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

Abstract

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.