The magazine MAQ The magazine MAQ ART December 2018 | Page 65

They covered each side of this bilayer with the breathable polymer nanoporous polyethylene, which is transparent to infrared radiation. The polymer above the copper is only half as thick as that covering the carbon. When the metallic side faces a warm surface such as skin, therefore, the heat readily travels through the thin polymer to the bilayer by conduction, passes through the metal to the carbon and is emitted to the surroundings. If the material is turned around, however, the thicker polymer hinders conduction, and the heat that does reach the bilayer is emitted much less readily by the metal surface. The novel material could allow the creation of clothing that can keep you warm if worn one way round, but cool you down if it’s turned inside out.

Schematic of dual-mode textile.

(A) Traditional textiles only have single emissivity, so the radiation heat transfer coefficient is fixed. (B) For a bilayer thermal emitter embedded in the IR-transparent nanoPE, when the high-emissivity layer faces outside and the nanoPE between the skin and the emitter is thin, the high emissivity and high emitter temperature results in large heat transfer coefficient, so the textile is in cooling mode. (C) The textile is flipped, and the low emissivity and low emitter temperature cause the heat transfer coefficient to decrease. The textile now works in heating mode.