glass components in walls and roofs in the future.
Maximising natural light is an important element of building design and can save on energy costs. However, traditional glass roofs and walls can present problems such as glare, lack of privacy and overheating. Alternative solutions, such as coatings and light-diffusing materials, have not yet provided a comprehensive remedy.
The new polymer-based micro-photonic multi-functional metamaterial (PMMM) consists of microscopic pyramids made of silicone. These micro-pyramids are about ten micrometres in height – about one-tenth the diameter of a hair. Their design gives the PMMM film several useful characteristics, including light diffusion, self-cleaning and radiative cooling, while also maintaining a high level of transparency.
‘A key feature is the ability to efficiently radiate heat through the Earth’s atmosphere’s long-wave infrared transmission window, releasing heat into the cold expanse of the universe. This allows for passive radiative cooling without electricity consumption,’ explained Bryce S Richards, a professor at IMT and LTI.
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The researchers tested the material’s properties and measured its light transmittance, light scattering, reflection properties, self-cleaning ability and cooling performance both in the lab and in experiments under open skies under real outdoor conditions. The results showed that the material achieved cooling of 6°C compared to the ambient temperature. Additionally, the material showed a high spectral transmittance, or transparency, of 95 per cent. In comparison, glass typically has a transparency of 91 per cent. At the same time, the micro-pyramid structure scattered 73 per cent of the incoming sunlight, resulting in a blurry appearance.
‘When the material is used in roofs and walls, it allows for bright yet glare-free and privacy-protected indoor spaces for work and living. In greenhouses, the high light transmittance could increase yields because the photosynthesis efficiency is estimated to be nine per cent higher than in greenhouses with glass roofs,’ said Gan Huang, a group leader at IMT.
The micro-pyramids also give the PMMM film superhydrophobic properties, similar to that of a lotus leaf, which impart a self-cleaning ability on the material. Water that falls on the material beads up into droplets, removing dirt and dust from the surface. This makes the material easy to maintain and durable.
‘Our newly developed material has the potential to be used in various areas and makes a significant contribution to sustainable and energy-efficient architecture,’ Richards said.
‘The material can simultaneously optimise the use of sunlight indoors, provide passive cooling and reduce reliance on air conditioning,’ said Huang. ‘The solution is scalable and can be seamlessly integrated into plans for environmentally friendly building construction and urban development.’
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The research has been published in Nature Communications.