Scientists have developed low-cost glass panels that can selectively allow and block light, paving the way for eco-friendly smart windows that absorb heat in the winter and reflect it in summer.
The principles behind this smart glass technology are simple. It starts with two sheets of plastic separated by a thin cavity.
The plastic contains tiny cube-shaped structures that make the material retroreflective, meaning that it bounces light back to its source, like a bicycle reflector does. Then the chamber is filled with a fluid called methyl salicylate - an inexpensive wintergreen extract that happens to be the active ingredient in some over-the-counter pain relief creams. The liquid has optical properties, or interaction with visible light, that match the optical properties of the retroreflective plastic.
When combined, the light can pass through, and the system becomes transparent. This is called refractive index matching.
The smart glass system can switch from transparent to reflective a thousand times without degrading, according to a study published in the journal Optics Express.
Instead of utilising cubes, the smart glass relies on the total internal reflection of one-dimensional structures layered perpendicularly.
It is highly reflective at up to a 60-degree angle of incidence, an improvement over the previous prototype.
"It performed better than we thought it would based on our theoretical understanding," said Keith Goossen, associate professor at the University of Delaware in the US.
Goossen used 3D printing to make his prototypes, but this technology could eventually be manufactured at a high volume and low cost using injection molding. He is now testing his system over a wide range of temperatures to see how it performs, especially as it approaches temperatures that could cause the fluid within to freeze, which will be between three and 16 degrees Fahrenheit, depending upon the eventual fluid that is used.