>Squid and several other cephalopods can rapidly shift the colors in their skin, thanks to that skin's unique structure. Engineers at the University of Toronto have drawn inspiration from the squid to create a prototype for "liquid windows" that can shift the wavelength, intensity, and distribution of light transmitted through those windows, thereby saving substantially on energy costs. They described their work in a new paper published in the Proceedings of the National Academy of Sciences. > >“Buildings use a ton of energy to heat, cool, and illuminate the spaces inside them,” said co-author Raphael Kay. “If we can strategically control the amount, type, and direction of solar energy that enters our buildings, we can massively reduce the amount of work that we ask heaters, coolers, and lights to do.” Kay likes to think of buildings as living organisms that also have "skin," i.e., an outer layer of exterior facades and windows. But these features are largely static, limiting how much the building "system" can be optimized in changing ambient conditions. > >... > >Kay and his colleagues thought the structure of squid skin might hold the key to creating dynamic, tunable building facades. “Sunlight contains visible light, which impacts the illumination in the building, but it also contains other invisible wavelengths, such as infrared light, which we can think of essentially as heat,” said Kay. “In the middle of the day in winter, you’d probably want to let in both, but in the middle of the day in summer, you’d want to let in just the visible light and not the heat. Current systems typically can’t do this: they either block both or neither. They also have no ability to direct or scatter the light in beneficial ways.” > >So Kay et al. constructed a prototype microfluidics system featuring flat sheets of plastic containing an array of thin channels for pumping fluids. Adding customized pigments or particles to the fluid changes what wavelength of light gets through, as well as the direction in which that light is distributed. Those sheets can be combined into layered stacks, with each stack performing a different kind of optical function, such as filtering the wavelength, tuning how the transmitted light scatters indoors, and controlling the intensity—all managed with small digitally controlled pumps. > >According to Kay, this simple and low-cost approach could enable the design of "liquid-state, dynamic building facades" with tunable optical properties to save energy on heating, cooling, and lighting. While their prototype is a proof of concept, the team ran computer simulations of the system's likely performance as a dynamic building facade, responding to changing ambient conditions. Their models showed a single layer controlling the transmission of near-infrared light would result in a 25 percent savings. Adding a second layer controlling the transmission of visible light could achieve closer to 50 percent in energy cost savings.

This looks to be some interesting research with particular applications to building science and energy performance of buildings. Hopefully further testing and development can provide us with usable systems to help architects and engineers design and build more energy efficient and comfortable buildings in the near future.