Nanocrystal ‘painted’ films may someday help relieve summer heat
Normal coatings, such as paint, heat up in the sun. The new crystal films get the surface cooler than the air around them when exposed to sunlight. They do this by reflecting the sun’s rays and releasing that heat into outer space.
The new films don’t get their colour from pigments. The new films’ colour comes from tiny crystals of cellulose made of plant fibers. This is known as structural colour. Those chemicals work by reflecting just the colours of light we see and absorbing the rest. The films also emit heat (infrared wavelengths) which can then escape the atmosphere. Under sunlight, the films cooled to 4 degrees Celsius (7 degrees Fahrenheit) below the air temperature. If used to help keep buildings cool in the summer sun, he notes, these coatings might cut the need for air conditioning.