Humidity-gated, temperature-responsive photonic infrared reflective broadband coatings

Abstract

The fabrication of temperature responsive photonic polymers remains a challenge. Here, we report the fabrication of humidity-gated temperature-responsive infrared reflective photonic coatings using an easy-to-process bar-coating technique. At high humidity the hydroscopic cholesteric liquid crystalline polymer is able to absorb water vapour from the air causing swelling of the photonic coating. By increasing the temperature, water is desorbed from the coating, resulting in a reversible 420 nm shift of the photonic reflection band. In particular, it is shown that temperature-responsive single-layered broadband IR reflective coatings, prepared by creation of a pitch gradient of the cholesteric liquid crystals, might be suitable for smart window applications in high relative humidity environments such as greenhouses.