Thermochromic, self-luminescent solid-solid phase change composite membrane from polyethylene glycol entanglement for thermal management, shape memory and information encryption

Phase change materials (PCMs), capable of absorbing and releasing thermal energy during phase transitions, hold significant potential for thermal energy storage applications. Low molecular weight polyethylene glycol (LPEG, Mw = 8000 g/mol) stands out as an exceptional PCM owing to its environmental benignity, non-toxicity, non-corrosiveness, high storage capacity, minimal volume variation during phase transition, chemical stability, low supercooling degree, and cost-effectiveness. However, LPEG undergoes a solid-liquid phase transition, which leads to leakage issues. To address this, ultra-high molecular weight PEG (HPEG, Mw = 8 × 106 g/mol) was incorporated with LPEG to fabricate solid-solid phase change membranes via physical entanglement of internal molecular chains. These membranes exhibit excellent thermal stability and solid-solid phase transition behavior, accompanied by a high phase change enthalpy of 173.5 J/g, endowing them with superior thermal insulation performance and favorable cyclic thermal reliability. Additionally, thermal-induced shape memory effect was achieved through the reversible crystallization-melting of HPEG molecular chains. Upon integration with thermochromic microcapsules and afterglow luminescent particles, the membranes further demonstrate thermochromic and photoluminescent properties. Consequently, the resulting solid-solid phase change composite membranes can be applied in thermal insulation for high-temperature equipment, nighttime indication, and information encryption, thereby offering a promising strategy for the development of multifunctional polymeric phase change materials.