Octodecane-cellulose nanofiber flexible composites for latent heat storage

While phase change material (PCM)-encapsulated, emulsion-templated monolithic composites are promising for latent heat storage, they are usually rigid, which hinders their wide applications. Here, we report the fabrication of PCM (octodecane, OD)-encapsulated, emulsion-templated monolithic composites with wide-temperature-range flexibility for latent heat storage. The composites were prepared from OD-in-cellulose nanofiber (CNF) suspension emulsions through interfacial reaction and subsequent drying. Composites from freeze drying showed flexibility at temperature over the melting point of the encapsulated OD (30 °C), while composites from heat drying were flexible at temperatures even below the melting point of the encapsulated OD (such as at 20 °C). The wide-temperature-range flexibility could result from the reduced bonded OH groups within CNFs and the presence of voids with nanofibrous walls. The two types of the composites showed controllable external shapes, robust compression and good encapsulation, without fracture at a high compressive strain of 70% and without leakage at a compressive strain below 30%. Moreover, the composites possessed high reproducibility, extremely high heat capacity (up to 250 J.g−1, even slightly higher than that of bulk OD), high reusability and stability, without obvious deterioration in heat capacity after 100 heating–cooling cycles. The feature that combines wide-temperature-range flexibility, mechanical robustness, high heat capacity and good reusability/stability enabled the OD-encapsulated monolithic composites to be excellent candidates for latent heat storage.