Preparation and Properties of Cellulose Nanocrystal-Based Structurally Colored Radiative Cooling Composite Films

Abstract

Radiative cooling lowers its own temperature by emitting heat into outer space, is a green, low-carbon, and sustainable cooling strategy. Most radiative cooling materials have monotonous appearance colors, mostly white or transparent, and the addition of traditional colorants will cause the materials to absorb heat, reducing radiative cooling performance. Structurally colored cellulose nanocrystal/polyethylene glycol (CNC/PEG) composite radiative cooling films were prepared by self-assembly method, and the composite films were combined with porous cellulose acetate (CA) membranes to obtain structurally colored radiative cooling bilayer composite films. The results show that the CNC/PEG composite films have bright structural colors with obvious birefringence phenomenon. As the PEG content increases, the pitch of the composite film structure increases, and the color changes from blue-green to red. The CNC/PEG structurally colored composite film has the highest reflectance in the visible light band up to 68.5%, and the emissivity in the atmospheric window band is up to 93%, with an ambient cooling effect of about 3.4°C. The CNC/PEG-CA bilayer composite film has the highest reflectance in the visible light band up to 91.8%, and the emissivity in the atmospheric window band is up to 32.2%. Compared with the composite film, the bilayer composite film has better cooling performance, with a temperature difference of about 14.3°C compared to the ambient temperature. In outdoor tests, compared with the ambient temperature, the composite film can achieve a cooling effect of about 2°C, and the bilayer composite film can achieve a cooling effect of about 6°C.