Cross-overlapped flat-silver/hexagonal boron nitride for translucent heat-reflective coatings

Abstract

Multifunctional heat-reflective coatings are increasingly in demand for use in energy-efficient buildings and vehicles, as well as for optoelectronic devices. Conventional heat-reflective coatings (e.g. dielectric/metal/dielectric (DMD)) exhibit poor structural flexibility and combine complex fabrication process of multilayered structures, which hinders their scalable production. Herein, a low-cost translucent heat reflective mechanism is presented using single-coat composite film of flat-silver (flat-Ag) and hexagonal boron nitride (hBN) as an alternative to the multilayered DMD structure. The conversion of grey Ag-nanoparticles into shiny flat-Ag results in significant enhancement (~7 times) in infrared (IR) reflection. The dielectric-hBN layers integrated with flat-Ag improves the visible transmittance and heat-dissipating properties of coatings. The flat-Ag/hBN ink sprayed onto a flexible, transparent, and adhesive substrate of polydimethylsiloxane (PDMS) exhibits excellent IR-reflection (~70%) with ~57% visible transmittance. When irradiated by an IR heat source, the film displays 8.9 ± 0.5 °C lower temperature than those of uncoated surfaces, that results in reduction of the interior air-temperature by 5.4 ± 0.5 °C compared to the uncoated control. This newfabrication process of heat-reflective coatings with structural flexibility and optical transparency has great potentials to be used for thermal management in building and transportation sectors.