Radiative cooling in hybrid polymeric films: from design optimization to quantitative performance evaluation

Passive daytime radiative cooling (PDRC) reduces heat load by reflecting solar radiation while emitting thermal energy through the atmospheric window. This thesis investigates polymer- based strategies that couple intrinsic vibrational emissivity with optical design to deliver scalable, flexible cooling films. First, free-standing styrenic block copolymers—SIS, SBS, and SEBS—were fabricated by solution casting and characterized via FTIR and UV–Vis–NIR spectroscopy to relate backbone chemistry to spectral response across 0.4–25 μm. Angular and polarization studies showed minimal spectral variation, indicating isotropic radiative behavior suitable for real-world orientations. Building on this baseline, an SBS platform was combined with surface-modified TiO2 to enhance solar back-scattering while preserving mid-IR emissivity, with processing routes optimized for uniform dispersion and free-standing films. Finally, molecular emissivity tuning was explored by doping PMMA with zinc-phthalocyanine derivatives at controlled concentrations, strengthening vibrational bands within the 3–5 μm and 8–13 μm windows while maintaining visible transparency. Across these systems, a unified, dimensionless figure of merit was introduced to couple solar-weighted absorbance with mid- IR emissivity, enabling fair comparison independent of weather or test setups. The results establish structure–property relationships: unsaturated styrenics intrinsically favor emission, scattering additives raise solar reflectance when compatibilized, and organic chromophores offer a tunable route to 24-hour thermal management. The materials are free-standing, solution- processed, and mechanically compliant, supporting large-area manufacturing and deposition on non-planar substrates. Overall, this work advances a multiscale design framework—from polymer chemistry to optical engineering and molecular doping—for passive radiative cooling coatings and films, and outlines guidelines for standardized spectral evaluation without relying on site-specific temperature measurements.