Unravelling the mechanism of coloration and prolonged discoloration in abnormally thermochromic PDMS nanocomposites.

Traditional thermochromic materials prioritize high sensitivity and rapid discoloration. Reversible thermochromism with delayed discoloration is highly desirable for applications like thermal history indicators and energy-saving windows, yet it has rarely been achieved. Here, we construct such thermochromic composites simply by assembling hydrophobic silica nanoparticles in a polydimethylsiloxane (PDMS) matrix. The films transition from colorless and translucent to blue within minutes when heated above 60 °C and retain their blue color for over eight hours at 20 °C. Remarkably, the discoloration time can be further extended by lowering the environmental relative humidity. Integrating measurements of water absorption, refractive indices, and optical model calculation, we demonstrate that the coloration rises from the combined effects of Rayleigh scattering and multiple scattering and the prolonged discoloration time is surprisingly caused by the gradual absorption of moisture. This unique thermochromic material opens new avenues for advancing thermochromic technology applications.