Semi-Reversible Thermochromism in Polydiacetylene–PDMS Hybrid Structures

Thermochromic materials that change color in response to temperature have been extensively explored in point-of-use temperature indicators, smart textiles, energy-saving coatings and biomedical monitoring devices. Polydiacetylene (PDA) undergoes a thermally induced blue-to-red transition that is typically irreversible, limiting its use in temperature-responsive sensing. Here, we examine the origin of semi-reversible thermochromism in PDA–PDMS hybrid structures by comparing four architectures: core–shell PDA@PDMS particles, nested-PDAs|PDMS particles, PDA/PDMS composites, and PDA|PDMS laminates. The observed reversibility arises from the melting of residual unpolymerized 10,12-pentacosadiynoic acid (PCDA), its migration into the PDMS matrix, and UV-induced formation of new PDA domains. Systems containing larger PCDA reservoirs show clearer semi-reversible behavior, whereas limited PCDA content results in weak or negligible recovery. Laminate experiments further reveal that PDMS thickness and PDA polymerization time influence thermochromic kinetics through their effects on heat transport and PCDA availability. These results clarify the mechanism of semi-reversible thermochromism in PDA-based materials and offer practical considerations for designing thermally responsive PDA systems.