When it comes to scrutinizing architectural materials for their energy efficiency, one offender stands out above the rest: glass. Windows and curtain walls act as one of a building’s main outlets for heating and cooling losses, and as society advances into its more environmentally-conscious future, new, passive solutions will need to be developed to mitigate buildings’ energy footprints. In recent years, various smart glass technologies have been designed to automatically regulate light and heat based on environmental conditions. Yet their high price tags have prevented them from achieving widespread application. Now, a team of MIT researchers may have discovered an alternative to smart glass that could come at an affordable price.
The method involves stretching a material to increase its transparency. The research team - made up of 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 - first developed a theory to predict exactly how much light is transmitted through a material, given its thickness and degree of stretch. Think, for example, of how a latex balloon becomes more transparent as it is inflated. The group then applied this theory to create a soft color composite - a material that changes color or transparency in response to external stimuli, in this case mechanical force. To create the composite, they chose a thin stack of PDMS - a highly elastic, transparent polymer - mixed with a solution of black, micron-sized dye particles. At rest, the material is opaque. But as it is mechanically deformed by stretching or inflating, the material allows more and more light through.
“We can predict and characterize the evolution of light as we strain it,” says López Jiménez. “If you give me the initial material properties and measure the incoming light intensity, we know exactly how much light will go through with deformation.”
The widespread use and affordability of PDMS make it a strong candidate for commercial application, but the research group plans to continue testing their theory with more complex surfaces and textures to achieve optimum efficiency.
“Soft color composites offer exciting opportunities to provide materials with switchable and tunable optical properties,” Reis says. “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.”