Mechanically strong, flexible, and multi-responsive phase change films with a nacre-mimetic structure for wearable thermal management

Abstract

Phase change materials (PCMs) are a highly promising candidate for thermal energy storage owing to their large latent heat and chemical stability. However, their intrinsic brittle induces poor flexibility and low mechanical strength, which limits them use for wearable thermal management. And, the electrical insulation and weak solar absorption make them lack multi-responsive capability. Herein, we report a facile strategy to synthesize mechanically strong and flexible multi-responsive phase change films by stirring an aqueous dispersion of cellulose nanofibrils (CNFs), MXene (Ti2C3) nanosheets, and polyethylene glycol (PEG), followed by air-drying self-assembly and coating with hydrophobic fluorocarbon. The hydrogen bonds and nacre-mimetic synergistic toughening networks formed by ternary CNFs, Ti2C3 nanosheets, and PEG endow films with high mechanical strength (16.7 MPa) and strain (10.4%), which are 18.6 and 8.7 times higher than those of pure PEG film, respectively. The films exhibit outstanding flexibility and do not crack or fracture even when bent, twisted, and folded into a complex small boat. Meanwhile, the laminar structure formed by the self-assembly Ti3C2 nanosheets enhances electrical conductivity (3.95 S/m) and solar absorption, affording excellent electro-thermal (68.3%–81.0%) and solar-thermal (85.6%–90.6%) conversion efficiency, thus achieving multi-response to external stimuli (electron/solar radiation). In addition, the as-prepared films also deliver large latent heat (136.1 J/g), outstanding cyclic and shape stability, leak-free encapsulation even under compressed at above 5000 times its weight, excellent hydrophobicity (131.4°), and self-cleaning function. This work paves the way for developing flexible, mechanically strong, and self-cleaning phase change film with multi-responsive function for wearable thermal management devices under high humidity condition.