Thermal-driven cellulose-based hydrogels with reversible phase transition for smart optical regulation

Solar radiation through windows substantially elevates thermal loads across buildings and vehicles, presenting critical safety hazards as interior temperatures can reach life-threatening levels. Herein, a hydroxypropyl cellulose-based hydrogel system was developed for solar regulation, exhibiting reversible optical switching between opaque and transparent states with remarkable durability. The main compositional features dictating the phase transition temperature were systematically evaluated using machine learning feature screening, guiding the empirical development of adaptive thermal regulation in hot climates. The hydrogel windows demonstrate significant solar modulation capabilities, reducing solar power transmission and lowering indoor temperatures under direct sunlight during the hot summer. By incorporating polyacrylamide (PAM) and CaCl₂, the hydrogel material gains reinforced mechanical strength and multi-responsiveness (temperature, humidity, and stress). In addition, the unique properties of the hydrogel, enabled by ion coordination and polymer chain movements, facilitate novel applications including dynamic optical encryption and stress-based writing interfaces. The findings highlight the hydrogel's potential as a versatile material for thermal-responsive smart devices, optical encryption, interactive writing, and passive-cooling technologies.