Structured Filler-Enabled Pore-Interface Engineering in Polydimethylsiloxane for Passive Radiative Cooling

Passive radiative cooling (PRC) materials require efficient solar scattering, high thermal emissivity, and mechanical compliance, yet constructing hierarchical pore-interface architectures that simultaneously enhance particle scattering, interface scattering, and flexibility within a single polymer system remains challenging. Here, we report a structured filler-induced pore-interface engineering strategy for flexible PRC films. Carboxymethyl cellulose (CMC) and silane-modified SiO2 nanoparticles were electrostatically assembled into a spatially organized CMC@SiO2 filler, which simultaneously acts as a scattering unit and a pore-forming scaffold. Upon incorporation into polydimethylsiloxane (PDMS), the structured filler induces hierarchical pore architectures with SiO2-decorated pore walls, generating coupled particle-scattering and pore-interface scattering pathways. The Finite-Difference Time-Domain simulations reveal that the multiscale architecture broadens solar scattering across the 0.25-2.5 μm range through enhanced refractive-index contrast and multiple-scattering effects. Benefiting from the coupled contribution of SiO2 scattering centers, hierarchical pore interfaces, and the intrinsic mid-infrared (MIR) emissivity of PDMS, the resulting film achieves a solar reflectivity of 94.6% and a MIR emissivity of 95.2%. The film delivers a maximum sub-ambient cooling of 7.1 °C under direct sunlight. Building energy simulations further predict an average annual cooling-energy reduction of 10.4% across representative climate zones in China. This work establishes a structured filler-enabled hierarchical pore-interface engineering strategy that integrates scattering enhancement, porous architectures, and polymer flexibility, offering a general route toward scalable and high-performance PRC materials.