Sep 14, 2010
Visitors to MIT’s hallowed “Infinite Corridor” will now encounter a bold new sight: at the far end of this grand artery in building 8 stands unveiled the gleaming Laboratory for Advanced Materials (LAM). The glittering glass facades offer a glimpse into what will eventually be a shared facility for the processing and characterization of a variety of “smart materials” that, true to the Institute’s visionary founding ethos, will bring together an interdisciplinary team of researchers to solve pressing problems in energy, information, and other technologically important fields. LAM will complement the Center for Materials Science & Engineering, another large interdisciplinary consortium of nanotechnology researchers funded by the National Science Foundation, further cementing MIT’s preeminence in materials-related research.
The recent opening of LAM coincides with MIT’s broader thrust into research domains that seek to impart sophisticated functionality to otherwise ordinary materials, oftentimes with profound consequences. Take for example Thermeleon (a portmanteau of thermal and chameleon), recent winners of the Making and Designing Materials Engineering Competition (MADMEC). They designed a temperature-sensitive polymer coating for roof tiles that magically turns white under the scorching summer sun and black in the frigid winter cold. Thermeleon’s clever and inexpensive coating offers an elegant solution for homes everywhere to maximize both heat reflection in the summer and heat retention in the winter, thereby offering a straightforward and practical means for regulating indoor household temperature.
A number of earlier technologies have also tried to use temperature-sensitive coatings for different applications. Hypercolor’s popular line of leuco dye containing t-shirts could mark hand prints, thermal printing is used by supermarkets everywhere to inexpensively print receipts, Moving Color manufactures tiles for interior decorations that respond to heat, and the Coors Brewing company now makes and markets “cold activated” beer can designs (developed by Chromatic Technologies) that indicate when the drinking temperature is optimal.
Thermeleon’s original idea sought to replicate the mechanism behind the popular lava lamps, whereby heating a wax decreases its density relative to its liquid environment and causes it to rise to the surface. After some cooling, the now lower-density wax eventually sinks back down only to be reheated once again. Thermeleon’s initial approach for thermally-activated roof coatings, therefore, consisted of a similar liquid-based system in which the wax would start out black and transition to white when heated. This idea was ultimately abandoned after considering the complexity involved. Instead, Thermeleon turned to a much simpler concept: a phase—changing-polymer gel that undergoes a reversible phase transition at a specified temperature—which the team can predetermine over a range of approximately 0 to 100 degrees Celsius. Below a given critical temperature, the polymer dissolves in the gel producing a homogeneous and clear solution that, when paired with a black background, will absorb light. When the temperature rises above the transition temperature, the polymer phase separates from the gel solvent to form a heterogeneous, white mixture that strongly scatters (i.e., reflects) light from the solar spectrum. Preliminary testing shows that 70% of the incident solar energy is absorbed by the black coating while 80% is reflected by the white coating.
Thermeleon has explored various ways to bring their product to the market. Several options include embedding the polymer coating as a hard tile with a glass front and plastic back, a flexible tile with a plastic front and back, and also a paintable system that can be applied over existing roof shingles. Currently the team is busy investigating the lifespan of their device under typical environmental conditions, in particular studying the effect of prolonged exposure to damaging UV radiation, which breaks bonds in the polymer chains. These are among the several technical issues that need to be resolved before the commercial viability of this technology can be accurately assessed. I sat down with Thermeleon cofounder Joseph Walish, currently a postdoctoral research associate in the Department of Materials Science & Engineering, to discuss his group’s invention.
MITER: How will the polymer coating stand up to the hostile northeastern US snow, rain, sleet, and ice?
JW: For the prototype that we showed at the MADMEC contest there would be little effect from snow, rain, ice, etc., since the active material is sandwiched between a clear top layer and a black backing. Future versions of the technology will be more like paint and are also expected to be quite robust. A big problem with most color changing paints and coatings is that they rely on dyes and pigments, which will quickly degrade with heat and UV exposure. We haven’t finished long-term tests yet but expect our system to be much, much more robust.
MITER: What effect will constant UV solar radiation have on the chemical bonds keeping the long polymer chains intact?
JW: UV degradation is a concern and we are looking into doing long-term testing, but even if the molecular weight of the chains is decreased due to UV damage there will still be a color changing effect. It might occur at a slightly different temperature but there will still be an effect. You can also add radical scavengers and UV stabilizers, which will prolong the life of the polymer.
MITER: How resilient is the coating to erratic or sudden shifts in temperature?
JW: The system is incredibly robust to sudden and erratic shifts in temperature.
MITER: To what extent does the enhanced heating and cooling provided by a rooftop coating actually affect household temperature?
JW: This depends a lot on how well the roof is insulated. If you have a perfectly insulated roof where no heat from the outside world is transferred indoors, then the color of your roof doesn’t matter. For most of the world this isn’t the case, so if you have an older roof the color could matter a lot. There are also added benefits for white roofs in the summer because lower roof temperatures make roof-mounted AC units more efficient. Also, in terms of the wider environment, white roofs reduce the “heat island effect” which may have some benefits in terms of global warming.
MITER: What are some of the other technical challenges that are being explored?
JW: Ha-ha, that’s a secret. More to come soon…
MITER: An even simpler alternative to thermally-activated coatings would be to make all rooftops uniformly white, a radical approach expounded by Dr. Steven Chu, current secretary of the Energy Department, who estimates that 20 years worth of heat trapping gases could be eliminated from the atmosphere in one year if every roof top in the world was painted white. What do you think of this?
JW: I agree that in some areas a non-color changing paint would be best: white roofs in areas that are always hot and sunny and black roofs in areas where it’s always cold and sunny. While there are many regions in the world that are in these two categories, there are large areas that are in between those two extremes. Our solution would be applicable in these “in-between” areas. Identifying these areas is where computer modeling comes in. We’ve made some initial connections in this area and have already made some initial forays into answering the question of where it makes most sense to deploy color changing building materials.
Thermeleon is currently actively engaged in research to improve the robustness of their coating and, pending the outcome of more research, will decide whether to pursue partnerships with manufacturers. Winning the MADMEC competition last year brought Thermeleon a torrent of media coverage, which they hope to leverage into meaningful business ventures. MADMEC is a nascent annual competition sponsored by the Department of Materials Science and Engineering, which seeks to promote materials-related ventures and enhance the department’s prominence in entrepreneurship (which currently boasts the burgeoning battery giant A123 and surgical optical scalpel manufacturer Omniguide, both founded by current faculty members). These types of competitions are healthy and ensure that MIT is well poised for further innovation in smart materials research.
Product: color-changing roof tiles for regulating indoor temperature
Industry: energy efficiency