Phase‐Change Composite Films Integrating Thermal Energy Storage and Radiative Cooling for Solar‐Heating Suppression

Phase‐change materials offer high‐density latent heat storage and dynamic temperature regulation, but integrating thermal buffering with solar‐heating suppression and radiative heat dissipation in mechanically robust films remains challenging. Here, a multifunctional phase‐change composite film was fabricated by incorporating SiO 2 ‐encapsulated n‐octadecane microcapsules (MPCM) and TiO 2 nanoparticles into a Ca 2 ⁺‐crosslinked PVA/SA/CMC (PSC) matrix. The core–shell MPCMs provided latent heat storage and additional scattering interfaces, whereas TiO 2 enhanced solar reflection. The resulting PSC/MPCM/TiO 2 film exhibited a rough multiphase morphology and a tensile strength of ~12.8 MPa. It delivered melting and crystallization enthalpies of 60.14 and 61.06 J g −1 , respectively, and maintained stable phase‐transition behavior over 200 heating–cooling cycles. The film achieved a solar‐weighted reflectance of 77.78% and a long‐wave infrared (LWIR)‐weighted emissivity of 97.70% within the 8–13 μm atmospheric window. Under 1000 W m −2 simulated solar irradiation, its back‐surface steady‐state temperature was ~13°C–14°C lower than that of a directly irradiated bare‐thermocouple reference under the employed test configuration. Transient heating–cooling tests showed that MPCM melting and crystallization delayed temperature rise and moderated temperature fluctuations, while outdoor day–night measurements confirmed reduced heat accumulation and smoother thermal responses. A steady‐state energy‐balance model further predicted a net radiative cooling power of ~62 W m −2 at ambient temperature under 600 W m −2 solar irradiation. These results demonstrate the complementary roles of solar reflection, long‐wave infrared emission, and latent heat storage in passive heat rejection and dynamic thermal buffering, highlighting the potential of this composite film for building‐envelope thermal management.