Leaf-inspired ZnO-Cr2O3/epoxy coatings with tailored visible–NIR reflectance for spectral camouflage applications

Abstract

The difference in spectral response between the target and the background is very crucial to avoid target detection by surveillance systems in the visible (VIS) and near-infrared (NIR) spectral regions. In this study, ZnO–Cr 2 O 3 /epoxy composite coatings were developed using compressed-air spraying with varying ratios of ZnO and Cr 2 O 3 nanopowders to replicate the spectral reflectance of natural foliage ( Pongamia Pinnata leaves). Spectral reflectance was studied through Diffuse Reflectance Spectroscopy (DRS), while microstructural and chemical analysis were performed using Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). ZC-40, with 40 wt% filler (comprising 80% ZnO and 20% Cr 2 O₃) in an epoxy resin, achieved a visible reflectance of 25–28% and a NIR reflectance of 50–55%, closely resembling the spectral response of natural leaves in the 400–1200 nm wavelength range. The coating was also thermally stable up to 350 °C, had scratch resistance greater than 20 N, and had an excellent adhesion rating of 5 A (ASTM-3350-Method A). Additionally, a cosine similarity over 99% confirmed its strong spectral similarity with natural leaves, highlighting its potential for multispectral camouflage applications.