Transformable carbon nanotube network-reinforced hydrogels and organogels for phase change cold storage

Water, salt solution and many conventional organic solvents exhibit melting temperatures nearly or well below zero degree, and functional phase change composites based on these components will be useful in energy and environmental areas. Here, we report the design and fabrication of a series of composite hydrogels and organogels consisting of water, NaCl/water eutectic solution, n-undecane and n-heptanol held by a built-in carbon nanotube (CNT)-polymer skeleton, respectively. We adopt an initially uniform yet transformable CNT network to mix with gel precursors and obtain densified CNT-reinforced pore walls by in situ gelation. These composite gels realized solid-liquid phase transition in temperatures ranging from -10 to -36 °C, with reduced supercooling, large enthalpy (120 to 200 J/g), enhanced structural stability and anti-leakage property, and the effects of CNTs on thermal and mechanical properties are investigated systematically. We demonstrate that by wrapping the composite gels around pipe models with cold liquid flow, the temperature increase process could be substantially prolonged, owing to efficient latent heat release during phase change. Our CNT-reinforced hydrogels and organogels, made by a general facile approach, have many potential applications as cold energy storage and transformation media in liquefied natural gas industry, food and biomedical fields.