Flexible Composite Phase-Change Films with Multiscale Fibrous Networks toward High-Performance Thermal Management

Phase-change materials (PCMs), harnessing their high latent heat capacity, have demonstrated remarkable potential in sustainable thermal management by enabling significant reductions in energy consumption and environmental footprint, yet their advancement remains constrained by persistent challenges, including compromised thermal conductivity, phase leakage, mechanical rigidity, and limited environmental responsiveness. Herein, we propose a strategy based on hierarchically engineered multiscale fibrous network encapsulation to fabricate flexible composite phase-change films. The proposed film integrates waterborne polyurethane (WPU) and aramid nanofibers (ANF) as the structural matrix with carbon nanofibers (CNF) and carbonized cellulose (CC) as thermal fillers, effectively encapsulating poly(ethylene glycol) (PEG) through interfacial hydrogen bonding. The resultant ultrathin (0.15 mm) flexible film demonstrates exceptional mechanical–thermal synergetic properties: high tensile strength (13.21 MPa), enhanced latent heat (84.22 J/g), good thermal reliability over 120 melting/solidification cycles, and remarkable shape recovery behavior in response to both thermal and solar stimuli. Implemented in high-power flexible electronics thermal management, our composite phase-change films achieve a remarkable temperature reduction of 10 °C during continuous operation, outperforming conventional PCMs. This work establishes a universal multiscale structural engineering strategy toward high-performance adaptive PCMs for next-generation thermal management systems.