The rubbery material they used called polydimethylsiloxane has dark regions when at rest but gets more and more transparent as you stretch it. One of the researchers, Francisco López Jiménez, says the decision to undertake the project was a happy accident. "We were just playing with the material, and we soon got interested in how we can predict this and get the numbers right."
They prepared some small pieces of material for their experiments, adding color to them by mixing in micron-sized dye particles.
MIT describes the group's process as follows:
In initial experiments, the researchers shone a light through the polymer structure infused with dye particles and characterized the amount of light transmitted through the material, without any deformation. They then stretched the polymer perpendicular to the direction of light and measured both the thickness of the polymer and the light coming through.
They compared their measurements with predictions from their equation, which they devised using the Beer-Lambert Law, a classical optics theory that describes the way light travels through a material with given properties. The team combined this theory with their experimental analysis, and derived a simple equation to predict the amount of light transmitted through a mechanically deformed PDMS structure.
López Jiménez says in the future, manufacturers can create smart windows much more affordable than see-through screens being developed by some companies today. That's possible by putting layers of the polymer on top of each other. Any manufacturer can find out how much pressure to apply on windows to turn them transparent by using the group's equation. He expects the smart windows to ultimately lower heating and air conditioning bills since a house's or building's residents can control how much sunlight to let in.