Scientists tune polymer material’s transparency

From MIT

If you’ve ever blown up a balloon or pulled at a pair of pantyhose, you may have noticed that the more the material stretches, the more transparent it becomes. It’s a simple enough observation: the thinner a material, the more light shines through.

Now MIT scientists have come up with a theory to predict exactly how much light is transmitted through a material, given its thickness and degree of stretch. Using this theory, they accurately predicted the changing transparency of a rubber-like polymer structure as it was stretched like a spring and inflated like a balloon.

Francisco López Jiménez, a postdoc in MIT’s Department of Civil and Environmental Engineering, says the researchers’ experimental polymer structure and their predictive understanding of it may be useful in the design of cheaper materials for smart windows — surfaces that automatically adjust the amount of incoming light.

“For buildings and windows that automatically react to light, you don’t have to spend as much on heating and air conditioning,” López Jiménez says. “The problem is, these materials are too expensive to produce for every window in a building. Our idea was to look for a simpler and cheaper way to let through more or less light, by stretching a very simple material: a transparent polymer that is readily available.”

López Jiménez envisions covering window surfaces with several layers of the polymer structure. He says designers could use the group’s equation to determine the amount of force to apply to a polymer layer to effectively tune the amount of incoming light.

The research team — which includes López Jiménez; Pedro Reis, the Gilbert W. Winslow CD Associate Professor of Civil and Environmental Engineering and Mechanical Engineering; and Shanmugam Kumar of the Masdar Institute of Science and Technology in Abu Dhabi — has published its results this week in the Journal Advanced Optical Materials.