Reversible Phase‐Change‐Induced Transparency Switching and Dynamic Thermal Regulation Gel for Energy‐Efficient Smart Windows

Inefficiencies in window thermal management account for a substantial portion of energy losses in buildings, highlighting the urgent need for advanced, energy‐efficient active thermal control measures in architectural design. In this study, we present a novel strategy that integrates eutectic phase change materials (lauric acid and methyl palmitate) within a poly (methoxyethyl acrylate) organic gel framework, denoted as PEPG, which achieves temperature‐responsive optical transparency switching and passive thermal regulation. By leveraging crystal‐melt phase transitions, the proposed system achieves dual‐mode regulation: It facilitates energy‐efficient daylighting through a transparent homogeneous phase at temperatures exceeding the fusion threshold ( T lum = 96.03%) while simultaneously providing privacy protection via a microphase‐separated heterogeneous phase at temperatures below the solidification threshold (Δ T sol = 77.13%). Notably, the temperature‐induced reversible phase transition allows for dynamic regulation of heat (Δ H m = 130.10 J/g) without requiring auxiliary energy input, thereby enabling autonomous maintenance of indoor temperatures within the human thermal comfort zone (20°C–26°C). Furthermore, the tailorable crosslinking density of PEPG extends its applicability into wearable thermal management suits and adaptive heat‐dissipation interfaces for compact electronics. This work establishes a new paradigm for multifunctional soft materials, effectively bridging the gap between energy‐saving technologies and personalized thermal comfort solutions.