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Comment Separation Processes

Multilayer membrane for climate control

By Mary Page Bailey |

A triple-layer, porous membrane system developed at the Functional Materials Laboratory at Eidgenössische Technische Hochschule Zürich (www.fml.ethz.ch) can be fashioned into evaporative curtains to cool and humidify indoor spaces, potentially decreasing the energy demand for climate-control systems. Juxtaposing opposite forces — in this case, layering a hydrophilic membrane layer between two hydrophobic outer layers — allows a water film to remain stabilized between the dry outer layers. “This open, porous system lets the water film evaporate outward on both sides of the materials. At the same time, the inner porous system is able to refill itself from a water reservoir,” explains Mario Stucki, the lead developer of this technology. “The immense heat of evaporation of water cools the membrane’s surroundings,” he continues.

The triple-layer membrane materials are assembled via the template removal method, in which hard template particles made from soluble salts are dispersed as templates in dissolved polymer solutions. When the solution is spread, and the solvent is removed, a solid, multiphase layer is produced. This base layer is then coated with an additional layer of liquid dispersion, resulting in the formation of multilayer complexes. According to Stucki, template removal is the only membrane production method that allows for straightforward multilayer laminate assembly, as other methods would require the application of adhesives between the layers. Another benefit of these membranes is that the pore size is extremely small, which enables water to be effectively contained within the layers. “At larger pore sizes, the top and bottom layer would leak the water and possibly lead to much faster fouling,” he adds. Stucki and his team have demonstrated this passive cooling process with membrane samples 10 x 10 cm2 in size. The template-removal method has previously been demonstrated on industrial-scale coating and drying machines, says Stucki, so scaling up this technology for mass production is certainly feasible.

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