Science looks to poplar trees for 'cool roof' technology

The idea is simple, the poplar tree, over eons, has developed micro-fibers on the undersides of its leaves that can reflect both light and heat from the sun; thus, when the sun shines directly on the tree, it turns its leaves upside down to protect the insides of the leaves from extreme heat and the ensuing loss of moisture.

The Chinese team has been working on spinning polymers into long protective hollow fiber coatings that could in theory reflect sunlight, and thus reduce the amount of heat that is absorbed when sunlight shines on a roof. To test their results, they covered a swath of material with diarylethene, a compound that changes color when heated, then covered that with their polymer film, and then let the sun shine. They found that the more closely they could emulate the structure of the natural fibers on the poplar leaves, the less the diarylethene changed color.

And while the results the team has managed to show so far are promising, there is still a pretty serious obstacle standing in the way of developing a commercial product that could help homeowners or businesses cut their summer cooling costs; the polymers are just not resistant enough to stand up to the constant barrage of heat, cold, wind and other weather conditions.

Song says he and his team will continue to work with the polymers to see if they can come up with something stronger but will also continue with what they've developed thus far, perhaps even branching out in to other areas, such as lighting applications or in developing waterproofing substances since their polymer film turned out to be water resistant as well.

More information: Highly reflective superhydrophobic white coating inspired by poplar leaf hairs toward an effective "cool roof", Changqing Ye, Mingzhu Li, Junping Hu, Qunfeng Cheng, Lei Jiang and Yanlin Song, Energy Environ. Sci., 2011, Advance Article. DOI:10.1039/C0EE00686F

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