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Published on January 26th, 2016 | By: Stephanie Liverani


Tunable, transparent polymer material could be key to cheaper energy-efficient windows

Published on January 26th, 2016 | By: Stephanie Liverani

[Image above] MIT researcher Francisco López Jiménez demonstrates the change in transparency when a polymer is stretched to help illustrate his theory that predicts exactly how much light is transmitted through a material. Credit: MIT; YouTube



The northeastern part of the United States is slowly recovering from the aftermath of winter storm Jonas, but the winter season is still in full swing. That means icy temps and higher energy bills for most of us.


Some of us sacrifice comfort for frugality, opting to keep that thermostat low and winter coats within reach. The struggle is real.


Those who own homes and buildings know that window replacement is a big investment, but an effective way to boost energy efficiency. And scientists, engineers, and researchers are hitting the pavement hard when it comes to innovating cost-effective alternatives to current smart window technology so more of us can afford to integrate this solution into our homes and businesses. 


Last July, we covered research from the University of Texas at Austin, where scientists are developing a material that allows windows to let light pass through without transferring heat and, on the flip side, to block out light while allowing heat transmission.


The U.S. Department of Energy’s Los Alamos (N.M.) National Laboratory is creating new sunlight harvesting technology that can turn a nearly transparent window into an electrical generator using what they are calling “quantum dot solar windows.”


Other researchers are focused on smarter coatings for existing glass. Scientists at the Georgia Institute of Technology in Atlanta created a polymer coating for glass that can change the lens color of glasses instantly with a small, user-controlled electrical current.


Engineers at Michigan State University developed a ‘clear’ alternative to existing photovoltaic technology that can be retrofit to existing glass-covered buildings—and they say it’s scalable.


But most recently, scientists at the Massachusetts Institute of Technology are working with a readily available transparent polymer that may be useful in the design of cheaper materials for smart windows 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,” Francisco López Jiménez, a postdoc in MIT’s Department of Civil and Environmental Engineering, says in an MIT news release. “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.”


The team came 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 came up with an equation to accurately predict the changing transparency of a polymer structure as it was stretched like a spring and inflated like a balloon, the release explains.


Check out this MIT video, in which the researchers explain the concept. 

Credit: MIT; YouTube


The polymer material (PDMS) changes color or transparency in response to external stimuli, such as electrical, chemical, or mechanical force, the release explains. With no deformation, the structure appears opaque. When stretched or inflated, the material lets in more light.


López Jiménez says layers of this polymer can be applied to an existing window’s surface, and the group’s equation can be used to determine the amount of force to apply to a polymer layer to effectively tune the amount of incoming light.


“Soft color composites offer exciting opportunities to provide materials with switchable and tunable optical properties,” Pedro Reis, a member of the research team and associate professor of civil and environmental engineering and mechanical engineering at MIT, says in the release. “Applying this relatively simple but both robust and predictable mechanism is an exciting challenge worth pursuing for concrete engineering applications such as indoor light control through smart windows.”


The research, published in Advanced Optical Materials, is “Soft color composites with tunable optical transmittance” (DOI: 10.1002/adom.201500617).


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