Dual-bioinspired and ultra-flexible photothermal eutectogels for highly efficient passive anti-freezing

Icing and frosting always cause troubles in present-day human activities, appealing for effective anti-freezing strategies to break through the bottleneck. Inspired by "predominant metabolites in the body fluid of cold-tolerant animals" and "poikilotherms that increase body temperature by absorbing solar energy", natural deep eutectic solvents (NADES) and carbon nanotubes (CNTs) were incorporated within calcium alginate (CA) backbone to fabricate dual-bioinspired and ultra-flexible photothermal eutectogels (CNTs/NADES@CA). Normal CNTs (nCNTs) and hydroxylated CNTs (hCNTs) were used to investigate the effects of hydrogen-bonding networks of NADES on the dispersal/aggregation behaviours of nCNTs/hCNTs. Molecular dynamics (MD) simulation proved that hCNTs could form intense hydrogen-bonding interactions with NADES and disperse more uniformly, ultimately contributing to better mechanical properties. Spectral characteristics covering solar absorption and infrared emissivity showed that higher nanofiller loading could cause increased infrared emissivity, leading to more thermal energy loss during photothermal conversion. Besides, moisture absorption–desorption tests further confirmed the excellent function reproducibility and sustainability of the materials. One of the hCNTs-based eutectogels (4%-hCNTs) behaving the best in photothermal conversion was selected for anti-freezing tests concerning anti-frosting, anti-icing, and deicing capacities, announcing that the CNTs/NADES@CA could be highly efficient for passive anti-freezing. This study proposed a highly efficient nanofiller dispersion strategy enabled by NADES to fabricate ultra-flexible photothermal eutectogel by a physically simple method, and it is hoped that this work could open up new avenues for bioinspired materials and attract more concerns for the proposed dual-bioinspired anti-freezing strategy.