Flexible phase-change composite films for infrared thermal camouflage and photothermal energy storage

To meet the requirement of multipurpose applications in infrared thermal camouflage and solar photothermal energy storage, we have developed a series of multifunctional composite films based on polyurethane (PU) as a flexible matrix and double-layered phase-change microcapsules as an additive. The double-layered microcapsules were first constructed by encapsulating n-docosane as a phase-change material in a titanium dioxide shell, followed by depositing a polyaniline (PANi) functional layer. Then, the microcapsules were incorporated into the PU matrix to form the composite films through in situ polycondensation. A high latent heat capacity of over 130 J g−1 was achieved by the microcapsules as a result of a high n-docosane loading. This can generate an effective thermal buffer for the composite films and thus endow them with a good thermal camouflage capability. The composite films also show good solar energy-storage performance thanks to their superior sunlight absorptivity derived from the PANi coating layer of the microcapsules. The composite films present a much higher surface temperature (68.6 °C) than pure PU film (41.9 °C) under simulated sunlight irradiation for 1488 s. In addition, the composite films exhibit a self-cleaning surface and high flexibility. Integrating the double-layered microcapsules and flexible PU matrix may provide an innovative strategy for developing flexible functional films for infrared thermal camouflage and photothermal energy storage applications.