Reporting in the Journal of Materials Chemistry, researchers reveal they have developed an intelligent window coating that, when applied to the glass of buildings or cars, reflects the sun’s heat so you don’t get too hot under the collar.


While conventional tints block both heat and light the coating, which is made from a derivative of vanadium dioxide, allows visible wavelengths of light through at all times but reflects infrared light when temperature rise over 29 degrees Celsius. Wavelengths of light in this region of the spectrum cause heating so blocking infrared reduces unwanted rays from the sun.



The coating’s ability to switch between absorbing and reflecting light means occupants benefit from the sun’s heat in cooler conditions but when temperatures soar room heating is reduced by up to 50 per cent.



Professor Ivan Parkin, of UCL’s Department of Chemistry and senior author of the paper, says:



“Technological innovations such as intelligent window coating really open the door to more creative design. The current trend towards using glass extensively in building poses a dilemma for architects. Do they tint the glass, which reduces the benefit of natural light or face hefty air conditioning bills?



“While the heat reflective properties of vanadium dioxide are well recognised the stumbling block has been the switching temperature. It’s not much good if the material starts to reflect infrared light at 70 degrees Celsius. We’ve shown it’s possible to reduce the switching temperature to just above room temperature and manufacture it in a commercially viable way.”



Vanadium dioxide’s properties are based on its ability to alternate between acting as a metal and semiconductor. The switch between reflecting or absorbing heat is accompanied by a small change in the structure of the material, where the arrangement of electrons changes. Vanadium-vanadium bonds are stable below the transition temperature, which ‘lock’ the electrons and prevent conduction. Above the transition temperature these vanadium-vanadium bonds break and the electrons are free to conduct electricity making the material metallic.



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