Melanin-Inspired Stable Dispersion of Molten Salt Nanofluids

Inorganic molten salt nanofluids have the potential to enable many thermal applications but often suffer from serious detrimental aggregation. Inspired by the melanin-dispersing mechanism, herein, we achieve stable uniform dispersion of various nanoparticles within molten salts through <i>in situ</i> polymerization of l-dopa in the presence of inorganic salt ions. Molten salt cations (Li⁺, K⁺, and Na⁺) can enhance the polymerization kinetics and modulate the oxidation self-assembly process, promoting the formation of melanin-like poly(l-dopa) (PLD) particles with rough surfaces. The salt ions can form a thick cation-anion alternative charge distribution layer on the surfaces, which enables the long-term homogeneous dispersion of PLD and PLD-coated functional particles within a variety of molten salts. The resultant molten salt nanofluids have shown boosted solar absorptance and enhanced specific heat capacity, which make them suitable for direct harvesting of medium-temperature solar-thermal energy. Such a dispersing strategy can help unlock the door to explore controlled fabrication of highly ionic fluidic functional materials with stable dispersion for a wide range of applications.